Detectors behind suspended ceilings. Fire protection behind false ceiling

Requirements against fire protection spaces behind false ceilings and under double floors appeared relatively recently, but managed to undergo a number of significant changes. Currently, the type of automatic fire fighting system is determined based on the amount of combustible mass of one meter of cable line. The article presents methods for determining the volume of combustible cable mass and discusses the development of technical solutions used to protect spaces behind false ceilings and under double floors. These spaces, in contrast to the main premises, are characterized by more difficult conditions: difficulties in installation and maintenance, the presence of air currents, dust, etc. This determines the search for special technical solutions that provide a high level of protection while reducing the overall cost of installation and maintenance.

Requirements for NPB 110-03

As in the general case, the level of protection required for spaces behind false ceilings and under double floors depends on the magnitude of the fire load, taking into account its specifics. If there is practically nothing to burn, then protection is not required, a relatively small volume of an automatic fire alarm installation (AUPS) is sufficient, a large volume of automatic fire extinguishing installation (AUPT) is required. According to the previous version of NPB 110-99 "List of buildings, structures, premises and equipment to be protected by automatic fire extinguishing installations and automatic fire alarms" p. 3.11. Spaces behind suspended ceilings and double floors when air ducts, pipelines or cables (wires) are laid in them, including when they are jointly laid, with more than 12 cables (wires) with a voltage of 220 V and above with insulation from combustible and slow-burning materials, regardless of area and volume required AUPT, and when laying from 5 to 12 cables (wires) with a voltage of 220 V and above, AUPS was required regardless of the area. It was allowed not to protect the space behind suspended ceilings and under double floors when laying cables (wires) in steel water and gas pipes, when laying pipelines and air ducts with non-combustible insulation, and when laying cable routes with the number of cables and wires less than 5 with voltage of 220V and above with insulation from combustible and slow-burning materials. Those. or the ceiling space must be isolated from the cable steel pipe, which will not allow the spread of fire, or the cable itself must burn.

Of course, the number of cables (wires) is weakly related to the fire load, for example, it was possible not to protect the overhead space if 4 power cables of the VVG 1x1.5 type (section 1.5 mm 2) with a diameter of 5 mm were laid and if 4 power cables of the VVG type were laid 1x240 (section 240 mm 2) with a diameter of 27.7 mm. In 2003, these requirements were significantly changed: the criterion in the form of the number of wires, which was previously used to determine the choice of protection level, was replaced by the total volume of combustible mass. In the current NPB 110-03 according to clause 11 of Table 2, the spaces behind suspended ceilings when laying air ducts, pipelines with insulation made from materials of the combustibility group G1-G4, as well as cables (wires) that do not spread combustion (NG ) and having the code fire hazard PRGP1 (according to NPB 248), including when they are jointly laid with a total volume of combustible mass of 7 or more liters per 1 meter of cable line, they are protected by fire extinguishing systems, with a total volume of combustible mass from 1.5 to 7 liters per 1 meter of cable line - fire alarm. It also states that the volume of the combustible mass of cable (wire) insulation should be determined according to the method approved in the prescribed manner.

Spaces behind suspended ceilings and under double floors are not equipped with automatic installations when laying cables (wires) in steel water and gas pipes or steel solid boxes with openable solid covers, when laying pipelines and air ducts with non-combustible insulation, when laying single cables (wires) of the NG type for powering lighting circuits and when laying cables (wires) of the NG type with a total volume of combustible mass of less than 1.5 liters per 1 meter of cable line behind suspended ceilings made of materials of the NG and G combustibility groups. Moreover, if the building (room) as a whole AUPT is subject to protection, the space behind false ceilings, when laying air ducts, pipelines with insulation made of materials of the G1-G4 combustibility group or cables (wires) with a volume of combustible mass of cables (wires) of more than 7 liters per 1 meter of the cable line must be protected with appropriate settings, but if the height from the ceiling to the false ceiling does not exceed 0, 4 m, then the installation of a fire extinguisher is not required. Fire alarm used regardless of the distance between the overlap and false ceiling.

The volume of combustible mass of the cable line

A cable line can consist of a different number of cables of several types (Fig. 1) and in order to calculate the volume of combustible mass of a cable line, it is necessary to have the value of the insulation volume of each type of cable. As a rule, the cable has several layers of insulation made of various materials and various sizes. For example, in a low-voltage multi-core lancabel, there is a multi-colored polyethylene insulation of copper conductors and an outer sheath made of polyvinyl chloride plastic compound (Fig. 2).

Rice. 1. Fragment of a cable line

The method for determining the volume of the combustible mass of the cable, given in the Explanation to NPB 110-03, was taken practically unchanged from GOST R IEC 332-3-96 "Testing cables for non-propagation of combustion. Testing wires or cables laid in bundles", namely clause 2.3. The technique is universal and, as a result, quite complicated and can actually be used, perhaps, only for certification tests, otherwise it is difficult to ensure and confirm the reliability of the results obtained. Obviously, due to the lack of standardized methods for directly measuring the volume of cable insulation, its value is determined based on the mass and density of cable insulation samples.

Rice. 2. Lankabel construction.

For measurement, a cable sample with a length of at least 0.3 m is taken with cut surfaces perpendicular to the cable axis to ensure an accurate measurement of its length. The sample is disassembled into its constituent elements and the weight of each non-metallic material is determined. Non-metallic materials, the mass of which is less than 5% of the total mass of non-metallic materials, may be ignored. If the electrically conductive screens cannot be removed from the insulating material, these components are taken as one unit when measuring their mass and determining density. Further, the density of each non-metallic material (including porous materials) is determined by the appropriate method and, as an example, reference is made to section 8 of GOST 12175 "General test methods for insulation and sheath materials electrical cables. Density determination methods. Water absorption and shrinkage tests. "In this GOST, the main method for determining the density of materials is the suspension method given in clause 8.1., According to which ethyl alcohol (to determine the density of less than 1 g / cm 3) or zinc chloride solution density equal to or more than 1 g / cm 3) place three pieces of cable insulation 1-2 mm long. Then distilled water is added until the sample reaches a suspended state in the liquid. Then the density of the liquid is determined with a hydrometer and fixed with an accuracy of three decimal places as density According to the Explanation to NPB 110-03 and according to GOST R IEC 332-3-96, it is sufficient to determine the density values ​​​​with an accuracy of the second decimal place, and for tape and fibrous materials, the density values ​​\u200b\u200bare taken equal to 1.

As a control method, GOST 12175 clause 8.2 provides a pycnometric method, which uses samples weighing from 1 to 5 g, scales with an error of not more than 0.1 mg, a pycnometer with a capacity of 50 cm 3, a working fluid (96% ethyl alcohol) and liquid bath with thermostat. During the test, the weight of an empty and dry pycnometer, as well as a pycnometer with cable insulation samples, is determined. Sample segments must be immersed in the working fluid and all air must be removed from them, for example, by evacuating a pycnometer placed in a desiccator. After stopping the evacuation, the pycnometer is filled with a working liquid, the temperature of which is brought to (23 ± 0.5) ° C in a liquid bath, while the pycnometer must be filled to its maximum capacity. Then the outer surface of the pycnometer is wiped dry and weighed together with its contents, after which the contents are removed and the pycnometer is filled with working fluid. The air must be removed. Determine the mass of the pycnometer with its contents at a temperature of (23±0.5)°C. Based on the density of 96% ethanol 0.7988 g/cm 3 at a temperature of 23°C, the mass of the sample segments, the mass of liquid required to fill the empty pycnometer and pycnometer with samples, their density is determined. Also, GOST 12175 allows the use of a gradient method for determining the density of materials according to GOST 15139.

Based on the found density? i of each non-metallic material, its mass m i and the length of the taken segment l and, its volume Vi is determined in 1 meter of cable in liters:

Vi = m i /(? i x l),

where m i is the mass of the i-th material in kg, ? i is the density of the i-th material in kg / dm 3, l is the length of the cable sample in meters.

The desired volume V of non-metallic materials contained in 1 m of cable is equal to the sum of the individual volumes V 1 , V 2 ... of each type of material. To determine the amount of combustible mass of insulation of one meter of cable line, it is necessary to multiply the results obtained for each type of cable by their number in the cable line and add them up. The result obtained must be compared with 7 or 1.5 liters.

1.5 and 7 liters of combustible mass

At present, five years after the release of NPB 110-03, the volume of the combustible mass of the cable in liters of one meter of cable can be found in the technical specifications. The volume of cable insulation depends not only on its geometric dimensions, but also on its design. The cross-sectional area of ​​the conductors does not exactly match its nominal value, voids may be present in multi-core cables, a cable with twisted cores does not have a strictly cylindrical shape and its "average" diameter is usually less than the maximum specified in the technical specifications, etc. Therefore, the volume of cable insulation can differ both up and down from the value calculated from the outer diameter and cross section of the conductors given in the passport data. However, for preliminary calculations of the volume of the combustible mass of the cable line, you can focus on the geometric dimensions. For a round cable with a diameter of d (mm), with metal conductors with a cross section of s (mm 2), in the amount of n pieces, the insulation volume of one meter of cable is approximately equal to the total volume of this cable minus the volume of the metal conductor, taking into account the coefficient 10 -3 for conversion to liters:

V \u003d 10 -3 (? d 2 / 4 - ns)

Table 1 for comparison shows the volume of combustible mass of some brands cables VVGNG-LS for a voltage of 660 volts, given by the manufacturer and calculated by formula (2). The discrepancy does not exceed a few percent.

Table 1

Dividing 7 liters and 1.5 liters by the passport value of the insulation volume in one meter of cable, we determine at what number of cables the volume will be 7 and 1.5 liters, respectively. For example, if a power cable of the brand 2x1.5 with a diameter of 7.6 mm is used, then in order for the combustible mass of a cable line meter to be 7 liters, it must consist of 165 cables, respectively, for 1.5 liters - of 34 cables! Cable brands with large conductor cross-sections have a significant amount of insulation, for example, a 2x50 brand cable has a diameter of 26.4 mm and already 1 meter of a cable line from 15 cables has an insulation volume of 7.5 liters, and from 3 cables - 1.5 liters.

Low-voltage cables, even stranded ones, have a much smaller volume of insulation, one meter of cable can contain only a few milliliters of combustible mass and it is quite difficult to obtain a volume exceeding 1.5 liters, not to mention 7 liters. For example, Table 2 shows data on various brands of lancabel. Even using a 10x0.5 brand lancable with the largest diameter of 5.06 mm, in order to collect 1.5 liters of combustible mass in 1 meter, the cable line must consist of 117 cables, and for 7 liters - of 547 cables!

table 2

If the cable line consists of cables of different brands, then the volume of combustible mass is naturally determined by summing the volumes for each type:

V=? n j V j ,

where n j is the number of cables of the j-th type; V j is the insulation volume of 1 m of cable of type j.

Of course in the final calculation must be used exact values volumes of combustible mass of each type of cable provided by cable manufacturers.

Protection methods

Requirements for fire protection of spaces behind the false ceiling and under the raised floor were introduced only from January 1997. In NPB 110-96 "List of buildings, structures, premises and equipment to be protected by automatic fire extinguishing and fire detection installations", spaces behind a suspended ceiling and under removable floors, etc. used for laying electrical cables were classified as cable structures with mandatory protection automatic extinguishing or fire detection systems. There were no recommendations regarding the type of fire detector to protect spaces behind false ceilings, and, based on the minimum additional costs, almost everywhere in the space above the ceiling they began to install maximum heat contact detectors - the cheapest, but not providing early fire detection. At that time, the possibility of protecting two spaces at the same time with one smoke detector embedded in a false ceiling was considered: the main room and the space above the ceiling (Fig. 3 a).

Rice. 3. Protection of the ceiling space.
a) does not comply with regulatory requirements;
b) complies with regulatory requirements

The decrease in the efficiency of smoke detection when the smoke detector is moved from the ceiling to distances significantly exceeding 0.3 meters, which was not allowed according to clause 4.3 of SNiP 2.04.09-84 "Fire automation of buildings and structures", operating in 1985 - 2001, is not was taken into account, since at that time the comparison was made with completely inefficient thermal maximum detectors. Although experimental studies have shown that the detection time of a test fire source when smoke detectors are located at a distance of 0.3 m from the ceiling increases by 2–5 times (Fig. 4). And when the detector is installed at a distance of 1 m from the ceiling, it is possible to predict an increase in the time for detecting a fire by a factor of 10-15.

In addition, when the detector was inserted into the false ceiling, the design of the chimney changed, its distance from the false ceiling was significantly reduced, which reduced the efficiency of smoke detection in the main room. As you know, when smoke spreads in a room, a layer of clean cold air remains near the ceiling. Based on this position, the sensitive elements of smoke and heat detectors should be located at some distance from the ceiling. According to European requirements, the smoke detector inlet and the heat detector sensor must be at least 25 mm from the floor.

Rice. 4. Smoke detector response time.
1 - on the ceiling;
2, 3 - at a distance of 0.3 m from the ceiling.

Detailed experimental studies of physical processes during the installation of a smoke detector in a false ceiling, carried out by FGU VNIIPO EMERCOM of Russia, taking into account real operating conditions, revealed additional negative points. Here is a fragment of an interview with the head of the fire automation department of the Federal State Unitary Enterprise VNIIPO Zdor Vladimir Leonidovich in 2003 (Safety Algorithm No. 2, 2003): " At one time, some manufacturers of smoke fire detectors became interested in the possibility of their use for simultaneous control of both the ceiling and the main space of the protected premises. In order to get an answer to the question - can a detector installed on a false ceiling simultaneously detect smoke both in the ceiling space and in the main space, VNIIPO specialists conducted a series of tests of the so-called double-acting detectors. During the tests, test fires were installed in the overhead space (a smoldering cotton rope was used). During the experiment, it was found that the smoke, propagating in the space above the ceiling, through additional holes in the upper part of the double-acting detector housing, enters the smoke chamber of such a detector and causes it to operate. At the same time, the time of smoke detection by a double-acting detector is comparable to the time of smoke detection by detectors installed on the main ceiling of the overhead space. On the basis of this experiment, some manufacturing firms were issued an opinion by VNIIPO on the possible use of their detectors for the simultaneous control of two zones.

VNIIPO specialists decided to continue the experiments. It is known that in various rooms, both in the main space and in the overhead space, there may be chaotic or organized horizontal air flows. With this in mind, an additional series of tests was carried out. The results of these tests showed that the sensitivity of the detectors to a greater extent depends on the presence of horizontal air currents in the room. In this case, the so-called spray effect is affected. In an ordinary atomizer, over an open tube located vertically and placed in a container with a liquid, air is passed in a horizontal direction, as a result of which at the top of the tube

a vacuum is created, which ensures that the contents of the can are sucked through the tube. A similar effect is obtained with a detector. If there is a horizontal air flow in the ceiling space, then the detector will play the role of the same tube, that is, air from the main room will be sucked through it. As a result, if a fire occurs in the overhead space, the smoke from this fire will not enter the detector, since the suction air is coming from the main room. And, accordingly, vice versa, if there is a horizontal air flow in the pre-ceiling space, then air is sucked in from the over-ceiling space, which will prevent smoke from being detected in the main room.

Thus, air currents significantly reduce the effectiveness of smoke detectors in detecting fires. After obtaining such results, and also taking into account the experience of operating double-acting at various facilities, it was decided not to give any more conclusions about the possibility of their application ...".

NBP 88-2001 "Fire-extinguishing and signaling installations. Design norms and rules" (instead of SNiP 2.04.09-84) put into effect since 2002 clarified the requirements regarding the protection of spaces behind suspended ceilings. In a letter dated May 6, 2002, ref. No. 30/9/1259 of the GUGPS of the Ministry of Emergency Situations of Russia indicated that "... the installation of smoke fire detectors in a false ceiling for the simultaneous protection of the above-ceiling and sub-ceiling spaces contradicts the requirements of paragraphs 12.18, 12.19 and 12.23 of NPB 88-01, introduced from 01.01.2002 to replace SNiP 2.04.09-84.

In accordance with the requirements of clause 12.18, point fire detectors should be installed under the ceiling (ceiling). If it is not possible to install detectors directly under the ceiling, they can be installed on walls, columns, cables, special fittings and other supporting structures at a distance of 0.1 to 0.3 m from the ceiling, taking into account the dimensions of the detector.

When these detectors are installed in a suspended ceiling, air flow will be possible through them, which will be an obstacle to the entry of smoke masses into the fire detectors, which will contradict the requirements of clause 12.19.

In accordance with the requirements of clause 12.23, fire detectors installed above the false ceiling must be addressable, or connected to independent fire alarm loops.

In addition, in Appendix 12, clause 3.1, on the choice of types of fire detectors, depending on the purpose of the protected premises and the type of combustible load to protect spaces behind false ceilings, it is recommended to use only smoke detectors and, therefore, comparison with heat detectors has become meaningless.

It is very important to comply with the requirement to determine the location of the fire - the main room, or ceiling space. Indeed, depending on the place of fire, the actions of the personnel should differ significantly: in the first case, it is possible to use primary fire extinguishing means, in the second, it is necessary to turn off the voltage of the power lines. Thus, the classic solution is the installation of addressable smoke detectors or included in separate loops in each volume, on the floor with remote indication and on the suspended ceiling (Fig. 3b).

However, it is not uncommon to install fire detectors and plumes in the ceiling space after installing air ducts and laying cable lines becomes almost impossible. And in the simplest case, the installation of detectors in each space more than doubles the complexity of installing and maintaining a fire alarm. These factors at one time determined the popularity of sensors for "two volumes", although at first glance it was clear that in the overhead space the sensor is located on the "floor", and the smoke from warm air will fill the upper part of the volume, in addition, the air flow from the overhead space passing through the smoke chamber will prevent the ingress of smoke in the event of a fire in the main room. For this reason, the design of European detectors provides for sealing technological holes, for example, those used for mounting SMD light and photodiodes, to exclude vertical air flows through the smoke chamber when mounted on a false ceiling.

Rice. 5. Two point smoke detector

More recently, a so-called two-point smoke detector has been proposed to protect the main room and the ceiling space. These are, in fact, two fire detectors, separated by a considerable distance (up to 600 - 800 mm) vertically and structurally interconnected by a bar (Fig. 5). A mounting ring and a base are installed on the suspended ceiling, in which the lower part of the detector is fixed with the first smoke chamber located in the main room, while the second smoke chamber is located in the upper part of the overhead space. On the main body of the detector there are two red indicators of the "Fire" mode for each space separately and a multifunctional yellow indicator "Fault" for determining dustiness or desensitization for each smoke chamber (Fig. 6). For this detector, a special 6-pin base was developed (Fig. 7), which provides not only the connection of the upper lower sensors of the detector to separate loops, but also the break of each loop when the detector is removed. Closing/opening of the conductors of the loops is not done through a jumper in the detector as usual, but using two additional contacts. When the detector is installed in the base, the main contacts are shifted in the vertical plane and their closure of the 1st with the 5th contact and the 3rd with the 6th contact.

Rice. 6. Indication of the "Fire" mode behind the false ceiling

Rice. 7. Six pin base

The smoke chamber of the upper sensor is housed in a small housing with a diameter of only 50 mm, which ensures ease of installation of the detector. Installation and removal of a two-point detector is carried out from the main room: the upper sensor with a rod is "threaded" through the central rectangular hole in the base and the lower sensor is connected to the base like a conventional smoke detector. The use of this technical solution significantly reduces the amount of installation work and simplifies maintenance in comparison with the classical method of protecting the main room and the ceiling space - separate smoke detectors in each volume. When the upper smoke chamber of the two-point detector is located at a distance of up to 0.3 m from the ceiling, this technical solution fully complies with the current regulations and provides effective protection for two spaces.

Thus, this point-to-point smoke detector has a unique technical capability in terms of regulatory requirements. To date, this is the only smoke detector certified in Russia to protect the space above the ceiling and the main room.

I. Not bad, expert, Ph.D.

The issue of fire safety in the premises is of paramount importance. Sometimes people's lives depend on the installation of several sensors. How and in what cases are alarm sensors installed behind a plasterboard false ceiling?

The problem is solved in different ways: someone will play it safe and put more detectors than necessary, and there will be those who will try to save money. Most the right approach to the case involves resolving the issue with the help of regulatory documents.

Fire and smoke detectors

In instruction on fire safety it is said that the type of fire system required is determined by the volume of combustible mass per linear meter of wiring.

The distance between the suspended and load-bearing ceiling is unimportant, but some install detectors only when it is at least 40 cm. This is wrong.

When there is nothing to burn, then sensors and fire-fighting measures are useless.

In order not to make a mistake, calculate the volume of materials that are capable of supporting combustion. They examine the space behind the false ceiling and find the area with the densest arrangement of wiring and other communications. Cables located at a distance of up to 30 cm from each other are taken into account.

If the resulting amount is less than 1.5 liters, then it is not necessary to install detectors behind the suspended ceiling.

When the volume of combustible substances is in the range from 1.5 to 7 liters per meter, a plume is required behind the ceiling, and therefore sensors.

In the case when it exceeds 7 liters, the installation of a complete fire extinguishing system is required. When the height of the space between the ceilings is less than 40 cm, an automatic fire extinguishing system is not installed, but a loop is required.

Fire detectors

Fire sensors

Detectors are classified according to many parameters. The trigger source is:

• Warm.
• Flame.

They also differ in the nature of the detection zone:

• Point. Most of the smoke and heat detectors belong to this type. They control parameters only at the installation point.
• Linear. These are used less often, but are able to control temperature changes and the appearance of smoke in a part of the linear space of the room.

The connection with the control device is carried out in two ways, so the detectors are divided:

• Wired.
• Wireless.

Addressable alarm systems are able to identify each individual detector.

The autonomous detector is equipped with a built-in battery and a sound annunciator. It does not require connection to the device. This makes it difficult to check functionality and makes it difficult to use in large rooms.

More recently, two-point sensors have appeared. Such a sensor consists of two detectors in one housing, but spaced from each other by 60-80 cm on the stem vertically. One is mounted and controls the situation on the main ceiling, and the second - on the suspended one.

Two point fire detector

A 6-pin base is offered for it, providing connection of both sensors to separate loops. This solution simplifies the installation and dismantling of detectors serving the interceiling space on suspended ceilings.

Smoke detectors

A smoke detector is needed where a fire can be accompanied by a large release of smoke. This is true in offices, commercial enterprises, various clubs, cinemas, etc., therefore, detectors of this type are widely used.

Modern fire detectors have a very presentable appearance and do not spoil the interior. Many of them are installed using the tie-in method, which makes it possible to use them on false ceilings.

The interceiling space should not deceive the operators of the premises. Failure to attach the cable wiring to the bearing surface is a gross violation.

Often fluorescent lamps cause false alarms. This can happen even if the rules for arranging lamps and sensors are observed. There are cases when the detectors reacted to pickups from fittings ceiling mounts. Therefore, when choosing, pay attention to the quality of the device.

Linear infrared sensor

When equipping large rooms with fire alarms, it is preferable to take linear rather than point detectors. They are more expensive, but in general the system will be cheaper due to:

• Reducing the required number of detectors.
• Simplify installation and reduce the consumption of component materials.

When sensors are not required

The guidance documents of the fire authorities state that the interceiling space is not equipped with detectors in the following cases:

• The wiring is hidden in insulated steel tubes or boxes.
• The wires are in tubes with insulation that does not burn.
• A single conductor of the NG type power supply was laid.
• NG-type wiring was laid with a volume of combustible substances less than 1.5 liters per 1 m.

Rules for installing sensors

How many and where to install detectors is described in the instructions. It is recommended to set multipoint.

When a point sensor is mounted in the interceiling space, it should be at least 0.1 m away from the wall, and placed at a distance of 0.1 to 0.3 m from the ceiling. It should not be placed in the corner between the wall and the ceiling. From the detector to the lamps in a straight line - at least 0.5 m. They are arranged so that a free space of 50 cm is formed around each.

Wireless smoke detector

If there is no ventilation, the sensor is placed behind the false ceiling in the upper part of the free space.

Conventional detectors for interceiling space are connected to a separate loop. It is recommended to install above the main sensor, mounted in a suspended plasterboard ceiling. The detector must be equipped with a remote indicator light.

Connecting the detector provides a check of the operability and serviceability of the detector itself and the loop. The total number of sensors in one loop does not exceed 20 units.

Detector installation procedure

The installation algorithm is as follows:

• First determine the required quantity, location and installation step. It must be understood that in some cases they will have to be placed not only on or in a false ceiling, but also behind it.
• Then proceed to the actual installation. Attach detectors only to load-bearing elements. That is, on the frame, and in the interceiling space - to the concrete floor. Two ways to mount detectors: overhead and mortise.

Installing the first way is easier, but not as pretty. To embed, special rings or other devices are required. In addition, the detectors are made of plastic and metal, which is preferable. Each modification has additional means of installation intended only for it. But recent fire safety regulations prohibit the use of such mounts, as they make it difficult to detect heat generation.

On plasterboard ceilings, the installation of sensors using the tie-in method is most often used. He is the most handsome. Ceilings made of plastic panels are generally unsuitable for overhead installation - too weak.

The wiring diagram and wiring specifications are important.

Fire detector connection diagram

Fire regulations recommend the use of fire resistant cables braided, flame retardant and flame retardant, with copper conductors with a cross section of at least 0.5 mm. The scheme is found on the packaging of sensors and the control unit - manufacturers do not save on this. They are simple and in most cases identical to each other. The main thing is to observe the sequence and correct connection of the contacts.

Connecting the sensor is allowed only when the power is off. They work slowly, without fuss. After installing and connecting the circuits, re-check the correctness, and then proceed to check the operability of the system as a whole. This work it is recommended to leave it to the professionals.

Calculation of the number of sensors

The documents say that point detectors (both smoke and heat) are required to be installed in each ceiling compartment with a width of 0.75 m or more, fenced with building elements protruding from the ceiling by 0.4 m or more.

The standards of different countries are different. The British standard BS5839 specifies that sensors be placed so that their detector sensing elements are located below the ceiling at a height of 2.5 to 60 cm for smoke, and for heat - from 2.5 to 15 cm.

How many should there be? The answer is at least two pieces, although one point sensor covers up to 25 square meters the area of ​​the room under the false ceiling. The space between the ceilings is more difficult to control, the conditions for the spread of fire and smoke there can be very different from those in the room, hence such requirements.

If you "translate" the regulatory documents, it becomes clear that each separate section of the space between the ceilings must have:

• Three sensors, if they are included in instrument loops with two response thresholds or in three separate instrument loops with one response threshold.

Layout of fire detectors

• Four detectors, if they are connected in pairs in two different instrument loops with the same threshold.
• Two detectors, if they are connected according to a scheme that requires at least two sensors to operate in turn with a mandatory guarantee of the possibility of timely replacement of a non-working one.
• Two detectors, if they are connected according to the scheme, when the operation of one sensor is sufficient.

Let's sum up the disappointing results. Despite the fact that the rules are written in incomprehensible language, we summarize the following:

• Behind the ceiling, detectors must be installed in the amount of two pieces, if they are addressable.
• At least three will be required if they are analog. At least four, if they are analog, and in addition, they are connected to two loops of the control device with one response threshold.

The video can be in general terms familiarize yourself with the announcer:

• Installation of one addressable sensor in the room is allowed if the warning system is not type 5, the alarm system does not control fire extinguishing, and also in the absence of negative consequences from false positives for humans.

In addition, you must comply the following measures security:

The wiring of fire extinguishing and alarm systems with different supply voltages is laid in separate boxes. If open laying is performed, and there is no protection against electromagnetic interference, there must be at least 0.5 m between bundles with wiring of different voltages. Between single cores, this distance can be halved.

Few people will install a fire system at home behind the ceiling. Such things are installed in organizations and therefore are carried out as such, with a serious approach and compliance with all fire safety standards.

In contact with

Over the past three years, many of the regulations governing the placement of fire detectors have changed twice. To replace NPB 88-2001* “Fire extinguishing and alarm installations. Design Norms and Rules” in November 2008 a new set of rules SP 5.13130.2009 “Fire protection systems. Fire alarm and fire extinguishing installations are automatic. Design Norms and Rules”, which for the first time regulated the options for arranging detectors in rooms with sloping ceilings, with decorative suspended lattice ceilings, etc. Change No. 1 to the set of rules SP 5.13130. significant adjustments, with some requirements returned from NPB 88-2001*. It is also necessary to note the fundamental differences in the requirements for the placement of fire detectors in our and foreign normative documents. Our standards, unlike foreign ones, contain only requirements, there is no explanation of physical processes. This gives rise to various interpretations, often erroneous, moreover, the main provisions have no theoretical justification. There are no formal grounds for choosing the most effective solution, taking into account the physical processes of detecting fire factors in specific conditions. As a rule, the probability of evacuation of people and material damage in the event of a fire is not assessed when designing fire automation systems. Therefore, a long process of harmonization of our fire safety standards is ahead, and with a high probability we can expect the release of amendment No. 2 to the set of rules SP 5.13130.2009 in the near future, then amendment No. 3, etc. For example, it is quite possible that clause 13.3.7 of SP 5.13130.2009, according to which “the distances between the detectors, as well as between the wall and the detectors, given in tables 13.3 and 13.5, can be changed within the area shown in tables 13.3 and 13.5″.

The first part of the article discusses the placement of point fire detectors in the simplest case, on a flat horizontal ceiling in the absence of any obstacles to the spread of combustion products from the source.

physical processes

In the European standard BS 5839 for fire detection and alarm systems for buildings, part 1 Code of practice for the design, installation and maintenance of systems, each section and each paragraph first sets out the physical processes to which attention should be paid, and then how consequence, requirement. For example, why it is necessary to take into account the specifics of work and the type of automatic fire detectors when placing them.

“Heat and smoke detectors rely on convection to carry hot gas and smoke from the hearth to the detector. The location and spacing of these detectors should be based on the need to limit the time spent on this movement, and subject to sufficient concentration of combustion products at the location of the detector. Hot gas and smoke will generally be concentrated in the highest parts of the room, so this is where heat and smoke detectors should be located. Since the smoke and hot gases from the hearth rise up, they are diluted with clean and cold air, which enters the convective jet. Consequently, as the height of the room increases, the size of the source required to activate heat or smoke detectors increases rapidly. To some extent, this effect can be compensated for by using more sensitive detectors. Linear smoke detectors with an optical beam are less sensitive to the effect of a high ceiling than point-type detectors, since with an increase in smoky space, the length of the beam affected by smoke increases proportionally ...

The effectiveness of an automatic fire detection system will be affected by obstructions between heat or smoke detectors and combustion products. It is important that heat and smoke detectors are not installed too close to obstructions to the flow of heated gas and smoke to the detector. There is a "dead space" near the wall-ceiling junction where heat or smoke detection will not be effective. Since hot gas and smoke spread horizontally parallel to the ceiling, there is similarly a dead layer near the ceiling, this precludes installation with the sensing element of the heat or smoke detector flush with the ceiling…”.

Rice. 1. NFPA 72 smoke distribution model

In the American fire alarm standard NFPA 72, explanations, reference data and calculation examples are given in appendices, the volume of which is almost 1.5 times the volume of the main text of the standard. NFPA 72 states that in the case of a flat horizontal ceiling and in the absence of additional air currents, the smoke forms a cylinder of a certain height centered on the projection of the hearth (Fig. 18). With distance from the center, the specific optical density of the medium and temperature decrease, which determines the limitation of the smoky space at the first stage of the development of the source.

Positioning requirements for point detectors per BS 5839

According to the BS 5839 standard, the protection radius for smoke detectors is 7.5 m, for heat detectors - 5.3 m in horizontal projection. Thus, it is easy to determine the placement of detectors in a room of any shape: the distance from any point in the room to the nearest smoke MT in horizontal projection should be no more than 7.5 m, from the thermal one - no more than 5.3 m. This value of the protected area determines the installation according to square grille of smoke detectors after 10.5 m, and for heat detectors - after 7.5 m (Fig. 2). Significant savings the number of detectors (approximately 1.3 times) is achieved in large rooms when using the arrangement of detectors on a triangular grid (Fig. 3).

Rice. 2. Placement of smoke and heat detectors according to BS 5839

Rice. 3. Arrangement of smoke detectors on a triangular grid

Rice. 4. Placement of smoke detectors in a rectangular room

In extended rooms, it is also considered that the smoke detector monitors the area at a distance of no more than 7.5 m in horizontal projection. For example, in a room 6 m wide, the maximum distance between the detectors is 13.75 m and the distance from the detector to the wall is 2 times less, which is 6.88 m (Fig. 4). And only for corridors whose width does not exceed 2 m, the provision applies: only points closest to the center line of the corridor require consideration, respectively, it is allowed to install smoke detectors at intervals of 15 m and at a distance of 7.5 m from the wall.

NFPA 72 Point Detector Placement Requirements

According to NFPA 72, in the general case, on horizontal smooth ceilings, point detectors are placed in a square grid with a step S, the perpendicular distance from the wall to the detector should not exceed S/2. In addition, it is indicated that any point on the ceiling should be no further than 0.7S from the nearest detector. Indeed, the diameter of the circumference of the area protected by one detector when they are arranged on a square grid with a step S is equal to the diagonal of the square S x S, the value of which is S√2. Accordingly, the radius of the protected zone is equal to S√2/2, which is approximately equal to 0.7S.

Moreover, for thermal detectors, the square grating step S is calculated based on ensuring the detection of the source by the QCR power during the time tCR, so that by the time the extinguishing tDO starts or the AUPT is turned on, its value does not exceed the specified power QDO, for example, no more than 1055 kW (1000 Btu / sec ). The calculations take into account the quadratic dependence of the source power growth on time (Fig. 5). The appendices give examples of calculations and reference data for various types of materials and products.

Rice. 5. Dependence of the power of the fire seat on time

With the initial value of the square grating spacing S = 30 feet, i.e. 9.1 m, it is assumed that the detector protects the area in the form of a circle with a radius of 6.4 m (9.1 m x 0.7). Based on this concept, NFPA 72 gives examples of the dimensions of rectangles that fit within a 6.4 m radius circle (Figure 6) and can be protected by a single detector located in the center:

Rice. 6. Rectangles inscribed in a circle with a radius of 6.4 m

A \u003d 3.1 m x 12.5 m \u003d 38.1 m 2 (10 ft x 41 ft \u003d 410 ft 2)
H \u003d 4.6 m x 11.9 m \u003d 54.3 m 2 (15 ft x 39 ft \u003d 585 ft 2)
C \u003d 6.1 m x 11.3 m \u003d 68.8 m 2 (20 ft x 37 ft \u003d 740 ft 2)
D = 7.6 m x 10.4 m = 78.9 m 2 (25 ft x 34 ft = 850 ft 2)

The maximum area obviously corresponds to a square inscribed in a circle of 9.1 m x 9.1 m = 82.8 m 2 (30 ft x 30 ft = 900 ft 2). Placement of detectors in rooms rectangular shape recommended by dividing their area into rectangles that fit into a circle with a radius of 6.4 m (Fig. 6).

Rice. 7. Placement of detectors in rectangular rooms

In a non-rectangular room, the detector placement points can be defined as the intersections of circles with a radius of 6.4 m centered at the corners of the room furthest from the center (Fig. 7). Then, the absence of points outside the circles with a radius of 6.4 m with centers at the points of placement of the detectors is checked and, if necessary, additional detectors are installed. For the room shown in Fig. 8, it turned out that 3 point detectors were quite enough.

Rice. 8. Placement of detectors in non-rectangular rooms

British standard fire start

IN complex systems, where a false alarm can lead to significant material damage, additional measures are applied, including work on 2 detectors. For example, in the British standard BS 7273-1 on gas fire extinguishing in order to avoid unwanted release of gas in the case of automatic operation of the system, the operation algorithm, as a rule, should assume the detection of a fire simultaneously by two separate detectors. Moreover, the activation of the first detector should at least lead to the indication of the “Fire” mode in the fire alarm system and to the activation of an alert within the protected area. In this case, the arrangement of detectors, of course, should ensure the control of each point of the protected premises by two detectors with the possibility of identifying the activation of each of them. In addition, in this case, the fire alarm and warning system must be designed in such a way that in the event of a single break or short circuit loop, it detected a fire in the protected area and, at least, left the possibility of turning on the fire extinguishing manually. That is, if maximum area, controlled by one detector, is X m 2 , then in the event of a single failure of the loop, each fire detector must provide control of an area of ​​​​maximum 2X m 2 . In other words, if in the normal mode double control of each point of the room is provided, then in case of a single break or short circuit of the loop, single control should be provided, as in a standard system.

This requirement is quite simply technically implemented, for example, when using two radial loops with the installation of detectors in “pairs” or one ring loop with short-circuit insulators. Indeed, in the event of a break or even a short circuit of one of the two radial loops, the second loop remains in working condition. In this case, the arrangement of the detectors should ensure the control of the entire protected area by each loop separately (Fig. 9).

A higher level of performance is achieved when using ring loops in addressable and addressable analog systems with short circuit isolators. In this case, in the event of a break, the ring loop is automatically converted into two radial ones, the break location is localized, and all detectors remain operational, which keeps the system functioning in automatic mode. In the event of a short circuit on the analog addressable loop, only the devices between two adjacent short circuit isolators are switched off. In modern analog addressable systems, short-circuit isolators are installed in all detectors and modules, so that even if the loop is short-circuited, the operation is not disturbed.

It is obvious that systems with one two-threshold loop used in Russia do not meet this requirement. In the event of a break or short circuit of such a loop, a “Fault” signal is generated, and the fire is not detected until the malfunction is eliminated, the “Fire” signal is not generated for one detector, which makes it impossible to turn on the fire extinguishing manually after receiving it.

Our norms: past and present

Our requirements for the placement of fire detectors were first defined a quarter of a century ago in SNiP 2.04.09-84 “Fire automation of buildings and structures”. This document specified the standard distances between smoke and heat point detectors when installed on a square grid, which have not changed since then. According to 4.1 SNiP 2.04.09-84, fire alarm installations should have generated an impulse to control fire extinguishing, smoke removal and fire warning installations when at least two automatic fire detectors installed in one controlled room are triggered. In this case, each point of the protected surface had to be controlled by at least two fire detectors. Moreover, the maximum distance between the redundant detectors was equal to half of the standard, respectively, the detectors in the fire extinguishing systems were installed in “pairs” (Fig. 9), which ensured the strict implementation of double control of the area of ​​​​the room and the close response of the detectors in case of fire.

The control of technological, electrical and other equipment, blocked with the installation of a fire alarm, was allowed to be carried out when one fire detector was triggered. But in practice in simple installations fire alarm, the notification was switched on from one detector with a single control of the area of ​​\u200b\u200bthe premises and the placement of detectors at standard distances. A separate paragraph contained a general requirement: “At least two automatic fire detectors should be installed in one room.” And until now, the fulfillment of this requirement implies, as it were, the redundancy of fire detectors, which is actually provided only in small spaces, the area of ​​which does not exceed the standard for one detector. Moreover, the illusion of redundancy creates the basis for an almost complete lack of maintenance, and even more so there are no requirements for periodic monitoring of the sensitivity of the detectors, respectively, test equipment is not produced. For example, in a room of 9 m x 27 m with 3 non-addressable smoke detectors, to ensure redundancy, one detector must have a radius of the protected zone of more than 14 m and provide control of the entire room, i.e. 243 m 2 . Any of the extreme detectors can fail uncontrollably, and the malfunction may not be detected for several years.

But in practice, equipment of the same type has approximately the same time between failures, which determines the almost simultaneous failure of all detectors in the room and in the building. For example, there is a loss of sensitivity of all smoke detectors due to a decrease in the brightness of the optocoupler LEDs. Moreover, such a massive failure of domestic fire detectors is defined by GOST R 53325-2009 “Fire fighting equipment. Technical means fire automatics. General technical requirements. Test methods”, since “the mean time between failures of fire detectors must be at least 60,000 hours”, i.e. less than 7 years, and “the average service life of a fire detector must be at least 10 years”.

The “area controlled by one detector” indicated in tables 4 and 5 of SNiP 2.04.09-84 is quite rightly indicated in today’s SP 5.13130.2009 as “the average area controlled by one detector”. However, for 25 years, we have not yet determined the maximum area protected by one detector in the form of a circle with a radius of 0.7 from the standard distance. Instead, in SP 5.13130.2009, clause 13.3.7, very strange in content, appeared, according to which “the distances between the detectors, as well as between the wall and the detectors, given in tables 13.3 and 13.5, can be changed within the area given in tables 13.3 and 13.5″?! That is, not like in NFPA 72, rectangles inscribed in a circle with a radius of 0.7 from the standard distance, but any aspect ratio of a rectangle with a constant area. For example, for smoke detectors with a room height of up to 3.5 m and a width of 3 m, the distance between the detectors can be increased to 85/3 = 28.3 m! Whereas, according to NFPA 72, the average area controlled by the detector in this case is reduced to 38 m 2, and the distances between the detectors should not exceed 12.5 m (Fig. 6), in addition, paragraph 13.3 remained in SP 5.13130.2009. 10, according to which “when installing point smoke detectors in rooms with a width of less than 3 m, the distances between the detectors indicated in Table 13.3 can be increased by 1.5 times”, i.e. only up to 13.5 m.

Near future

Over the past decade, the development of our standards has been determined by the fight against false alarms of domestic fire detectors, moreover, without regular maintenance. Moreover, the requirements for the protection of detectors from external influences, which have not met the operating conditions for a long time, are not planned to be increased. But our DIPs are the cheapest in the world, however, and they can only be certified by us in accordance with GOST R 53325-2009. Even in neighboring countries, they switched to European standards of the EN54 series, the scope of tests and requirements in which are much higher. But at the same time, installation requirements are simplified: effective protection and high reliability eliminate the mandatory requirement to install at least two detectors of any type, and even detectors without automatic health monitoring are installed one at a time in the room. For fire alarms, the placement of detectors is carried out on the basis of a single control of each point of the protected area, in case of fire extinguishing - double.

But we, it turns out, have not yet implemented all the ways to increase the reliability of the “Fire” signals. In the draft new edition of GOST 35525, the “Fire” signal from any threshold fire detector is perceived by the control panel as false and can only identify it as “Attention”. It is allowed to generate a “Fire 1” signal only either from one detector, if the “Fire” mode is confirmed after a re-request, or from 2 detectors without a re-request, if they are activated for a time not exceeding 60 s. The “Fire 2” signal, which is required by clause 14.1 of the set of rules of SP 5.13130.2009 for generating signals for automatic control of fire extinguishing, smoke removal, warning or engineering equipment, in the general case should be generated only by two “Fire 1” signals per time no more than 60 s. Moreover, this algorithm for the formation of FACP signals "Fire 1" and "Fire 2" must be performed when working with threshold detectors of any type: thermal maximum and maximum differential, smoke linear, flame and thermal cable, since other algorithms for these detectors are not provided.

Thus, protection against false positives has the highest priority for us and its increase is carried out by reducing the level of fire safety. When will the signal "Fire 2" be generated when implementing this algorithm? In most cases, never, and for several reasons. The set of rules SP 5.13130.2009 in this case prescribes the installation of detectors in increments of half the standard. That is, the detectors are located at different distances from the source, and their activation with a difference of 1 - 2 minutes. unlikely. For a technically competent implementation of the proposed algorithm, the detectors must be located in close proximity, i.e., they must be installed in “pairs”, and, taking into account the failure of one of them, in “triples”, moreover, with the same orientation to the air flow to eliminate the spread in sensitivity from the direction of the air flow, as shown in Fig. 10 Photoshop tools.

Rice. 9. Arrangement of detectors in “pairs” with inclusion in two loops

In addition, for the simultaneous operation of the detectors, it is necessary to install detectors with exactly the same sensitivity in “triples”. Even an allowable discrepancy between detectors in sensitivity by 1.6 times will determine the difference in response of several minutes with smoldering fires. Therefore, it will be necessary to accurately measure the sensitivity of each detector and indicate it on the label. The manufacturer will have to select packs of detectors with the same sensitivity. Naturally, it is necessary to ensure the stability of the sensitivity level during operation, not only due to circuit solutions and the choice of the element base. Absolutely identical operating conditions must be provided, up to the same dusting of the smoke chamber. Obviously, for smoke detectors, it will be necessary to introduce mandatory precision dust compensation. Etc.

Moreover, our 2-threshold control panels issue one signal with one relay, no matter how it is called, either one by one or by two detectors and already, as a rule, with a re-request. Moreover, the duration of the re-request, oddly enough, is not limited by the norms and already occurs 2 minutes. and more. Therefore, when the first detector is triggered, even after a re-request in our 2-threshold control panels, the output signal is not generated, therefore, ventilation, air conditioning, thermal curtains, etc. are not turned off, which significantly affects the distribution of smoke and will determine a significant delay in the operation of the second detector if it is located on long distance from the first. With open fires, the temperature in the room quickly rises, and with a significant amount of time spent on re-requests, it is likely that the “Fire” mode will not be confirmed by the detector due to high temperature. Please note that most fire detectors have an operating temperature range of no more than 60 degrees C.

What happens with a false positive? Practice shows that low-quality detectors “false” in normal conditions, even though it is re-requested. In addition, any smoke detector in the absence of maintenance at high level dusting of the smoke chamber goes into operation, despite the resets. According to this algorithm, after 60 seconds, subsequent signals from other detectors are considered false alarms. Thus, one faulty detector disrupts the operation of the entire loop, and possibly all loops, depending on the design of the control panel. Moreover, this is a well-known property of all threshold devices and it is not clear why it is not taken into account in the standards. Why is there no time limit for troubleshooting in threshold fire systems? In the “Methodology for determining the calculated values ​​of fire risk in buildings, structures and structures of various classes of functional fire hazard”, the probability of effective operation of the fire alarm system is allowed to be taken equal to 0.8. This means that during a service life of 10 years, it is completely inoperable for 2 years, or an average of 2.4 months each year. And according to statistics, the efficiency of fire alarm installations during fires is even lower: in 2010, out of 981 installations during a fire, only 703 completed the task, that is, they worked with a probability of less than 0.72! Of the remaining 278 installations, 206 did not work, 3 did not complete the task (21.3% in total) and 69 (7%) were not turned on. In 2009, it was even worse, out of 1021 installations, only 687 completed the task, with a probability of 0.67!!! For the remaining 334 installations: 207 did not work, 3 did not complete the task (20.6% in total), and 124 (12.1%) were not included. Why not extend the action of SP 5.13130.2009 of the application “Determining the set time for detecting a malfunction and eliminating it” to threshold systems? After all, here we are not talking about one room with one addressable analog detector, but from several rooms to entire objects without automatic fire protection. How will the current situation change with the introduction of a new edition of GOST 35525? “Lozhnyak” will finally defeat the fire?

So, it seems that the development of fire systems in this direction is coming to a logical conclusion. The cost of cheap detectors will be too expensive. In the draft new edition of GOST 35525, fire tests of fire detectors on test sources were introduced into the certification test program. Finally find out what level of fire protection our fire detectors provide. Moreover, if the requirements for re-requests in the control panel remain in GOST 35525, then tests must be carried out without fail with two maximum re-requests in time to simulate the detection of a fire by our false-proof devices.

Obstacles to the impact of fire factors on detectors

In the general case, with a horizontal overlap, due to convection, hot gas and smoke from the hearth are transferred to the overlap and fill the volume in the form of a horizontally located cylinder (Fig. 10). When rising up, the smoke is diluted with clean and cold air, which is drawn into the updraft. Smoke occupies the volume in the form of an inverted cone with a vertex at the location of the hearth. When propagating along the ceiling, the smoke also mixes with clean cold air, while its temperature decreases and lift is lost, which determines the limitation of the space filled with smoke on initial stage fires in large rooms.

Obviously, this model is valid only in the absence of extraneous air flows created by supply and exhaust ventilation, air conditioners and in a room free from any objects on the floor near the paths of distribution of the smoke-gas-air mixture from the fire source. The degree of impact of obstacles on smoke flows from the source depends on their size, shape and location relative to the source and the detector.

Requirements for the placement of fire detectors in rooms with racks, with beams and with ventilation are present in various national standards, but differ significantly depending on the origin, despite the generality of physical laws.

Requirements of SNiP 2.04.09-84 and NPB88-2001

Requirements for the placement of fire detectors were first defined in 1984 in SNiP 2.04.09-84 “Fire automation of buildings and structures”, these requirements were set out in more detail in NPB 88-2001 “Fire extinguishing and alarm installations. Design norms and rules, as amended in NPB88-2001*. Currently, the set of rules SP 5.13130.2009 with Amendment No. 1 is in force. It is obvious that the development of new versions of documents each time was carried out on the basis of the previous one by adjusting individual paragraphs and adding new paragraphs and applications. For example, we can trace the development of our requirements over a 25-year period regarding the placement of detectors on columns, walls, cables, etc.

The requirements of SNiP 2.04.09-84 regarding smoke and heat fire detectors say that “if it is impossible to install detectors on the ceiling, it is allowed to install them on walls, beams, columns. It is also allowed to suspend detectors on cables under the coverings of buildings with light, aeration, skylights. In these cases, the detectors must be placed at a distance of no more than 300 mm from the ceiling, including the dimensions of the detector.” In this paragraph, the requirements for the distance from the ceiling for various conditions placement of fire detectors relative to the directions of air flows and the maximum allowable distance for heat and smoke detectors. According to the British standard BS5839, fire detectors must be installed on the ceiling so that their sensing elements are located below the ceiling in the range from 25 mm to 600 mm for smoke detectors and from 25 mm to 150 mm for heat detectors, which is logical in terms of detecting various stages of development of the focus. Unlike smoke detectors, heat detectors do not detect smoldering fires, but at the stage open fire there is a significant increase in temperature, accordingly, there is no stratification effect, and if the distance between the ceiling and the temperature-sensitive element is more than 150 mm, this will lead to unacceptably late fire detection, i.e., make them practically inoperable.

On the other hand, if detectors suspended on cables and mounted on the lower surfaces of beams are affected by horizontal air currents, then when placed on walls and columns, it is necessary to take into account the change in the direction of air currents. These structures are obstacles to the horizontal spread of smoke, thus forming poorly ventilated areas in which the placement of fire detectors is not allowed. The NFPA shows a drawing indicating the area where detectors are not allowed to be installed - this is the angle between the wall and the ceiling with a depth of 10 cm (Fig. 11). When installing a smoke detector on a wall, its upper part should be at a distance of 10-30 cm from the ceiling.

Rice. 11. NFPA 72 Requirements for Mounting Smoke Detectors on a Wall

A similar requirement was introduced later in NPB 88-2001: “When installing point fire detectors under the ceiling, they should be placed at a distance of at least 0.1 m from the walls” and “when installing point fire detectors on walls, special fittings or fastening them on cables should be placed at a distance of at least 0.1 m from the walls and at a distance of 0.1 to 0.3 m from the ceiling, including the dimensions of the detector. Now, on the contrary, the restrictions for placing detectors on the wall have been applied to detectors suspended on a cable. In addition, for some reason, the mention of “special fittings” was often associated with the installation of detectors on the wall and special brackets were designed for mounting the detectors in a horizontal position, which, in addition to additional costs, significantly reduced the efficiency of the detectors. The air flow, in order to get into the horizontally oriented smoke chamber of the detector mounted on the wall, must, as it were, go “into the wall”. At relatively low speeds, the air flow smoothly flows around obstacles and “wraps up” near the wall without going into the corner between the wall and the ceiling. Therefore, a horizontally mounted smoke detector on the wall is transverse to the airflow, as if the detector were installed vertically on the ceiling.

After an adjustment two years later, in NPB 88-2001*, the requirements were divided: “when installing point detectors on walls, they should be placed<…>at a distance of 0.1 to 0.3 m from the ceiling, including the dimensions of the detector” and separately entered the maximum allowable distance of the detector from the ceiling when the detectors are suspended on a cable: “<…>the distance from the ceiling to the lowest point of the detector must be no more than 0.3 m. Naturally, if the detectors are installed directly on the ceiling, then when they are suspended on a cable, there is no reason to take them away from the ceiling by 0.1 m, as when placed on a wall.

Requirements of SP 5.13130.2009

In SP 5.13130.2009, paragraph 13.3.4, which sets out the requirements for the placement of detectors, was significantly revised and significantly increased in volume compared to previous versions, but it is difficult to say that this has added clarity. As in previous versions, all possible installation options are listed in a row: “if it is not possible to install detectors directly on the ceiling, they can be installed on cables, as well as walls, columns and other supporting building structures”. True, a new requirement has appeared: “when installing point detectors on walls, they should be placed at a distance of at least 0.5 m from the corner”, which is well combined with European standards and with general requirement introduced later in Amendment No. 1 to SP 5.13130.2009.

The range of distances from the ceiling of 0.1-0.3 m specified in NPB88-2001 for installing detectors on the wall was excluded, and now the distance from the ceiling when installing detectors on the wall is recommended to be determined in accordance with Appendix P, which contains a table with minimum and maximum distances from the ceiling to the measuring element of the detector, depending on the height of the room and the angle of inclination of the ceiling. Moreover, Appendix P is titled as “Distances from the upper point of the overlap to the measuring element of the detector”, on the basis of which it can be assumed that the recommendations of Appendix P relate to the placement of detectors in the case of inclined ceilings.

For example, with a room height of up to 6 m and floor slope angles of up to 150, the distance from the ceiling (the upper point of the floor) to the measuring element of the detector is determined in the range from 30 mm to 200 mm, and with a room height of 10 m to 12 m, respectively - from 150 up to 350 mm. At floor inclination angles over 300, this distance is determined in the range from 300 mm to 500 mm for a room height of up to 6 m and in the range from 600 mm to 800 mm for a room height of 10 m to 12 m. Indeed, with inclined ceilings, the upper part of the room not ventilated, and for example in NFPA 72 in this case it is necessary to place smoke detectors in the upper part of the room, but only below 4” (102 mm) (Fig. 12).

Rice. 12. NFPA 72 Sloped Detector Placement

In the set of rules SP 5.13130.2009, information regarding the placement of detectors on the wall in a room with a horizontal ceiling in Appendix P, apparently, is missing. In addition, it can be noted that in the set of rules SP 5.13130.2009 there is a separate clause 13.3.5 with requirements for the placement of detectors in rooms with sloping ceilings: “In rooms with steep roofs, for example, diagonal, gable, four-slope, hipped, serrated, having an inclination of more than 10 degrees, some of the detectors are installed in the vertical plane of the roof ridge or the highest part of the building<…>". But in this paragraph, there is no reference to Appendix P and, accordingly, there is no prohibition on installing detectors literally “in the very high part buildings”, where their efficiency is much lower.

It should be noted that paragraph 13.3.4 refers to point fire detectors in general, i.e. both smoke detectors and heat detectors, and significant distances from the ceiling are allowed only for smoke detectors. Apparently, Appendix II is applicable only for smoke point detectors, this is indirectly indicated by the maximum height of the protected premises - 12 m.

Installation of smoke detectors on false ceilings

Clause 13.3.4 of the set of rules SP 5.13130.2009 states that “if it is impossible to install detectors directly on the ceiling, they can be installed on cables, as well as walls, columns and other supporting building structures.” It is enough to refer the suspended ceiling to the “bearing” building structures, and in order to formally fulfill this requirement, the bases of point detectors are sometimes screwed onto the corners of the Armstrong tiles. However, point detectors, as a rule, are light in weight, they are not linear smoke detectors, which do not only have a significant mass and dimensions, but must also maintain their position throughout the entire period of operation in order to avoid false alarms.

The placement of detectors on a false ceiling is defined in the requirements of paragraph 13.3.15 of the set of rules SP 5.13130.2009, although initially it refers to a perforated suspended ceiling, but in the absence of perforation, at least two conditions given in this paragraph are not met:

and as follows: “If at least one of these requirements is not met, the detectors must be installed on a false ceiling in the main room< >. Right on the false ceiling.
Many smoke detector manufacturers offer mounting kits for mounting detectors into false ceilings, which improves appearance premises (Fig. 13).

Rice. 13. Inserting the detector into a suspended ceiling using a mounting kit

In this case, the requirement given in clause 4.7.1.7 of GOST R 53325-2009 is usually met with a margin, according to which the design of the smoke detector “should ensure the location of the optical camera at a distance of at least 15 mm from the surface on which the IPDOT is mounted” (fire smoke detector optoelectronic point). It may also be noted that according to the British standard BS5839, fire detectors must be installed on the ceiling so that their sensing elements are located below the ceiling in the range from 25 mm to 600 mm for smoke detectors and from 25 mm to 150 mm for heat detectors. Accordingly, when inserting foreign smoke detectors into a suspended ceiling, mounting kits ensure that the flue is located 25 mm below the ceiling.

Contradictions in Change #1

When adjusting in clause 13.3.6 of the set of rules of SP 5.13130.2009, a new and categorical requirement was introduced: “The horizontal and vertical distance from the detectors to nearby objects and devices, to electric lamps in any case should be at least 0.5 m” . Notice how the phrase “in any case” exacerbates this requirement. And one more general requirement: “The placement of fire detectors should be carried out in such a way that nearby objects and devices (pipes, air ducts, equipment, etc.) do not interfere with the effects of fire factors on the detectors, and sources of light radiation, electromagnetic interference do not affect the detector’s performance ".

On the other hand, by new version clause 13.3.8, “point smoke and heat fire detectors should be installed in each section of the ceiling with a width of 0.75 m or more, limited by building structures (beams, girders, ribs of slabs, etc.), protruding from the ceiling at a distance of more than 0.4 m”. However, to fulfill the unconditional requirement of clause 13.3.6, the width of the compartment must be at least 1 m plus the size of the detector. With a compartment width of 0.75 m, the distance from the detector, even without taking into account its dimensions, “to nearby objects” is 0.75/2 = 0.375 m!

Another requirement of clause 13.3.8: “If building structures protrude from the ceiling at a distance of more than 0.4 m, and the compartments they form are less than 0.75 m wide, the area controlled by fire detectors, indicated in tables 13.3 and 13.5, is reduced by 40%”, also applies to floors with beams over 0.4 m in height, but the requirement of clause 13.3.6 does not allow installing detectors on floors. And the Appendix P already mentioned here from the set of rules SP 5.13130.2009 recommends the maximum distance from the upper point of overlap to the measuring element of the detector 350 mm at overlap angles up to 150 and at a room height of 10 to 12 meters, which excludes the installation of detectors on the lower surface of the beams. Thus, the requirements introduced in clause 13.3.6 exclude the possibility of installing detectors under the conditions specified in clause 13.3.8. In some cases, this regulatory problem can be solved by using linear smoke or aspiration detectors.

There is one more problem with the introduction in clause 13.3.6 of the requirement “Distance from detectors to nearby objects<…>in any case, it must be at least 0.5 m. We are talking about the protection of the ceiling space. In addition to the mass of the cable, air ducts and fittings, the suspended ceiling itself is often located at a distance of less than 0.5 m from the ceiling - and in this case, how to satisfy the requirement of clause 13.3.6? Relate the false ceiling to 0.5 m plus the height of the detector? Absurd, but the exclusion of this requirement for the case of overhead space is not mentioned in clause 13.3.6.

British standard BS 5839 requirements

Similar requirements in the British standard BS 5839 are set out in more detail in a significantly larger number of paragraphs and with explanatory figures. Obviously, in the general case, objects near the detector have different influence depending on their height.

Ceiling barriers and obstacles

First of all, a restriction is given on the placement of point detectors near structures of considerable height, located on the floor and significantly affecting the detection time of controlled factors, in an approximate translation: “Heat and smoke detectors should not be installed within 500 mm of any walls, partitions or obstacles for smoke and hot gas streams such as structural beams and air ducts, in case the obstacle height is more than 250mm”.

The following requirement applies to structures of lower height:

Rice. 14. The detector must be separated from the structure, the height of which is up to 250 mm, at least twice its height.

“Where beams, ducts, luminaires or other structures adjacent to the ceiling and obstructing the flow of smoke do not exceed 250 mm in height, detectors should not be installed closer to these structures than twice their height (see Fig. 14) ". This requirement, which is absent in our standards, just takes into account the size of the “dead zone” depending on the height of the obstacle that the air flow has to go around. For example, with an obstacle height of 0.1 m, it is allowed to move the detector from it by 0.2 m, and not by 0.5 m, according to clause 13.3.6 of the code of rules SP 5.13130.2009.

The following requirement, also missing from our codes, concerns beams: “Ceiling obstacles, such as beams, exceeding 10% of the total height of the room must be considered as walls (fig. 15)”. Accordingly, abroad, in each compartment formed by such a beam, at least one detector must be installed, and our detectors, respectively, 1, or 2, or 3, or even 4 according to SP 5.13130.2009, but this is a topic for a separate article.

However, it should be noted that the requirement of clause 13.3.8 “Point smoke and heat fire detectors should be installed in each compartment of the ceiling ...” leaves open the question, what is the minimum number of them in each compartment? Moreover, if we consider the 13th section of the set of rules of SP 5.13130.2009, then according to clause 13.3.2 “at least two fire detectors should be installed in each protected room, switched on according to the “or” logic circuit, and according to the 14th section for installation two detectors in the room, a number of conditions must be met, otherwise the number of detectors must be increased to 3 or 4.

Rice. 15. Beams exceeding 10% of the total height of the room should be considered as walls

Free space around the detector

And finally, we got to the analogue of our requirement, clause 13.3.6 of the set of rules of SP 5.13130.2009, however, the common value with the requirement of the BS 5839 standard is practically only 0.5 m: “The detectors must be placed in such a way that free space within 500 mm below each detector” (Fig. 7). That is, this requirement specifies a space in the form of a hemisphere with a radius of 0.5 m, and not a cylinder, as in SP 5.13130.2009, and applies mainly to objects in the room, and not on the ceiling.

Rice. 16. Free space around the detector 500 mm

Ceiling space protection

And the following requirement, also missing in SP 5.13130.2009 with amendment 1, is the placement of detectors in the overhead space and under the raised floor: “In non-ventilated spaces, the sensitive element of fire detectors should be located in the upper 10% of the space or in the upper 125 mm, depending on which is greater” (see Fig. 17).

Rice. 17. Placement of detectors in the overhead or underground space

This requirement shows that this case should not be associated with the requirement of a free space of 0.5 m around the detector for rooms and excludes the possibility of “inventing” the detector to protect two spaces.

Critical airflow rate

For smoke detectors, the main characteristic is usually the sensitivity measured in the smoke duct in dB/m. However, in real conditions, the efficiency of detecting the source of a smoke detector in most cases depends on the so-called critical speed - the minimum speed of the air flow at which smoke begins to enter the smoke chamber of the detector, overcoming aerodynamic resistance. That is, to detect a fire, it is necessary not only to have smoke of sufficient specific optical density at the location of the smoke detector, but also a sufficiently high air flow velocity in the direction of its smoke intake. The American fire alarm standard NFPA 72 for smoke detectors provides a calculation using the critical airflow rate method. It is believed that if the critical speed of movement of the smoke-gas-air mixture from the source was reached at the location of the smoke detector, then the concentration of smoke is sufficient to generate an alarm.

In the US UL standard for smoke detectors, the sensitivity of the smoke duct detector is measured at a minimum airflow velocity of 0.152 m/s. (30 ft/min.). In NPB 65-97, the minimum air flow velocity in the smoke duct, at which the sensitivity of the smoke detector was measured, was to be set equal to 0.2 ± 0.04 m/s, as in the European standard EN 54-7 for smoke point detectors. However, in the current GOST R 53325-2009 clause 4.7.3.1, this value was replaced by an air flow velocity range of 0.20÷0.30 m/s, and in the draft new edition of GOST R 53325, the same range is defined as : "set the airflow speed to (0.25 ± 0.05) m/s". Based on what experimental studies was this adjustment made, which determines the possibility of a significant decrease in the efficiency of domestic smoke detectors compared to European and American detectors? And some fire detectors with “high” protection against dust due to a decrease in the area of ​​​​the chimney, with a critical speed of slightly less than 1 m / s, stop responding to smoke during real fires.
In a room with a flat horizontal ceiling, hot gas and smoke from the hearth rises due to convection, while it is diluted with clean and cold air, which is drawn into the upward flow. The American Fire Alarm Standard NFPA 72 Smoke Detector Determination Guide provides a model for the spread of smoke from a hearth to account for the effect of stratification. Smoke occupies the volume in the form of an inverted cone with an angle equal to 22 0, respectively, at a height H, the radius of the area filled with smoke is 0.2 N. When spreading along the ceiling, the smoke also mixes with clean, cold air, while its temperature decreases, lift is lost and the airflow speed becomes below critical. These physical processes determine the impossibility of detecting a source with a point smoke detector at significant distances and limiting the maximum distance to the detected source, and not the area, as in our standards.

Rice. 18. Free divergence of smoke from the hearth

Compartments of the premises, dedicated parts of the premises, protected zones

The set of rules SP 5.13130.2009 clause 13.3.9 contains the requirement: “Point and linear, smoke and heat fire detectors, as well as aspiration ones, should be installed in each compartment of the room formed by stacks of materials, racks, equipment and building structures, the upper edges of which separated from the ceiling by 0.6 m or less. As already noted, this requirement is not new, but there is no clarity regarding the minimum number of detectors in each compartment. It is clear that if the room is divided into compartments, then the smoke accumulates in the same compartment with the fire, and, as in separate rooms, it is necessary to install at least 2 detectors each with the logic of generating the “or” signal, or at least 3-4 detectors when generating signals when not triggered. less than two fire detectors connected according to the logical "and" scheme. Moreover, it is obvious that if in 3 compartments of the room one detector is installed in a two-threshold loop, then the system will be inoperative even if all the detectors and the device are in full working order. However, what justification can be found in the requirements of the set of rules SP 5.13130.2009 for installing more than one detector in a compartment, if the requirements for distances are provided. After all, design is usually carried out on the basis of a minimum cost for equipment, and rarely anyone thinks about the efficiency and working capacity.
According to clause 13.3.2, in the room, as well as 30 years ago, it is required to install at least two fire detectors, switched on according to the “or” logic scheme without any reservations, although in clause 13.3.3 the assumption of installing one detector is given not only in the protected premises, but also in "dedicated parts of the premises". Clause 14.2 also states that at least two detectors according to the logical scheme “or” are installed “in the room (part of the room)<…>» with placement at standard distances. And in clause 14.3, already “in a protected room or protected area<…>» There must be at least 2-4 detectors. And in the 3rd section of clause 3.33 there is the term "fire alarm control zone (fire detectors)", which is defined as "a set of areas, volumes of the premises of the facility, the appearance in which fire factors will be detected by fire detectors."
The variety of terms used in the set of rules SP 5.13130.2009 without defining them significantly complicates the fulfillment of the requirements set forth in them in this way. Excessive savings in equipment can only be limited by the general requirement given in clause 14.1: “The formation of signals for automatic control of warning, smoke removal installations or engineering equipment of the facility should be carried out in a time not exceeding the difference between the minimum value of the time for blocking escape routes and the evacuation time after the fire alert. And when one detector is installed in 3 compartments of the room, the formation of a “fire” signal will occur only when the fire zone covers several compartments. If 2 detectors are installed in each compartment, then, provided that both detectors are operational, a “fire” signal will be generated adequately, but if one of them fails, the requirement will not be met. The ambiguity of requirements and confusion with terms could be avoided if it were determined, as in the British standard BS 5839, that when the room to be protected is divided by partitions or shelving, the top edge of which is located within 300 mm from the ceiling, (rather than 600 mm, as in SP 5.13130.2009), they should be considered as solid walls that rise to the ceiling (Fig. 19). If such a definition were present in SP 5.13130.2009, then there would be certainty when determining the number of detectors depending on their type.

Rice. 19. Partitions are treated like walls to ceiling

Floors with beams

The British standard BS 5839 contains requirements for the placement of fire detectors in several paragraphs. According to the type of beam, it can be divided into at least 3 classes: single linear beams, frequent linear beams (Fig. 20) and beams that form cells like honeycombs. For each type of beam, the corresponding requirements for the installation of detectors are given.

Rice. 20. Combination of shallow and deep beams

In amendment No. 1 to the set of rules of SP 5.13130.2009 in clause 13.3.8, they returned to the wording from NPB 88-2001 clause 12.20, which is based on the requirements of SNiP 2.04.09-84 clause 4.4: “Smoke and heat fire detectors should be installed in each compartment of the ceiling, limited by building structures (beams, girders, plate ribs, etc.) protruding from the ceiling by 0.4 m or more. And here, similarly to compartments formed by stacks, it is necessary to formulate a requirement for how many detectors of each type should be installed in each compartment and how. Due to the uncertainty of the requirements, often in each part of the room, divided by a tall beam, one detector is installed (Fig. 21).

Rice. 21. There is one detector in each compartment, at least 2 in the room.

In addition, the influence of a beam on the spread of smoke along the ceiling depends not only and not so much on the height of the beam, but on its relation to the height of the ceiling. In the British standard BS 5839, in the American standard NFPA 72, the ratio of the height of the beam to the height of the floor is considered. If the height of an individual beam exceeds 10% of the height of the room, then the smoke from the hearth will mostly fill one compartment. Accordingly, when placing the detectors, the beam is considered as a solid wall, and the detectors are installed, as usual, on the floor.

Rice. 22. Placement of detectors relative to the beam according to BS 5839

In the case of frequent arrangement of beams, smoke and heated air are distributed along the ceiling in the form of an ellipse. Moreover, the upper part of the openings formed by the beams remains poorly ventilated, and the detectors are installed on the lower surface of the beams. According to NFPA 72, if beam height to ceiling height D/H is greater than 0.1 and beam spacing to ceiling height W/H is greater than 0.4, detectors must be installed in each compartment formed by the beams. It is quite obvious that this value is determined on the basis of the smoke divergence radius at the height H, equal to 0.2 N (Fig. 1), respectively, the smoke can actually fill one compartment. For example, detectors are installed in each compartment with a ceiling height of 12 m, if the beams are in increments of more than 4.8 m, which is a significant difference from our 0.75 m. less than 0.1 or the ratio of beam spacing to ceiling height W/H is less than 0.4, then the detectors must be installed on the underside of the beams. In this case, the distance between the detectors along the beams remains standard, and across the beams it is reduced by half (Fig. 23).

Rice. 23. Distances along the beams are standard, and across are reduced by 2 times

The British standard BS 5839 also discusses in detail frequent linear beams (Fig. 24) and longitudinal and transverse beams that form, as it were, honeycombs (Fig. 8).

Rice. 24. Ceiling with beams. M - distance between detectors

BS 5839-1:2002 requirements for allowable distances between detectors across beams depending on ceiling height and beam height are shown in Table 1. us, no, and the distances across the beams are reduced by 2-3 times.

Table 1
Where, H is the height of the ceiling, D is the height of the beam.

For beams in the form of honeycombs, fire detectors are installed on a beam with a relatively small cell width, less than a quadruple beam height, or on the ceiling with a cell width greater than a quadruple beam height (Table 2). Here, the beam height limit of 600 mm appears (unlike our 400 mm), but the relative height of the beam is also taken into account - an additional border, 10% of the height of the room. Table 2 shows the radius of the controlled area of ​​the smoke and heat detectors, respectively, the distance between the detectors with a square grating is √2 larger.

Rice. 25. Longitudinal and transverse beams divide the ceiling into honeycombs

table 2
Where, H is the height of the ceiling, W is the width of the cell, D is the height of the beam.

Thus, our regulatory requirements differ significantly from foreign standards, and the need to use several of our detectors instead of one detector not only makes it impossible to harmonize our standards, but also creates difficulties in determining the area protected by the detector and the logic of the system. As a result, in practice, we get a low efficiency of fire protection in the presence of a fire automation system. According to the statistics presented by VNIIPO in the collection "Fires and fire safety in 2010", with 2198 fires at facilities protected by fire automatics, 92 people died and 240 people were injured, and in total there were 179,500 fires, in which 13,061 people died and 13,117 people were injured.

Igor Neplokhov - expert, candidate of technical sciences
Published in the journal “Protection Technologies” No. 5, 6 - 2011

In Russia, at the legislative level, it is prescribed that fire protection systems must be installed in all organizations and institutions. This is the responsibility of the leader. A fire detector is one of the main components of such systems, so its installation is inevitable.

We will try to understand the requirements for installing fire detectors behind a false ceiling.

When should sensors be installed?

Fire detectors behind a suspended ceiling are installed when there is something to burn or in a place where wires and cables accumulate. To find such places and make sure of their potential danger, you need to:

1. Calculate the volume of combustible materials;
2. Find an area with a dense accumulation of wires that are up to 30 cm apart;
3. Count the number of wires;
4. Add up the data on the volume of combustible substances per meter of cable (see manufacturer's manual).

*When the height of the suspended ceiling is less than 40 cm, fire extinguishing is not installed.

Beyond this point, sensors do not need to be installed when:

• The wires are laid in steel water and gas pipes or boxes with openable solid covers;
• Pipeline and air duct with non-combustible insulation;
• A single cable for powering lighting circuits is of the NG type.

Where to put?

For installation behind a false ceiling, the sensors are mounted on the floor and only on the floor. From the side of the room, they are mounted on carriers. structural elements or ropes. In the case of suspended ceilings - on their stiffeners, since the plates have low resistance to fire and mechanical stress.

Which sensor to choose?

In general terms, fire detectors can be found in our other article, but here we will focus on choosing the type of detector to be placed behind a false ceiling.

There are classifications by type, by the size of the protected area and by the connection of the entire system. According to table M from SP 5.13130.2009, it is recommended to choose smoke detectors. Point detectors are more suitable in size, since linear ones are for rooms with high ceilings. On the last point, we recommend the address system, since it is inconvenient to look behind the suspended ceiling, and this way you can quickly find out the location of the fire. Or you can provide a light indicator from the side of the room.

Suppliers are also offering new two-point sensors that are ideal for suspended ceiling protection. They are a rod, ending with sensors on both sides. Thus, one detector will protect the space behind and under the false ceiling. The price for them is higher, however, it is not required to additionally install sensors indoors.

Instead of a conclusion

This article is to be used as a guide only. Installation of a fire alarm system cannot be carried out independently; only organizations licensed by the Ministry of Emergency Situations have this opportunity.

During the construction of the building, fire safety is of paramount importance. The lives of people depend on the installation of the necessary sensors. For this reason, alarm sensors are installed in the room. If there is a plasterboard structure on the ceiling, these appliances can be installed on it. In this case, some questions arise: what are the requirements for fire safety? When is the installation of detectors necessary, and when not?

fire system requirements

The fire safety documents indicate that the sensors are defined by the value of the combustible mass of one meter of wiring. They are not installed in those places where there is nothing to burn. But, if they are necessary, there are requirements for them:

1. During installation, keep the distance between the base ceiling and the false ceiling, it should be enough to accommodate the wires and sensors.
2. Correctly count the number of appliances and combustible materials to ensure full safety.
3. Examine the ceiling surface carefully to identify the area where the cable and other communications are most dense. Wiring should be 30 cm apart.
4. Determine the linear footage of each brand of cable separately. To do this correctly, refer to a special table with data on combustible substances (measured in liters).
5. If the number is less than 1.5 liters, then there is no need to install detectors behind the false ceiling. Otherwise, it is necessary to install a loop, and hence sensors.

Type of sensors

These devices have differences and can be divided according to some parameters. Sources of sensors triggering are heat, smoke and fire.

They differ in the nature of detection.

Dotted are smoke and heat detectors, which control the situation only in the place where they are installed. Used most often.

Linear - these are sensors used less often, they control the increase in temperature or smoke in parts of the linear space of the building.

They are connected to control devices by wired and wireless methods.

Addressable is a signaling system that identifies each individual detector.

Autonomous - these are sensors that are equipped with a sound annunciator and a built-in battery. There is no need to connect it to the device, since use in large buildings makes it difficult to check the operation.

Two-point sensors have recently become known on the market. What are they? These are two devices located in the same housing, but located at a distance of 80 centimeters from each other. One sensor controls the base ceiling, and the second - suspended. From separate loops, both sensors are connected to a 6-pin base. This option simplifies both the dismantling and installation of devices that serve the space between the ceilings.

Smoke detector

Install such devices in places where ignition can be accompanied by big amount smoke. These are office premises, cinemas, clubs and commercial enterprises.

Modern detectors are quite attractive in appearance, they do not spoil the interior. They are mounted using the tie-in method, which helps to use them on ceilings made of drywall sheets.

The grossest violation is the refusal to fix the wiring loops directly to the control devices.

Sensors can work falsely and this is sometimes facilitated by fluorescent lamps. This happens when the norm of the distance of sensors and lamps is not adhered to. The devices also react to the aiming of the ceiling fixation fittings. To avoid this, choose a quality product.

Infrared Linear Sensor

When a fire alarm is needed in large rooms, it is recommended to purchase just this type of sensor, and not a point one. The price is certainly higher, but the equipment of the entire system will cost several times cheaper.

When sensors are not required

• The wires are hidden in corrugated pipes or special steel boxes.
• Cables in insulated tubes.
• The laying is made by single-core wiring electrical supply NG type.
• NG-type wiring was used, but which does not contain combustible substances more than 1.5 liters per meter.

Installation of sensors

Where and how many devices to install is written in the recommendations. It is advised to install multipoint. When installing a point sensor behind a suspended structure, keep a distance of at least 0.5 meters from the wall, and 0.1 - 0.3 meters from the ceiling. Laying sensors is prohibited in the corners between the ceiling and walls. The distance from the fixtures should be at least half a meter and they should be positioned so that there is free space around each fixture at a distance of 0.5 meters.

When mounting a wireless device in the absence of ventilation, place them behind the structure in free space, only in the upper part.

Conventional detectors require separate loops for connection in the space between ceilings. Install above the main sensor which is mounted in the ceiling. Provide the sensor itself with a powerful light indicator. Connecting the device provides control of the health and operation of the sensor and the electrical circuit.

Installation instructions

To begin with, the number, place, distance of devices is determined. Sometimes sensors have to be mounted both in the suspended structure and behind it.

Sensors can only be fixed to load-bearing parts: on a frame or concrete floor.

There are two types of sensor gasket: mortise and invoice.

The second method is simpler, but not aesthetically pleasing. To make a tie-in, use special rings or other devices. Please note that the sensors are made of plastic or metal.

On the plasterboard ceilings tie-in installation is more often used, it has a beautiful appearance, and on plastic panels, only this method is used, because the material is too weak for overheads.

Sensor connection diagram

Fire safety standards recommend the use of only fire-resistant and insulated cables that do not spread combustion. Their cores must be copper and with a cross section of at least 0.5 mm. The diagram is located on the packaging with the sensor and on the control unit. They are not complex and are similar to each other. The main thing is to observe the sequence of work and connect the contacts correctly.

Connect the device only when the power is off. After mounting and connecting the circuit, it is better to check once again how correct the connections and the performance of the system are.

Sensor placement

Four detectors are required if they are connected in pairs to different loops having the same threshold.

Two devices, if the connection was made according to a scheme that requires sequential operation of at least two devices and with a guarantee of replacement if necessary.

Two sensors, if they were connected to the circuit, when one device is triggered.

From this it follows that the norms are as follows: two sensors are necessarily mounted behind the ceiling structure, if they are addressable by type. The same amount is required if the devices are analog.

If they are analog, but the connection comes from two electrical circuits control devices that have one response threshold.

It is allowed to install one address type sensor in the room if the alarm system does not control the fire extinguishing and guarantees the absence of false alarms.

Security measures

If the supply voltage is different, then the wiring for the fire extinguishing and alarm system is mounted in separate boxes. If the laying is carried out in an open way, and there is no protection, then the distance between the wiring and bundles with different voltages should be no less than 0.5 m. Using single-core wires, the distance is halved.

In crowded places, fire safety is monitored more strictly. Entertainment or nightclubs and other establishments have special security requirements.

When installing plasterboard ceilings, you may encounter the same problems. The design must comply with fire safety standards, besides, have an aesthetic appearance and be functional.

The cellular ceiling complies with these standards. It is made of aluminium. This is a material that does not burn and does not contribute to the spread of fire. The design is open, like gratings with different sizes and drawings. Such properties help to install a fire alarm for drywall construction without interfering with the functioning of installed systems.

The cost of suspended ceilings includes ventilation, installation of utilities, installation of fixtures and electrical wires.

The requirements that are put forward to the sensor, arranged behind the ceiling, are that nothing prevents it from working at the right time, and those in the room can leave it. For this reason, the material should not be combustible, destroyed by high temperature or exposure to flame. A properly installed ceiling mounted fire alarm is effective. Mineral fiber does not catch fire and slows down the fire process, which allows for the evacuation of people. The standard thickness of mineral fiber boards is 1.5 centimeters. They protect from fire from above and below the space between the ceilings and the entire room.

Since the action of these sensors, if installed at home, saves people's lives, they are mounted in apartments and houses. The alarm, which is located behind the false ceiling, warns of smoke or fire. For this reason, the unpleasant consequences that fire brings can be avoided. After all, fires often occur at a time when people are sleeping and cannot have time to escape. This leads to the fact that residents get severe poisoning with fumes or smoke, in other cases, a fatal outcome is even possible.

Fire detectors are divided into fire and smoke. They have the same function - to warn of danger.

They differ only in that smoke alarm triggered when there is smoke or a heat source. Such sensors are used most often and their cost is affordable. The fire alarm can be triggered by a single sensor.

At home, it is enough to have one sensor that runs on batteries. Some devices operate on a 120 volt network, and if the electricity is turned off, then they are powered by a battery. The batteries should be changed once a month.

Installation Requirements

These are the points that apply so that later there are no problems and errors.

1. The sensor is connected in such a way that after dismantling it does not interfere with the operation of others.
2. The surface on which it is installed must not be transferred without the use of a tool. In addition, the device itself should be turned so that the optical indicator looks towards the main entrance to the room.
3. The control panel is placed closer to the central entrance. If the object is on round-the-clock duty, an indication and control panel is installed in the room where the guard is located.
4. In the building where the main fire safety system is located, other local systems connected to it to provide signals: "Fault" or "Fire".

How to install detectors, see this video: