Regulatory documentation fire detectors ceiling space. Why and when do you need fire detectors behind a false ceiling

Fire safety is an important factor that must be taken into account in the design and construction of real estate, regardless of their type and purpose. Distinctive feature many structures are characterized by the complex shape of their premises, especially the ceilings. Quite often, they have different shapes, including suspended ceiling structures. In this case, there is a need to install fire detectors behind false ceiling... Their presence will allow protecting the ceiling, and in some cases also the main space of the room.

Why install sensors behind a false ceiling?

Quite often, suspended ceilings are used not just as an element of the interior design of a room, but as an additional engineering structure that allows you to hide:

• duct and exhaust channels;
• lighting wiring;
• power cables supplying various equipment.

The presence of these elements increases the likelihood of a fire in the near-ceiling space several times, therefore, requires additional control. In addition, the danger also arises due to the fact that various gases accumulate in the upper area of ​​the room, and the temperature is several degrees higher than at floor level. In order to protect the ceiling space, the fire alarm must include detectors in this area as well.

Rules for installing fire detectors on a suspended ceiling

In accordance with the normative documentation, the installation of detectors must be carried out on supporting structural elements or cables. Fire detectors are installed on walls, ceilings, columns, and suspended ceilings. The structural element of the suspended ceiling is its stiffening ribs, which retain their load-bearing functions for a longer time than themselves. ceiling tiles... Unlike manufacturers who recommend placing detectors on slabs, the rules for installing fire equipment are strictly forbidden to mount ceiling-mounted fire detectors. The fact is that the slabs have low mechanical stability and low fire resistance. In addition, the detection of fire factors should be carried out at a distance of 1.5 ... 2 cm to the plane of the ceiling, and if the detector is installed on a plate, this condition will not be met.

In some cases, smoke and heat sensors behind false ceilings can be used to protect both the ceiling space and the entire room. This is possible in cases where false ceilings with large perforations are installed in the premises. Fire safety rules stipulate that such an installation is possible if:

• perforation has a periodically repeating pattern, and its area is at least 40% of the entire area of ​​the false ceiling;
• the minimum size of one perforation hole must be at least 1 cm;
• the thickness of the elements of the suspended structure should not exceed the minimum cell size by more than three times.

If the listed rules are not followed, fire detectors must be installed on the suspended ceiling or on the walls of the room.

Installation and placement requirements

During the installation and placement of detectors on ceiling structures, their effective sensitivity radii should be taken into account.

For smoke detectors, the protection radius is 7.5 m, and for heat detectors - 5.3 m.

If the fire detector is installed on a sloped ceiling, the radius should be taken into account using the horizontal projection of the sensitive area of ​​the detector. A "square or triangular array" arrangement can be used to mount the sensors. For large rooms, the latter option is more profitable, since it saves the required number of detectors, protecting the entire surface of the room.

The detector sensor, which is attached to the supporting elements of the suspended structure, must be positioned so that its sensitive element is below the level of the ceiling plane by:

• 2.5 ... 60 cm - for a smoke detector;
• 2.5 ... 15 cm - for a heat detector.

The presence of this distance will allow the sensors to effectively perform their functions and determine the factors of the start of a fire at an early stage. It is prohibited to mount the sensors flush with the plane of the false ceiling.

Tips for an efficient installation behind a false ceiling

Placement of sensors fire alarm behind a false ceiling must be carried out in such a way that it is possible to determine where the fire has occurred. Therefore, protection systems in buildings with suspended structures should provide for the installation of address devices in the ceiling space or connected via a separate loop. You should also provide for the removal of the light indication to outer surface false ceiling, which will visually identify the triggered sensor.

To simplify the procedure for ensuring the fire safety of the ceiling space, it is recommended to use sensors of a special design. Such devices are, in fact, a dual detector with two active zones.

It is mounted in such a way that one sensitive zone is located on the outside of the false ceiling and monitors the situation inside the room, and the second, on an extension cord, is located in the zone behind suspended structure... On the outer part of such a sensor there are two indicators, each of which is responsible for the operation of an external or internal sensitive element.

Conclusion

Installing fire detectors in the space behind a false ceiling is another step towards ensuring a high level of fire safety at the facility and eliminating possible dangerous situations. Thanks to a wide selection of different smoke and heat detectors, offered in different design solutions, you can choose the most the best option devices that are easy to install and efficient to operate. To correctly select and install fire detectors at the facility to protect the space behind false ceilings, you should contact special companies specializing in the installation of fire safety systems.

Suspended ceilings have become widespread in recent years. They are installed as in residential buildings and in offices. In addition to beauty and functionality, safety requirements also apply to them. One of the important factors is the installation of a security and fire alarm system in the operated premises. In particular, it is necessary to provide fire protection behind the suspended ceiling. The standards are spelled out in the set of rules SP5. 13130. 2009 "Systems of counter fire protection... Automatic fire alarm and extinguishing installations. Norms and rules of design "and the system of governing documents RD 009-01-96" Installations of fire automatics. Technical content rules ".

When to install detectors

As a rule, all kinds of engineering cables and wiring are hidden behind a suspended ceiling. To determine whether it is necessary to install fire alarm equipment there, it is necessary to inspect the ceiling space and determine:

• the volume of materials that support combustion. Take into account those cables that are located at a distance of 30 cm from each other;
• the number of wires of each brand;
• the volume of combustible substances. This indicator is given in liters and is determined by the directory of cable manufacturers.

The resulting figures for each brand of wires are added together and, depending on the result obtained, determine the need to install fire detectors. They are needed if the volume of combustible substances exceeds 1.5 liters. If this figure is higher than 7 liters, a complete installation of a fire extinguishing system is required. Also, the installation of sensors is not required if the wiring is hidden in insulated steel boxes or tubes or is represented by a single conductor of power supply of the NG type.

What sirens are used

To protect the ceiling space, detectors are used that differ in several parameters:

• according to the principle of operation. The source for activation is an increase in the temperature in the room, smoke or an open fire;
• by the nature of the detection zone. There are point and line sirens. Determine the parameters of ignition at the point of installation or in a part of the linear space, respectively;
• according to the principle of connection with a control device. Wired sensors are connected to each other and to the main unit by means of cables. Wireless work using a radio channel.

You can buy sirens to protect the ceiling space on our website at competitive prices. To do this, use the service on the site. Any questions you may have can be clarified by contact phone numbers, online chat or through a call back.

The use of materials from the site of the company CJSC "UNITEST" is possible only when placing an active link to the site www.unitest.ru

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. Norms and design rules ”in November 2008, a new set of rules SP 5.13130.2009“ Fire protection systems. Automatic fire alarm and extinguishing installations. Norms and design rules ”, which for the first time regulated the options for the placement of detectors in rooms with inclined ceilings, with decorative suspended lattice ceilings, etc. Introduced from June 20, 2011, amendment No. 1 to the set of rules SP 5.13130.2009 introduced 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 regulatory documents. Our standards, unlike foreign ones, contain only requirements, there is no explanation of physical processes. This gives rise to different interpretations, often erroneous, moreover, the main provisions do not have a theoretical basis. 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, no assessment is made of the likelihood of evacuation of people and material damage in the event of a fire when designing fire automation systems. Consequently, there is a long process of harmonization of our fire safety standards, and with a high probability we can expect in the near future the release of amendment No. 2 to the set of rules of SP 5.13130.2009, then amendments No. 3, etc. For example, it is quite possible that it will be significantly adjusted p. 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 given in tables 13.3 and 13.5”.

The first part of the article examines 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 hearth.

Physical processes

BS 5839 European Standard for Fire Detection and Alarm Systems for Buildings, Part 1 Code of Practice for the Design, Installation and Maintenance of Systems, in each section and in each paragraph, first outlines the physical processes to look out for and then how consequence, claim. For example, why it is necessary to take into account the specifics of the 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 source to the detector. The location and pitch of these detectors should be based on the need to limit the time spent on this movement, and provided there is a sufficient concentration of combustion products at the location of the detector. Hot gas and smoke will generally concentrate 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 upward, they are diluted with clean and cold air, which enters the convective stream. Consequently, as the height of the room increases, the size of the hearth, 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 the length of the beam exposed to the smoke increases proportionally with the increase in the smoke area ...

On efficiency automatic system fire detection will be affected by barriers between heat or smoke detectors and combustion products. It is important that heat and smoke detectors are not installed too close to obstructions for the flow of heated gas and smoke to the detector. There is a “dead space” near the junction of the wall and ceiling, where heat or smoke detection will not be effective. Since hot gas and smoke spread horizontally parallel to the ceiling, there is also a stagnant layer near the ceiling, this excludes installation with the sensing element of the heat or smoke detector flush with the ceiling ... ”.

Fig. 1. Model of smoke distribution according to NFPA 72

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 specifies 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 in the projection of the hearth (Fig. 18). With distance from the center, the specific optical density of the medium and the temperature decrease, which determines the limitation of the smoky space at the first stage of the development of the focus.

Positioning requirements for point detectors to BS 5839

According to BS 5839, 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 source in a horizontal projection should be no more than 7.5 m, from the heat one - no more than 5.3 m. This size of the protected area determines the installation according to square lattice smoke detectors after 10.5 m, and thermal - 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).

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

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

Fig. 4. Arrangement of smoke detectors in a rectangular room

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

NFPA 72 Point Detector Siting Requirements

According to NFPA 72, in the general case, on horizontal smooth ceilings, point detectors are placed on a square grid with a step S, the perpendicular distance from the wall to the detector should be no more than S / 2. In addition, it is indicated that any point on the ceiling must be no more than 0.7S from the nearest detector. Indeed, the diameter of the circle of the area protected by one detector when they are arranged on a square lattice 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 area is S√2 / 2, which is approximately equal to 0.7S.

Moreover, for thermal detectors, the pitch of the square grating S is calculated on the basis of ensuring the detection of the source with the power QCR, during the time tCR, so that by the time of the start of extinguishing tDO or turning on the AUPT, its value does not exceed the specified power QDO, for example, no more than 1055 KW (1000 Btu / sec ). The calculations assume a quadratic dependence of the growth of the source power on time (Fig. 5). The appendices give examples of calculations and reference data for different types materials and products.

Fig. 5. Dependence of the power of the fire source on time

With the initial square grating pitch S = 30 feet, i.e. 9.1 m, it is assumed that the detector protects an area in the form of a circle with a radius of 6.4 m (9.1 mx 0.7). Based on this concept, NFPA 72 provides examples of rectangle sizes that fit into a 6.4 m radius circle (Figure 6) and can be protected by a single detector located in the center:

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

A = 3.1 mx 12.5 m = 38.1 m 2 (10 ft x 41 ft = 410 ft 2)
H = 4.6 mx 11.9 m = 54.3 m 2 (15 ft x 39 ft = 585 ft 2)
C = 6.1 mx 11.3 m = 68.8 m 2 (20 ft x 37 ft = 740 ft 2)
D = 7.6 mx 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 mx 9.1 m = 82.8 m 2 (30 ft x 30 ft = 900 ft 2). Placement of detectors in rooms rectangular it is recommended by dividing their area into rectangles that fit into a circle with a radius of 6.4 m (Fig. 6).

Fig. 7. Placement of detectors in rectangular rooms

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

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

Fire extinguishing according to British standard

IN complex systems where false positives can result in 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 gas start-up in the case of automatic operation of the system, the algorithm of operation, as a rule, should assume that a fire is simultaneously detected 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 the notification within the protected area. In this case, the arrangement of the detectors, of course, should ensure the control of each point of the protected room 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 should be designed in such a way that, in the event of a single break or short circuit of the loop, it detects a fire in the protected area and, at least, leaves the possibility of activating the fire extinguishing manually. That is, if maximum area controlled by one detector is X m 2, then in case of a single failure of the loop, each fire detector must provide an area control of a maximum of 2X m 2. In other words, if double control of each point of the room is provided in normal mode, 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 technically quite simple to implement, for example, when using two radial loops with the installation of detectors in “pairs” or one ring loop with short-circuit isolators. Indeed, in the event of a break or even a short circuit of one of the two radial stubs, the second stub remains operational. In this case, the arrangement of the detectors should ensure control of the entire protected area by each loop separately (Fig. 9).

A higher level of operability is achieved when using loop loops in addressable and analogue addressable 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 point is localized, and all detectors remain in an operable state, which keeps the system functioning in an automatic mode. In the event of a short circuit in the analogue addressable loop, only the devices between two adjacent short circuit isolators are disconnected. In modern analogue 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 the systems with one two-threshold loop used in Russia do not meet this requirement. In the event of an open or short circuit of such a loop, a “Fault” signal is generated, and the fire is not detected until the malfunction is eliminated, a “Fire” signal is not generated for one detector, which makes it impossible to turn on 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 grille, which have not been changed since then. According to 4.1 SNiP 2.04.09-84, fire alarm installations were supposed to generate an impulse to control fire extinguishing, smoke removal and fire warning installations when at least two automatic fire detectors installed in one controlled room were triggered. In this case, each point of the protected surface had to be monitored by at least two fire detectors. Moreover, the maximum distance between the duplicate detectors was equal to half 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 close in time response of the detectors in case of fire.

Control of technological, electrical and other equipment blocked with a fire alarm installation was allowed to be carried out when one fire detector was triggered. And in practice, in simple fire alarm installations, the notification was switched on from a single 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 reservation 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 detectors, respectively, test equipment is not produced. For example, in a room measuring 9 mx 27 m with 3 conventional smoke detectors, to ensure redundancy, one detector must have a radius of the protected area 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.

And in practice, equipment of the same type has approximately the same MTBF, 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 equipment. Fire automation equipment. General technical requirements. Test methods ”, since“ the mean time between failures of fire detectors must be at least 60,000 hours ”, that is, 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, in today's SP 5.13130.2009, is quite rightly indicated 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 of 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 as in NFPA 72 rectangles inscribed in a circle with a radius of 0.7 of 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 distance between the detectors should not exceed 12.5 m (Fig. 6), besides, in SP 5.13130.2009, clause 13.3 remained. 10, according to which “when installing point smoke detectors in rooms with a width of less than 3 m, the distance between the detectors specified in Table 13.3 may be increased by 1.5 times,” that is, only up to 13.5 m.

Near future

Over the past decade, the development of our standards is determined by the fight against false alarms of domestic fire detectors, moreover, without regular maintenance. Moreover, it is not planned to increase the requirements for the protection of detectors from external influences, which have not met the operating conditions for a long time. But our DIPs are the cheapest in the world, however, and they can only be certified in accordance with GOST R 53325-2009. Even in the neighboring countries, they switched to the 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 performance monitoring are installed one at a time in the room. For fire alarm, the placement of detectors is based on a single control of each point of the protected area, for fire extinguishing - double.

But it turns out that we have not yet implemented all the ways to increase the reliability of the "Fire" signals. In the draft of the new edition of GOST 35525, the “Fire” signal from any threshold fire detector is perceived by the PPKP as false and can only identify it as “Attention”. It is allowed to generate the “Fire 1” signal only 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 within a time period 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 to generate signals for automatic control of fire extinguishing, smoke removal, warning or engineering equipment, in general, should be generated only by two signals "Fire 1" for time no more than 60 s. Moreover, this algorithm for generating the Fire 1 and Fire 2 signals by the control panel must be performed when working with threshold detectors of any type: thermal maximum and maximum differential, linear smoke, flame and thermal cable, since other algorithms are not provided for these detectors.

Thus, protection against false alarms has the highest priority for us, and its increase is carried out by reducing the level of fire safety. When will the Fire 2 signal be generated when this algorithm is implemented? In most cases, never, and for several reasons. The set of rules of SP 5.13130.2009 in this case prescribes the installation of detectors with a half step of the standard. That is, the detectors are at different distances from the hearth, and their activation with a difference of 1 - 2 minutes. unlikely. For a technically competent implementation of the proposed algorithm, the detectors should be in close proximity, that is, they should be installed in “pairs”, and taking into account the failure of one of them - “triplets”, and 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 by means of photoshop.

Fig. 9. Arrangement of detectors "in pairs" with inclusion in two loops

In addition, for simultaneous triggering of detectors, it is necessary to install detectors with exactly the same sensitivity in the "triplets". Even the permissible discrepancy of the detectors in sensitivity by 1.6 times will determine the difference in response in a few minutes with smoldering foci. Therefore, it will be necessary to measure the sensitivity of each detector with high accuracy and indicate it on the label. The manufacturer will have to match detector packs with the same sensitivity. Naturally, it is necessary to ensure the stability of the sensitivity level during operation, not only due to circuitry solutions and the choice of the element base. Exactly the same operating conditions must be ensured, up to the same dustiness in 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, whatever you call it, either one at a time or two detectors and, 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 panel, the output signal is not generated, therefore, ventilation, air conditioning, thermal curtains etc. are not switched off, which significantly affects the distribution of smoke and will determine a significant response delay of the second detector if it is located at a great distance from the first. With open foci occurs rapid rise temperature in the room, and with a significant amount of time for resets, it is likely that the "Fire" mode will not be confirmed by the detector due to the high temperature. It should be borne in mind that for most fire detectors, the operating temperature range does not exceed 60 degrees C.

What happens if a false positive is detected? Practice shows that low-quality detectors "false" in normal conditions, even though the request is repeated. In addition, any smoke detector in the absence of maintenance with a high level of dustiness in the smoke chamber goes into operation, despite overflows. According to this algorithm, after 60 s, 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 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 actuation 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 in case of fires is even lower: in 2010, out of 981 installations in case of fire, only 703 completed the task, that is, they worked with a probability below 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 included. 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 “Determination of the established time for detecting a malfunction and its elimination” to threshold systems? After all, here we are talking not about one room with one analogue addressable detector, but from several rooms to entire objects without automatic fire protection. How will the current situation change with the introduction of the new edition of GOST 35525? Will the "False" 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 of the new edition of GOST 35525, fire tests of fire detectors for test centers have been introduced into the certification test program. Finally, it will become clear what level of fire protection our fire detectors provide. Moreover, if the requirements for re-requests in the PPKP remain in GOST 35525, then the tests in mandatory must be carried out with two maximum retries in time to simulate fire detection with our deceptive devices.

Obstacles to the impact of fire factors on detectors

In the general case, with horizontal overlap due to convection, hot gas and smoke from the hearth is transferred to the overlap and fills the volume in the form of a horizontally located cylinder (Fig. 10). As it rises upward, the smoke is diluted with clean and cold air, which is drawn into the upward flow. The smoke occupies a volume in the form of an inverted cone with the apex at the location of the hearth. When spreading along the ceiling, smoke also mixes with clean cold air, while its temperature decreases and lifting force is lost, which determines the limitation of the space filled with smoke by initial stage fire 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 of any objects on the ceiling near the paths of the smoke-gas-air mixture from the fire. The degree of impact of obstacles on smoke streams from the hearth depends on their size, shape and location relative to the fire and the detector.

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

SNiP 2.04.09-84 and NPB88-2001 requirements

Requirements for the placement of fire detectors were first defined in 1984 in SNiP 2.04.09-84 “Fire automation of buildings and structures”, in more detail these requirements were set out in NPB 88-2001 “Fire extinguishing and alarm installations. Norms and design rules, as amended in NPB88-2001 *. Currently, there is a set of rules for SP 5.13130.2009 with Amendment No. 1. It is obvious that the development of new versions of documents each time was carried out on the basis of the previous one by correcting individual points and adding new points and annexes. 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, they can be installed on walls, beams, columns. Suspension of detectors on cables under the roofs of buildings with light, aeration, skylights is also allowed. 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 different conditions placement of fire detectors in relation to the directions of air flows and the value of the maximum allowable distance for heat and smoke detectors. According to 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 from the point of view of detecting various stages of development of the focus. Unlike smoke detectors, heat detectors do not detect smoldering fires, and at the stage of open fire a significant increase in temperature occurs, respectively, 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 an unacceptably late fire detection, i.e. that is, it will make them practically inoperable.

On the other hand, if detectors suspended on cables and installed on the lower surfaces of the beams are affected by horizontal air currents, then when placed on walls and on columns, it is necessary to take into account the change in the direction of the air currents. These structures are obstacles to the horizontal spread of smoke, while poorly ventilated areas are formed in which the placement of fire detectors is not allowed. The NFPA shows a drawing indicating the area where detectors are not allowed - 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.

Fig. 11. NFPA 72 Requirements for Wall Mounting Smoke Detectors

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 from the walls of at least 0.1 m” 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 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, restrictions on the placement of detectors on the wall have been attributed to detectors suspended on a cable. In addition, the mention of “special fittings” for some reason 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 installed on the wall, must, as it were, go “into the wall”. At relatively low speeds, the air flow smoothly flows around the obstacles and “wraps around” near the wall, without going into the corner between the wall and the ceiling. Consequently, a horizontally placed smoke detector on the wall is transverse to the air flow, as if the detector were installed vertically on the ceiling.

After adjusting two years later, in NPB 88-2001 *, the requirements were divided: “when installing point detectors on walls, they should be placed<…>at a distance from 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 should 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 relate them from the ceiling by 0.1 m, as when placed on a wall.

Requirements of SP 5.13130.2009

In SP 5.13130.2009, clause 13.3.4, which sets out the requirements for the placement of detectors, has been 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 are listed in a row. possible options installations: “if it is impossible to install the detectors directly on the ceiling, they can be installed on cables, as well as on 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 the detectors on the wall was excluded, and now it is recommended to determine the distance from the ceiling when installing the detectors on the wall in accordance with Appendix P, which contains a table with the 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 entitled as “Distances from the upper point of overlap to the measuring element of the detector”, based on 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 overlap tilt angles up to 150, the distance from the overlap (upper point of overlap) to the detector measuring element is determined in the range from 30 mm to 200 mm, and with a room height from 10 m to 12 m, respectively - from 150 up to 350 mm. At angles of inclination of the floor over 300, this distance is determined in the range from 300 mm to 500 mm at a room height of up to 6 m and in the range from 600 mm to 800 mm at a room height from 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).

Fig. 12. Placement of detectors with inclined overlap according to NFPA 72

In the set of rules of SP 5.13130.2009, information on the placement of detectors on a wall in a room with a horizontal overlap in Appendix P, apparently, is absent. In addition, it can be noted that in the set of rules of SP 5.13130.2009 there is a separate clause 13.3.5 with the requirements for the placement of detectors in rooms with inclined ceilings: “In rooms with steep roofs, for example, diagonal, gable, hipped, 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 of installing detectors literally “in the highest part of the building”, where their effectiveness is much lower.

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

Installation of smoke detectors on a false ceiling

Clause 13.3.4 of the set of rules of 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 on walls, columns and other supporting building structures”. It is enough to attribute the suspended ceiling to the load-bearing building structures, and 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 lightweight, they are not linear smoke detectors, which really have not only significant weight and dimensions, but must also maintain their position throughout the entire service life in order to avoid false alarms.

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

and as stated below: “If at least one of these requirements is not met, the detectors should be installed on a false ceiling in the main room< >... It is directly on the false ceiling.
Many manufacturers of smoke detectors produce mounting kits for inserting detectors into a suspended ceiling, which improves the appearance of the room (Fig. 13).

Fig. 13. Mounting 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 “must ensure the location of the optical camera at a distance of at least 15 mm from the surface on which the EITI is mounted” (smoke detector optical-electronic point). It can also be noted that according to British 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 installing foreign smoke detectors into a suspended ceiling, mounting kits ensure that the smoke inlet is located 25 mm below the ceiling.

Contradictions in amendment No. 1

When correcting 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 must be at least 0.5 m” ... Notice how the phrase “anyway” adds to 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 impact of fire factors on the detectors, and light sources, electromagnetic interference do not affect the detector's performance ”.

On the other hand, according to new version p. 13.3.8, “point smoke and heat detectors should be installed in each compartment of the ceiling with a width of 0.75 m and more, limited building structures(beams, girders, slab edges, 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 formed by them 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 detectors to be installed on the floor. And the already mentioned Appendix P from the set of rules of 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 ”. It is about protecting the ceiling space. In addition to the weight 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 how, in this case, to satisfy the requirement of clause 13.3.6? Allocate the suspended ceiling by 0.5 m plus the height of the detector? It's absurd, but the exclusion of this requirement for the case of a ceiling-mounted 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 much larger number of paragraphs and with explanatory figures. Obviously, in the general case, objects near the detector have various influences 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 ceiling and significantly affecting the detection time of the controlled factors, in an approximate translation: “Heat and smoke detectors should not be installed within 500 mm of any walls, partitions or obstacles for streams of smoke and hot gases, such as structural beams and air ducts, when the height of the obstacle is more than 250 mm ”.

The following requirement applies to structures of lower height:

Fig. 14. The detector must be at least two heights from the structure, the height of which is up to 250 mm.

“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 two of their heights (see Fig. 14) ”. This requirement, which is absent in our standards, takes into account the size of the “dead zone” depending on the height of the obstacle that the air flow has to bend around. For example, with an obstacle height of 0.1 m, it is allowed to carry the detector from it by 0.2 m, and not by 0.5 m, according to clause 13.3.6 of the set of rules of SP 5.13130.2009.

The next requirement, which is also missing from our code, applies to beams: “Ceiling obstructions such as beams that exceed 10% of the total room height should be treated as walls (fig. 15)”. Accordingly, abroad in each compartment formed by such a beam, at least one detector should 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 “Spot smoke and heat 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 “in each protected room, at least two fire detectors should be installed, included according to the logical scheme“ or ”, 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.

Fig. 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 in clause 13.3.6 of the set of rules of SP 5.13130.2009, however, in common with the requirement of the BS 5839 standard, there is practically only a value of 0.5 m: “Detectors should be placed in such a way that free space within 500 mm below each detector ”(Fig. 7). That is, this requirement sets the 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 refers mainly to objects in the room, and not on the ceiling.

Fig. 16. Free space around the detector 500 mm

Ceiling protection

And the next requirement, which is also absent in SP 5.13130.2009 with amendment 1, is the placement of detectors in the ceiling 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 whether , which is more ”(see Fig. 17).

Fig. 17. Placement of detectors in a ceiling or underground space

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

Critical air flow 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 a source of a smoke detector in most cases depends on the so-called critical speed - the minimum air flow rate 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 to have a sufficiently high air flow velocity in the direction of its smoke intake. The American fire alarm standard NFPA 72 for smoke detectors is calculated using the critical air velocity method. It is considered that if the critical speed of movement of the smoke-gas-air mixture from the hearth has been reached at the location of the smoke detector, then the concentration of smoke is sufficient to generate an alarm.

In the American UL standard for smoke detectors, the sensitivity of a smoke duct detector is measured at a minimum air velocity of 0.152 m / s. (30 ft / min.). In NPB 65-97, the minimum air flow rate in the smoke duct, at which the sensitivity of the smoke detector was measured, had 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 currently valid GOST R 53325-2009 clause 4.7.3.1, this value was replaced by the range of air flow velocities 0.20 ÷ 0.30 m / s, and in the draft new edition of GOST R 53325, the same range is defined as : "Set the speed of the air flow (0.25 ± 0.05) m / s". On the basis of what experimental studies was this correction carried out, which determines the possibility of a significant decrease in the effectiveness of domestic smoke detectors in comparison with European and American detectors? And some fire detectors with "high" protection against dust due to a decrease in the area of ​​the smoke outlet, with a critical speed of slightly less than 1 m / s, stop responding to smoke in real fires.
In a room with a flat horizontal ceiling due to convection, hot gas and smoke from the hearth rises upward, while it is diluted with clean and cold air, which is drawn into the ascending stream. The NFPA 72 US Fire Alarm Sizing Guide provides a model for the propagation of smoke from a source to account for the effect of stratification. Smoke occupies a 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 propagating along the ceiling, smoke also mixes with clean, cold air, while its temperature decreases, lifting force is lost and the air flow rate becomes below critical. These physical processes determine the impossibility of detecting a focus 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.

Fig. 18. Free divergence of smoke from the hearth

Room compartments, dedicated parts of the room, protected areas

The set of rules SP 5.13130.2009 p. 13.3.9 contains the requirement: “Point and linear, smoke and heat fire detectors, as well as aspirating 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 spaced 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 hearth, and, as in separate premises, it is necessary to install at least 2 detectors each with the "or" signal generation logic, or at least 3-4 detectors when signals are generated when at least two fire detectors are triggered, connected according to the "and" logic circuit. Moreover, it is obvious that if one detector in a two-threshold loop is installed in 3 compartments of the room, then the system will be inoperative even if all detectors and the device are in full serviceability. However, what justification can be found in the requirements of the set of rules of SP 5.13130.2009 for installing more than one detector in a compartment, if the distance requirements are met. After all, design is usually carried out based on a minimum of equipment costs, and rarely anyone thinks about work efficiency and performance.
According to clause 13.3.2, in a room, like 30 years ago, it is required to install at least two fire detectors connected according to the logical "or" scheme without any reservations, although in clause 13.3.3 the installation of one detector is allowed not only in the protected area, but also in the “allocated parts of the premises”. Clause 14.2 also states that at least two detectors are installed according to the logic "or" 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 third section of clause 3.33 there is the term "fire alarm (fire detectors) control zone", which is defined as "a set of areas, volumes of premises of an object, the appearance in which fire factors will be detected by fire detectors."
The variety of terms used in the set of rules of SP 5.13130.2009 without their definition significantly complicates the fulfillment of the requirements set out in them in this way. Excessive saving of equipment can be limited only by the general requirement given in clause 14.1: “Formation of signals for automatic control of alarm, smoke removal or engineering equipment of the facility should be carried out for a time not exceeding the difference between the minimum value of the time for blocking escape routes and the time of evacuation after fire notification ”. 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 fulfilled. Confusion of requirements and confusion with terms could be avoided if it was determined, as in British standard BS 5839, that when the protected area is divided by partitions or shelving, the upper edge of which is located within 300 mm from the ceiling, (and not 600 mm, as in SP 5.13130.2009), they should be considered as solid walls that rise to the ceiling (Fig. 19). If SP 5.13130.2009 had a similar definition, then there would be certainty in determining the number of detectors depending on their type.

Fig. 19. Partitions are considered wall to ceiling

Overlapping with beams

In British standard BS 5839, the requirements for the placement of fire detectors are contained in several clauses. By type, beams 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.

Fig. 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 was based on the requirements of SNiP 2.04.09-84 clause 4.4: "Smoke and heat fire detectors should be installed in each section of the ceiling, bounded by building structures (beams, purlins, slab edges, etc.) protruding from the ceiling by 0.4 m or more. " And here, similar to the compartments formed by stacks, it is necessary to formulate the requirement for how many detectors of each type should be installed in each compartment and how. Due to the ambiguity of the requirements, often in each part of the room, divided by a tall beam, one detector is installed (Fig. 21).

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

In addition, the influence of the 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. British standard BS 5839, American standard NFPA 72 deals with the ratio of beam height to floor height. If the height of an individual beam exceeds 10% of the height of the room, then most of the smoke from the hearth will 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.

Fig. 22. Positioning 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 floor 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 the ratio of the height of the beam to the height of the ceiling D / H is greater than 0.1 and the ratio of the pitch of the beams to the height of the ceiling 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 radius of divergence of smoke at a height of H equal to 0.2 N (Fig. 1), respectively, smoke can really fill one compartment. For example, detectors are installed in each compartment with a ceiling height of 12 m, if the beams go in increments of more than 4.8 m, which is significantly different from our 0.75 m.Another requirement of NFPA 72: if the ratio of the height of the beam to the height of the ceiling is D / H less than 0.1 or the ratio of the pitch of the beams to the height of the ceiling W / H is less than 0.4, then the detectors should 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 is halved (Fig. 23).

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

British Standard BS 5839 also details frequent linear beams (fig. 24) and longitudinal and cross beams forming like a honeycomb (Fig. 8).

Fig. 24. Beamed ceiling. M - distance between detectors

BS 5839-1: 2002 requirements for permissible detector spacings across beams based on ceiling height and beam heights are given in Table 1. As in NFPA 72, the maximum spacing along beams remains standard, no 1.5x increase as for us, no, and the distances across the beams are reduced by 2-3 times.

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

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

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

table 2
Where, H - ceiling height, W - cell width, D - beam height.

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 objects protected by fire automatics, 92 people died and 240 people were injured, and there were 179,500 fires in which 13 061 died and were injured 13,117 people.

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 manager. 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 suspended ceiling.

When should the sensors be installed?

Fire detectors behind a false ceiling are installed when there is something to burn or in a place of accumulation of wires and cables. 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 at a distance of up to 30 cm from each other;
3. Count the number of wires;
4. Add up the data on the volume of combustible substances per meter of cable (see the manufacturer's manual).

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

Apart from this point, the 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 line with non-combustible insulation;
• A single cable for powering the lighting circuits is of the NG type.

Where to put it?

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 load-bearing structural elements or cables. In the case of suspended ceilings - on their stiffening ribs, since the slabs have low resistance to fire and mechanical stress.

Which sensor should you choose?

IN general outline fire detectors can be found in our other article, but here we will focus on choosing the type of sensor for placement 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 fire detectors. In terms of size, point detectors are more suitable, since linear detectors are for rooms with high ceilings. On the last point, we recommend an 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, an indicator light could be provided on the side of the room.

Suppliers are also offering new point-to-point sensors that are ideal for protecting suspended ceilings. They represent 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 should only be used as an introductory material. The installation of a fire alarm cannot be carried out independently, only organizations licensed by the Ministry of Emergency Situations have this opportunity.

The requirements for fire protection of spaces behind suspended ceilings and under double floors have appeared relatively recently, but have undergone 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 the cable line. The article provides methods for determining the volume of the combustible mass of a cable and considers the development of technical solutions used to protect spaces behind suspended ceilings and under double floors. These spaces, in contrast to the main premises, are characterized by more difficult conditions: difficulties in installation and maintenance, presence of air currents, dust, etc. This determines the search for special technical solutions that provide a high level of protection while reducing overall installation and maintenance costs.

REQUIREMENTS FOR NPB 110-03
As in the general case, the level of required protection of 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 is sufficient for an automatic fire alarm installation (AUPS), a large volume requires an automatic fire extinguishing installation (AUPT). According to the previous version of NPB 110-99 "List of buildings, structures, premises and equipment subject to protection automatic installations fire extinguishing and automatic fire alarm "p. 3.11. Spaces behind false ceilings and double floors when laying air ducts, pipelines or cables (wires) in them, including when they are jointly laid, with a number of cables (wires) of more than 12 voltage of 220 V and above with insulation from combustible and hardly combustible 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 spaces 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 voltage of 220V and more with insulation from combustible and hardly combustible materials. Those. either the ceiling space must be insulated from the cable with a steel pipe that will prevent the spread of the fire, or the cable itself must be on fire.

Of course, the number of cables (wires) is weakly related to the fire load, for example, it was possible not to protect the ceiling space if 4 power cables type VVG 1x1.5 (section 1.5 mm2) with a diameter of 5 mm and if 4 power cables of type VVG 1x240 (section 240 mm2) with a diameter of 27.7 mm are laid. In 2003, these requirements were significantly changed: the criterion in the form of the number of wires that was previously used to determine the choice of the level of protection was replaced by the total volume of combustible mass. In the currently operating NPB 110-03 according to clause 11 of Table 2, the spaces behind suspended ceilings when laying air ducts in them, pipelines with insulation made of materials of the G1-G4 flammability group, as well as cables (wires) that do not propagate combustion (NG ) and having a fire hazard code PRGP1 (according to NPB 248), including when they are jointly laid with a total volume of a combustible mass of 7 or more liters per 1 meter of a cable line, they are protected by fire extinguishing systems, with a total volume of a combustible mass from 1.5 to 7 liters for 1 meter of cable line - fire alarm. It is also indicated there that the volume of combustible mass of the insulation of cables (wires) must be determined according to the procedure approved in the prescribed manner.

Spaces behind suspended ceilings and under double floors, automatic installations are not equipped when laying cables (wires) in steel water and gas pipes or steel continuous ducts 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 less than 1.5 liters per 1 meter of cable line behind suspended ceilings made of materials of the NG and G flammability group. Moreover, if the building (room) as a whole must be protected by AUPT, spaces behind suspended ceilings, when laying air ducts in them, pipelines with insulation made of materials of the G1-G4 flammability group or cables (wires) with a combustible mass of cables (wires) more than 7 liters per 1 meter of the cable line must be protected with appropriate installations, but if the height from the floor to the false ceiling does not exceed 0, 4 m, a fire extinguishing installation is not required. The fire alarm is used regardless of the distance between the ceiling and the false ceiling.

CABLE LINE COMBUSTION VOLUME
A cable line can consist of a different number of cables of several types (Fig. 1) and to calculate the volume of combustible mass of a cable line, it is necessary to have the amount of insulation for each type of cable. Typically, the cable has several layers of insulation various materials and various volumes. For example, in a low-voltage multicore Lankabel there is polyethylene multi-colored insulation of copper conductors and an outer sheath made of PVC compound (Fig. 2).

Fig. 1. Fragment of the cable line

The method for determining the volume of the combustible mass of the cable, given in the Explanation to NPB 110-03, is taken practically unchanged from GOST R IEC 332-3-96 “Testing of cables for flame retardancy. Testing of wires or cables laid in bundles ", namely paragraph 2.3. The technique is universal and, as a result, rather 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 hosted methods for directly measuring the volume of cable insulation, its value is determined based on the mass and density of cable insulation samples.

Fig. 2. Lankabel design.

For measurement, take a sample of a cable with a length of at least 0.3 m with cut surfaces perpendicular to the axis of the cable to ensure 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 disregarded. If the electrically conductive shields cannot be removed from the insulating material, these components are taken as a whole when measuring their mass and determining their 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 shell materials. electrical cables... Methods for determining density. Tests for water absorption and shrinkage ”. 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 / cm3) or to a solution of zinc chloride (to determine the density equal to or more than 1 g / cm3), three pieces of cable insulation with a length of 1-2 mm are placed. Distilled water is then added until the sample is suspended in the liquid. Then the density of the liquid is determined with a hydrometer and recorded with an accuracy of three decimal places as the density of the test samples. 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 ​​are taken equal to 1.

PROTECTION METHODS
The requirements for fire protection of spaces behind the raised ceiling and under the raised floor were introduced only in January 1997. In NPB 110-96 "The list of buildings, structures, premises and equipment subject to protection by automatic fire extinguishing and fire detection installations", spaces behind the suspended ceiling and under removable floors, etc., used for laying electrical cables, were classified as cable structures with compulsory protection automatic installations for extinguishing or detecting fire. There were no recommendations regarding the type of fire detector for protecting spaces behind suspended ceilings, and, based on a minimum of additional costs, practically everywhere in the ceiling space, they began to install maximum thermal contact detectors - the cheapest, but not providing early fire detection. At that time, the possibility of protecting two spaces simultaneously with one smoke detector embedded in the suspended ceiling was considered: the main room and the ceiling space (Fig. 3 a).

Fig. 3. Protection behind the ceiling. a) does not meet regulatory requirements; b) meets regulatory requirements

A decrease in the efficiency of smoke detection when the smoke detector is allocated 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 automatics of buildings and structures", operating in 1985 - 2001, not was taken into account, since at that time the comparison was carried out with completely ineffective 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 of detecting a fire by a factor of 10-15.

In addition, when the detector was inserted into the suspended ceiling, the design of the smoke intake 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 a certain distance from the ceiling. According to European requirements, the smoke outlet of the fire smoke detector and the sensor of the heat detector must be at a distance of at least 25 mm from the ceiling.

Fig. 4. The response time of the smoke detector. 1 - on the ceiling; 2, 3 - at a distance of 0.3 m from the overlap.

Detailed experimental studies of physical processes when installing a smoke detector in a suspended 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 department of fire automatics of FSUE VNIIPO Zdor Vladimir Leonidovich 2003 (Safety Algorithm No. 2, 2003): “ At one time, some manufacturers of smoke detectors became interested in the possibility of their use for simultaneous control of both the ceiling and the main space of the protected room. 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 carried out a number of tests of the so-called double-acting detectors. During the tests, test fires were installed in the ceiling space (a smoldering cotton rope was used). During the experiment, it was found that smoke, spreading in the ceiling space, through additional holes in the upper part of the double-acting detector housing, enters the smoke chamber of such a detector and triggers its operation. 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 ceiling space. On the basis of this experiment, some manufacturing firms were issued a conclusion by VNIIPO on the possible use of detectors of their production for the simultaneous control of two zones.
VNIIPO specialists decided to continue the experiments. It is known that in different premises, both in the main space and in the ceiling space, irregular or organized horizontal air currents can exist. With this in mind, an additional series of tests was carried out. The results of these tests showed that the sensitivity of the detectors is more dependent on the presence of horizontal air flows in the room. In this case, the so-called spray effect is affected. In an ordinary spray bottle above an open tube, located vertically and placed in a can of liquid, air is passed in a horizontal direction, as a result of which a vacuum is created at the top of the tube, which ensures that the contents of the cartridge 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 that very tube, that is, air from the main room will be sucked in through it. As a result, if a fire occurs in the ceiling space, the smoke from this fire will not enter the detector, since air is sucked in from the main room. Conversely, if there is a horizontal air flow in the pre-ceiling space, then air is sucked in from the ceiling space, which will prevent the detection of smoke in the main room.
Thus, air currents significantly reduce the detection efficiency of fires with smoke detectors. After obtaining such results, and also taking into account the experience of operating double-sided action at various facilities, it was decided not to give any more conclusions about the possibility of their application ... ".

Commissioned since 2002 NBP 88-2001 “Fire extinguishing and signaling installations. Design Norms and Rules "(instead of SNiP 2.04.09-84), the requirements for the protection of spaces behind suspended ceilings have been clarified. In a letter dated 06.05.2002, ref. No. 30/9/1259 GUGPS EMERCOM of Russia indicated that “... the installation of smoke detectors in the suspended ceiling for the simultaneous protection of the above-ceiling and sub-ceiling spaces contradicts the requirements of clauses 12.18, 12.19 and 12.23 NPB 88-01, introduced from 01.01.2002 instead of 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 impossible to install detectors directly under the ceiling, they can be installed on walls, columns, cables, special fittings and others. 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, an air flow will be possible through them, which will be an obstacle on the way of smoke masses entering 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 room and the type of combustible load for protecting spaces behind suspended ceilings, it is recommended to use only smoke detectors, and therefore the 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 the ceiling space. Indeed, depending on the place of fire, the actions of personnel should differ significantly: in the first case, it is possible to use primary fire extinguishing means, in the second, it is necessary to disconnect the voltage power lines... Thus, the classic solution is the installation of addressable smoke detectors or those included in separate loops in each volume, on a ceiling with remote indication and on a suspended ceiling (Fig. 3b).

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

Fig. 5. Two-point smoke detector

More recently, a so-called two-point smoke detector was proposed to protect the main room and the ceiling space. These are, in fact, two fire detectors, spaced at a considerable distance (up to 600 - 800 mm) vertically and structurally connected by a rod (Fig. 5). A mounting ring and a base are installed on the false 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 ceiling 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" to determine dust content or decrease in sensitivity 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 loop conductors is performed not 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 displaced in the vertical plane and the 1st contacts are closed with the 5th contact and the 3rd with the 6th contact.

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

Fig. 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 makes the detector easy to install. Installation and removal of a point-to-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 volume installation works and simplifies Maintenance compared with in the classic way protection of the main room and ceiling space - with separate smoke detectors in each volume. When the upper smoke chamber of the point-to-point detector is located at a distance of up to 0.3 m from the ceiling, this technical solution fully complies with the current standards and provides effective protection of two spaces.

Thus, this point-to-point smoke detector has a unique technical capability in terms of regulatory requirements... Today it is the only smoke detector certified in Russia to protect the ceiling space and the main room. The main technical solutions implemented in this point-to-point fire detector are protected by invention patents and utility model patents.

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