18.03.2017, 12:18

Zaitsev Alexander Vadimovich, scientific editor of the journal “Security Algorithm”

Here and there you can find a variety of materials about “ultra-early fire detection”: from individual articles to teaching aids. In one case, the authors are trying to prove that some “philosopher’s stone” has been found that solves all the problems of detecting a fire at the earliest stage, even when it does not exist yet. In another case, other specialists begin to figure out how to organize organizational measures for fire safety at sites taking into account this possibility.

But after some time, it turns out every time that one or another proposed technical means is far from an ideal solution. And if they have any additional features, then they are not universal, or the use of these technical means is not economically justified.

A comparative analysis of the use of certain means for fire detection should, to some extent, help get rid of myths that arise from time to time.

I would like to immediately note that this analysis cannot be objective and final for a long period of time. Everything flows, everything changes. New technologies appear, new problems appear and, accordingly, ways to solve them. The task of specialists will be to try to get to the bottom of the matter every time they make another statement about the possibility of “ultra-early detection” of a fire, because we all know very well that miracles do not happen in the world.

“SUPER EARLY DETECTION” WHAT AND WHY

As usual, I would like to start with some existing definitions or terms related to “ultra-early detection” or even just “early detection”. But no definitions have yet been invented on this topic.

It must be understood that the occurrence of a fire is characterized by several, sometimes unrelated, environmental parameters by which it can be detected:

■ flames and sparks;

■ heat flow and elevated temperature environment;

■ increased concentration of toxic combustion and thermal decomposition products;

■ reduced visibility in smoke.

As a result, it is through these indirect environmental parameters that the fact of a fire can be detected using technical means. Unfortunately, any of the indirect parameters is not a fully absolute criterion.

Heat comes from both heating objects and heat treatment products that we cannot do without in life.

Powerful lights, welding, and direct sunlight can simulate flames.

Toxic products in a gaseous state are one of the signs of civilization and human presence.

Smoke, being one of the types of aerosols, is sometimes not much different from other aerosols (steam, dust, etc.).

As soon as the developers of fire detection tools begin to talk about the high sensitivity of their fire detectors (FD), the question immediately arises about the likelihood of false alarms due to the presence of background values ​​not related to the fire. And immediately work begins to protect fire detectors from false alarms, down to reducing sensitivity to reasonable values. This is the basis of the spiral of development of fire detection equipment.

The strangest thing here is that this is happening in a country in which only a couple of years ago they began to evaluate the real sensitivity of broadcasters to fire. During this time our domestic producers and a very small part of users, at best, have only just begun to understand what kind of detectors they had to deal with until recently.

Not a single trendsetter from foreign countries associated with the production of fire detectors has any thoughts of prohibiting anyone from producing or using something. It meets the requirements of the standards - that’s it, it is a full-fledged market participant. And here we must not forget that our standards for detectors are almost 90% consistent with European ones, and there is no concept of “extra-early” detectors in either one or the other. There will be a definition, requirements and assessment methods will be developed, then there will be something specific to talk about. In the meantime, it makes sense to deal with what we have.

In the last few years, when fire tests for fire detectors were finally included in GOST R 53325-2012 “Fire automatic equipment”, it seems that it became possible to evaluate or at least compare certain fire detectors in terms of response time when conducting standardized test fires (TF). To some extent, the results of these tests can be correlated with the time of detection of an actual fire.

A fire detector cannot be included in the honorable caste of “super-early ones” only on the basis that it was ahead of the rest in some type of test fires.

Of course, someone may suggest that if a fire detector responds to all these test fires in all cases without exception, for example, ten times faster than others, then it can and should be classified as “extra early”. But this will only be an excuse. But as a consequence, there will certainly immediately follow a proposal to ban the use of all other types and types of fire detectors, or at least to obtain some preferences in use. Then, however, it turns out that the manufacturers got a little excited, did not take into account the side effects, did not evaluate the economic efficiency, etc.

"ULTRA-EARLY" OR TIMELY DETECTION

Today there is no such task as organizing “ultra-early fire detection.” There is a requirement for timely detection, and in each specific case it may have different numerical indicators.

In particular, it is precisely the timely detection of a fire that is discussed in Article 83 of the “Technical Regulations on Fire Safety Requirements.”

How is timeliness determined? And this question has an answer in the same Technical regulations in Article 54. The task is to detect a fire in the time required to turn on warning systems to organize the safe evacuation of people.

To implement the requirements for timely detection, there are existing standards and rules in the field of fire safety, in which all these issues are strictly linked into a single system of fire protection of the facility, starting from architectural and planning solutions and ending with smoke ventilation and internal fire water supply.

The economic indicators of “ultra-early detection” also cannot be discounted; everyone knows how to count money.

So tell me why the term “timely fire detection” is bad. Why does it not suit someone and why use non-existent and undefined terms. Why constantly confuse technical capabilities with marketing delights.

COMPARISON OF SOME FIRE DETECTION METHODS

As has already been written here, several years ago in our country there was a real opportunity to compare fire detection methods within the framework of fire tests using our domestic fire detectors. And this, of course, had to be taken advantage of.

I don’t want to reveal all the secrets in this article: who, where and when. What specific detectors there were and from which manufacturers is not in my competence, but I can say with full responsibility that the source data on which I will rely exists, and not in one copy. Maybe when the time comes, this data will be available to everyone, but not now. In this article, I really don’t want to either praise or scold anyone. Moreover, not all manufacturers of the samples used were even aware of these tests. The only thing I can note is that there were no random participants, only the best.

Before we begin to consider any results, it should be noted that they were not obtained during certification tests of specific samples in accordance with standard methods, but as part of certain research work. Therefore, in particular, instead of the required 4 samples of point optoelectronic smoke detectors from one manufacturer, several similar detectors were used different manufacturers. They did roughly the same thing with gas fire alarms.

Moreover, to obtain additional information for subsequent analysis, in addition to standard test fires, approximately the same tests were carried out with modified characteristics of the test fire load, but I do not consider it necessary to present their results.

And yet, during test fires, in addition to the response time, other parameters should be monitored, but since all the detectors were simultaneously in similar conditions during the tests, I am omitting this question with a clear conscience, the main thing is that the parameters do not go beyond the limits provided for by the standard .

Table 1 shows the ratio of the time required for the activation of fire detectors during test fires TP2 - TP5 to the standardized one. If you try to translate this into a more accessible language, then the percentage of time that was needed to detect a fire for one or another type of detector, in relation to the standardized time. For example, the maximum response time for TP3 is 750 seconds, and the detector was triggered after 190 seconds. It turns out to be only 25% of the time from the limit value. It worked four times faster than required - now we can put him in the “super early” caste, but let’s not rush.

Table 1. The ratio of the time required for the activation of fire detectors at TP2 - TP5, in relation to the standardized

					according to TP2-TP5
Maximum operating time of MP, s
IPDOT standard nephelometric
IPDOT experimental absorption
IPDOT tubeless		no data
IPDA (sensitivity class A) imported with the maximum possible length of the air pipeline
		no data
IPG semiconductor
IPG electrochemical

Since the article is not of a scientific nature, but is only informational, for greater clarity, the values ​​​​presented in the table under consideration are very rounded in nature without any probabilistic dependencies.

STANDARD FIRE DETECTORS SMOKE OPTICAL-ELECTRONIC SPOINT DETECTORS (IPDOT)

The one who has always raised doubts is the IPDOT. And here the first and very unexpected conclusion appears. Our domestic IPDOTs, which no one takes seriously in terms of the capabilities of timely fire detection and are used only in accordance with their cost, have, it turns out, a very decent margin in detection time in relation to the normalized one. And this should only make you happy. Unfortunately, in our country not all of them are like that, especially serial ones. But all the same, they can do it whenever they want.

Now imagine what they would be like if they still applied the developments that have long been used in modern foreign EITIs.

EXPERIMENTAL ABSORPTION TYPE IDPOT

This is a very interesting way to detect smoke. This IP does not use the principle of light scattering of the emitter from smoke particles in the measuring chamber, which is called the nephelometric method, but the principle of light absorption (absorption method), like linear fire detectors, only with a very short control section. Two entire articles in the journal “Security Algorithm” were devoted to both the detection method and the detector itself used in this analysis, so I will not consider here the details of the design of this IP.

Oddly enough, but it is he who most claims to be the “ultra-early” fire with a four-fold generalized margin for all test fires. Of course, what else could it be if its aerodynamic resistance to air flows is reduced to zero, there are no problems with the statics of the body and it is not afraid of flying dust. But what does the second journal article show us?

of the two already mentioned. It turns out that work on increasing sensitivity, and with it reducing the time to detect a fire, is just beginning. During the comparative tests that I am writing about here, very interesting patterns were discovered. Their implementation can bring a lot of new and interesting things, and then again there will be a reason to conduct a comparative analysis. And now these are only experimental single copies, and it is still very difficult to say how much the technical and economic indicators of these detectors will justify our hopes.

IPDOT CHAMBERLESS

This type of IPDOT does not have a measuring zone closed by the body and labyrinths. Sometimes this type of IPDOT is classified as a detector with a virtual detection zone, since it is located outside the detector housing. Naturally, this type of detector, just like the absorption type IPDOT, has no aerodynamic resistance to air flows. Consequently, no time is required to overcome the static potential of the body, and no additional energy is required to overcome the labyrinth to the measuring zone. This is the well-deserved result - a three-fold generalized reserve for all test fires. If desired, he can also be classified as a “super-early” caste.

This is very promising direction development of fire detectors, especially if we take into account the results achieved in imported detectors with a similar method of detecting smoke. It is a pity that in our country practically no attention is paid to this area; abroad this is no longer a special case (Fig. 1).

Rice. 1. Options for tubeless IPDOT

THE ASPIRATION MAN, HE IS THE ASPIRATION MAN

Almost everyone knows about the features and exceptional capabilities of aspirating fire detectors (AFDA). Here a detector from a foreign manufacturer was used, and then only as a kind of standard. He is one of the leaders in our table. You just need to understand that not everything is so simple.

Somewhere, in some grocery store within walking distance, you have seen IPDA with your own eyes. I personally don't. Why? And it’s like climbing into a tractor with a tool for laparoscopic operations. Somehow it happened historically that when this type of detector appeared on the market, few people understood that this was not a universal detector for all occasions. And, despite its popularity among specialists, it was used to a very limited extent.

But when manufacturers realized that this type of detector needed to be positioned completely differently, the cart moved. And it really turned out that in some areas of fire protection there are no analogues to it. In the last two or three years, a sufficient number of articles have appeared on this topic, and everything has fallen into place. “Render unto Caesar the things that are Caesar’s, and the things that belong to God that are God’s.”

WHAT IS THE AMBIGUITY OF JUDGMENT ABOUT IPDA?

The IPDA processing unit itself has unsurpassed sensitivity. No one will even argue with this. If you use it to control a small volume, then the IPDA may end up in the mode “if you sniff very closely, the wire has not yet overheated, but is already warm and even smells a little, and something may happen to it someday, but not now, but a little later." The only question that immediately arises is how much it will cost. A lot, but in some cases this is justified.

The same IPDA can be used to control large areas of several thousand square meters, just as stated in the documentation for it. But here you will need to immediately understand that in this case you will have to forget about the crazy sensitivity to fire in each individual room. The gain will only be due to the delivery time of the smoke-air mixture, and even then it will not be that big. But in the same deep-frozen warehouses or in elevator shafts, you can’t put anything else. And does this make sense? once again mention its ability to “ultra-early detect” a fire. Hardly.

SMOKE IONIZATION FIRE DETECTOR (IPDI)

Now we can move on to the sad stuff.

IPDI is what older specialists are constantly nostalgic for. This is their favorite “radioisotope nickname”. It was argued that if IPDOTs can detect only “light smoke,” then the “radioisotope” detector can detect any kind, be it light or dark, and very quickly. And the problem is only with the “green” ones, because of which they have tightened the disposal of these detectors as much as possible.

This myth arose back when the threshold for triggering the IPDOT in the Smoke Channel installation was within 0.5 dB/m (GOST 26342-84), and not as it is now 0.05-0.2 dB/m. Moreover, now IPDOT is obliged to detect not only “light” smoke, but also all others.

Over the past 30 years, a lot has changed, only IPDI has remained the same. And now the opportunity has arisen to compare them with the new generation of fire detectors. And not just based on the response threshold in the smoke duct, which is the least of our interests, but during fire tests.

And what turned out to be - average and even very good. Few people need to use a fairly average detector given today's difficulties in handling radioisotope materials.

It is also necessary to take into account the weak point of IPDI - for them it makes no difference what aerosol particles to detect: smoke, steam, dust. So they still don’t have a way to combat this.

Maybe we have all been nostalgic for so many years in vain and will forgive these “greens” for their “meanness”; without them, it is unlikely that we would have begun to seriously engage in alternative directions.

FEATURES OF APPLICATION OF FIRE GAS DETECTORS (IGD)

A little over ten years ago, there was a wave of using IPG for early fire detection abroad.

The basis was the postulate that every fire is preceded by smoke from smoldering and carbon monoxide (carbon monoxide). This carbon monoxide diffuses instantly throughout the premises, much faster than smoke reaches ceiling smoke detectors; this diffusion is not particularly affected by convection air currents. This distribution method allows you to install fire detectors almost anywhere in the controlled premises.

And based on these postulates, we immediately started talking about the possibility of “ultra-early fire detection” using IPG (CO). A holy place is never empty, manufacturers of sensors for IPG (CO) immediately appeared, fortunately they already had similar tasks in industrial automation.

But in the process of developing standards for IPG (SO), we were faced with the fact that they cannot be sensitive to all the main test fires. Well, we left only TP2 (smoldering wood) and TP3 (smoldering cotton with glow) in the requirements and came up with one additional TP9 (smoldering cotton without glow). But left behind are all synthetics and flammable liquids, which can also emit smoke. The producers of IPG (SO) stubbornly hid this from everyone, but you can’t wear an awl in your pants for a long time.

It turned out that when synthetics smolder, it is not carbon monoxide that is released, but hydrogen chloride, which all these IPGs (CO) cannot detect. So, if synthetics surround us everywhere, then with cotton, which must smolder for the IPG (CO) to work, in our Everyday life much more difficult, it still needs to be found. And then can IPG (SO), which has the ability to detect fire from a limited list of combustible materials, be used as a self-sufficient and universal fire detector?

As a result, a couple of years ago the wave of IPG (SO) abroad completely died out, and people began to forget about it.

And when in our country we had the opportunity to compare everything together, it turned out that the idea of ​​“ultra-early fire detection” using IPG (SO) collapsed at the same time, just as it had done abroad several years earlier. And we had to forget about deep diffusion as a fact that had not been confirmed in practice, and as a consequence, it was impossible to arbitrarily install IPG (CO) in rooms, even behind a cabinet, even under a cabinet.

But what about there, abroad? They didn’t worry too much about it and didn’t break their spears. They very smoothly moved from IPG (SO) to multi-criteria fire detectors. And this is where all the developments in IPG (SO) came in very handy. We in Russia still have to comprehend all this first, especially since we do not yet have such a class of fire detectors as multi-criteria.

SOME FEATURES OF IPG TECHNOLOGIES

It should be immediately noted that carbon monoxide (CO) sensors come in two types: electrochemical sensors of the electrolytic type and metal-oxide semiconductor sensors. The former consume practically no electricity, but have a limited service life due to the use of electrolyte, the latter have a fairly long service life, but also have high energy consumption.

For electrolytic type sensors, the service life begins to count from the moment they are removed from a special container in which they are stored in warehouse conditions for their subsequent installation in the IPG. The technical characteristics and price of the carbon monoxide sensor itself, about 1-2 thousand rubles, are decisive for IPG (CO).

Today, only one manufacturer of these sensors in the world (Nemoto Sensor Engineering Co) can provide a 10-year service life guarantee. All the rest so far guarantee no more than five years, and a couple of years ago there was no more than three years of work.

The limited service life of carbon monoxide sensors does not allow the widespread use of both IPGs themselves and their combinations with thermal or smoke detection channels. Almost all manufacturers of fire automatic equipment, with the exception of IPG, indicate in their documentation the period

service for at least 10 years. In practice, the service life is rarely less than 15 years; after all, this is not the cheapest pleasure. Not a single foreign manufacturer allows you to independently replace carbon monoxide sensors in detectors, while honestly stating their service life of 5 years.

This is “ultra-early detection” using IPG, and the opportunities are still illusory, and the difficulties are objective.

SO TO BE OR NOT TO BE “SUPER EARLY FIRE DETECTION”

This issue should be resolved by the direct customers of fire safety services. If all the requirements of regulatory documents are met, if the manufacturer does not produce products that do not meet the declared characteristics, then nothing extra may be needed.

If someone wants to distinguish himself, he can put an IPDOT in his electrical panel next to the electricity meter, hide the same one behind the refrigerator and behind the TV, and go to bed with a calm soul. This method of “ultra-early detection” of a fire may even be the most economically effective compared to others. But who can force it to be used and on what basis?

If you particularly wish, you can install an aspiration detector in the office of the head of a particular organization, at his request and for his money, which will be triggered every time during heated disputes with subordinates. Well, the customer’s desire is the law.

In this article I have never mentioned linear smoke detectors (LSD). Also very a good thing, it just so happens that they did not take part in the research trials. If IPDL is used with maximum sensitivity at short distances, then the fire detection time is reduced several times. What is not “ultra-early detection”. It’s very simple, and you don’t need to invent anything new, I tested it myself. It’s just that low economic efficiency does not allow such decisions to be made.

No one, either abroad or in our country, will agree to additional requirements to ensure “ultra-early detection” of fire. As a result, this term should be excluded from everyday practice; it should not be used on occasion or not and mislead others with it. We don't need these myths.

LITERATURE

1. GOSTR 53325-2012 “Fire fighting equipment. Fire automatic equipment. Are common technical requirements and test methods."

In January 2017, work began on the draft interstate standard “Fire alarm control devices. Fire control devices. General technical requirements. Test methods". The next stage was the draft set of rules “Fire alarm systems and automation of fire protection systems. Design norms and rules." In the drafts of new documents, the tasks at hand are identified, and the necessary requirements aimed at their implementation are attached to them. Each requirement is a consequence or cause of other requirements. Together they form a completely interconnected system.

• For buildings and structures that store priceless collections and at the same time are objects with large numbers of people, timely and reliable fire detection is key. But there are objective reasons why traditional fire alarm systems remain either unacceptable or not reliable enough for cultural heritage sites. The best decision aspiration detector. That is why a whole list of cultural sites around the world are equipped with WAGNER products.

  Modern development microprocessor electronics and information technology have made it possible to approach the problem of fire detection in a fundamentally new way: from the analysis of a set of individual sensor elements that continuously measure atmospheric parameters in the vicinity of the detector (concentration of solid particles and carbon monoxide, air temperature), to the ability to recognize “sufficiency” in the measured values » fire conditions in the shortest possible time. Bosch's technology for continuous analysis of seven environmental parameters helps improve the reliability of fire alarm system detection and significantly reduce the likelihood of false alarms, even in difficult conditions operation.

  For reliable fire detection in sites with special operating conditions, such as the presence of corrosive gases, high humidity, high temperatures and air pollution, Securiton offers a system based on the MHD635 LIST temperature sensitive cable. This is the system high level safety, easy to install and install and does not require maintenance. Thermal sensitive cable Securiton MHD635 is used at the following sites: road and railway tunnels; tunnels and metro stations, track facilities; conveyor systems and automatic lines; cable tunnels and trays; warehousing and racking; industrial furnaces; deep freezers; cooling and heating devices; objects Food Industry; parking lots, walking excavators, ship mechanisms.

  The SecuriSens ADW 535 thermal differential linear detector from Securiton combines a proven operating principle with the latest advances in sensor and processor technologies. Thanks to the extremely resistant sensor tube, SecuriSens ADW 535 can be used where traditional fire detectors cannot be used. Durability and maintenance-free design make the ADW 535 the ideal solution. SecuriSens ADW 535 fully meets the requirements for modern linear thermal detectors, such as: full automatic monitoring of large spaces, resistance to aggressive environments, extreme humidity and high temperatures, the ability to distinguish real dangers from false ones. SecuriSens ADW 535 is a smart device that works great even in the most difficult conditions.

• For 2019, it is planned to develop a new national standard “Fire Alarm Systems. Manual for design, installation, maintenance and repair. Performance test methods." The article discusses issues related to maintenance and repair. It is important that, due to incomplete or incorrect formulations, service organizations do not end up in the extreme and are not forced to eliminate shortcomings they made at the design stage. It is imperative to test all systems as a whole at sites during scheduled maintenance to check their functioning according to the algorithms specified by the project.

• Target of this material– consider the main aspects of legislative regulation of the implementation of federal state control (supervision) over the activities of legal entities and individual entrepreneurs, and especially over the activities of legal entities with special statutory tasks and departmental security units.

This system is designed to detect the initial stage of a fire, transmit notification of the place and time of its occurrence and, if necessary, turn on automatic fire extinguishing and smoke removal systems.

An efficient system alerts fire danger is the use of alarm systems.

The fire alarm system must:

Quickly identify the location of the fire;

Reliably transmit a fire signal to the receiving and control device;

Convert the fire signal into a form convenient for perception by the personnel of the protected facility;

Remain immune to the influence of external factors other than fire factors;

Quickly identify and report faults that impede the normal functioning of the system.

Industrial buildings of categories A, B and C, as well as objects of national importance, are equipped with fire-fighting automatic equipment.

The fire alarm system consists of fire detectors and converters that convert fire factors (heat, light, smoke) into an electrical signal; a monitoring and control station that transmits a signal and turns on a light and sound alarm; and automatic installations fire extinguishing and smoke removal.

Detecting fires at an early stage makes them easier to extinguish, which largely depends on the sensitivity of the sensors.

Detectors, or sensors, can be of various types:

- heat fire detector– an automatic detector that responds to a certain temperature value and (or) the rate of its increase;

- smoke detector– automatic fire detector that responds to aerosol combustion products;

- radioisotope fire detector – a smoke fire detector, which is triggered due to the influence of combustion products on the ionized flow of the detector’s working chamber;

- optical fire detector– a smoke fire detector that is triggered due to the influence of combustion products on the absorption or propagation of electromagnetic radiation from the detector;

- fire flame detector– reacts to electromagnetic radiation of the flame;

- combined fire detector– reacts to two (or more) fire factors.

Heat detectors are divided into maximum, which are triggered when the temperature of the air or the protected object rises to the value by which they are adjusted, and by differential, which are triggered at a certain rate of temperature increase. Differential thermal detectors can usually also operate in maximum mode.

Maximum thermal detectors are characterized by good stability, do not give false alarms and have a relatively low cost. However, they are insensitive and even when placed at a short distance from places of possible fires, they operate with a significant delay. Differential type heat detectors are more sensitive, but their cost is high. All heat detectors must be placed directly in work areas, so they are subject to frequent mechanical damage.

Rice. 4.4.6. Schematic diagram detector PTIM-1: 1 – sensor; 2 – variable resistance; 3 – thyratron; 4 – additional resistance.

Optical detectors are divided into two groups : IR – direct vision indicators who must “see” the fire, and photovoltaic flue. The sensing elements of direct vision indicators are of no practical importance, since they, like heat detectors, must be located in close proximity to potential sources of fire.

Photoelectric smoke detectors are triggered when the luminous flux in the illuminated photocell weakens as a result of smoke in the air. Detectors of this type can be installed at a distance of several tens of meters from a possible fire source. Dust particles suspended in the air can cause false alarms. In addition, the sensitivity of the device noticeably decreases as fine dust settles, so the detectors must be inspected and cleaned regularly.

Ionization smoke detectors For reliable operation, it is necessary to thoroughly inspect and check it at least once every two weeks, remove dust deposits in a timely manner and adjust sensitivity. Gas detectors are triggered when gas appears or its concentration increases.

Smoke detectors designed to detect combustion products in the air. The device has an ionization chamber. And when smoke from a fire enters it, the ionization current decreases and the detector turns on. The response time of a smoke detector when smoke enters it does not exceed 5 seconds. Light detectors are designed according to the operating principle ultraviolet radiation flame.

The choice of automatic fire alarm detector type and installation location depends on the specifics technological process, type of flammable materials, methods of their storage, room area, etc.

Heat detectors can be used to monitor premises at the rate of one detector per 10 - 25 m 2 of floor. A smoke detector with an ionization chamber is capable (depending on the installation location) of serving an area of ​​30 - 100 m 2. Light detectors can control an area of ​​about 400 - 600m2. Automatic detectors are mainly installed on the stream or suspended at a height of 6 - 10 m from the floor level. The development of the algorithm and functions of the fire alarm system is carried out taking into account the fire danger of the facility and architectural and planning features. IN given time The following fire alarm systems are used: TOL-10/100, APST-1, STPU-1, SDPU-1, SKPU-1, etc.

Rice. 4.5.7. Diagram of automatic smoke detector ADI-1: 1.3 – resistance; 2 – electric lamp; 4 – ionization chamber; 5 – diagram of connection to the electrical network

This system is designed to detect the initial stage of a fire, transmit notification of the place and time of its occurrence and, if necessary, turn on automatic fire extinguishing and smoke removal systems.

An effective fire danger warning system is the use of alarm systems.

The fire alarm system must:

* - quickly identify the location of the fire;

* - reliably transmit a fire signal to the receiving and control device;

* - convert the fire signal into a form convenient for perception by the personnel of the protected facility;

* - remain immune to the influence of external factors other than fire factors;

* - quickly identify and transmit notification of faults that impede the normal functioning of the system.

Industrial buildings of categories A, B and C, as well as objects of national importance, are equipped with fire-fighting automatic equipment.

The fire alarm system consists of fire detectors and converters that convert fire factors (heat, light, smoke) into an electrical signal; a monitoring and control station that transmits a signal and turns on a light and sound alarm; as well as automatic fire extinguishing and smoke removal installations.

Detecting fires at an early stage makes them easier to extinguish, which largely depends on the sensitivity of the sensors.

Automatic fire extinguishing systems

Automatic fire extinguishing systems are designed to extinguish or localize a fire. At the same time, they must also perform the functions of an automatic fire alarm.

Automatic fire extinguishing installations must meet the following requirements:

* - response time must be less than the maximum permissible time for free development of a fire;

* - have the duration of action in extinguishing mode necessary to extinguish the fire;

* - have required intensity supply (concentration) of fire extinguishing agents;

* - reliability of operation.

In premises of categories A, B, C, stationary fire extinguishing installations are used, which are divided into aerosol (halocarbon), liquid, water (sprinkler and deluge), steam, and powder.

Sprinkler systems for extinguishing fires with sprayed water have become the most widespread at present. To do this, a network of branched pipelines is installed under the ceiling, on which sprinklers are placed at the rate of irrigation with one sprinkler from 9 to 12 m 2 of floor area. There must be at least 800 sprinklers in one section of the water system. The floor area protected by one sprinkler type SN-2 should be no more than 9 m 2 in rooms with increased fire hazard (when the amount of combustible materials is more than 200 kg per 1 m 2; in other cases - no more than 12 m 2. The outlet hole in the sprinkler head is closed with fusible lock (72°C, 93°C, 141°C, 182°C), when melted, water sprays, hitting the deflector. The intensity of irrigation of the area is 0.1 l/s m 2.

Sprinkler networks must be under pressure capable of delivering 10 l/s. If at least one sprinkler is opened during a fire, a signal is given. Control and alarm valves are located on visible and accessible places, and no more than 800 sprinklers are connected to one control and alarm valve.

In fire hazardous areas, it is recommended to supply water immediately over the entire area of ​​the room. In these cases, group action units (deluge units) are used. Deluge sprinklers are sprinklers without fusible locks with open holes for water and other compounds. At normal times, the water outlet to the network is closed by a group action valve. The intensity of water supply is 0.1 l/s m 2 and for rooms with increased fire danger (with the amount of combustible materials 200 kg per 1 m 2 or more) - 0.3 l/s m 2.

The distance between drenchers should not exceed 3 m, and between drenchers and walls or partitions - 1.5 m. The floor area protected by one deluge should be no more than 9m2. During the first hour of fire extinguishing, at least 30 l/s must be supplied

The installations allow automatic measurement of controlled parameters, recognition of signals in the presence of an explosive and fire hazardous situation, conversion and amplification of these signals, and issuance of commands to turn on actuators of protection.

The essence of the process of stopping an explosion is the inhibition of chemical reactions by supplying fire extinguishing compounds to the combustion zone. The possibility of stopping an explosion is due to the presence of a certain period of time from the moment the conditions of the explosion arise until its development. This period of time, conventionally called the induction period (f ind), depends on the physico-chemical properties of the combustible mixture, as well as on the volume and configuration of the protected apparatus.

For most flammable hydrocarbon mixtures, fiind is about 20% of the total explosion time.

In order to automatic system explosion protection meets its intended purpose, the following condition must be met: T ASPV< ф инд, то есть, время срабатывания защиты должно опережать время индуктивного периода.

Conditions safe use electrical equipment is regulated by the PUE. Electrical equipment is divided into explosion-proof, suitable for fire hazardous areas, and normal. In explosive areas, it is allowed to use only explosion-proof electrical equipment, differentiated by levels and types of explosion protection, categories (characterized by a safe gap, that is, the maximum diameter of the hole through which the flame of a given combustible mixture is not able to pass), groups (characterized by T with a given combustible mixture).

In hazardous areas and areas external installations special electric lighting equipment made in an anti-explosion version is used.

Smoke hatches

Smoke hatches are designed to ensure that adjacent rooms are smoke-free and to reduce the concentration of smoke in the lower zone of the room in which the fire occurred. By opening smoke hatches, more favorable conditions are created for the evacuation of people from a burning building, and the work of fire departments to extinguish the fire is facilitated.

To remove smoke in the event of a fire in the basement, the standards provide for the installation of windows measuring at least 0.9 x 1.2 m for every 1000 m 2 of area basement. The smoke hatch is usually closed with a valve.

IN Russian Federation About 700 fires occur every day, killing more than 50 people. Therefore, preserving human life remains one of the most important tasks of all security systems. Recently, the topic of early fire detection has been increasingly discussed.

Developers of modern fire-fighting equipment compete to increase the sensitivity of fire detectors to the main signs of a fire: heat, optical radiation from the flame and smoke concentration. A lot of work is being done in this direction, but all fire detectors are triggered when at least a small fire has already broken out. And few people discuss the topic of detecting possible signs of a fire. However, devices that can record not a fire, but only the threat or probability of a fire, have already been developed. These are gas fire detectors.

Comparative analysis

It is known that a fire can occur either from a sudden emergency situation(explosion, short circuit), and with the gradual accumulation of dangerous factors: accumulation of flammable gases, vapors, overheating of the substance above the ignition point, smoldering insulation of electrical cables from overload, rotting and heating of grain, etc.

In Fig. Figure 1 shows a graph of the typical response of a gas smoke detector to a fire starting with a burning cigarette dropped on a mattress. The graph shows that the gas detector responds to carbon monoxide after 60 minutes. after a burning cigarette hits the mattress, in the same case the photoelectric smoke detector reacts after 190 minutes, the ionization smoke detector - after 210 minutes, which significantly increases the time for making a decision to evacuate people and eliminate the fire.

If you record a set of parameters that can lead to the start of a fire, then you can (without waiting for flames or smoke to appear) change the situation and avoid a fire (accident). Upon early receipt of a signal from a gas fire detector, maintenance personnel will have time to take measures to weaken or eliminate the threat factor. For example, this can be ventilating the room from flammable vapors and gases; if the insulation overheats, turn off the cable power and switch to using a backup line; if there is a short circuit on the electronic board of computers and controlled machines, extinguish a local fire and remove the faulty unit. Thus, it is the person who makes the final decision: to call fire department or eliminate the accident on your own.

Types of gas detectors

All gas fire detectors differ in sensor type:
- metal oxide,
- thermochemical,
- semiconductor.

Metal oxide sensors

Metal oxide sensors are manufactured based on thick film microelectronic technology. Polycrystalline aluminum oxide is used as a substrate, onto which a heater and a metal oxide gas-sensitive layer are applied on both sides (Fig. 2). The sensitive element is placed in a housing protected by a gas-permeable shell that meets all explosion and fire safety requirements.

Metal oxide sensors are designed to determine the concentrations of flammable gases (methane, propane, butane, hydrogen, etc.) in the air in the concentration range from thousandths to units of percent and toxic gases (CO, arsine, phosphine, hydrogen sulfide, etc.) at level of maximum permissible concentrations, as well as for the simultaneous and selective determination of oxygen and hydrogen concentrations in inert gases, for example in rocket technology. In addition, they have a record low electrical power required for heating for their class (less than 150 mW), and can be used in gas leak detectors and fire alarm systems, both stationary and portable.

Thermochemical gas detectors

Among the methods used to determine the concentration in atmospheric air flammable gases or vapors of flammable liquids, the thermochemical method is used. Its essence lies in measuring the thermal effect (additional increase in temperature) from the oxidation reaction of flammable gases and vapors on the catalytically active element of the sensor and further converting the received signal. The alarm sensor, using this thermal effect, generates an electrical signal proportional to the concentration of flammable gases and vapors with different proportionality coefficients for different substances.

When various gases and vapors burn, the thermochemical sensor produces signals of different sizes. The same levels (in % LEL) of various gases and vapors in air mixtures correspond to unequal output signals from the sensor.

The thermochemical sensor is not selective. Its signal characterizes the level of explosion hazard determined by the total content of flammable gases and vapors in the air mixture.

In the case of monitoring a set of components, in which the content of individual, previously known flammable components varies from zero to some concentration, this can lead to a control error. This error also exists under normal conditions. This factor must be taken into account to set the limits of the range of signal concentrations and the tolerance for their change - the limit of the permissible basic absolute response error. The measurement limits of the detector are the lowest and highest concentration values ​​of the component being determined, within which the detector carries out measurements with an error not exceeding the specified one.

Description of the measuring circuit

The measuring circuit of the thermochemical converter is a bridge circuit (see Fig. 2). Sensitive B1 and compensating B2 elements located in the sensor are included in a bridge circuit. The second branch of the bridge - resistors R3–R5 are located in the signaling unit of the corresponding channel. The bridge is balanced by resistor R5.

During catalytic combustion of an air mixture of flammable gases and vapors on the sensitive element B1, heat is released, the temperature increases and, consequently, the resistance of the sensitive element increases. There is no combustion at compensating element B2. The resistance of the compensating element changes with its aging, changes in supply current, temperature, speed of movement of the controlled mixture, etc. The same factors also act on the sensitive element, which significantly reduces the bridge imbalance (zero drift) caused by them and the control error.

With stable power to the bridge, stable temperature and speed of the controlled mixture, the imbalance of the bridge with a significant degree of accuracy is the result of changes in the resistance of the sensing element.

In each channel, the sensor bridge power supply ensures a constant optimal temperature of the elements by regulating the current. As a rule, the sensitive element B1 itself is used as a temperature sensor. The bridge imbalance signal is taken from the bridge diagonal ab.

Semiconductor gas sensors

The operating principle of semiconductor gas sensors is based on a change in the electrical conductivity of the semiconductor gas-sensitive layer during chemical adsorption of gases on its surface. This principle allows them to be effectively used in fire alarm devices as alternative devices to traditional optical, thermal and smoke alarms (detectors), including those containing radioactive plutonium. And the high sensitivity (for hydrogen from 0.00001% volume), selectivity, speed and low cost of semiconductor gas sensors should be considered as their main advantage over other types of fire detectors. The physical and chemical principles of signal detection used in them are combined with modern microelectronic technologies, which leads to low cost of products in mass production and high technical characteristics.

Semiconductor gas-sensitive sensors are high-tech elements with low power consumption (from 20 to 200 mW), high sensitivity and increased speed up to fractions of seconds. Metal oxide and thermochemical sensors are too expensive for this use. The introduction into production of gas fire detectors based on semiconductor chemical sensors, manufactured using group technology, can significantly reduce the cost of gas detectors, which is important for mass use.

Regulatory Requirements

Regulatory documents for gas fire detectors have not yet been fully developed. The existing departmental requirements RD BT 39-0147171-003-88 apply to oil and gas facilities gas industry. NPB 88-01 on the placement of gas fire detectors states that they should be installed indoors on the ceiling, walls and other building structures of buildings and structures in accordance with the operating instructions and recommendations of specialized organizations.

However, in any case, in order to accurately calculate the number of gas detectors and correctly install them at the site, you must first know:
- the parameter by which safety is monitored (the type of gas that is released and indicates danger, for example CO, CH4, H2, etc.);
- volume of the room;
- purpose of the premises;
- availability of ventilation systems, air pressure, etc.

Summary

Gas fire detectors are next-generation devices, and therefore they still require domestic and foreign companies involved in fire protection systems, new research studies to develop the theory of gas emission and distribution of gases in rooms of different purposes and operation, as well as conducting practical experiments to develop recommendations for the rational placement of such detectors.

As you know, a day of data center downtime costs tens or even hundreds of millions of dollars. For continuous operation, the data center must be protected from many hazards, including fire. In large American and European data centers, aspiration systems for early detection of fires are actively used for this purpose.

Specifics of fire detection in data centers

A data center is a high-tech facility that consumes more electricity than a typical office. An important requirement for data centers is maintaining a certain indoor air temperature. Serves this purpose special system air conditioning, with the help of which internal air flows are created between and inside the racks, ensuring the removal of excess heat and a comfortable temperature for equipment operation.

Such a complex air conditioning system requires special approach to fire detection. The fact is that in the presence of strong air currents, conventional fire detectors are ineffective for detecting smoke or heat radiation. Smoke driven by air currents may not enter the smoke chamber of the detector. And if it does get into the chamber, then by that moment the maximum concentration of smoke in the room has been reached, so that when the detector is triggered, the spread of fire is already inevitable. Therefore, modern data centers use active aspiration fire alarm systems.

Currently, aspiration fire alarm systems are produced only abroad; their main manufacturers are Bosch, Safe Fire Detection, Securiton, System Sensor and Xtralis (it owns the Vesda and Icam equipment brands, the latter was recently purchased by it).

Systems of this class, for example, Vesda and Icam from Xtralis, Titanus from Bosch Security or aspiration detectors System Sensor of the same company, are already used in many countries around the world at facilities of this type, including in Russia.

Historical reference In 1967, American researchers Ahlquist & Charlson first created a nephelometer device to measure air transparency and the degree of air pollution, allowing one to monitor the carbon dioxide content on city streets. This device was improved and released to the market in the United States. In 1970, the Australian Commonwealth of CSIRO used the nephelometer in research forest fires. A little later, the CSIRO was contacted by the APO, the main postal department, with an order to study the problem of fire prevention in postal services. The purpose of the study was to find the most suitable technology for fire protection of telephone exchanges, computer rooms and cable tunnels. The sources of risk at these sites were cables that were heated by electric current or hot plates. In this study, CSIRO used nephelometers to monitor smoke levels in ventilation ducts. Subsequently, this research gave impetus to the development of a highly sensitive device capable of detecting smoke at the early stage of a fire. The release of an improved version of this device to the market was a huge leap in the development of early smoke detection systems.

It should be noted that the requirements of some international insurance companies already stipulate the use of early fire detection systems, including as a means of reducing insurance payments. And in the regulations of the largest international IT companies, the early fire detection system is part of the fire safety system.

Principle of operation

Aspiration systems are early fire detection systems. As a rule, they have a modular architecture that allows the system to be adapted to specific operating conditions and building layout. The main components of such a system are a pipeline for drawing air from the controlled area and the detector itself, which can be placed anywhere inside or outside the protected premises.

The pipeline is usually used PVC pipes. Using adapters, angles, tees and other accessories, you can create flexible networks of pipelines for air intake, taking into account the characteristics of each individual room. In this case, the aspiration detector itself creates a vacuum in the piping system to ensure a continuous intake of air from the monitored area through specially made holes. These actively produced air samples pass through a detection chamber where they are tested for smoke particle content. In addition, for example, in the VESDA system, dust and contaminants are first removed from the air sample using a built-in filter, and then the sample is fed into the aspirating detector chamber. This prevents contamination of the camera's optical surfaces.

The air sample enters a calibrated chamber in the detector where a laser beam passes through it. When smoke particles are present in the air, light scatters within the chamber and is immediately detected by the highly sensitive receiving system (Fig. 1). The signal is then processed and displayed on a bar graph display, alarm threshold indicators and/or graphic display. The sensitivity of the detector can be adjusted and the air flow is continuously monitored for detection of pipeline damage.

Aspiration detectors are conventionally divided into two categories. The first is PIB (Point in the box) type detectors, in which conventional high-sensitivity smoke detectors are used as a detection chamber, for example, ASD-Pro or LASD from System Sensor with a sensitivity of 0.03 to 3.33%/m. The second group is aspiration detectors such as VESDA, Icam or Titanus, which have their own built-in smoke detection chambers with a sensitivity range from 0.005 to 20%/m for VESDA, from 0.001 to 20%/m for Icam and from 0.05 to 10%/m m at Titanus. We will consider only detectors of the second group, since they have the largest sensitivity range compared to PIB, which makes it possible to detect a fire at the wire melting stage and set the highest threshold for starting a gas fire extinguishing system in data center premises.

Features and Benefits

Classic fire alarm systems do not go off until there is smoldering or fire. At this stage of the fire, fighting the fire becomes difficult. The most important advantage aspiration systems is that they detect an incipient fire and provide early warning of a fire. The smoke detection camera's intelligent processor analyzes the data received and decides whether it matches any typical fire patterns. At the same time, external factors that can cause false alarms are suppressed.

So, what are the main advantages of aspiration systems?

1. Reliable fire detection for early warning. Highly sensitive sensors detect a fire at its earliest stage - in the pyrolysis phase, even before visible smoke particles spread (for example, when a wire or other electronic element of equipment begins to melt). In most cases, such systems prevent significant material damage, since they quickly identify a failed element that can be de-energized, preventing an incipient fire from entering the active phase. In addition, aspiration systems make it possible not to activate an active (usually gas) fire extinguishing system and save the money required to recharge gas cylinders.

2. Reducing the number of false positives. Thanks to intelligent signal processing from sensors in aspiration systems, external factors such as dust, drafts or electrical interference, which often cause false alarms, are suppressed. This ensures greater sensitivity and reliability of the system, even in rooms with high ceilings or extreme temperatures, as well as in dirty or high humidity environments.

3. Fast installation and easy maintenance. Detectors can be installed anywhere, both indoors and outdoors, to make them easier for service technicians to access. Aspiration systems are invisible in the room, and their maintenance does not require high qualifications. Information about all faults, such as pipeline damage, filter contamination, etc., is displayed on the display screen. Thus, personnel do not have to spend a lot of time identifying system malfunctions; it can be serviced as information becomes available.

The main and fundamental difference between aspiration systems and conventional systems with passive smoke sensors is the active sampling of air from communication and server cabinets of the data center, using a built-in fan operating on the principle of a vacuum cleaner. Another important difference is the higher sensitivity of the detectors, which makes it possible to detect smoke particles invisible to the human eye, with a concentration of 0.005%/m for the VESDA system, 0.001% for the Icam or 0.05% for the Titanus.

An important feature is the presence of a built-in (like the VESDA system) and/or external filter where the intake air is cleaned. Such filters allow the operation of aspiration systems in heavily contaminated rooms without constant cleaning or replacement of laser chambers, which, in turn, increases the service life of the system and reduces its maintenance costs.

Areas of use

In some cases, the use of aspiration systems brings tangible results compared to conventional passive detectors. First of all, these are enterprises and companies where the continuity of production or business processes is of paramount importance, and downtime is unacceptable. These are, for example, telecommunication systems and server rooms of financial organizations, communal facilities and medical sterile rooms (operating rooms), energy and transport systems. Aspiration systems are also useful when it is necessary to eliminate false activation of the active fire extinguishing system, which leads to large expenditures of time and money for the restoration of the facility.

Aspiration systems are preferred in areas where smoke detection is difficult, such as high air flows or high atrium spaces (shopping malls, Sport halls, theaters, museums, etc.). They are also used in rooms where access for Maintenance impossible or difficult; they are optimal for protecting the space behind suspended ceiling and under raised floors, elevator shafts, industrial areas, air ducts, and prisons and other places of detention. Another area of ​​application is in extreme conditions environment: heavy dust, gas contamination, humidity, very high or very low temperatures (for example, in power plants, paper or furniture factories, in auto repair shops, mines). Finally, aspiration systems are used if it is important to preserve the design of the room and smoke detection devices need to be hidden.

Construction of an aspiration system in a data center

Typically, data center equipment is located in locked cabinets, so the most effective solution to protect these areas is to sample from the cabinets. In the case of aspiration systems in data centers, tubes with suction holes are routed over racks with installed equipment. The flexible tubing system allows sampling both above and inside cabinets using capillaries, providing the most reliable smoke detection in fully enclosed cabinets, as well as in cabinets with top ventilation (Figure 2).

How much does fire protection cost? The cost of a fire protection solution for a specific data center depends on the volume and area of ​​the premises, as well as the number of separately protected system components. In any case, this cost does not exceed 1% of the cost of equipment installed in the data center. For example, the price of a 15-channel Icam detector, capable of protecting 15 racks of equipment, is 10-11 thousand euros, the deviceVESDA VLP, which can protect up to 2000 sq.m., costs 4-5 thousand euros, and Titanus protects up to 400 sq.m. and costs 2000-4000 euros.

Active air suction and its subsequent analysis for the content of smoke particles in the aspiration chamber makes it possible to build a system in such a way that air flows in the room do not affect smoke detection. For example, using the Icam sensor, you can protect up to 15 racks by laying a separate capillary tube in each of them, and also provide targeting, determining the location of the fire with the accuracy of an individual cabinet. The principle of operation of the Icam sensor is the alternate intake of air from each tube and its further analysis for the content of smoke particles in the detection chamber.

The Titanus system has a ROOM-IDENT function that provides early fire detection and location. One detector can monitor up to five rooms or five racks using only one tube. The process of determining the source of fire by the ROOM-IDENT system includes four stages, and the result is displayed on the detector.

Stage 1(Normal Mode): The piping is used to collect and evaluate air samples in multiple rooms.

Stage 2(early fire detection): air suction and analysis. If smoke is present, an alarm will immediately sound for early response.

Stage 3(reverse circulation): when the alarm signal is activated, the suction fan is turned off and the second, discharge fan is turned on, blowing all smoke particles out of the pipeline in the opposite direction.

Stage 4(location determination): after the pipeline is purged, the direction of air movement changes again. Based on measurements of the time it took for smoke particles to reach the detection module, the system determines the location of the fire.

Using a flexible piping system, with a single VESDA sensor it is possible, for example, to monitor the space not only above the racks, but also behind the false ceiling and raised floor, as well as cable trays, which are present in any data center and are often a source of fire. In addition, VESDA system detectors are built into a rack, which saves space and ensures the design uniformity of all equipment in the data center.

Another key point in organizing a reliable fire detection system is air intake directly from the supply and exhaust ventilation grille of the room. The resulting smoke inevitably enters the air flow, so installing a pipe system with intake holes on the air return grille of the circulation system ensures instant detection of an incipient fire at a very early stage.

Taking air samples directly next to the exhaust ventilation grille allows you to catch smoke particles in the air even if the created air flows have bypassed all other intake pipes in the room. This is due to the fact that through exhaust ventilation all the air contained in the room circulates, which means that not a single particle of smoke contained in the air will pass past the intake opening (Fig. 3).

The ability to set different levels of fire danger allows you to program the system for appropriate reactions at different stages of fire development, for example, turning off air conditioning equipment or starting active fire extinguishing systems. For example, you can set several pre-alarm thresholds or the highest sensitivity to determine the moment of melting of equipment elements. If this sensitivity threshold is exceeded, a pre-alarm signal will be transmitted to the fire station so that personnel can identify the melting point and turn off the power to the equipment, preventing the spread of the fire.

You can also set the sensitivity to medium, and the system will detect the moment of heavy smoke in the room, when it is difficult to find the place or equipment that is causing the smoke. If this sensitivity threshold is exceeded, you can program the system to turn off the air conditioners. The lowest sensitivity is set for the level of smoke in the room, when it is impossible to prevent further spread of the fire without active fire extinguishing systems. When this sensitivity threshold is reached, the gas fire extinguishing system is programmed to turn on (Fig. 4).

Turning on fire extinguishing systems is the second stage of preventing the spread of fire in a data center, when the development of a fire can no longer be stopped using simple actions: turning off a smoking server, air conditioning systems, etc. For active fire extinguishing, as a rule, gas fire extinguishing systems are used, using two principles for organizing fire extinguishing in a data center. The first is general gas fire extinguishing, when the total area of ​​the data center is extinguished. The second is rack gas fire extinguishing, when a separate rack is extinguished. The latter principle applies to racks with special-purpose equipment, where data loss will cost more than installing and operating a fire suppression system. But this is a topic for a separate article.

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Timely detection of a fire in a data center can prevent the loss of equipment and critical data, as well as forced downtime, associated with financial and material costs for the company. Investing in reliable system Fire alarms in data centers guarantee the organization protection against future costs for the restoration of electronic equipment and information lost in a fire. Sometimes these financial losses are incomparably greater than the cost of an early fire detection system.