Today in Russia, the capabilities of fire detectors with a gas channel are greatly underestimated.
The questions of the TZ are answered by the general director of the company «ETRA-spetsavtomatika» Evgeny SAIDULIN
The primary task of a fire alarm system, the main elements of which are fire detectors, is to detect a fire at the earliest stage, when the fire can still be easily localized and thus save people's lives and material assets.
Fire detectors, the most common at present in Russia, detect the following fire factors: a change in the optical density of air as a result of smoke (smoke optoelectronic detectors), an increase in temperature or the rate of temperature increase (thermal maximum, differential, maximum-differential detectors), the appearance of an open flame (flame detectors).
But there are also gas fire detectors, the main function of which is early detection of fires.
Technical Specifications:
— Please tell us how a gas fire detector works.
Evgeny SAIDULIN:
— Anyone can easily explain how a gas fire alarm (GFA) works. Let's recall the situation: a garbage can is burning somewhere in the neighboring yard. We don't see any smoke yet, there is no flame either, but the smell of burning… It can be felt quite far from the burning can, in any weather. So, this smell is only what a person can smell. However, other gases are released during combustion that a person does not perceive: carbon monoxide, hydrogen, hydrocarbons, and the GFA must determine the presence of such gases in the air and, based on this, issue a fire signal. To deny the change in the gas composition of the air during smoldering and fire, or to consider it insignificant, is, at a minimum, ignorant.
Gas fire detectors do not react to smoke, but to the presence of gas molecules in the air. As a rule, such gas is carbon monoxide (CO). Why is this important? Let's remember physics. Smoke spreads by convection: mixing with air, it gradually fills the space. At the same time, the smoke cools down and at the first stage of combustion «spreads» below. Smoke optical fire detectors are located on ceilings, and often — on high ceilings. In order for the smoke to be recorded by the detector, it must fill the entire space evenly. As a rule, by this time the fire will be at such a stage when there can no longer be talk of minimizing damage.
When smoldering or burning, carbon monoxide is released along with smoke, and much faster. It is this gas, which fills the space faster than smoke, that the gas fire alarm is designed to detect. The gas PI does not need the gas to fill the entire space at all. It will raise the alarm already at a concentration of 40 molecules of carbon monoxide per million molecules of air. Like a dog's sensitive nose, the alarm will «smell» a fire starting at the very beginning of smoldering.
In order not to be unfounded, I will quote the VNIIPO document «Fire automatic equipment. Scope. Selection of type. Recommendations»:
Quote: «… For example, according to experimental data on the development of a fire source of cellulose-containing materials, gaseous products of thermal decomposition are released during the first 20 minutes, then visible smoke products appear, registered by smoke detectors at the 40th minute. The appearance of threshold levels of excess temperature in the room is detected after 2-2.5 hours, depending on the height of the room; an open flame can be detected before the heat detectors are triggered.»
Technical Specifications:
— As far as is known, carbon monoxide is extremely dangerous to human health and life.
Evgeny SAIDULIN:
— Carbon monoxide is one of the most toxic gases, colorless and odorless, spreading evenly throughout the entire volume. The maximum permissible dose of carbon monoxide in a room is considered to be 0.002%, lethal — 0.4-0.5% (death of an adult occurs within 5-30 minutes, depending on the state of health and age). First, a person loses orientation in space, then — dies.
It should be noted that carbon monoxide is the main cause of death in fires. 80% of deaths in fires are associated with carbon monoxide poisoning. Such tragedies especially often happen to sleeping people. And here the use of a gas fire alarm becomes almost the only way out, since it will give an alarm in a timely manner and really save lives. In foreign applications of gas fire alarms, this property is called «protection of sleepers».
TZ:
— What do you think are the main advantages of gas fire alarms?
Evgeny SAIDULIN:
— Since gas, unlike smoke, spreads by diffusion, it is not affected by either the height of the ceilings or the temperature in the room. Thus, information about problems «in the atmosphere» reaches the detector very quickly. This is especially important for hidden, smoldering fires. A cigarette butt in a trash can, wiring insulation, furniture upholstery, plastic can smolder for a very long time, especially if there is no large influx of oxygen that provokes the growth of flame. In such cases, a gas PI is triggered 10-15 times faster than a smoke optical detector and really prevents a fire.
A gas PI is indispensable in places with large crowds of people, where it is necessary to have some time for evacuation. It is ideal for work in cold warehouses and archives.
The sensitive electronic element – the main component of this fire-fighting “nose” – is not subject to clogging and dust. This means that the sensitivity of the gas PI does not depend on the service life. Based on the experience of using gas PI, the service life in “dirty” rooms (smoky, dusty, with air flows of different temperatures) is 3-5 years without maintenance.
Technical Specifications:
— You know, it seems that the GPI is some kind of panacea…
Evgeny SAIDULIN:
— In no case. Considering gas PI a panacea is the same as saying: let's remove a couple of sense organs from a person, everything will still function. We are talking about adding sense organs to fire alarm systems, gas PI is a kind of sixth sense of the ASPS.
Once again, what are the useful properties of gas PI: fire detection at the smoldering stage, at a low temperature of the fire source and maintaining operability in the presence of heavy dust, smoke, and air mixing. Taking these properties into account, we can determine the applicability of gas PI.
It is necessary to take into account one serious nuance: gas PI are not PDC gas detectors. The difference is very significant and is related to the higher speed of gas PI.
Technical Specifications:
— And what about industrial facilities, with fire-hazardous and explosive production?
Evgeny SAIDULIN:
— For such facilities, such properties of gas PI as detection of smoldering fires and maintenance-free operation for a long time (we are talking about months and years) are of interest.
Let's take, for example, a workshop where carbonated water is bottled. Such an object is characterized by high humidity and the presence of aerosols. Fire alarms will have to be serviced almost every day. Considering the height of the suspension — not a very pleasant task. For gas PI, this kind of interference does not exist.
The use of gas PI in ore mines has revealed another convenience of use: maintaining the ability to detect a fire in dusty conditions and powerful air flows. For example, gas PI are built into ventilation systems, and their task is to detect a fire when air is pumped at a speed of 2000 liters per second.
The development of gas PI is directly related to the development of the element base, in particular the gas sensor. The main requirement for the sensitive element is selectivity to gases, that is, response only to the gas that is selected as a sign of fire, smoldering.
The next important parameter is the service life of the sensor. Therefore, the first gas PIs used semiconductor sensors with a service life of 10 years or more. The sensor is good, but it consumes a lot of energy. The emergence of low-power sensors with a service life of 6-8 years made it possible to move on to the next generation of gas PIs, expanding the scope of their application.
Technical Specifications:
— Are there any objects where the use of gas PIs is ineffective?
Evgeny SAIDULIN:
— Of course, there is. The effectiveness of a particular type of PI is determined by the prevailing factor of the fire. I repeat once again, there is no absolute, ideal type of PI.
A gas PI is ineffective if there is a fairly quickly developing fire in a fairly clean room. In this case, powerful convection flows appear, which outpace the diffusion processes in terms of propagation speed, which means that a smoke PI will definitely work faster.
A gas fire detector is definitely useless when burning flammable liquids, since this process involves complete and rapid combustion with the release of pure heat. Perhaps this problem can be solved by aerosol fire detectors.
Naturally, gas fire detectors cannot be used in rooms where there may be levels of carbon monoxide that cause false alarms. These are, as a rule, garages, gasoline engines. Only a combination of different types of fire detectors allows fire detection in different types of fires, with different relative locations of the fire source and the fire detector.
Technical Specifications:
— How does the Russian legislative base interpret the use of gas PI?
Evgeny SAIDULIN:
— Almost nothing. When writing GOST R 53325-2009, this type of PI was «lost» along with NPB 71-98 «Gas fire detectors. General technical requirements. Test methods.» This causes difficulties in certifying gas PI.
SP 5.13130.2009 recognizes this type of detectors, giving carte blanche to the operating manual and recommendations for the use of the manufacturer's gas PI, although approved by «authorized bodies.» In fact, this is the only hole in the fence that allows the use of gas PI.
Technical Specifications:
Why, in your opinion, are gas PIs still in low demand on the Russian market?
Evgeny SAIDULIN:
— The first and main one I named is a weak regulatory framework. When smoke PIs were introduced in the 80s of the last century, the situation was difficult, since the cost of smoke PIs was tens of times higher than the cost of maximum thermal PIs. However, a regulatory framework for their use was quickly proposed, installers and designers were trained. And this, of course, made a big contribution to reducing fire losses. Now, gas PIs are being introduced by consumers who are not very interested in the shortcomings of the regulatory framework, the main thing for them is that it does not burn. It seems that the set of rules SP 5.13130.2009 allows the use of gas PIs, but does not offer a standard (template) solution, which is inconvenient for most designers.
The second reason is the high cost of the gas fire detector. However, I cannot help but notice that, firstly, even this cost is incomparably small compared to the efficiency, and secondly, the reduction in the cost of the product is directly related to demand.
Technical Specifications:
— How is this area developing in the leading Western countries?
Evgeny SAIDULIN:
— One can envy. If millions of sensors for gas fire detectors are produced per year, then someone needs it.
I am reading the article «Gas Fire Detectors Prove Their Efficiency at Coal-Firing Enterprises» (Safety & Technology), date — April 1999. We have not yet reached the European level of 12 years ago.
Again, it is well supported by the regulatory framework: LPS1265, EN54-26, in the American NFPA72 it is described right down to typical gas detector placement schemes. So there is foreign experience, and it is very positive. The main thing is to adopt it.