Gas fire extinguishing systems for high-rise buildings.
How to build a reliable and efficient fire safety system for a multifunctional high-rise building that guarantees trouble-free operation of all systems in an emergency and ensures unimpeded evacuation of people from a building of any number of storeys, as well as quick and effective fire localization and extinguishing.
Facilities where fires can lead to mass casualties among people located at these facilities and the surrounding area, with hazardous and harmful production facilities, as well as hazardous fire factors and their secondary manifestations, must have fire safety systems that ensure the lowest possible probability of a fire.
The main problems of fire safety of multifunctional high-rise buildings include:
exceeding the standard height and number of storeys for these buildings;
lack of federal-level regulatory documents regulating fire safety requirements for high-rise buildings and multifunctional complexes.
Temporary technical conditions (norms) are developed and approved for such objects. Thus, temporary norms MGSN 4.19-05 have been developed for the construction of high-rise objects in Moscow, and attempts are being made to develop such norms in other cities, for example, for the construction of the high-rise multifunctional public and business center «Okhta» in St. Petersburg.
The concept of fire protection for such facilities is based on the provisions of GOST 12.1.004-91 and ensures the protection of the facility in the event of a fire on any floor or in any fire compartment. For facilities that do not comply with current standards, GOST 12.1.004-91 establishes requirements for the development of projects for compensating means and systems for ensuring fire safety at the stages of construction, reconstruction and operation of facilities.
When selecting equipment for an automatic fire alarm system, fire extinguishing, notification and evacuation systems, as well as when developing algorithms for controlling fire zones (compartments) and the entire complex as a whole, the main criteria should be the reliability and survivability of all systems that ensure the safety of people in an emergency.
The reliability of a high-rise building's fire protection system depends on many factors, which can be divided into five components:
reliability of the technical equipment itself;
reliability in the area of power supply;
redundancy and duplication of control over security systems;
professional technical maintenance;
protection of technical equipment, as well as power and low-current electrical circuits by fire extinguishing systems.
That is, one of the means that ensures the safety and survivability of technical systems, as well as the safety of people in multifunctional high-rise buildings and complexes, are automatic fire extinguishing systems.
Automatic fire extinguishing systems are divided into:
water and foam fire extinguishing systems;
gas fire extinguishing systems;
powder and aerosol fire extinguishing systems;
water mist fire extinguishing systems.
Each of the above systems, due to their importance and significance in fire extinguishing issues, can be dedicated to an entire article.
This article is devoted to new innovative products in the field of gas fire extinguishing and issues of the prospects for the use of gas fire extinguishing systems in multifunctional high-rise buildings and complexes.
Despite the high cost, the most effective of the fire extinguishing systems used, causing minimal damage during a fire, are automatic gas fire extinguishing systems. The unique ability of gas to penetrate into the most inaccessible places and effectively affect the source of fire has become widespread in the use of fire extinguishing gases in automatic gas fire extinguishing systems in all areas of human activity. Depending on their chemical properties, fire extinguishing compounds can be divided into gases that are harmless in terms of their impact on human health, conditionally harmless gases that displace oxygen from the protected premises during a fire, and harmful gases. Harmless gases can be removed from the premises after a fire through general ventilation, conditionally harmful and harmful gases must be removed through specialized gas and smoke removal systems.Most fire extinguishing agents currently used in Russia are obsolete and do not meet the increasing requirements for protecting modern facilities. The global trend in fire extinguishing development is toward using installations with “clean gases” that are safe for humans and the environment and are highly effective in suppressing fires without causing even minimal damage to the protected facility or personnel. This is due to the adoption of the Montreal Protocol in 1987 on restricting the use of compounds, which included freons 114, 1301, 1211. The solution to this problem was the development of systems based on hydrofluorocarbons (freon 125, 227-ea). However, in December 1997, the Kyoto Protocol was adopted on restricting the use of compounds that cause the greenhouse effect. The above-mentioned freons were included in the compounds prohibited for use. The restrictions adopted by the Montreal and Kyoto Protocols forced scientists to begin developing a fire extinguishing composition that must meet new strict requirements. These are:
high efficiency in extinguishing fire;
– safety for people;
safety for expensive equipment;
zero ozone-depleting potential;
– short lifespan in the atmosphere;
no impact on the global greenhouse effect.
Hundreds of different alternatives were considered, but none of them met the new requirements, until a rather unusual combination came to the attention of scientists — fluoroketone C-6. Previously, this class of chemicals was considered unsuitable for use in fire safety, but, oddly enough, it was fluoroketone C-6 that turned out to be the answer to the question the whole world was looking for. The 3M corporation began producing this fire extinguishing composition, which was named 3M™Novec™1230. At first glance, 3M™Novec™1230 looks like simple water, but it has significantly different properties.
3M™ Novec™ 1230 is based on six-carbon molecules and belongs to the class of fluorinated ketones. The substance with weak molecular bonds absorbs heat much better than water and has a boiling point of only 49 °C. These properties are extremely important when extinguishing fires, especially at an early stage, since 3M™ Novec™ 1230 intensively absorbs the heat of the incipient fire. 3M™ Novec™ 1230 does not conduct electricity, which means that electronic equipment is not at risk of short circuiting. In addition, as soon as it penetrates the device, due to the heat it emits, the substance immediately turns into a gaseous state and evaporates. In addition, under the influence of ultraviolet radiation from the sun, 3M™ Novec™ 1230 molecules decompose in just five days, unlike freons, which decompose only after decades of exposure to the atmosphere. 3M™ Novec™ 1230 has a lower fire extinguishing concentration (4.2% versus 10–12% for freon 125). The 3M™ Novec™ 1230 fire extinguishing composition suppresses fire using a combination of physical and chemical properties. The fire extinguishing mechanism is based on the cooling effect.
For comparison: freon 125 has a 100% chemical reaction, while inergen reduces the oxygen content. Novec™ 1230 does not reduce the oxygen content in the room, and clinical trials have shown it to be harmless to humans.
When filling the Novec™ 1230 gas fire extinguishing module, it is poured in as a liquid, and then the propellant gas (nitrogen) is pressurized to an operating pressure of 24.8 bar.
Comparative characteristics of GFFS (Table 1):
As can be seen from Table 1, Novec™1230 has the lowest extinguishing concentration — 3.4% with NOAEL 10%! Even when extinguishing with such safe compositions as freon 227 and inergen, the gas concentration in the immediate vicinity of the spray nozzle can significantly exceed the regulatory framework and in most cases exceed NOAEL. Exceeding NOAEL can have an adverse effect on the cardiovascular and central nervous systems, as well as the lungs of a person. Novec™1230 gas has almost three times the guaranteed reserve, which makes it absolutely safe for people.
Let us designate the places that are subject to protection by modular gas fire extinguishing systems in a high-rise building.
Cable power and low-current wiring, like nerves, penetrate the building structure of a high-rise building. For ordinary buildings, cable risers (niches) for interfloor wiring are usually made in one typical place on stairwells. All security system cables are grouped in one specially designated place, and it is easy to imagine what will happen if these connections are broken on one of the lower floors in the event of an emergency (fire).
According to all technical conditions for high-rise construction in the fire protection sections, a high-rise building is divided into fire compartments (approximately 16 to 20 floors). Each fire compartment must be autonomous in managing the safety and life support systems in any emergency, especially in the event of a communication failure with the central control center. How to ensure the most reliable communication between the systems inside the fire compartment and outside it? How to protect cable wiring? Cable channels in most cases are located in close proximity to evacuation routes, so the most effective method of protection is gas fire extinguishing using a gas that is safe for humans. To use gas fire extinguishing systems in cable risers, sealed interfloor splits are required. The technology of gas fire extinguishing of splits will be determined by the relevant project.As a rule, a multifunctional high-rise building may contain a large number of electrical panels, equipment and server rooms, as well as archive rooms. For the safety of people located and working in a high-rise building, these rooms must be protected by a gas fire extinguishing system with an extinguishing agent that is safe not only for electrical and paper products, but also for people themselves.
In multifunctional high-rise buildings and complexes, to ensure a high degree of reliability of the systems, it is recommended to use modular (autonomous) gas fire extinguishing units that are safe for people and integrate them into the automated fire protection control system of the building.
The uniqueness of multifunctional high-rise buildings and facilities requires an appropriate approach to the selection of technical means, the correct selection of fire extinguishing technologies, and the management of the entire fire protection complex of the building itself and the people in it.