Means and methods of extinguishing fires

 

The combustion process is terminated if the burning hearth isolated from the air; the oxygen concentration is reduced to a lower limit (for most substances – 12 – 15%); burning material is cooled below the temperature of self-ignition or ignition; it carried out an intensive inhibition (inhibition of the chemical reaction and the flame speed) and in some other cases.

Methods of fire extinguishing can be classified by type of applied fire extinguishing agents (compositions), the method of their application (filing), the environment, purpose and etc. All extinguishing methods are mainly divided into superficial quenching, also known as surface fire extinguishing (can be used for all types of fires), and volumetric quenching, is to create a district fire environment that does not support combustion (can be used to a limited extent – compartments, galleries, etc.).

Substances which contribute to the creation of these conditions are known as fire extinguishing. They must have a high quenching effect at relatively low flow, be cheap and safe to handle, does not harm the materials and articles. Extinguishers main ingredients are water, aqueous solutions, steam, foam, carbon dioxide, inert gases, halogenated hydrocarbons, compressed air, powder, sand, earth.

Water and based thereon extinguishing agent (aqueous emulsion, water vapor, etc.) have a high heat capacity and heat of vaporization. Along with the advantages, it has properties that limit its application field. Water is ineffective at quenching for oil and many other flammable liquids, since they continue to burn and float on its surface. Water is electrically conductive and cannot be used to extinguish flammable objects under electric voltage.

The foam is characterized by multiplicity and stability. Multiplicity of foam is the ratio of its volume to the volume of the original product. Stability is the time from the moment of its receipt to the complete disintegration. The foam is divided into chemical and mechanical air. It is used to extinguish flammable liquids, combustible liquids and petroleum products. Extinguishing agents with effect achieved by insulating the surface from the ambient air.

Carbon dioxide in the gaseous state and a snow used in fire extinguishers and fixed systems for extinguishing fires in enclosed spaces and small open fires. Extinguishing concentration is about 30% by volume. Carbon dioxide does not conduct electric current, so it can be used to extinguish the electrical installations under voltage.

Inert gases used to extinguish fires, reduce the concentration of oxygen in the air and reduce the heat of reaction due to the heat loss for heating. These include: nitrogen, argon, helium, flue and exhaust gases. Relative concentration of gas is 30 – 36% by volume.

Halocarbons (gas or liquid) inhibit combustion reaction, so they are called inhibitors, or deterrents. These include methyl bromide, methylene iodide, methyl bromide, dichlorofluoromethane and etc.

Compressed air is used to extinguish a combustible liquids with flashpoint temperature above 60 ° C by mixing them. Burning stops when the temperature of upper layer of the burned liquid becomes below the ignition temperature.

Powder compositions based on sodium carbonate are used most widely in spite of their high cost, the difficulty in the operation and storage. In particular, they are the only means of extinguishing for alkali metals and organometallic compounds. To extinguish such fires are also used sand, soil, fluxes.

There are primary, stationary and mobile fire extinguishing equipment. The primary fire extinguishing agents include fire extinguishers, hydropump (small piston pumps), buckets, barrels of water, shovels, boxes with sand, asbestos cloth, felt mats, felt mats, crowbars, saws, axes. Fire extinguishers are chemical foam (OHP-10, OHPB-10 and others), carbon dioxide (OU-2, OU-5, OU-8, OU-15), combined carbon dioxide and brominethyl (OUB-3, OUB-7), freon (OH-3), powder(OPS-6, OPS-10). Fig. 10.1 shows the devices fire extinguishers OHP-10 and OU-2.

а	b

 

Fig. 10.1. Fire extinguishers:

 a – chemical foam OHP-10 (1 – body; 2 – acid glass; 3 – side handle; 4 – neck adapter; 5 – neck; 6 – handle; 7 – stock; 8 –cover; 9 –spring; 10 – water jet; 11 – rubber valve; 12 – the bottom); b – carbon dioxide
OU-5 (1 – cylinder, 2 – filling; 3 – siphon tube; 4 – the snow faucet;
5 – handle; 6 – fuse; 7 – shut-off valve)

 

Stationary fire extinguishing means are fixedly mounted devices, pipelines and equipment, which are intended to supply extinguishers to places of ignition. They are a means of fire water supply, sprinkler and deluge installation, fire communication devices and signaling.

Fire water supply of populated areas and industrial enterprises can be without water pipes (natural and artificial ponds, reservoirs) and plumbing. Fire water supply without water pipes allowed for relatively small enterprises (territories no more than 20 hectares) with production categories D, E (Г, Д) and water consumption in the external firefighting no more than 20 l/s.

The plumbing water supply is more reliable and perfect. Water is made up of water intake facilities, pumping station of the first lift, water supply treatment plant; clean water reservoirs from which water pumping station is served by the second lift in the water pipes water supply system and water tower. Fire water supply is usually combined with running water for other purposes. For water withdrawals on the fire water lines need to install fire hydrants underground and elevated performance. The walls of buildings, fences are appropriately marked to find the hydrants. Fire hydrants are placed at a distance of no more than 150 meters from each other, not further 2.5 meters from the edge of the road and not less than 5 meters from the walls of buildings. To extinguish fires in the initial stage inside buildings provided internal fire line. Interior fire hydrants with attached thereto hoses and nozzles installed in niches and lockers at the entrances, on floors heated stairwells, corridors and other places available at a height of 1.35 m above floor level.

Sprinkler systems are designed for automatic feeding of water or air-mechanical foam to extinguish a fire inside the building. They are water, used in heated rooms (air temperature is above 4 °C), and air, arranged in unheated rooms. Sprinkler system is a system of pipes, which are installed sprinkler heads. The opening in the diaphragm head closes glass valve stem and held fusible lock, consisting of curved plates, which are interconnected by low-melting solder on the basis of bismuth, lead, cadmium and tin.

Solder designed for a specific melting point. When air temperature at the room reaches solder melting point, lock is destroyed, and the opening of a sprinkler head starts to enter the water or foam.At the same time an alarm is triggered.

Deluge sprinkler installation differs from that in the deluge valve heads are missing valve and fusible lock. Deluge installations are manual and automatic switching-on of a group action valve. When turned on automatically at the same time an alarm is triggered.

The area of ​​the floor, protected by a one sprinkler valve should not exceed 12 m², and the deluge – 9 m². Application area of a sprinkler and deluge systems is defined SNIP 21-01-97.

Fire communication and alarm systems have a significant impact on the successful firefighting. Fire communication is a complex of communication devices, which allow make reports of fire quickly and promptly give the necessary orders to eliminate it. Fire alarm system consists of fire detectors, communication lines and receiving stations.

Fire communication by its intended purpose is divided to communicate notices, dispatch and communications on fire.

Radial and annular (more economical) schemes are used for switching detectors. Detectors are divided into heat, ultraviolet radiation (light), ionization (smoke), ultrasound, infrared, and etc. According to the operation principle detectors are divided into maximum and differential. The maximum detectors react to certain absolute values ​​of the controlled parameter. Differential detectors respond only to a certain rate of change of the controlled parameter.

Mobile firefighting equipment – fire trucks are divided into basic, with pumps for water and other extinguishing substances to the fire, and special, without pumps, and designed for various works to extinguish the fire. The main fire trucks are fire trucks, water tankers, pumps, fire trains, ships, tanks, planes and others. Special machines are vehicles communication services and lighting, ladders, self-fire monitors, and others.

At the industrial enterprise, the responsibility for the observance of the necessary fire prevention mode and timely implementation of fire prevention measures is assigned to the head of the enterprise and the heads of subdivisions. Heads of enterprises are obliged to: ensure the full and timely implementation of fire safety and fire requirements of construction standards for the design, construction and operation of facilities under their jurisdiction; organize the company fire department, volunteer fire brigades (VFB) and fire-technical commission (FTC) and control them; include the necessary provisions for the maintenance of fire protection, the acquisition of firefighting equipment; appoint persons responsible for fire safety departments and enterprise structures.

Company principals have the authority to impose disciplinary sanctions on violators of rules and fire safety requirements, to raise the question of bringing perpetrators of violations of these rules to justice.

All workers when applying for a job get an introductory and primary (in the workplace) instruction on fire safety measures on the approved program with the corresponding registration. There are classes on the fire-technical minimum at sites with increased fire danger. Repeated briefings and instructions should be held at least once a year.

General and workshop fire safety instructions are developed for each enterprise (workshop, laboratory, workshop, warehouse, etc.) in accordance to the «Rules of fire safety in Russia» PPB-01-93.

Development of fire protection measures and monitor of  its implementation by enterprises in our country provides by the State Fire Supervision.

Special attention in an industrial plant requires protection from static electricity and lightning.

Control questions for self-examination:

 

1. What does the fire prevention mean?

2. What issues are solved in the design and construction of an industrial facility?

3. How can we improve the fire resistance of buildings and structures?

4. What is the meaning of zoning industrial enterprise?

5. What is taken into account when constructing fire breaks and fire barriers?

6. Designing safe evacuation of people in case of fire.

7. What determines the time necessary to evacuate people from the production areas?

8. What are the conditions necessary for the termination of combustion?

9. The classification of methods and means of fighting fires.

10. In which case, you should use following substances to extinguish fires:

a) water;

b) foam;

c) inert diluents;

g) halocarbon composition;

d) refrigerants or compressed gas;

e) powders;

g) combined compositions?

11. What are the main ways of the extinguishing agent (composition) supplying?