Gas extinguishment

Carbon dioxide and certain halon compounds have a specialized application for fires in electrical equipment where a non-conducting medium is important. All are toxic to a degree, and operate either by smothering the fire or by a chemical reaction which inhibits combustion. Gas extinguishers must not be used in a confined space because of the toxic risk or the risk of asphyxiation. 

Gas extinguishers may be used for enclosed spaces. These are largely meant for small fires or fires where electrical hazards are probable. 

When we suppress fires we inhibit their growth and spread. There are various means of fighting and suppressing fires. We will look at five methods of suppressing fires which are isolation, water, gas extinguishants, foams, and solid extinguishants. 

Gas extinguishants are not used as commonly as water but in some cases are more effective and the preferred method if the fire is in an enclosed space and the equipment in the room is very valuable (computers, motor control centers, etc,). There is no water damage or dry powder damage to the equipment or messy cleanup. 

Carbon dioxide (see Figure 6-4) is the most common gas extinguishant. It acts as a coolant, a blanketing agent, by reducing oxygen levels, and as a combustion inhibitor. 

In using a gas extinguisher, a static charge may build up at the cylinder or in the pipeline due to the flowing carbon dioxide. It may be hazardous, therefore, in the presence of explosive gases. 

BS EN 12094 Fixed fire-fighting systems. Components for gas extinguishing media (Parts 5,8 13) BS EN12259 Fixed fire-fighting systems. Components for sprinkler and water spray systems (parts 1-4) BS EN 12416 Fixed fire-fighting systems. Powder systems (parts 1 2)... 

Smouldering fires can occur in many sites, such as coal-dust storage, com silos or wood-chip silos in chipboard factories. Conventional methods of fire-extinguishing often fail in these types of situation, mainly because neither water (with or without additives), foam nor powder can reach the fire if it is deep within a pile of stored material. Gas-extinguishing is then the method of choice. 

A colourless gas, b.p. — 59-C/740 mm. Used as a relatively non-toxic propellant gas in fire fighting apparatus, e.g. dry-powder extinguishers. Made by the bromination of fluoro-form, CHF3. 

The two major difficulties facing the analyst/mass spectrometrist concern firstly how to get the whole of the sample into the plasma flame efficiently and secondly how to do so without destabilizing or extinguishing the flame. Although plasma flames operate at temperatures of 6000 to 8000 K, the mass of gas in the flame is very small, and its thermal capacity is correspondingly small (Figure 15.1). 

Fire Hazard. Although chlorosulfuric acid itself is not dammable, it may cause ignition by contact with combustible materials because of the heat of reaction. Open fires, open lights, and matches should not be used in or around tanks or containers where hydrogen gas may be collected because of the action of chlorosulfuric acid on metals. Water, carbon dioxide, and dry-chemical fire extinguishers should be kept readily available. 

Foam Production This is important in froth-flotation separations in the manufac ture of cellular elastomers, plastics, and glass and in certain special apphcations (e.g., food products, fire extinguishers). Unwanted foam can occur in process columns, in agitated vessels, and in reactors in which a gaseous product is formed it must be avoided, destroyed, or controlled. Berkman and Egloff (Emulsions and Foams, Reinhold, New York, 1941, pp. 112-152) have mentioned that foam is produced only in systems possessing the proper combination of interfacial tension, viscosity, volatihty, and concentration of solute or suspended solids. From the standpoint of gas comminution, foam production requires the creation of small biibbles in a hquid capable of sustaining foam. 

Figure 19.3 Theory of ionization and deionization of gas atoms to extinguish the arc plasma...

As the moving contact moves away, so the arc plasma elongates, losing its initial intensity, and as it approaches the current zero, it loses the most of it. The gas, on the other hand, cools and regains its lost mass, while its pressure in the chamber continues to build to its optimum level, making it more capable of extinguishing a less severe arc plasma. The interrupter can thus be adjusted to blow out the arc at the first current zero, while clearing heavy to very heavy fault currents. 

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