Class B fire extinguishers

Are class B fire extinguishers no more than 50 ft. apart ... 

Use Class B extinguishers for fires involving flammable solvents and gasoline. Class B fire extinguishers cut off oxygen supply to the fire, which hinders release of combustible vapors. Extinguishers appropriate for Class B fires should contain a red square with the letter B. The travel distance for Class B extinguishers must not exceed 50 ft. 

Class B fire extinguisher ratings identify how many square feet the extinguisher can handle. As an example a 5-BC rated unit should be able to handle a five square-foot area. 

The penetration and eooling aetion of water is required with Class A fires, e.g. those involving paper, wood, textiles, refuse. Water is applied in the form of a jet or spray foam or multi-purpose powder extinguishers are alternatives. Extinguishment of a Class B fire ean be aehieved by the smothering aetion of dry ehemieal, earbon dioxide or foam. Most flammable liquids will float on water (refer to Table 6.1 under Speeifie gravity ), so that water as a jet is unsuitable a mist may, however, be effeetive. Water is also widely used to proteet equipment exposed to heat. Dry powders are effeetive on flammable liquid or eleetrieal fires. 

The extinguishing agent in a class C fire extinguisher must be electrically non-conductive. Both carbon dioxide and dry chemicals can be used in electrical fires. An advantage of carbon dioxide is that it leaves no residue after the fire is extinguished. When electrical equipment is not energized, extinguishers for class A or B fires may be used. 

Potassium bicarbonate has greater extinguishing capability on Class B fires than sodium bicarbonate and is usually foam compatible. This characteristic permits emergency response personnel to fight fire more effectively. 

Properly designed water mist systems can be effective on both liquid fuel (Class B) and solid fuel (Class A) fires. Research indicates that fine (i.e., smaller than 400 microns) droplets are essential for extinguishing Class B fires, although... 

Multipurpose dry chemical extinguishers (20-A 80B-C) should be provided in warehouses and shop buildings where wood, paper, plastics, and other flammable solids, as well as flammable liquids, may be stored. In grease manufacturing and compounding or similar operations where little or no wood, paper, and similar combustibles are stored, but where flammable liquids may be prevalent, potassium bicarbonate dry chemical extinguishers should be used. Extinguishers should be located not more than 75 ft (23 m) away from any potential Class A fire hazard and not more than 50 ft (15 m) from Class B fire hazards. 

Class C Electrical fires Fires that involve energized electrical equipment where the electrical nonconductivity of the extinguishing media is of importance. (When electrical equipment is deenergized, fire extinguishers for Class A or Class B fires can be used safely.)... 

Class B Fires. These are fires in flammable liquids (oils, gasoline, solvents, etc.), where a blanketing or smothering effect is essential to put the fire out. This effect keeps oxygen away from the fuel, and can be obtained with carbon dioxide, dry chemical (essentially sodium bicarbonate), foam, or a vaporizing-liquid type of extinguishing agent. Water is most effective when used as a fine spray or mist... 

Class B fires occur with liquid hydrocarbons and similar combustible liquids. Foam, dry-chemical, halocarbon, and C02 extinguishers are recommended. 

The type of extinguisher is keyed to the type of fire. Extinguishers for Class A fires often use water. The water cools the fuel so that it does not react as readily. The steam that is produced helps displace the oxygen-containing air around the fire. Carbon dioxide extinguishers can also be used. Because carbon dioxide is denser than air, it forms a layer underneath the air and cuts off the O2 supply. Water cannot be used on Class B fires. 

Foray [Ansul]. TM for a monoammonium phosphate-based formulation used to extinguish fires in flammable liquids (Class B fires) and in combustible materials such as wood and paper (Class A fires). 

Class B fires involve flammable or combustible liquids such as gasoline, kerosene, grease and oil. The numerical rating for Class B extinguishers indicates the approximate number of square feet of fire it can extinguish. 

First, and most importantly, water is not a useful extinguishing agent for Class B fires. Most organic solvents have a density less than that of water and are usually immiscible with water. The water neither covers the fire nor does it dilute the organic liquid to a nonflammable condition. Thus, the force of the stream of water from either a pressurized water (PW, Class A) portable extinguisher or from a fire hose serves mostly to spread the fire. Because of this, you will probably not find a PW extinguisher in chemistry labs, and furthermore, you should avoid the temptation to throw a beaker of water on a Class B fire. 

Class B fires are best extinguished by either CO2 (BC) or dry chemical (BC or ABC) extinguishers and these should be the type of extinguishers that are located in, or near, the lab. Always determine where the fire extinguishers are, and what type they are, before working in any lab. (See Chemical Connection 2.2.1.2 Applications of General Chemistry Principles in a CO2 Extinguisher.)... 

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