Exercise 3. Read text D Extinguishing Agents

Selecting the appropriate type of fire extinguisher it’s important to take extinguishing agents into account. Each Class of fire is best fought with a specific extinguishing agent. Every extinguisher has a label identifying Classes of fires it can be used for, and the type of fire extinguishing agent it contains.

The following is a list of commonly used fire extinguishing agents.

Water. Cooling is the most common of fire extinguishment, and water is the most effective cooling agent because it has the greatest capacity for heat absorption. However, it can’t be used for all classes of fires because it’s conductive. Water-based fire extinguishers are usually used in fighting Class A fires.

Carbon Dioxide (CO₂). Carbon dioxide is an effective agent for extinguishing fires by the method of dilution. Carbon dioxide can be used in extinguishing Classes B and C fires, as well as electrical fires.

Multi-Purpose Dry Chemical (Powder ). This is a dry chemical agent called ammonium phosphate. The main extinction method with powders is blanketing but it may be effectively combined with other methods: cooling, diluting, inhibiting a chemical chain reaction. These powders are mostly used in fighting Class A fires.

Ordinary Dry Chemical (Powder). This dry chemical agent called sodium bicarbonate extinguishes a fire mostly by blanketing and inhibition. Extinguishers with sodium bicarbonate are usually used in Classes B and C, and electrical fires.

Special Powders. There is no type of extinguishing agent best suited for all Class D fires. Every hazard should be regarded separately. Still, commonly used are special powders such as sodium chloride, dry graphite, dry copper, etc. with the same extinction methods as other powders.

Foams (AFFF, FFFF). Foam is a highly effective extinguishing agent for blanketing fires. Aqueous film-forming foam (AFFF) (known as “light water”) and film-forming fluoroprotein foam (FFFF) are particularly well suited for use on flammable liquids and gases fires due to the ability of the agent to float on the liquid surface and break the interaction between the fuel and the flame, thus preventing reignition.

Wet Chemical (Wet Potassium Salts). Wet chemical is typically based on the solution of potassium acetate. It has blanketing and cooling effects on fires involving cooking oils, fats and greases.

Halogenated Agents (Halon). Halogenated agents extinguish fires by inhibiting a chemical chain reaction. They are similar to carbon dioxide, but still more effective because they require a lower concentration of an agent for extinguishment. Halon fire extinguishers are listed for Classes A, B, C and electrical fires.

Exercise 4. Say if it’s true or false. Correct the false sentences.

1) Water has a blanketing effect on fire.

2) The main extinguishing method with ordinary dry chemicals is cooling.

3) Wet chemicals have the same extinction method as halogenated agents.

4) Halon inhibits a chemical chain reaction.

5) Water is the best extinguishing agent for Class D fires.