Extinguishing Media

Question 1

What role do free radicals play in the combustion process?

Answer 1

‘Free radicals’ are highly re-active fragments of molecules, that react with oxygen and worsen the combustion process. The substance in Dry Chemical can stop this process.

Question 2

State the four (4) types of extinguishing media that fire agencies have access to on the appliances:

Answer 2

• Water
• Foam
• Dry chemical (powder) (mono ammonium phosphate)
• Carbon dioxide (Co2)

Question 3

Define the meaning of the following acronyms in relation to foam:

• FFF
• AFFF
• ARF
• ATC-ARF

Answer 3

FFF:

Film Forming Foam

AFFF:

Aqueous Film Forming Foam

ARF:

Alcohol Resistant Foam

ATC-ARF:

Alcohol Type Concentrate

Question 4

What type of extinguishing media interrupts the flame chain reaction by scavenging the ‘free radicals’

Answer 4

Dry Chemical - breaks the chain reaction

Question 5

List the five (5) classes of fire and provide an example of each:

Answer 5

• Class A (flammable solids) - wood, paper
• Class B (flammable liquids) - petrol, paint
• Class C (flammable gas) - LP Gas, acetylene
• Class D (combustible metals) - sodium, magnesium
• Class F (cooking oil and fat) - deep fryer, bbq’s, commercial kitchens

Note: Class E is a subcategory of Class D as electricity is not a fuel.

Question 6

What are the four (4) principles of fire extinguishment when using extinguishing media:

Note: Know how to draw both the Fire Triangle and Fire Tetrahedron

Answer 6

• Cutting off the oxygen supply by smothering the fire
• Reducing the temperature of the fire by cooling the fuel.
• Removing the fuel and so starving the fire
• Interfering with the combustion process by interrupting the chemical chain reaction.

Question 7

What is the most appropriate extinguisher for a Class A fire:

Answer 7

Water

(Any types of extinguisher can be used on solid carbonaceous materials - cooling)

Question 8

What is the most appropriate extinguisher for a Class B fire:

Answer 8

Foam

(CO₂ and Dry Chemical extinguishers may also be used - smothering with foam or interrupting with dry powder)

Question 9

What is the most appropriate extinguisher for a Class C fire:

Answer 9

CO₂

(Dry Chemical extinguishers may also be used - starve the fire by turning off the fuel supply)