Fire Theory & Classes Practice Questions

1. The fire triangle consists of three elements. Which answer correctly names all three?

• A.Heat, oxygen, and carbon dioxide
• B.Fuel, heat, and oxygen✓
• C.Fuel, flame, and smoke
• D.Ignition source, combustible material, and water

Why: The fire triangle requires fuel (combustible material), heat (ignition energy), and oxygen (typically from air, which is 21% O2). Removing any one side of the triangle extinguishes the fire. Carbon dioxide is a product of combustion and an extinguishing agent, not a component of the triangle; smoke and flame are byproducts, not elements.

2. A fire involving burning wood, paper, and rope on a vessel's deck is classified as which class?

• A.Class B
• B.Class C
• C.Class A✓
• D.Class D

Why: Class A fires involve ordinary combustibles — wood, paper, cloth, rope, and similar solid organic materials. These fires leave an ash residue. Class B involves flammable liquids and gases. Class C involves energized electrical equipment. Class D involves combustible metals such as magnesium or titanium.

3. An electrician is working on an energized switchboard when insulation ignites. This fire is classified as:

• A.Class A because the insulation is a solid combustible
• B.Class C because energized electrical equipment is involved✓
• C.Class B because the melting insulation behaves like a flammable liquid
• D.Class D because copper wiring is a metal

Why: Class C designates fires involving energized electrical equipment. The key criterion is that the equipment is electrically energized, making water or conductive foam agents dangerous to the firefighter due to shock risk. A non-conductive agent (CO2, dry chemical) must be used. If the equipment is de-energized first, the fire may be reclassified as Class A.

4. Class K fires involve which type of fuel and are most commonly found where?

• A.Kerosene and petroleum distillates — in cargo tanks
• B.Cooking oils and greases — in commercial kitchen equipment✓
• C.Compressed gases — in engineering spaces
• D.Cordite and explosive compounds — in magazine spaces

Why: Class K (NFPA classification) covers fires in cooking appliances involving high-temperature cooking oils and animal or vegetable fats. These fires occur in commercial galley deep fryers and griddles. Wet chemical agents (potassium acetate/potassium citrate) are the correct extinguishing agent — they saponify the fat and create a barrier. Water or dry chemical can cause violent splatter.

5. Smothering as a method of extinguishment works by:

• A.Reducing the fuel's temperature below its flash point
• B.Removing or cutting off the oxygen supply to the fire✓
• C.Interrupting the chemical chain reaction of combustion
• D.Removing combustible fuel from the vicinity of the fire

Why: Smothering removes the oxygen side of the fire triangle by covering the fire (foam blanket, fire blanket, closing compartment vents) or displacing oxygen with an inert gas (CO2, steam). Cooling attacks the heat side. Starving (fuel removal) attacks the fuel side. Chain-reaction inhibition (halogenated agents, dry chemical) attacks the fourth side of the tetrahedron.