FST Fire Extinguishers 5 — Questions and Answers
Question 1: Which agent is prohibited from being used on a Class D (combustible metal) fire?
- Copper powder extinguishing agent
- Dry sand applied manually
- Water or water-based agents (Correct answer)
- Graphite-based dry powder
Correct answer: Water or water-based agents
Water reacts violently with many burning metals such as sodium, potassium, and magnesium, potentially causing explosions or spreading the fire; water-based agents are strictly prohibited on Class D fires.
Question 2: An extinguisher fails its hydrostatic test. What must the technician do?
- Retest immediately at a higher pressure to confirm the failure
- Condemn the extinguisher and render it inoperable before disposal (Correct answer)
- Repair the cylinder by welding and retest
- Return it to the manufacturer for warranty replacement
Correct answer: Condemn the extinguisher and render it inoperable before disposal
A cylinder that fails hydrostatic testing must be condemned and rendered permanently inoperable (typically by cutting or crushing) to prevent reuse.
Question 3: What does a 'loaded stream' fire extinguisher use as its agent?
- Water mixed with a Class B foam concentrate
- Water with an alkali metal salt anti-freeze additive (Correct answer)
- Compressed CO2 dissolved in water
- Water pressurized with nitrogen and a surfactant
Correct answer: Water with an alkali metal salt anti-freeze additive
A loaded stream extinguisher uses water with an alkali metal salt (such as potassium acetate or potassium carbonate) as an anti-freeze and fire-suppression additive.
Question 4: Per NFPA 10, who is authorized to perform the annual maintenance inspection of a portable fire extinguisher?
- Any trained building occupant who has completed a basic fire safety course
- A certified fire protection technician or qualified person with proper training and equipment (Correct answer)
- Only a licensed fire marshal or state inspector
- An insurance inspector with fire safety credentials
Correct answer: A certified fire protection technician or qualified person with proper training and equipment
NFPA 10 requires annual maintenance to be performed by a trained person with proper equipment and knowledge, typically a certified fire extinguisher technician.
Question 5: What is the purpose of the tamper indicator (seal) on a fire extinguisher?
- To indicate the date of the last recharge
- To show the extinguisher has been inspected and the safety pin has not been removed (Correct answer)
- To prevent accidental discharge during transport
- To seal the nozzle orifice and prevent moisture entry
Correct answer: To show the extinguisher has been inspected and the safety pin has not been removed
The tamper indicator (safety seal) wraps the safety pin to provide visible evidence that the extinguisher has not been used, tampered with, or accidentally activated.
Question 6: A multi-purpose dry chemical extinguisher uses which agent?
- Sodium bicarbonate
- Potassium bicarbonate (Purple K)
- Monoammonium phosphate (Correct answer)
- Potassium chloride
Correct answer: Monoammonium phosphate
Multi-purpose (ABC) dry chemical extinguishers use monoammonium phosphate as the active agent, which is effective on Class A, B, and C fires.
Question 7: When inspecting a wheeled fire extinguisher, which item is NOT a standard inspection check per NFPA 10?
- Verifying the pressure gauge is in the operable range
- Checking that tires and wheels are in serviceable condition
- Confirming the hose and nozzle assembly are free of obstruction
- Testing the extinguisher by discharging a small amount of agent (Correct answer)
Correct answer: Testing the extinguisher by discharging a small amount of agent
Monthly inspections are visual checks only; discharging agent is not part of routine inspection and would require recharging the unit before returning it to service.
FST Fire Extinguishers 5
Which agent is prohibited from being used on a Class D (combustible metal) fire?