Free EVT ARFF A-3 practice test: Extinguishing Agent Systems

Free EVT ARFF A-3 practice test: 10 questions

Questions from our AR3 bank, written to EVTCC's learning objectives and the 2024 NFPA 1900 and 1910. Tap an answer to see if you're right and why, or switch to Timed for the real test's pace. Every answer is below each question.

1. The primary extinguishing agent carried in bulk on an ARFF vehicle for a large flammable-liquid (fuel) fire is:

   AWater mixed with AFFF foam concentrate BBulk Purple-K dry chemical alone CBulk-stored Halotron clean agent DCarbon dioxide stored in cylinders
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   Answer: A. Water mixed with AFFF foam concentrate

   ARFF vehicles carry water and AFFF concentrate as the primary bulk agent; dry chemical and clean agents are complementary agents carried in smaller quantities.

   • B: PKP is a complementary agent carried in a much smaller quantity.
   • C: Clean agent is a secondary load, not the vehicle's bulk agent.
   • D: CO2 is not carried as the bulk agent for a large fuel fire.

2. AFFF extinguishes a fuel fire primarily by:

   AForming an aqueous film and foam blanket that seals fuel vapors BCooling the fuel below its flash point with water alone CChemically interrupting the flame chain reaction like dry chemical DDisplacing oxygen with an inert gas
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   Answer: A. Forming an aqueous film and foam blanket that seals fuel vapors

   Aqueous film-forming foam floats a vapor-sealing film and foam blanket over the fuel, separating it from oxygen and suppressing vapors.

   • B: Water cooling alone is not the primary AFFF mechanism.
   • C: Chain-breaking is how dry chemical works, not AFFF.
   • D: Inert-gas oxygen displacement describes CO2, not AFFF.

3. AFFF concentrate used in ARFF is most commonly proportioned into the water stream at approximately:

   A3 percent B25 percent C50 percent D90 percent
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   Answer: A. 3 percent

   Modern ARFF AFFF is typically proportioned at about 3 percent (some legacy concentrates at 6 percent); the concentrate is only a small fraction of the finished solution.

   • B: 25 percent is far above any AFFF proportioning rate.
   • C: 50 percent would waste concentrate and not form a proper solution.
   • D: 90 percent is essentially raw concentrate, not a proportioned solution.

4. In a balanced-pressure foam proportioning system, the foam concentrate is supplied to the proportioner at a pressure that is:

   ABalanced to match the water pressure at the proportioner BAlways fixed at 400 psi regardless of water pressure CZero until the water tank is empty DEqual to atmospheric pressure
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   Answer: A. Balanced to match the water pressure at the proportioner

   A balanced-pressure system keeps concentrate pressure matched to water pressure at the proportioner so the correct percentage is injected across a range of flows.

   • B: A fixed pressure would not stay balanced as water flow changes.
   • C: Concentrate must flow while foam is being made, not only when empty.
   • D: Atmospheric pressure could not inject concentrate against water pressure.

5. An around-the-pump proportioner introduces foam concentrate:

   AInto the pump intake using an eductor fed from pump discharge BInto the stream just downstream of the turret nozzle tip COnly back into the foam concentrate storage tank DBy gravity from the concentrate tank with no pump involved
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   Answer: A. Into the pump intake using an eductor fed from pump discharge

   Around-the-pump systems route a portion of pump discharge through an eductor that draws concentrate into the pump intake, mixing it before it reaches the discharge.

   • B: Agent that has left the nozzle is out of the system and cannot be mixed.
   • C: Returning concentrate to its own tank proportions nothing.
   • D: The arrangement works on pressure taken from the pump discharge.

6. A direct-injection (electronic) foam proportioning system meters concentrate based on:

   AMeasured water flow, injecting concentrate to hold the set percentage BThe color of the finished foam blanket as it spreads on the fuel CAmbient air temperature alone, with no reference to water flow DThe elevation angle the turret is set to while discharging
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   Answer: A. Measured water flow, injecting concentrate to hold the set percentage

   Direct-injection systems sense water flow and electronically inject the matching amount of concentrate to maintain the selected percentage across varying flows.

   • B: The blanket forms after application and is never sensed by the metering system.
   • C: Temperature says nothing about how much water is passing the injection point.
   • D: Turret angle changes where the stream lands, not the flow being proportioned.

7. The foam proportioning percentage of an ARFF vehicle is commonly verified during testing using:

   AA refractometer or conductivity meter on the foam solution BA tire-pressure gauge read at the pump discharge CA megohmmeter applied to the foam system's wiring DA tape measure run along the hose and nozzle
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   Answer: A. A refractometer or conductivity meter on the foam solution

   Refractometers (or conductivity meters) compare the finished solution to a calibration curve to confirm the concentrate percentage is within specification.

   • B: A pressure reading says nothing about what is dissolved in the solution.
   • C: Insulation resistance of wiring has no bearing on foam concentration.
   • D: A length measurement cannot establish a mixing percentage.

8. Dry chemical (PKP) is expelled from an ARFF dry-chemical system by:

   AA pressurized nitrogen expellant gas BThe main water pump CFoam concentrate pressure DSimple gravity feed
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   Answer: A. A pressurized nitrogen expellant gas

   A nitrogen (expellant) charge pressurizes the dry-chemical tank and pushes the powder through the hose and nozzle when the valve is opened.

   • B: The water pump moves water/foam, not dry chemical.
   • C: Foam concentrate does not pressurize the dry-chem tank.
   • D: Gravity cannot propel dry chemical through the hose.

9. Undertruck (belly) nozzles on an ARFF vehicle are provided to:

   ALay agent beneath the vehicle to protect it while driving through fire BPierce the aircraft's fuselage skin to apply agent inside CProportion concentrate into the water to make foam solution DRecharge the nitrogen expellant in the dry-chemical system
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   Answer: A. Lay agent beneath the vehicle to protect it while driving through fire

   Undertruck nozzles discharge agent under the chassis and tires so the vehicle can drive through burning fuel without igniting or damaging the undercarriage.

   • B: Belly nozzles point at the ground under the chassis and reach no aircraft structure.
   • C: Mixing happens at the pump, upstream of any discharge outlet.
   • D: They discharge agent; they are not a charging connection.

10. Selecting a dispersed (fog) pattern instead of a straight stream on an ARFF turret is done mainly to:

    ACover a wider area and gently blanket fuel without splashing it BReach the fire at the greatest distance the turret can throw CDo away with nozzle reaction at the turret entirely DTurn the foam solution into a dry-chemical discharge
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    Answer: A. Cover a wider area and gently blanket fuel without splashing it

    A dispersed pattern spreads agent over a wider area for gentle application, while a straight stream is used for reach and penetration.

    • B: Breaking the stream into droplets is what gives the reach away.
    • C: The same flow still leaves the nozzle, so reaction is reduced, not removed.
    • D: Pattern selection shapes the stream and cannot change the agent.