Practice Questions And Correct Answers

FDNY L-19: Supervision of Sanitary

Landfill Methane Recovery Facilities Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary reason for extracting landfill gas from a sanitary

landfill rather than allowing it to vent freely into the atmosphere?

• To reduce leachate production
• To prevent methane build-up and reduce greenhouse gas emissions
• To increase waste decomposition speed
• To reduce odors only

Answer: B

Rationale: Methane is a potent greenhouse gas and can accumulate to

explosive concentrations; controlled extraction prevents build-up, mitigates explosion risk, and reduces environmental impact.

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• Which of the following gas concentrations in landfill gas is most typical

for methane (CH₄)?

A. 5–10%

B. 20–30%

C. 40–60%

D. 70–85%

Answer: C

Rationale: Landfill gas typically consists of roughly 50% methane and 30–

40% carbon dioxide, though composition may vary.

• At what lower explosive limit (LEL) percentage of methane in air does

landfill gas become an explosion hazard?

A. 0.5%

• 5%

C. 15%

D. 25%

Answer: B

Rationale: Methane’s LEL is around 5% by volume in air; concentrations at

or above this can be ignitable if an ignition source is present.

• What is the primary purpose of a flame arrestor in a landfill gas piping

system? 2 / 4

• Increase gas flow rate
• Reduce gas moisture content
• Prevent flame propagation back into the gas well
• Remove hydrogen sulfide (H₂S) from the gas

Answer: C

Rationale: A flame arrestor stops a flame front from traveling backward

through the pipeline into the potentially explosive gas source.

• Which regulatory standard is most likely to govern landfill gas system

design and operation under New York City jurisdiction?

• OSHA 1910 Subpart Z
• NFPA 820 – Standard for Fire Protection in Wastewater Treatment and

Collection Facilities

• NFPA 30 – Flammable and Combustible Liquids Code
• NFPA 54 – National Fuel Gas Code

Answer: B

Rationale: NFPA 820 provides fire and explosion safety guidance pertinent

to waste-handling and gas-handling facilities, including landfill gas operations.

• What is the minimum frequency recommended for monitoring methane

concentrations in enclosed structures near a landfill gas collection system? 3 / 4

• Once a month
• Once a quarter
• Weekly
• Daily

Answer: C

Rationale: Weekly monitoring helps detect dangerous methane

accumulations early, before reaching flammable levels.

• During startup of a blower to extract landfill gas, what should be

verified first?

• Gas pressure at the flare stack
• Closure of all well-head valves
• Operation of automatic spark-ignition controls
• Moisture removal system functioning

Answer: C

Rationale: Automatic ignition control ensures that extracted gas is safely

combusted; verifying this before blower startup prevents unignited gas discharge.

• What is a primary advantage of a vertical gas extraction well over a

horizontal collector trench?

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