A ventilated pit in a minor repair garage for heavier‑than‑air fuel is considered unclassified provided there is ventilation of at least 1 ft3/min/ft2, where exhaust air is evaluated at a point within how many inches of the floor?

A ventilated pit in a minor repair garage for heavier‑than‑air fuel is considered unclassified provided there is ventilation of at least 1 ft3/min/ft2, where exhaust air is evaluated at a point within how many inches of the floor?

• A. 18
• B. 24
• C. 6
• D. 12

Answer: (D)

For heavier‑than‑air fuels, vapors hug the floor, so to accurately judge ventilation you measure the exhaust air right where those fumes would accumulate. When a pit is ventilated at a rate of at least 1 ft³/min per ft², the standard specifies evaluating the exhaust at a point within 12 inches of the floor. This placement captures the concentration where vapors are most likely to be present and ensures the ventilation is effectively removing them. Checking farther up the space could miss the lingering floor-level vapor pockets, underestimating risk.

For heavier‑than‑air fuels, vapors hug the floor, so to accurately judge ventilation you measure the exhaust air right where those fumes would accumulate. When a pit is ventilated at a rate of at least 1 ft³/min per ft², the standard specifies evaluating the exhaust at a point within 12 inches of the floor. This placement captures the concentration where vapors are most likely to be present and ensures the ventilation is effectively removing them. Checking farther up the space could miss the lingering floor-level vapor pockets, underestimating risk.