Why is a propane leak in a basement or pit especially dangerous?
- Propane is lighter than air and collects at the ceiling
- Propane is heavier than air and collects in low areas
- Propane has no odorant and cannot be smelled
- Propane burns only when it is mixed with natural gas
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B. Propane is heavier than air and collects in low areas
Propane vapor has a specific gravity of about 1.5, so it flows downward and pools in basements, pits and trenches where it can reach an ignition source. Like natural gas, commercial propane is odorized so leaks can be noticed.
Reference: NFPA 58 (LP-gas properties); NFPA 54
A natural gas furnace has an input rating of 80,000 Btu per hour. With gas at 1,000 Btu per cubic foot, how much gas does it use at full fire?
- 8 cubic feet per hour
- 32 cubic feet per hour
- 800 cubic feet per hour
- 80 cubic feet per hour
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D. 80 cubic feet per hour
Cubic feet per hour = input / heating value = 80,000 / 1,000 = 80 cfh. 32 cfh would be the figure for propane at about 2,500 Btu per cubic foot.
Reference: Gas pipe sizing basics: cfh = Btu/h input divided by heating value (IFGC 2021, Section 402; NFPA 54)
A residential natural gas appliance is supplied at about 7 in. water column. About how many psi is that?
- About 7 psi
- About 3 psi
- About 1/4 psi
- About 1/2 psi
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C. About 1/4 psi
One psi equals about 27.7 in. water column, so 7 / 27.7 = 0.25 psi. Low-pressure gas systems run at a small fraction of a pound, which is why they are measured with a manometer in inches of water column.
Reference: Pressure conversion: 1 psi = 27.7 in. w.c.