An owner or operator of a stationary source that has more than a threshold quantity of a regulated substance in a process must comply with the requirements in 40 CFR Part 68. How large would a pipe have to be to contain a threshold amount (10,000 pounds) of methane?

Assuming a methane gas density of 0.042 pounds per cubic foot, at 1 atm and 60 degrees F (Handbook of Compressed Gases, Compressed Gas Association), the volume occupied by 10,000 pounds of methane is 236,000 cubic feet at 1 atm; 47,000 cubic feet at 5 atm; and 24,000 cubic feet at 10 atm. For a pipe with a 2-inch diameter to contain 10,000 pounds of methane gas, it would have to be: 2,000 miles long at 1 atm; 400 miles long at 5 atm; or 200 miles long at 10 atm. For a pipe with a 3-inch diameter to contain 10,000 pounds of methane gas, it would have to be: 900 miles long at 1 atm; 180 miles long at 5 atm; or 90 miles long at 10 atm. For a pipe with a 4-inch diameter to contain 10,000 pounds of methane gas, it would have to be: 560 miles long at 1 atm; 111 miles at 5 atm; or 57 miles long at 10 atm.