Interstate natural gas pipelines & valves

[rollingstein]

Often there's these stories on TV about someone accidentally damaging a large diameter natural gas pipeline while digging a ditch etc. and then a huge raging fire.

What I'm wondering about is how frequently are shutoff valves installed on these lines. My intuition says ~30 miles apart at most. If so, how long does 30 miles worth of piped gas take to burn itself out. I'm just trying to get a rough estimate here.

In a flowing interstate pipe I think gas velocity is somewhere about 20 m/sec? Though not sure how to estimate the burn time after the valve is shut off.

 

[AlephZero]

This http://www.phmsa.dot.gov/staticfiles/PHMSA/DownloadableFiles/Files/rcv_rpt.fnl.pdf page 6 gives "10 minutes for a 5 mile stretch of 24 inch pipeline if the failure is near one end".

Page 15 makes the comment that "of 81 incidents studied, virtually all fatalities and injuries occurred within the first 3 minutes".

Page 16 gives a requirement of shutoff valves every 8 miles for some class of pipeline (I've no idea what the jargon means).

Another consideration is the length of time it takes to close any shutoff valves - estimated at 10 minutes for remote controlled valves and 30 to 40 minutes for manual valves. The general conclusion seems to be that RC values were technically feasible but don't have any economic benefit.

 

[SteamKing]

The term 'class' refers to the number of inhabited buildings within a certain distance of a gas pipeline. A Class 1 location is offshore, and presumably there are no inhabited buildings nearby. The other Class designations are defined in the Code of Federal Regulations, 49 CFR 192.5.