# San Bruno natural gas explosion

**URL:** <https://boards.straightdope.com/t/san-bruno-natural-gas-explosion/553432>\
**Category:** Factual Questions\
**Created:** [September 11, 2010, 9:04pm UTC](https://boards.straightdope.com/t/san-bruno-natural-gas-explosion/553432 "2010-09-11T21:04:55Z")\
**Posts on this page:** 3\
**Page:** 3

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**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\
**Post date:** [September 15, 2010, 12:10pm UTC](https://boards.straightdope.com/t/san-bruno-natural-gas-explosion/553432/41 "2010-09-15T12:10:55Z")

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> [@Dag\_Otto](#):
>
> > [@Snnipe\_70E](#):
> >
> > Thanks for the link. I have been having a hard time understanding an explosion that would nave been on the surface rippping an underground pipe. But what you have described maked sence.
> 
> What is shown in the video is pretty consistent with what the OPS and the TSA told me about the effects of an event at a regulator station. A fireball, with negligible blast/overpressure effects. In my case though, I was assured that the pipeline in question was equipped with excess flow devices that would shut off the gas if the flow exceeded a set point. I take it that these devices are not required everywhere.

It’s entirely possible they had a shutoff device, but even if they did, the gas is under high pressure, so the now-open-to-atmosphere section of the pipe contains a lot of gas.

Suppose you have a 2-foot-diameter pipe running at 500 psi, and the shutoff valve is five miles away. There’s about 2.8 million standard cubic feet of natural gas that will come out of that pipe before it equalizes to atmospheric pressure.

Don’t know what the actual pressure was in the San Bruno pipe, but 500 psi doesn’t seem outlandish. You can insert your own estimates for pressure and shutoff-valve spacing and tweak the estimate accordingly.

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**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\
**Post date:** [September 15, 2010, 7:18pm UTC](https://boards.straightdope.com/t/san-bruno-natural-gas-explosion/553432/42 "2010-09-15T19:18:00Z")

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it took two hours to manually shutoff the section, there was no automatic methods.

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**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\
**Post date:** [September 15, 2010, 10:33pm UTC](https://boards.straightdope.com/t/san-bruno-natural-gas-explosion/553432/43 "2010-09-15T22:33:20Z")

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> [@johnpost](#):
>
> it took two hours to manually shutoff the section, there was no automatic methods.

In a background article in the paper this morning, it was said that even after the pipe was shut off the valve was far enough away from the site of the break that the gas would still burn for an hour.

It also said that the first responders were convinced for quite a while that a plane crash was the source of the fire, not totally crazy given the proximity of San Bruno to SFO. They eventually figured out that plane crashes make smoke, and this fire did not. That slowed the proper response a bit. Not surprising, given the chaos at the site, and the impossibility of getting close enough to see the cause.

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