Gas pipe Explosion from lightning

The short answer:

http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=780

or:

http://www.techstreet.com/cgi-bin/detail?product_id=1534445

Interesting questions, Bob.

I've lived in Oklahoma most of my life. We have a large number of natural gas lines in this state, and of course, Oklahoma is known for thunderstorms and tornadoes. Yet, I do not remember any incidents involving lightning generated NG fires. Most NG fires that have happened were started by heavy equipment operators that accidentally rupture a buried line and generate a spark at the same time. But that doesn't happen as much now, because we have a statewide number for people to call whenever they plan on doing any construction related digging, and the agency that takes those calls will contact the utility companies and they will come out to mark their lines.

When lightning hits the ground, the electricity wants to spread out in all directions. If the strike is close to a conductor, the electrons will flow to it, because the conductor is the path of least resistance. I imagine the gas mains are buried deep enough that they are safe.

In most cases, the top layers of soil will be wet from rain, and so the lightning will not go very deep. In places where the pipelines come to the surface, a taller conductive structure nearby will probably draw the lightning to it.

3Doug - your remarks are very good. Now, starting from the famous idea of the "Explosion Triangle" me may discuss or estimate very subjectively the risk - probability of:

(a) presence of gas leakage from gas pipeline,

(b) is residual energy coming from the lightning rod enough to initiate explosion,

(c) is a proper volume of oxygen around the pipe to create explosion mixture between minimum and maximum limits = span of explosive mix.

I was the author of the ESD (ElectroStatic Discharge) Protection Standards for Petro-chemistry and even the energy from ESD are usually lower than this from lightning strikes there was basic rule: do not discuss, just follow the rules. And rule of thumb is: stay away as far as possible from the gas pipe explosion zone (according to rule of their classifications). Anyway, even the standard are very precise in solution, always the last approval is done after the test or set of tests to indicate safety of the installation - in this case the grounding system vs. pipeline grid.

I guess in many of US States the criminal negligence is determined after an Accident.

Many of companies, and some investigator do not publicize their findings as a result of lightning. I found googling some huge gas piping explosion that happened outside USA, e.g. in Australia, Turkey, Europe, South America. Same of them were indicated from lightning, even in residential area of the USA.

So keep eye on NFPA 780 (Lightning protection) and NFPA chapters on Gas pipelines; watch some manufacturers that are doing good job introducing mechanical and electrical solutions.

Your remark on soil condition and undefined direction of lightning discharge in the ground is of course valid, and they may decide of necessary distances asked by Bob?

I know that they are so different that, again, the only answer of their adequate distance can be received from tests / measurements.