Bonding piping - Fire Service

[inspector 102]

Occasionly we get called to ruptured gas lines only to find the main gas shut off valve box is plugged with dirt. We created a pipe connected to high pressure air tanks to blow out the curb boxes to get the wrench on the valve stem. The tanks are fiberglass, with a high pressure regulator, then 4 feet of 1/2" black iron pipe to stick in the valve box. Should the black pipe be connected to a ground conductor and ground rod stuck in the ground to eliminate any potentials? Normally the gas concentrate is high, but as a precaution does this sound proper? Overkill since tanks is fiberglass? Tank held by firefighter while in use, not sitting on ground. Any comments appreciated.

 

[mcclary's electrical]

Occasionly we get called to ruptured gas lines only to find the main gas shut off valve box is plugged with dirt. We created a pipe connected to high pressure air tanks to blow out the curb boxes to get the wrench on the valve stem. The tanks are fiberglass, with a high pressure regulator, then 4 feet of 1/2" black iron pipe to stick in the valve box. Should the black pipe be connected to a ground conductor and ground rod stuck in the ground to eliminate any potentials? Normally the gas concentrate is high, but as a precaution does this sound proper? Overkill since tanks is fiberglass? Tank held by firefighter while in use, not sitting on ground. Any comments appreciated.

Your concerns are warranted. Any time there's an air flow, it increase the chance for differences of potetial. I've seen dust collection syytems, draw a static arc to ground, continuously,,,,non stop spark,,,,,just like a spark plug. Beyween two pieces of metal duct work. When seperated, the arc would increase in length between the two pieces of duct, up to 1 1/2" long. Continuousally being renewed by the electrons in the flow of air. The duct work actually knock the p*ss out of workers around it. So you definately could strap this on ,,,,,flow air for a few seconds ,,,,have a potential difference, and the pipe could spark to the gas pipe. Since you're dealing with static, It could probably be remedied by short#10 thhn with going to a stake in ground. But the air flow itself is weakening the gas/air ratio while you're blowing. So an explosion may be impossible. But I can picture poptential differences causing sparks. Probably because I've seen it before first hand.

 

[barone]

I agree your concerns are justified. I would play it safe and think of a better way to clean out those boxes. It may be much easier to blow them out, but much more dangerous and it is always better to sweat than it is to blow up.

 

[jimport]

But the air flow itself is weakening the gas/air ratio while you're blowing. So an explosion may be impossible. But I can picture poptential differences causing sparks. Probably because I've seen it before first hand.

The air/gas ratio may initially be to rich to burn, however, the additional air blown in may bring the mixture back into the flammable range.

The lower flammable range for natural gas is 5%, the upper range is 15%.

 

[don_resqcapt19]

Are you really between LEL and UEL at the curb box? If you have a concern you could bond your pipe to the shut off riser to prevent any static discharge.