Digging up gas lines

MChalkley · May 1, 2002

Does anyone know how much danger is really involved in digging up gas lines? As in: How often do they blow up and why?

I busted one last Saturday and the police and fire departments evacuated the whole block. Then the gas guy came, got out a clamp with a ground rod attached to it, strolled over to the pipe, and sqeezed the pipe shut. That was it.

So, my next question is: Does anyone know of a source for these tools? I saw a couple of them in an Internet search, but they're $300!

njrqs · May 2, 2002

Mark

Ok so you buy the tool and then each time you dig one up you just close it off and cover it up hey????

Shonky /w3tcompact/icons/laugh.gif

EdKing · May 2, 2002

I think the biggest danger with gaslines is the fact that a deisel engine will have a tendency to "take off" if it draws the gas in. It's like dumping the throttle wide open with no governor.

gordon · May 2, 2002

Good news is that the gas actually only will burn in a very narrow percentage of air mixture. To much gas and it won't explode and not enough gas and it won't even ignite. But when your in that nice window of 2.5-8% range of gas to air it sure does make for some pretty colors and even sometimes a nice BOOM to go with it.

Ever figure out why backhoe insurance is so costly?

Gordon

JATO_RaT · May 2, 2002

Mark, many times natural gas lines are broken by backhoes out here. Our gas company PG&E broke a very high pressure one at the job we were on and to us it was a huge deal. A massive dust storm from the escaping gas, the smell everywhere. I just wanted to run. The gas guys stood around laughing about how they do this all the time, no big deal. They weld right on the gas line while the line is hot. I don't get it. I know you need the right air mixture, but good grief, how and when do you know when that is. About the most costly thing to dig into is anything phone line related with one exception. On our nearest cross road at my old house were two aircraft petroleum lines to the 2 military air bases. Touch the outside with a hoe and it was automatic to shut the lines down, evacuate them and clean them. Intial minimum cost was $50,000. Puncture it and I believe you just shoot yourself to take the easy way out. No one uses hoes around them, they get out the shovels. Rat...

billfires · May 2, 2002

Rat, we have a $2500 meter that measures the LEL and UEL (lower & upper explosive limits) of flammible gases. Different gases have varying ranges where they will explode. I generally trust the people that deal with these things on an almost daily basis but also keep in mind that most "incidents" happen to people that are considered "experts" in their field.

Bill C

Bird · May 2, 2002

how much danger is really involved in digging up gas lines

A lot! Mark, I did gas leakage surveys for natural gas companies in '93 and '94. I think you need 4% to 15% natural gas to ignite it (different percentages for other gasses). So a trained and experienced guy can work reasonably safely in high concentrations of gas (so long as he has enough oxygen to breathe), but with high concentrations at a leak, how many people are going to know where, at the perimeter of the leaking gas, is the right concentration to ignite?/w3tcompact/icons/wink.gif And it doesn't take much of a spark to set it off (I notice you mentioned his ground rod on that clamp).

And another thing about digging up gas lines . . . what kind of pipe? There's still some cast iron lines out there, black pipe, wrapped pipe, and "plastic" pipe. Different techniques to repairing them, too, of course. I checked some gas mains that had been in the ground for over 70 years in Pennsylvania.

I'm one of those social pariahs who still smokes, and had several people ask me if it wasn't dangerous for me to be searching for leaks while smoking a cigarette./w3tcompact/icons/laugh.gif I always told them it was the safest time there was, because I was using instruments that would pick up minute quantities of any combustible hydrocarbons. I used a "flame pack" that would pick up the tiniest quantities (even from decomposing vegetation at times) and also a "combustible gas indicator" that would measure the concentration. It was an interesting job.

Egon · May 2, 2002

Usually its best to hand expose all lines when doing hoe work. They can be located and marked. The plastic lines have metal tracers with them.

Diesel equipement working around hydrocarbons should be equiped with a positive air shutoff so the engine can't run away or ignite the leak. In many places this is a requirement when using diesel engines.

Plastic pipe under low pressure can be bent back on itself to seal off the ends. The clamps for metal pipes are readily available at stores supplying oilfield supplies.

Its best to evacuate the area when there is a gas leak and let the utility company take over. They should isolate the line and let it bleed down to zero presure and then proceed with a repair suitable to the type of pipe in question.

The real bad leaks are those involving gasses heavier than air as they pool and can ignite at any time an ignition soure is encountered. Usually the leading edge of such a pool will be within the comustible range. Some of these leaks are purposely ignite to reduce hazard of large explosion.

Just some thoughts.

Egon

Golfgar4 · May 2, 2002

"How often do they blow up and why?"

Mark,

I cannot tell how often they blow up, but I can tell you that it can happen. A few years ago, one of our City crews was doing a minor excavation in our downtown area. They had called Diggers Hotline and all locates had been marked. At least they thought so!/w3tcompact/icons/sad.gif They hit a line that no one knew was there, and the two middle buildings in the block blew up! /w3tcompact/icons/shocked.gif

The back hoe was blown backward about 20' and the operator, who survived, landed about 40' away! As far as anyone knows, the explosion was caused by sparks as the bucket cut into the gas line.

Fortunately, no one was killed or seriously injured as this occurred during the lunch hour and almost all of the occupants were away from the buildings.

hosejockey2002 · May 2, 2002

It's actually a good thing when the gas ignites when the line is broken, as long as there are no structures too close. When the gas is burning, you can see exactly where it is and it doesn't have a chance to accumulate. Of course, it's usually not very good for the machine that hits the line!

gerard · May 2, 2002

One thing I learned during a "public safety" type meeting is that for natural gas the odorant is not added until the gas reaches a distribution facility. Prior to that, when in the in the high pressure transportation pipes that run state to state there is no "smell" if you get a rupture. Of course in those lines the PSI is around 800 so what you will see is a geyser of dirt blowing up from the ground! On those lines even if you detect the leak and close the pipe at the two nearest shutoffs it will still take a long time for the pressure to bleed off to 0. Anything you can smell is coming from the smaller feeder lines (which still doesn't mean I want to be close to one when it's leaking!)

MChalkley · May 2, 2002

Thanks, guys, for the excellent info, as always. A few responses:

Usually its best to hand expose all lines when doing hoe work. They can be located and marked. The line I hit had been marked, but the marks had been obliterated by traffic. We did hand-dig the ones we thought were close, and in fact hand-dug the correct one, but upon not finding any evidence of a line, and since we thought it was about 5 feet over, I finished it with the backhoe - big mistake...

The plastic lines have metal tracers with them. I've now invested in a <A target="_blank" HREF=http://www.pollardwater.com/emarket/Pages/P881%208840%20&%208850%20Locators.asp>pipe and cable locator</A> from Pollard Water, so that should help reduce the possibility of the exact same thing recurring.

Diesel equipement working around hydrocarbons should be equiped with a positive air shutoff so the engine can't run away or ignite the leak. In many places this is a requirement when using diesel engines. I did not realize this, and am glad to know it. Any ideas for sources of positive air shutoffs, and/or cost? I think investing in one would be a good idea, if they're not prohibitively expensive.

Plastic pipe under low pressure can be bent back on itself to seal off the ends. The problem with this method is that you have to have enough pipe exposed, and I'm not at all for digging around an active leak. I found, and invested in (I'm getting tired of all this "investing"...), a <A target="_blank" HREF=http://www.pollardwater.com/emarket/pages/p64403%20tc1%20clamp.asp>Timberline Squeeze-Off tool</A>, which I also got from Pollard Water, that works with all plastic lines up to 1" diameter (I also got the ground rod option, of course) - any bigger than that, and I'm not messing with it anyway...

Its best to evacuate the area when there is a gas leak and let the utility company take over. In principle, I definitely agree. However, this is the second gas line I've hit in 5 years, and the gas company took longer than 45 minutes to get there in each case. The first time, we found the cutoff valve long before they got there. This last time, though, there wasn't a cutoff valve to be found anywhere on the line. When the gas company got there, I asked them about it and they said there wasn't one. I thought they were required by law, but apparently not. At any rate, I no longer want to be at the mercy of an entity that can't be relied upon, either to locate the lines in the first place, or to shut them off if the "ounce of prevention" fails. It may just be my cynicism poking through, but I don't think the "One-call" folks are as meticulous about finding the utilities as I would be, since they're not in the "hot-seat" if they make a mistake. And I know from experience that the gas companies either aren't in a big hurry to get there, or aren't set up to deal with the situation in a timely fashion. I'm not saying they have a problem they can solve, but it's a problem I think I can at least minimize, if not solve completely. I don't have a "let's do something, even if it's wrong" mentality, but I don't know how many more of this sort of "hit" my nerves will take - much less the strain of hearing all that gas escape while the gas folks take an hour to show up... Something's got to be done - preferably not hitting any more - but if I do, I'd sure like to be able to shut it down in a few seconds myself.

Egon · May 2, 2002

The positive air shut off is just a simple slide valve placed on the air intake somewhere. Something like an RV tank drain valve would work.

On some lines there is a control room located somewhere which may have the ability to sense pressure and activate isolating valves. Some lines can take a long time to depressure. If the gas goes directely up into the air chances for explosions are much less than if it can be trapped by some type of structure.

For your own familys sake its best to stand well back and wait. Jumping right in the hole can have two different results. There may be an oxygen deficient atmosphere and you pass out. Your best friend will jump in to rescue you and he passes out to. All it takes to reduce you my level of brain function is about 4 min. without air. The other result can be a fire started from a remote ignition source at the leading edge of the gass cloud where the proper concentrations are present for a fire to start. Once started this will almost instantlly be back to the source and its barbeque time in the pit.
I know its hard to stand back and do nothing but theres a time to retreat so you can attack again.

With Hydrogen Sufide leaks there are many documented cases were the first individual and up to two or three rescuer's are found lying in a row. Sometimes the last one is revivable but maybe not.

Egon

hosejockey2002 · May 2, 2002

It's true that they don't add the odorant until it leaves the distibution facility. But those facilities are often pretty far from the end user, so they use high pressure distribution lines that can run upwards of 100 psi, which will definitely send a geyser of dirt into the air. On a side note, I read an article about a gas regulator failing, sending gas at 35 psi right up to residential meters (it usually arrives at about 2 psi). The gas blew right through the meter regulators and entered houses at over 20 psi instead of the usual 0.6 psi. Within minutes, they had over 20 homes burning in the same area. /w3tcompact/icons/shocked.gif

Bird · May 2, 2002

I no longer want to be at the mercy of an entity that can't be relied upon, either to locate the lines in the first place, or to shut them

Mark, I don't know you well enough to know what all your training and work experience includes, but unless you've been trained in gas leakage repair, I'd say to wait for the gas company (don't care if it does take them 2 hours to get out there); natural gas is lighter than air, will rise and dissipate and no harm done other than the monetary loss of that amount of gas unless something ignites it. You'd be a lot safer using your tractor from now on with no seat belt and no ROPS than you'd be trying to fix or stop a gas leak yourself unless you've been adequately trained to do that.

so they use high pressure distribution lines that can run upwards of 100 psi

And there's lots of them with that kind of pressure, hosejockey2002.

for natural gas the odorant is not added until the gas reaches a distribution facility.

Correct, of course, Gerard.

when in the in the high pressure transportation pipes that run state to state there is no "smell" if you get a rupture. Of course in those lines the PSI is around 800

The gauge was sitting on 975 psi the day I checked a distribution center on the Tennessee Pipeline in Pennsylvania./w3tcompact/icons/shocked.gif That oughta move some dirt and rocks if Mark ever digs that one up./w3tcompact/icons/wink.gif/w3tcompact/icons/laugh.gif

Dozernut · May 2, 2002

I am not an expert on gas by any means, but have been through a lot of training on hazmat. You probably already know this, but if by chance you would hit an LPG, propane line, it has different properties than natural gas. It is heavier than air and will seek out the lowest level and build up, effectively making a bomb. This can be set off by almost any electronic device (ie. a pager or cell phone). Had a few houses blow up because propane accumulated in the basement or crawl space and was ignited by the furnace or hot water heater.

MChalkley · May 2, 2002

Bird - You'd be a lot safer using your tractor from now on with no seat belt and no ROPS than you'd be trying to fix or stop a gas leak yourself unless you've been adequately trained to do that. Agreed, Bird. I do plan to take a safety course. A local gas company official I know has agreed to let me unofficially sit in on a certification class. "Unofficially", of course, because they can't (or maybe won't) give me official approval to do their job. But since he figures I'm probably going to do it anyway, with or without the training /w3tcompact/icons/wink.gif, the best thing is to let me take the training... /w3tcompact/icons/smile.gif

MossRoad · May 2, 2002

My brother in law was going to plant a tree for my grandmother. He dug a hole about 3 feet around and two feet deep. The call before you dig people marked it incorrectly and he chopped the line to the house. He tried to get down in the hole to find the source of the hissing and passed out. My grandmother, somewhere over 80 yrs old at the time, pulled his head out of the hole and probably saved his life.

I agree with the others that state it is best to get everyone away, including yourself, and wait for the gas company.

If you call before you dig, and it is marked incorrectly, and you back away, and the neighborhood blows up and you live, you will still not be held liable, legally or morally.

If you call before you dig, and it is marked incorrectly, and instead of backing away you attempt to stop the leak, and the neighborhood blows up, and you live, you probably will be held liable legally and you will morally feel like it was your fault.

I know that if a contracctor hit a gas line in my neighborhood that was marked incorrectly, I wouldn't blame him. But if he decided to try to plug it instead of waiting for the gas company and blew up my house, I'd think he was a @#$%^^&!!!

Bird · May 3, 2002

Mark, you ought to at least find such classes interesting. I did. Of course, even though I had the classroom training, policies of the company I worked for prohibited me from actually doing any of the repairs (and I agree with those policies). Although it wasn't unusual for gas company employees to ask me what to do or how to do it, and I'd give my opinion always emphasizing the fact that I was not qualified to do the repairs and it was personal opinion only. It was sorta like this forum and tractors; some folks thought I was more of an expert than I am./w3tcompact/icons/laugh.gif Gas companies are like any other company; some had very knowledgeable, competent people, and some . . . well, you know./w3tcompact/icons/wink.gif And I've seen the time when I called in a grade 1 leak and waited for 2 hours for someone to show up. On the other hand, on the biggest job I did (in Pennsylvania), the longest I ever had to wait was 15 minutes and that time the guy got out of the truck apologizing for being so far off and taking so long to get there. They were really great people to work with.

LPG, propane line, it has different properties than natural gas

Absolutely, Dozernut. The job I had was primarily natural gas leakage surveys, but I also did some for LPG; the instruments would work just fine on either one, but for exposed lines, and to pick up the smallest leaks, you want the intake of the instrument above the line for natural gas and below the line for LPG. And for underground lines, we made sure to explain that to customers so they'd understand that we might not find very small leaks. The instruments worked great to check the LPG lines in my RVs though./w3tcompact/icons/wink.gif

There's an LPG pipeline running through this area a couple of miles from us. And when I first moved here, I noticed a maintainer (road grader) sitting in a field and it wasn't moved for 4 years. Then a neighbor told me it had hit that pipeline, the operator shut it down and got away safely, but the entire machine was so thoroughly frozen by the escaping propane that it was not worth trying to repair.

skent · May 3, 2002

We had one locally about 10 years ago where a constuction crew hit a gas line. They waited an hour for the Gas Co to arrive. Just before they arrived, a house two blocks down was flattened by an explosion. Strange part was the house that blew up didn't have gas service.

It seems the gas, leaking into the soil found it's way underground along side the water lines and leaked through foundation cracks in the basement. When the electic heat in the house clicked on, that was all she wrote.

Luck had it that no one was home at the house that blew up, and the people that live on either side (had windows blown out) were at the site of the gas leak.

Nothing but schredded house parts for blocks.