BY FRANK MONTAGNA
Does your department pull electric manhole covers when operating at leaking gas main incidents? I suggest that you consider doing it, but only sometimes. A few years ago, I would have advised against it. Discussions with my local utility on response tactics for gas line leaks have changed my mind on the subject. The utility routinely and safely pulls these covers when the leaking gas collects in electric manholes and sewers.
Here are some safety guidelines relative to pulling manhole covers.
Never pull an electric manhole cover when underground wiring is burning or arcing.
Burning underground electrical cable insulation produces a thick black smoke that is high in carbon monoxide and other flammable combustion products. Frequently, the burning is accompanied by electric arcing. This arcing can ignite the combustion gases underground, resulting in a fireball exploding out of the manhole. When this occurs, the 300-pound manhole cover can be blown up into the air, sometimes as high as six stories. Additionally, the toxic and explosive combustion products will migrate through the underground conduit into surrounding buildings where they can ignite, explode, or poison building occupants. It would seem a logical tactic to remove the cover from a burning manhole, to prevent the manhole cover from flying into the air and to vent the smoke and combustible gases from the manhole. Although it seems logical, it is not a good idea.
When there is a fire in a manhole, pulling off the cover to release the pent-up products of combustion is a dangerous undertaking. By removing the manhole cover, you are admitting oxygen to an oxygen-starved explosive atmosphere. Remember, there is probably arcing in the hole. Think ignition source. You could be, in fact, causing the gases to ignite. When the ignition occurs, you will be standing close to the hole; that is not a good thing. You could be hit by the flying manhole or burned by the fireball that propels it out of the hole. In addition, the rocks and other debris that have settled in around the cover will be blown out like shrapnel, and you will be well within their range. I recommend that you never pull an electric manhole cover if there are burning or arcing wires in any manhole in the area, not just in the one you want to pull.
Why should you pull an electric manhole cover?
The reason for pulling the manhole cover at a natural gas line leak is to vent the collecting gas to the atmosphere. When the cover is removed, the gas, being lighter than air, rises out of the hole. Gas that is migrating toward the building is pulled back toward the now open manhole. Even though it may not completely stop the gas migration, it can slow it down, giving you more time to get into buildings, test for gas, and evacuate if necessary.
Some might argue against pulling manhole covers, saying, “It is the utility’s job to pull manhole covers; why not let the utility do it?”Although it is the utility’s job, the utility’s initial response is usually one man in a truck or car. At a serious underground leak, he has a lot to do, and he will be the only utility representative on the scene for the near future. On the other hand, we can typically put a lot of boots on the ground well before the utility cavalry arrives. The goal is to make it safer for us and for the people in the surrounding buildings. Pulling the covers can do this. If we help by pulling manhole covers, we can delay the buildup of dangerous levels of gas in surrounding buildings. This makes it safer for firefighters who must go into the buildings and for the occupants who might have to be evacuated. Pulling the manhole covers buys us time.
How and when should you pull a manhole cover?
Now for the “sometimes” I mentioned initially. When a natural gas line leaks underground, the leaking gas can migrate long distances underground and may even get into electric manholes and sewers. From here, it often travels along the electric conduit or sewer lines into buildings, where it collects. We have all seen or heard about buildings that suddenly explode as the result of an underground gas leak in the area. This is one way the gas gets into the building.
Before I tell you when or why you should pull a manhole cover, let me repeat: Do not pull an electric manhole cover when there is an underground electric incident in the area. As I said, these events often include arcing, and arcing provides an ignition source for the natural gas. Pulling the electric manhole cover off of the hole when it is full of natural gas and a spark or flame is present is just as dangerous as pulling it off at a manhole fire when it is full of carbon monoxide-rich smoke.
Get your utility to supply you with manhole hooks and to demonstrate how to pull the cover. Then, train your firefighters to do it. There are different types of covers, and there can be slightly different methods for pulling them. Remember, these covers are heavy. Two firefighters, each with his own hook, should pull the cover together.
Banging the cover a few times with the back of an ax will loosen it. The area behind the cover should be clear so the firefighters do not trip when they step back. Then, using two manhole hooks and following the utility’s procedure, the firefighters should synchronize their pulling efforts by counting off before they start to pull the cover.
Pulling manholes is not necessary at all leaking gas line incidents. Be guided by your utility. Let it ask for your help at an incident where it is needed. To avoid miscommunication, you might consider necessitating that the chief officer give approval before pulling the covers.
Prior to pulling a cover, have an on-scene utility worker test the manhole for stray voltage. Insulation on underground electric cables deteriorates over time, and stray voltage can leak out onto the manhole cover. If you pull the cover and stray voltage is present, a spark might ignite the gas. Don’t pull a manhole cover at a gas leak until it has been tested for stray voltage.
Gas utilities pull manhole covers at gas leak incidents routinely and safely. It is a standard operating procedure for my gas company. However, it is not something that should be done on individual initiative, but only in conjunction with your utility—and after training. Adding this procedure to your tactics may buy you time and save lives, possibly your own.
Pulling Manhole Cover Review
- Don’t pull electric manhole covers if there is arcing or smoking in any manholes in the area.
- Only pull electric manhole covers when asked by the gas utility representative and after it has been tested and found free of stray voltage.
- Gear up before pulling manhole covers, and have two firefighters pull the covers.
FRANK MONTAGNA, a 41-year veteran of the Fire Department of New York, has been a battalion chief for 25 years. He is assigned to the department’s Training Academy, where he is responsible for curriculum and officer development and simulation training. He wrote the department’s gas and electric procedure manuals. He is one of the creators of Fire Engineering’s simulations. He has a BS in fire science. He teaches a course for John Jay College based on his book Responding To Routine Emergencies. He has published numerous fire-related articles and frequently lectures on these topics.
Frank Montagna will present “Natural Gas Emergencies” on Wednesday, April 18, 2012, 3:30 p.m.-5:15 p.m., at FDIC in Indianapolis.
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