PLASTIC GAS MAINS: HAZARDS AND TACTICS
BY LEIGH T. HOLLINS
Natural gas leaks must be treated with the same respect as other flammable gas leaks. Propane or other liquefied petroleum gas (LPG) leaks may appear to some to be less hazardous than natural gas leaks because natural gas is lighter than air (vapor density is about 0.6), making it easier for it to dissipate. Also, since natural gas is a vapor, liquid releases and expansion ratios are not of concern. However, if civilians, firefighters, or property is involved in a natural gas explosion, the results will be the same as those for propane or other LPG leaks–injury and destruction.
Natural gas is a colorless and odorless vapor made up mostly of methane gas. The majority of natural gas is distributed throughout the country by large high-pressure pipelines, originating from the southwestern United States. When pipelines reach distribution stations, an odorant is added and pressures are lowered by regulators. Pipelines exiting the distribution station, known as distribution mains, are smaller in diameter and supply residential, commercial, and industrial customers.
Most distribution pipelines are made of steel, are larger than eight inches in diameter, and carry gas at more than 100 psi. Distribution mains typically are eight inches or less in diameter and are made of cast iron, steel, plastic (polyethylene), or steel with a plastic coating. They carry between 40 and 100 psi.
Plastic mains now are used in about 80 percent of the United States, according to a gas company representative in the Florida area. Black-colored plastic is widely used for eight-inch, 60- to 100-psi mains. Yellow, brown, or orange-colored plastic is used for 40- to 60-psi mains, which are from one-half to six inches in diameter. The closer the main gets to the consumer, the smaller it is and the less pressure it contains. When the natural gas finally reaches a residential customer, the pressure has been regulated down to only one-quarter psi at the appliance burning it.
MITIGATING A GAS LEAK IN A PLASTIC MAIN
The most common type of gas leak occurs when a gas main is ruptured by a shovel, trencher, or backhoe while digging or excavating. The damage could range from a small hole to a complete severing of the main. Gas leaks may also be caused by defects in the main, vibrations, and faulty connections.
Many gas leaks may go unnoticed for days or weeks and usually are detected by odor. Other signs of an underground gas leak are bubbles that form when it rains and dead vegetation in an otherwise green area.
The equipment needed to mitigate a gas leak is determined by the size of the gas main. The following would be the minimum equipment required:
–gas detectors/monitors for methane,
–temporary and permanent main sleeves (various sizes)
–two squeeze-off clamps (adjustable),
–high-pressure expandable plugs (up to 100 psi),
–arcless static ground kit,
–liquid dish detergent;
–nonsparking brass hand tools (locking pliers, adjustable wrench, hammer); and
Standard Operating Procedure
Your department should have an SOP that contains a predetermined course of action for handling gas leaks that includes at least the following items:
–the personal protective equipment to be worn,
–procedures for confirming a gas leak,
–the name and phone number of the gas company to be contacted
–guidelines for conducting a size-up,
–precautions for approaching the scene,
–precautions for avoiding ignition sources,
–guidelines for evacuating areas in danger,
–zoning for haz-mat incidents,
–procedures for handling static electricity,
–procedures for controlling leaks, and
–procedures for controlling the scene.
Firefighters must be properly trained in hazardous-materials emergency response, tactics, and procedures for handling gas leaks in plastic mains, SOPs, and scene safety. Practice clamping, plugging, and sleeving plastic mains using compressed air before an incident occurs. Firefighters attempting to stop the flow of gas from an underground plastic main are exposed to 100-percent gas and must enter and exit an invisible flammable vapor cloud to perform this duty. Therefore, it is imperative that they be properly equipped and trained.
RESPONDING TO AN INCIDENT
A call for a gas leak could mean anything from a liquid gasoline leak to a chlorine vapor leak. The word “gas” is very vague. The first priority is to identify the type of gas and the source of the leak, which may be very difficult at times.
Apparatus should approach from upwind, if at all possible, and be positioned a good distance from the reported leak until additional information has been obtained and the type of gas identified. The actual distance depends on the situation.
A gas detector can help lead you to the leak. Once 10 percent of the LEL (lower explosive limit) is detected, the following items should be considered:
notification of the gas company,
evacuation of civilians from the area,
a charged hoseline,
control of ignition sources,
setting up zones, and
calling additional resources as needed.
If the source of the leak is an underground plastic main, the first objective is to expose the main, usually with a shovel. Digging must be done in full bunker gear, including SCBA; a firefighter with a charged hoseline must be standing by. As soon as a piece of the main is exposed, antistatic procedures must be completed before continuing with the digging.
Static electricity is a hazard when a plastic main is involved because the static charge, built up as a result of the flow of gas, cannot find a ground on the plastic main. Plastic mains do not conduct electricity as steel mains do. The electrons build up on the plastic, waiting for anything such as a shovel, tool, or firefighter`s hand to lead them to ground. One videotape I viewed showed that the flow of gas from a plastic main generated enough static electricity to light a four-foot fluorescent light bulb.
The best method for dissipating the static electricity is to use an arcless static ground kit, a wide-mouthed plastic container with a screw-on lid. Attached to the lid is a brass spike and a roll of cloth approximately two inches wide and 20 feet long. Before using the kit, pour a small amount of liquid dishwashing detergent into the container, add water, and shake the container, drenching the roll of cloth with the soapy water. Remove the lid/ spike/cloth and pour the soapy water on the main near the leak. Push the brass spike into the earth near the excavation hole and drape or wrap the wet cloth over or around the plastic main, allowing the electrons to flow harmlessly to the ground without creating an arc or spark.
Some agencies use a bucket, burlap, and soapy water to accomplish the same objective. I prefer the kit. A two-ounce container of dishwashing soap can be placed inside the container along with the spike and cloth until needed, making a small self-contained kit that requires only water for use. Two very important items must be remembered: (1) Soapy water must be used to break the surface tension on the plastic; plain water will bead up and not provide a sufficient ground and (2) The main and cloth must be kept moist with the soapy water; if they are allowed to dry, the grounding of the electrons will cease.
Once antistatic procedures have been completed, clear the dirt from around the main to form a hole large enough to provide room for applying a clamp or sleeve. As a general rule, excavate two feet of diameter for every foot of depth the main is from grade–for example, a main 18 inches underground would necessitate that the excavation be at least three feet in diameter. Also, provide at least six inches of clear area under the main.
The next step is to determine the main size. A coffee can containing a short piece of each size of plastic main, stored inside each other, works great for this. The short piece of main can be taken into the excavation to compare sizes. It is very important to know the main size. Sleeves, expandable plugs, and adjustable squeeze clamps will work only if they are the appropriate size.
While digging out the main and determining its size, examine the main to determine the type of damage: Is the leak the result of a slice, pinhole opening, tear, rip, or complete break, for example? This information is necessary for determining whether the incident should be mitigated by stopping the leak (by clamp, sleeve, or plug) or taking only defensive actions (when the leak is large, equipment is not available, or some other condition concerning safety is involved).
Sleeve. When the main is not severely damaged, sleeving the main generally is the best method, since a successfully applied sleeve will stop the leak and not interrupt service to “downstream” consumers. Also, a sleeve can be used successfully on a dual-feed system or a main where residual back- feed pressure would normally be a problem. Sleeves are thin, steel, rubber-lined tubes with a split in the side to allow the tube to be placed over the main. A thick steel flange, tightened with a bolt or nut, is mounted on the side of the sleeve–a good comparison would be a very wide automotive hose clamp.
Sleeves come in many sizes; the proper diameter and length of a sleeve to use can be determined only after the main has been examined. For instance, if a two-inch-diameter main has a three-inch slice in it, a sleeve two inches in diameter but only two inches in length will not work. A sleeve two inches in diameter and four inches in length would be the proper size to seal the leak.
Plug. The second best method is to plug the leak. Although the chance of having a hole in the side of a main that will accept a plug is not very good, a plug sometimes can be used and the flow of gas can remain uninterrupted. If a main is completely severed, plugs cannot be used because of the high volume of gas leaking.
Plugs used for high gas pressures normally are made of expandable rubber and are mounted on a bolt, similar to expandable plugs used in boat hulls and live wells. Several styles and shapes are available. Another type of plug uses air pressure to inflate the plug after it is placed into the hole.
Clamp. The most commonly used method for stopping a leak in a plastic gas main is squeezing off the main with a clamp. This method is least desirable, however, because unless the main is on a dual-feed system, all service downstream will be interrupted–meaning that, although the clamp controls the leak, all consumers downstream will lose service and all pilot lights will have to be relit. This can be a major problem and is probably the reason gas companies are not very eager to let the local fire department know the locations of the distribution main valves. If a main is completely severed, downstream service already will have been interrupted, and firefighters will need to clamp the actively leaking main. A completely severed dual-feed system will have two very active leaks that will need clamping. Several squeeze-off clamp styles are available. Some will fit only one size main, while others have adjustable bases that can be set according to the size of the main.
When a main is to be squeezed off (clamped), it is very helpful to know the travel direction of the gas, which is not always easy to determine. Knowing where the gas distribution station is located will give you a guesstimate of the direction in which the gas is traveling.
If a clamp is successfully applied to the upstream side of the leak, the main may still leak for two reasons: (1) It is a dual-feed system, and a second clamp must be applied on the other side of the leak or (2) Residual pressure is back feeding from the downstream side of the main. In this case, a second clamp can be applied or firefighters can wait until all residual pressure bleeds off.
Additional methods. Other methods used to squeeze off plastic gas mains include the following:
fire hose clamps,
in the case of completely severed mains, simply folding the main to create a kink and taping it in place.
Some general items to be aware of when called to an incident in which gas is leaking from a plastic main include the following:
Tracer wires run alongside plastic mains so that metal detectors can detect the buried mains. To ensure a good seal, make sure the tracer wires are out of the way when applying a clamp or sleeve.
Use nonsparking tools.
Be sure the main is all plastic. Some mains are plastic-coated steel, and the clamps will break when attempting to squeeze off these plastic main look-alikes.
Some areas have buried propane tanks with underground propane lines.
Hose streams will not help dissipate the already lighter-than-air gas.
Do not fill the excavation hole with water from hose streams.
When leaving gas-leak areas, make sure firefighters “air out” before coming in contact with an ignition source.
Natural gas vapor clouds are invisible, even at 100 percent.
Natural gas is just as dangerous as other flammable gases.
Keep radios and pagers out of the “hot zone.” They are potential ignition sources.
Place squeeze-off clamps at least one foot away from the hole in the main to maintain the round shape of the main on both sides of the hole so gas company crews can apply a permanent sleeve under certain conditions.
Departments that handle leaks in gas distribution mains must ensure that firefighters have the appropriate tools and protective equipment, SOPs are followed, and training is undertaken on a regular basis. I recently saw a sign that said, “Knowledge is not what a person is taught; knowledge is what a person remembers.” I believe this and hope this article instills some “knowledge.” n
The equipment needed to mitigate a gas leak in a plastic main is determined by the size of the gas main. The crucial elements for successful mitigation are having the appropriate equipment available and knowing how to use it. Shown, from left, are a squeeze-off clamp, plugs, small sleeves, an arcless static ground kit, a gas detector, and large sleeves. (Photos by author.)
Cedar Hammock Fire Department`s training simulator provides realistic training in controlling gas leaks without exposing trainees to the hazards of gas. The simulator uses a five-hp air compressor, a control station, gas main markers, and an underground network of various sizes of plastic mains.
Firefighters in full gear prepare to clamp a two-inch plastic gas main under the protection of a charged hoseline. The red truck (right side of photo on right) is not an emergency response vehicle; it belongs to the trencher operator.
n LEIGH T. HOLLINS, a member of the fire service since 1976, is training director for the Cedar Hammock Fire Department in Bradenton, Florida, where he previously served as lieutenant and captain. Hollins is also director of Starfire Training Systems, Inc., in Manatee County, Florida. He is a Florida-state certified EMT, fire officer instructor, and fire inspector instructor.