Foam Stops Gas Leak Without Digging
A quick, easy way to isolate a gas main break under emergency conditions, such as a fire, is now part of the safety procedures of the Philadelphia Gas Works. The section of the main taken out of service can be as short as the distance to the next building service line on each side of the break.
If the emergency included a burning building, the gas company crew would not have to enter the immediate fire area because the sealing off of the main could be done by using the gas service lines in the basements of buildings on each side of the fire. This procedure limits the number of customers that must be temporarily deprived of gas service and also eliminates lost time looking for street shutoffs that may be difficult to spot at night or under ice and snow. Limiting the number of customers affected also simplifies the restoration of gas service.
Urethane foam, made right in the gas main, is used to plug the pipe on each side of a break. This system of plugging a main was adopted by the Philadelphia Gas Works after tests made on pipes up to 20 inches in diameter. In talking about this new method to fire officers and probationary firemen at the Philadelphia Fire Academy, LeRoy C. Schlagel, general supervisor of the distribution department of the Philadelphia Gas Works, explained that urethane foam solidifies in the main within a minute after it is generated. In tests on 6 and 4-inch cast iron mains, the gas flow has been stopped in 55 seconds.
The foam system consists of two aerosol cans containing the chemical components for generating urethane foam. A 1/8-inch flexible vinyl tube from each can terminates at a common nozzle, which accomplishes the mixing of the cans’ contents.
The foam-making packages are available in two sizes. One makes about 3/4 of a cubic foot of foam and the other creates about 10 cubic feet of foam. The smaller package is sufficient for plugging mains up to 8 inches in diameter, Schlagel said.
The nozzle and vinyl tubes are secured to a fish tape that is pushed through a 1 1/4-inch service line that has been disconnected in a customer’s basement. From maps, the gas company crew knows the distance from the basement wall to the main, and this distance is marked on the fish tape. When this distance (up to 50 feet) is reached, a wire on the package containing the two aerosol cans is pulled to release their contents. As the foam drops to the bottom of the main, it becomes rigid and a buildup continues until the main is plugged. This is done on each side of the break by using two different service lines.
The nozzle that the Philadelphia Gas Works uses is a modification of the one normally supplied with the package. The modified nozzle made of copper tubing will pass through a halfclosed curb cock.
Because gas mains in Philadelphia are generally 2 to 2 1/2 feet below the surface, Schlagel said, a bar can be driven through a steel or cast iron main. Then a 3/4-inch pipe can be driven into the main and a urethane foam unit nozzle can then be put into the main through the small pipe.
Experimentally, the Philadelphia Gas Works used a large foam package to plug a 20-inch dead end main. The gas flow, at about 1/4 psi, was approximately 106,000 cubic feet per hour. The main was pierced from the street surface to introduce the foam nozzle. In 2 3/4 minutes after foaming started, the gas pressure on the other side of the foam plug dropped to zero.