By Jack Naudi, Post-Dispatch

A single mistake made by a Laclede Gas Co. crew 30 years ago might have contributed to an explosion on Dec. 11 that destroyed a home in Manchester, injuring four members of a family.

As a result, Laclede Gas crews must inspect about 100 underground connections to see if the error was repeated.

Laclede Gas and staff members of the Missouri Public Service Commission, which regulates Laclede, early on determined the cause of the explosion: The failure of a “service tee,” a connection installed in 1974 between the main natural-gas line and the smaller gas line into the house.

The service tee was lying beneath a large tree and ruptured when a tree root butting up against the line pulled it out of a coupling. The service tee also was missing a “tubular stiffener,” a mandatory component designed to add strength.

PSC officials say it’s possible that the rupture would have occurred even if a tubular stiffener had been in place. The stiffeners are designed to bolster service tees during the expansion and contraction that occurs as the ground heats and cools, not to withstand tree roots.

“It might have happened anyway,” said Bob Leonberger, a supervisor in the PSC gas-safety department. “Without the stiffener, it might have happened sooner.”

Larry Adrian and three children suffered minor to serious injuries in the explosion at the home on Hagers Mill Court, near Big Bend Road and Highway 141. Several adjacent houses also were damaged.

Laclede crews have checked service tees installed about the same time as the one in Manchester, and all had tubular stiffeners.

“This was an isolated incident,” Leonberger said. Nonetheless, Laclede has agreed to check service tees in the next year to determine whether they have stiffeners. The company has estimated it will look at about 100 more service tees.

Although failure to include the stiffener violated PSC rules, Laclede doesn’t face a fine or other penalty.

Laclede spokesman George Csolak said the company will have to spend a nominal sum as crews check the service tees. The inspections generally will be done as Laclede conducts other underground work.