Ask The DP Pro – David Heldenbrand

Q What is the “DANGER ZONE” when a Gas Line is Fractured?

A By David Heldenbrand

DATA HAS been collected that shows that a danger zone exists after a gas line has been fractured. While it is very difficult to determine the severity of a fractured gas line leak, data has shown that very few fires or explosions occur past a 50-foot radius from a significant gas leak.

This information can be extremely useful for operators, construction workers, HDD crews, fire departments and any other first responders. Buildings or structures within this radius have a greater likelihood of a fire or explosion than buildings located farther away. Safety and evacuation decisions can be prioritized quickly and confidently with this information.

There are a number of factors that have been theorized to cause a building to explode from a gas leak, but examination of the data from hundreds of NTSB reports and other studies have shown that fires and explosions, even from a major leak, more than 50 feet from a building are extremely rare. Obviously, the closer the leak is to a building, the more likely the building is to be affected.

Bison Engineering, Inc. has been studying these issues for more than 30 years. Numerous issues and causes have been theorized by many people, but little data has been sorted and compared until now. Damage prevention to all underground utilities is very important, but when a gas line is impacted, serious consequences can result. Reducing risk exposure to people and structures is of utmost importance. Collecting and utilizing the correct information is critical.

The distance from a leak to a structure fire is independent of the initial pipeline pressure. Interestingly, data has also shown that relating soil type and the distance from a leak to a structure fire or explosion is, similarly, not proportional.

The furthest recorded distance from a gas line damaged by a contractor to an explosion is 240 feet. In that case, all the utilities were laid in the same ditch and were backfilled with fractured shale all the way to the foundation of the houses. The explosion occurred an hour after the gas line was damaged. Most incidents do not involve new backfill or loose backfill, however. Most incidents involve fully compacted, non-select backfill.

It has also been documented that natural gas has caused explosions and fires both uphill and downhill from pipeline damage or a significant leak. There are numerous examples of gas from fractured gas lines causing fires and explosions where the gas is coming from a source uphill from the explosion.

Extensive research has been conducted on this subject and the research has revealed some interesting facts, which you can learn more about by visiting

David Heldenbrand, Bison Engineering, Inc., is a licensed Professional Engineer and Certified Fire Investigator. He has been a licensed Professional Engineer since 1982 and has investigated more than 2,500 natural gas-related fires and explosions, along with propane-related incidents over the past 32 years. He also served as a district engineer for a natural gas transmission company and has conducted forensic investigations of natural gas and propane-related incidents. David can be reached at


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