Case Histories of Gas Line Damage and Gas Explosions

It is important to conduct full investigations when gas line damage and a resulting gas explosion occur. Bison Engineering has conducted extensive research on this subject from the available data. A number of variables usually contribute to each incident, so extracting the most information out of each incident is extremely important. In 2015, the American Petroleum Institute developed a recommended practice for Pipeline Safety Management Systems. API RP 1173 recommends a full investigation of each incident. From the data collected and analyzed, future incidents can be limited or prevented because risk assessments can be continually improved. I recommend that investigations include many parameters that have not been routinely recorded in the past.

We have reviewed hundreds of incidents and collected and sorted numerous conditions of those incidents. Just sorting basic data has revealed some useful patterns. We found through extensive testing and review that most structure explosions occur at a distance of less than 50 feet from the pipeline damage. Gas mains are usually routed along one side of a street. We have found that house fires and explosions usually occur on the same side of the street as the gas main. Why? Because the house on the other side of the street is more than 50 feet from the damaged pipe. Many additional questions could be answered with even more information. It’s important that the industry collect more complete information to answer these questions.

For example, how far can gas “travel” to cause an explosion? What is the transportation mechanism of soil gas migration? How do soil conditions affect soil gas migration explosions?

We concluded that collecting better information can provide much more comprehensive data to analyze for risk assessments. This can be done by simply sorting the data from each incident. First responders have to assess a broad range of parameters very quickly when they arrive at a site. They need the most accurate information available. With more comprehensive collection of data and a better analysis of each case, more targeted risk assessments can be utilized as tools in the future. Document:

1.Radial distance from the damaged pipe to the nearest structure and other damaged structures

2.Surface conditions radially from the damage

3.Radial distance of visual indications of gas flow from the ground

4.The time the damage occurred and the time of ignition

5.Soil type (even approximately, if necessary)

6.If the involved structure is at a higher or lower elevation than the pipe

7.Pipeline pressure

8.Extent of damage to the pipe and diameter of the pipeline

9.Location, depth and route of other utility lines near the damaged line

10.Extent of gas smell or lack of gas smell

Many of these items seem very routine but are missing in most reports. This basic data can be extremely useful for future risk analyses. All of these items can be readily assessed in an investigation and when sorted and analyzed, can provide guidelines for risk assessments by first responders.

David Heldenbrand is president of Bison Engineering. He is a licensed Professional Engineer and a Certified Fire Investigator. He can be reached at dave@

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