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Purging Gas Lines has Caused Tragedy in the Past
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It’s not known yet what caused Sunday’s explosion at the natural gas power plant that was under construction in Middletown. One theory is that it occurred when gas was being purged from a pipeline. Such purges are routine, but there have been times when they’ve resulted in tragedy.

Purging is the process of removing air or another gas from a pipeline. Daniel Horowitz of the U.S. Chemical Safety Boards say purging is done every day across the country in order to get pipelines ready to carry natural gas.”
 
“To fire up gas appliance or equipment you have to have pure gas coming out of line and there can’t be any air in the lines because that would be rather dangerous. So a step in putting new pipes into operation is generally to displace whatever gasses are in the pipe by opening the gas supply and venting  the gas out the other end of the pipe.”

But Horowitz says if gas is vented inside a building it can be a recipe for disaster.

“Where the gas can build up to an explosive concentration and then ignite.” 

Two years ago in San Diego, the purging of gas inside a Hilton Hotel that was under construction, led to an explosion. In June last year, a contractor was purging a gas pipe and venting it inside a building at a ConAgra Slim Jim plant in Raleigh, North Carolina. The gas built up and it exploded, killing four people. Horowitz says when gas builds up indoors even a small spark can cause a problem.”

“It doesn’t take very much to ignite a flammable atmosphere once it’s present. It could be an electrical switch. It could be an open flame. It could be a welding torch.”

Horowitz says workers should not rely on their sense of smell to detect when natural gas is present at dangerous levels, but instead use a gas monitor.

“When new gas pipes are put into service the smell that’s normally in natural gas, that warns people if there’s a gas release, can actually be absorbed by the pipes. So, instead of the natural gas smell that we are all used to, workers who are nearby new pipes may smell little or nothing at all and may not get warning  from their senses about a gas release.”

The Chemical Safety Board issued a safety bulletin on gas purging in October. And just last week it issued urgent recommendations calling for venting gas outside during a purging, evacuating all but the most essential workers, and using natural gas monitors. The National Fire Protection Association says its technical committee is scheduled to consider these recommendations two weeks from now. Meanwhile investigators from the Safety Board are arriving in Middletown to figure out the cause of the explosion.

For WNPR, I'm Nancy Cohen.