Something ignited the gas that was being used in a scheduled cleaning procedure at the Kleen Energy Plant in Connecticut.
The blast killed six people. 
Called a gas blow, the operation involved workers streaming natural gas through a pipe at a high velocity in order to remove debris from new piping. The photo to the right shows gas venting out of an open pipe shortly before the explosion on February 7th.
Gas blows are routine practice within the industry. U.S. Chemical Safety Board Lead Investigator Don Holmstrom said in a statement last week:
We strongly caution natural gas power plants and other industries against the venting of high-pressure natural gas in or near work sites. This practice, although common, is inherently unsafe.
Four people died last year during a gas blow at a ConAgra Slim Jim factory in North Carolina.
Initial calculations conducted by the USB determined that about 400,000 standard cubic feet of natural gas had been released into the atmosphere within the 10 minutes prior to the incident. Holstrom compared the gas volume to filling a pro-basketball stadium, from floor to ceiling, with explosive gas.
What sparked it is still unknown.
The CSB is trying to devise better safety codes for gas blows, but has yet to identify them. Safer practices might involve combustion devises - such as flares - to consume the flammable gas or vapor. Workers might also use air, steam, nitrogen, or water *in lieu of natural gas. (* edit)
Seen here in photos before and after the accident, the 620-megawatt Kleen Energy plant had been slated to open this summer.
Natural gas power accounts for about 20 percent of the nation’s electricity.
Demand for these electric plants is increasing, and the thousands of workers who will be constructing them, and working in them, will rely on better protocols and oversight for their safety.
