Santostefano said the explosion was related in some fashion to natural gas, but that the cause was still under investigation. He said the explosion appears to have occurred when operators attempted a "blow down" of natural gas pipelines, a procedure that involves the purging of gas from the pipelines.
http://www.courant.com/community/middletown/hc-middletown-ct-power-plant-explosion,0,3952195.story
Never heard “blow down” being used with purging gas lines. When we purge gas lines we always put N2 into the system ensuring at least one high point vent is open and don’t stop purging until we get no reading at the vent on the Drager combustible gas analyzer. Wonder how long and what diameter line they were trying to purge? Without looking at the P&ID’s, I believe our main gas line is a 12”. A guy I’m on shift with tonight has a friend who’s brother left the plant an hour before the explosion. We’ll be getting an update from him at halftime. I’ll post info as I get it.