MSHA said the explosion, which occurred within a sealed area on June 30, 2012, resulted in no apparent structural damage to the undisclosed operation’s 120-psi seals, but the forces from the explosion did severely damage three of the four PVC water drainage pipes installed through the lowest seal in the set.

“Testing and independent evaluations led to the conclusion that the Schedule 80 PVC pipes failed due to a rapid internal over-pressurization,” the agency said of its findings in the incident. “The only pipe remaining intact did so because the water trap assembly was not secured to the pipe. Pressure relief was provided when the forces dislodged the trap from the end of the pipe.”

Federal officials also released best practices for operations, including the incorporation of a pressure relief system in future water drainage systems that utilize PVC in 120 psi seals. As an alternative, operations can use other types of suitable nonconductive pipes as long as their strength is consistent with the seal.

MSHA said that anti-freeze is frequently used in water traps to maintain separation between a sealed atmosphere and the atmosphere in the active workings due to its evaporative properties. However, it is important to note that anti-freeze will degrade the PVC over time.

“If anti-freeze is used in PVC water traps, examiners should regularly examine them for signs of degradation,” officials said, adding that traps showing signs of degradation should be replaced.