New report finds that gas alarms went off shortly before deadly explosion at Clairton Coke Works

We’re learning more about what caused the deadly explosion at the Clairton Coke Works plant in August.

Channel 11 previously told you that Allegheny County District Attorney Stephen Zapalla thought cold water used to flush the line during maintenance may have had a significant role in the blast that killed 52-year-old Steven Menefee and 39-year-old Timothy Quinn.

U.S. Steel previously said an investigation done by a third party shows that as a gas valve was being flushed, too much pressure built up, causing the valve to fail. That in turn led to coke oven gas filling up the area and ultimately, an explosion.

Now, a new report from the U.S. Chemical Safety Board says workers were flushing the isolation valve inside battery 13 when gas monitors went off. Less than a minute after an evacuation call was issued, the explosion occurred.

The report says the valve split open along a “fully circumferential crack."

The safety board recovered at least nine valves from batteries 13 and 14. Four of them were damaged, but it’s unclear whether the damage happened before or after the explosion.

The report found that the last time U.S. Steel refurbished the valve that failed, which was manufactured in 1953, was in 2013.

The safety board is still investigating. The report states investigators are still collecting evidence and analyzing the following:

• The cause and source of the gas release
• Metallurgical analysis of cast iron valve components
• U.S. Steel’s use of cast iron materials in its coke oven gas systems
• Policies and procedures for valve maintenance and exercising
• U.S. Steel’s overall safety management systems

A final report will be issued once the investigation is complete.

U.S. Steel, in a statement, thanked the safety board for its work and claimed that the findings so far align with the company’s.

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