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Industrial Safety

Errors, little oversight led to gas drillers’ deaths in Pryor Trust gas well explosion

Chemical Safety Board recommends federal regulations, better worker protection

by Jeff Johnson, special to C&EN
June 13, 2019 | A version of this story appeared in Volume 97, Issue 24


Photo of a burned and collapsed natural gas drilling rig.
Credit: Chemical Safety Board
Five workers died in the Pryor Trust gas well fire when they were trapped in the driller's cabin (top left).

A drilling rig blowout and 7 h fire that killed five workers who were trapped in the rig’s small cabin were the result of a string of management and operator failures at an Oklahoma natural gas well last year.

In an investigation report released June 12, the US Chemical Safety and Hazard Investigation Board (CSB) also found there are few industry standards and no federal safety regulations specific to oil and gas drilling, despite their growing importance to the US economy. Oklahoma’s regulations seem more to encourage production than protect workers, the CSB says.

The direct cause of the accident at the Pryor Trust gas well was insufficient hydrostatic pressure in the form of heavy drilling “mud” needed to block natural gas from working its way to the surface during drilling operations. Also, rig workers failed to detect and respond to the release of mud and gas at the well’s surface and, as the tragedy unfolded, to fully activate a blowout preventer.

Among its recommendations, the CSB urges the federal Occupational Safety and Health Administration to develop regulations for the onshore drilling industry; oil and gas operations are specifically exempt from OSHA process safety management standards, the CSB notes.

Also, the CSB calls for the American Petroleum Institute, an industry trade association, to develop an adequate alarm system to warn workers of hazards. In this case, the alarm system had been turned off, but even if it had been activated, the system’s warning would have been confusing, the CSB says. The board also recommends that the API develop designs to protect workers in rig cabins.

The Pryor Trust gas well is a vertical and horizontal well, a type that dominates US oil and natural gas operations today, the US Energy Information Administration (EIA) says. Of 200,000 US wells, nearly all output comes from horizontal wells rather than vertical-only wells, a reversal of 20 years ago, the EIA says.

Red Mountain owns and operates the Pryor Trust well; Patterson-UTI Drilling Company was the drilling contractor. The CSB found that as of March 2019, Patterson had 171 active land-based rigs in the US and Canada.



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