A lack of regulations governing onshore drilling safety as well as shortcomings in safety management systems and industry standards utilized by the industry are among reasons cited for a fatal gas well blowout, says the U.S. Chemical Safety Board. In its final investigation report about the blowout that killed five workers at the Pryor Trust gas well on January 22, 2018, in Pittsburgh County, Okla., the CSB calls on regulators, industry groups, the state of Oklahoma and companies to address such gaps.

The cause of the blowout and rig fire was the failure of two preventive barriers that were intended to be in place to stop a blowout, says the CSB in its report. Those were the primary barrier (hydrostatic pressure in the well produced by drilling mud) and the secondary barrier (human detection of gas flowing into or expanding in the well and activation of the rig’s blowout preventer). The report explains that unplanned underbalanced drilling and tripping operations allowed a large quantity of gas to enter the well, and safety-critical operations called “flow checks” — used to determine if gas is in the well — were not performed.

In addition, the CSB found that the drilling contractor failed to maintain an effective alarm system. Likely due to excessive “nuisance” or unnecessary alarms, the entire alarm system was disabled by rig personnel. Ultimately, the lack of critical alarms contributed to workers being unaware that flammable gas was entering the well during operations before the incident.

At the time of the blowout, three workers were in the driller’s cabin. Two other workers who were on the rig floor ran into the driller’s cabin during the blowout and fire. All five were killed.

Learn more at www.csb.gov.