US Chemical Safety Board cites lack of Alarm Philosophy, Alarm Rationalization, and State-Based Alarming as Contributing Factors to Blowout in Oklahoma

On January 22, 2018, a blowout and rig fire at the Pryor Trust gas well killed five workers, who were inside the driller’s cabin on the rig floor. The cause of the blowout and massive fire was the failure of both the primary barrier—hydrostatic pressure produced by drilling mud—and the secondary barrier—human detection of influx and activation of the blowout preventer—which were intended to be in place to prevent a blowout.  

The CSB Investigation found that the alarm system had been turned off during the fourteen hours leading up to the blowout. This meant that the significant increase in volume (level) inside the trip tanks and mud pits, from an influx of gas into the well, was not detected; consequently the situation was not recognized and the blowout preventer was not closed.  The alarm system also was not effectively designed to alert personnel to hazardous conditions during different operating states (e.g., drilling, tripping, circulating, and surface operations) and would have sounded excessive non-critical alarms during the 14 hours leading to the blowout, which likely led to the drillers choosing to turn off the alarm system.

“Alarms were perceived as a nuisance or an annoyance.  We found that had the alarm system been on, most of the alarms that would have activated during the 14 hours leading up to the incident likely would have been irrelevant to detecting the problems in the well.”Lauren Grim, CSB Investigator

To ensure that the secondary barrier functions effectively, several alarm management recommendations were cited:

  • An alarm philosophy should be developed. – There was no guidance for how to define alarm set points for parameters that could be used during the various operating modes (tripping, circulating, surface operations) to identify a well control event.
  • Alarm rationalization should be performed– The implementation of an alarm system with only the rationalized alarms active could have led the drillers to keep the alarm system on, and to see only those alarms that were critical to detecting the well control event.
  • The Drilling Industry needs an Alarm Management Standard- Develop a standard on alarm management specifically for the drilling industry, based on guidance in ANSI/ISA 18.2 Management of Alarm Systems for the Process Industries, that addresses drilling’s unique dynamic environment and provides guidance on implementing a state-based alarm system for different operating modes. 
  • State-based Alarming capability should be provided– There could be different active alarms for each operation (e.g., drilling, tripping, circulating) such that alarms critical to a certain operation would not become a nuisance when operating in a different state where those alarms are not needed.

Thanks to the CSB for their thorough and informative work. Below you can watch the full video.

Read the CSB Report

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