Midland Resource Recovery explosions - update

Published:  29 September, 2017

More details have been released about two explosions that occurred within weeks of each other, resulting in the deaths of three workers at a facility in Philippi, West Virginia, US.

The explosion of May 24, 2017 killed two workers and severely injured one worker, including the founder and president of MRR.

A CSB investigation began on May 28, 2017 but less than a month later a second explosion took place killing an employee of a contractor.

MRR’s Philippi facility handles a variety of operations related to odorant services, including decommissioning old or unserviceable odorant equipment. The decommissioning process is necessary to remove mercaptan odour prior to equipment destruction, as even small quantities of released mercaptan can cause complaints and false natural gas leak concerns. Mercaptan is considered ideal as an odorant for natural gas, but it is difficult to remove the odour from equipment that has contained it.

The vessels involved in both of the incidents were Peerless MP-85 Odorizers. They were constructed of carbon steel and consisted of three interconnected tanks.

Example of the vessels that were involved in the explosions (picture: CSB)

The top tank was the mercaptan storage tank which held concentrated mercaptan. In the middle tank, a slip stream of the natural gas pipeline entered the vessel so that mercaptan could be added to the pipeline from the top tank. In some MP-85s there is an aluminium component in the interior of the middle tank as well. The bottom tank served as an overflow tank for the top and middle tanks.

The MRR process of decommissioning the MP-85s involves deodorising the tanks by adding dilute sodium hypochlorite to react with the mercaptan. The sodium hypochlorite oxidizes the mercaptan, neutralizing the odour. After the mixture has been allowed to react for some time, the resulting liquid is drained from the MP-85s. The vessels are then purged with air and cut into scrap metal.

On May 24, 2017 three MRR workers, including the company founder and president, were working to drain a number of MP-85s that had been filled with cleaning material about a month before.

Fourteen MP-85s had been filled with sodium hypochlorite and required draining. During the initial stages of the draining, one of the MP-85s violently exploded, killing two workers and seriously injuring the third worker. Workers were likely preparing to pump process water out of the top tank and were either removing plugs from the top of the top tank or beginning to pump out the liquid from the tank. The container that failed on May 24, 2017 shows a rupture of the vessel at both the top and middle of the tank.

The tank that failed in June (picture: CSB)

Less than a month later, on June 20, contractors, who had been hired to drain the remaining MP-85s, were beginning the process of draining another MP-85. Within a few minutes of initiating the draining, the middle tank ruptured, killing one of the contractors performing the work.

According to the CSB, the explosions likely occurred when unintended chemical reaction(s) caused highly reactive or unstable chemicals to form in the respective vessels, which resulted in the two explosions.

The CSB is continuing to investigate the primary causal factors of both incidents. Among the areas of interest, the investigation will examine the potential chemical reactions that could have led to the incidents, potential learnings for other industries using reactive chemicals, and the process safety management systems in connection that connected an end cap to the middle tank.

  • Operation Florian

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