This Final CSB Report issued December 17, 2019 discusses the investigation of two fatal explosions that occurred in 2017. An investigation of the first explosion on May 28, 2017 was in progress when the second explosion occurred on June 20,2017. The final report can be found at the following url: https://www.csb.gov/midland-resource-recovery-explosion-/
The CSB determined that the probable cause of these incidents was reactive, unstable chemicals that exploded when workers tried to drain the uncharacterized, chemically treated liquid from natural gas odorizer equipment during decommissioning It was found that sodium hypochlorite (also known as bleach), used to clean and deodorize the vessels, reacted with the remaining contents (e.g. process water) to generate reactive flammable gases. Other than the mercaptan odorant, other chemicals including methanol, diesel, and kerosene, could have been present in the odorization equipment. Formal hazard identification process were not employed to analyze or
characterize what chemicals were inside the odorizer vessels—and in what quantity—before decommissioning and chemically treating this equipment with sodium hypochlorite.
These incidents highlight the importance of: