On April 2, 2019, at 10:51 AM, an isobutylene vapor cloud exploded at the KMCO LLC chemical facility in Crosby, Texas, fatally injuring one worker, seriously burning two others, and injuring at least 28 more. The explosion followed the catastrophic failure of a cast iron y-strainer in the liquid isobutylene supply piping to a batch reactor. When the y-strainer failed, more than 10,000 pounds of isobutylene released to atmosphere. Workers manually approached the vapor cloud to close isolation valves. The isobutylene exploded while two operators were still within or near the vapor cloud.

The CSB found that cast iron -- brittle and unsuitable for hazardous chemical service for nearly a century -- had been used in the isobutylene piping. The y-strainer's failure was consistent with brittle fracture caused by pressure from liquid thermal expansion in isolated piping that lacked a relief device. KMCO's PHAs had never identified this scenario. An insurance company had recommended remote isolation for isobutylene systems nine years prior -- the recommendation was never implemented. No facility alarm was activated during the incident.

The CSB's final report, released December 21, 2023, did not issue formal recommendations because the KMCO facility was purchased by Altivia Oxide Chemicals in 2020, which dismantled the sulfurized isobutylene equipment. The lessons from KMCO apply broadly to any facility handling highly flammable liquefied gases.