July 6, 2023

CSB: Process Safety Failures Led to Fatal Propylene Release and Explosion

A fatal explosion in 2020 at a facility that performed specialty thermal spray coatings in Houston, Texas, was caused by a leak of propylene gas from a degraded rubber hose, according to a final report released last week by the U.S. Chemical Safety and Hazard Investigation Board. CSB found that the gas accumulated overnight in the facility and likely ignited when an employee arrived in the morning and turned on the lights. The CSB report describes several process safety failures that contributed to the incident, which killed two workers and a member of the public and damaged hundreds of nearby buildings.

The incident occurred on Jan. 24, 2020, at the Watson Grinding and Manufacturing Co. The leak of propylene, an extremely flammable hydrocarbon vapor, formed when a poorly crimped rubber hose that had lost its pliability became disconnected from a fitting inside a coating booth. Instead of using factory-crimped hose, Watson Grinding relied on its employees to crimp the hose manually. The hose was a replacement for what CSB described as a “more robust” copper tubing connection and was made of a grade of rubber unsuitable for propylene.

CSB found that an automated system for detecting leaks, sounding alarms, starting up an exhaust fan, and shutting off the gas supply was not functioning, and a manual shutoff valve at the propylene storage tank had not been closed at the end of the previous workday. The incident would have been prevented if either the valve had been closed or the safety system had been working, according to the report.

The coating building had been constructed following a 2008 incident that also involved a catastrophic explosion of propylene gas.

Following the 2020 incident, OSHA cited Watson Grinding for failing to provide effective information and training to employees on chemical hazards such as propylene, failing to ensure the equipment in the coating booths was gas-tight, and failing to ensure the propylene shutoff valve was closed at the end of each workday. Because the propylene stored at the facility was below the 10,000-pound threshold, it was not subject to the OSHA process safety management standard or the EPA risk management program rule.

More than 450 structures, including many homes, were damaged in the explosion. Two weeks later, a resident died from injuries sustained in his home as a result of the incident.

For more information, read the CSB news release or review the report (PDF).