A fire that severely burned four workers at the ExxonMobil refinery in Baton Rouge, La., occurred when operators inadvertently removed bolts that secured a piece of pressure-containing equipment to a plug valve. The uncontained valve came apart and released flammable hydrocarbons, forming a vapor cloud that quickly ignited and injured the workers. The explosion occurred on November 22, 2016.
Had a “hierarchy of controls” — a method of evaluating safeguards to provide effective risk reduction — been applied, the risks could have been mitigated, according to the final report and safety bulletin from the U.S. Chemical Safety Board (CSB). The CSB released a safety video describing the incident and ways to mitigate the risks that led to the explosion. (View the full video on the CSB's YouTube Channel.)
A contributing factor to the incident was the design of the supporting bracket for the gearbox and handwheel on the valve, says the CSB. Unbeknownst to the operators, the bolts used to secure the supporting bracket also connected the pressure-containing topcap for the valve.
At the time of the explosion, nearly all of the gearbox supports in the plant had been retrofit with a new support bracket. In the new design, no bolts for the gearbox support bracket connected to the valve or topcap.
The valve being manipulated at the time of the incident had not been retrofit with the new support. Instead, the bolts on the gearbox support bracket connected through the topcap of the valve. The bolts had to be removed to remove the support, it was not clear to the operators that the bolts must be reinstalled before actuating the plug valve.
A hierarchy of controls allows companies to evaluate safeguards to provide effective risk reduction. Within the hierarchy of controls, engineering controls are more effective than lower-level administrative controls, notes the CSB. As such, an engineering control such as improved valve design is more effective than a lower-level administrative control such as a sign warning workers that the gearbox support bracket connects to pressure-containing components.
In its safety bulletin and video, the CSB concluded that updating all of the older valves to the safer valve design, as was done to approximately 97 percent of the valves in the unit, would have ultimately prevented the incident.
The following key lessons to address the shortcomings were revealed by the investigation.
- Evaluate human factors. In relation to machinery and other equipment, interactions among humans and other elements of a system are associated with operational difficulties. Evaluating the human factor is especially important when the equipment is part of a process covered by the Occupational Safety and Health Administration’s Process Safety Management (PSM) standard. Apply the hierarchy of controls to mitigate the identified hazards.
- Establish detailed and accurate procedures for workers performing potentially hazardous work, including job tasks such as removing an inoperable gearbox.
- Provide training to ensure workers can perform all anticipated job tasks safely. This training should include a focus on processes and equipment to improve hazard awareness and help prevent chemical incidents.
Editor's Note: This story was updated to include a link to the CSB's safety video, "Fire in Baton Rouge."