[Video] Designed to Fail: Key Lessons from an Acetic Acid Release

On July 27, 2021, three contractors removed an actuator from an acetic acid reactor. The contractors inadvertently removed nuts that held a pressure-retaining valve cover in place.

The workers used a pry bar to try to remove the coupler from the valve stem, and the forces from the pry bar and the process fluid pressure inside the plug valve caused the unfastened valve cover and plug to eject from the plug valve body. Roughly 164,000 pounds of a 61.7% acetic acid mixture at 238 °F rapidly released from the open plug valve.

Two of the contract workers died from fatal chemical burns and inhalation. The other contract worker, and 28 other workers, sought medical treatment.

The United States Chemical Safety and Hazard Investigation Board (CSB, or “the Board”) investigates safety incidents and makes recommendations based on its findings. See its findings and recommendations in the Board's video below.

CSB Video: Designed to Fail

See US CSB's final report.

Four Key Lessons for the Industry

1. This isn't the first time.

"Multiple incidents have occurred in the chemical industry where employees have inadvertently removed pressure-retaining bolts from plug valves when attempting to remove actuating equipment. This has led to plug valves coming apart, releases of hazardous materials, and serious injuries and worker fatalities."

2. Design helps prevent human error.

"To prevent future incidents in which workers inadvertently remove pressure-retaining components from plug valves while attempting to remove actuating equipment, facilities should clearly mark or identify pressure-retaining bolts on existing plug valves, for example through color coding techniques and/or warning labels or signs."

3. Procedures help workers work safely.

"Facilities with plug valves should develop formal procedures for the removal of plug valve actuating equipment that require (1) a risk assessment of all plug valve actuator removal work to ensure sufficient procedures and safeguards are in place to prevent worker exposure to process fluid; (2) written procedures detailing actuator removal steps for the specific valve design; and (3) workers to be trained on the procedure before conducting the actuator removal work."

4. Contractors should be supervised.

"When contractors are conducting work on or near plant equipment containing hazardous materials, it is critical for the operating company to oversee the contractor work and ensure that it is conducted in a safe manner."

Takeaway: Stronger PSM and HazCom Compliance

This incident highlights how critical compliance with OSHA’s Process Safety Management (PSM) Standard and Hazard Communication Standard (HCS) are for keeping workers safe.

The PSM Standard exists to prevent or minimize the consequences of catastrophic releases of hazardous chemicals. Employees working at covered facilities must be trained “in an overview of the process and in the operating procedures” that emphasizes safety and health standards, emergency operations (including emergency shut down), and safe work practices [1910.119(g)(1)(i)].

Without adequate training and information about hazardous chemicals on site, employees may not take what could be life-saving precautions. In this instance, both companies perceived the task as simple. That perception, the lack of training for contracted workers, and unmarked pressure-retaining hardware resulted in the death of two workers and medical treatment for thirty others.

Tags: Chemical safety, CSB, hazard communication, HazCom, OSHA compliance, process safety management