The U.S. Chemical Safety Board released its final report into a 2017 explosion involving an industrial steam generation system that resulted in the death of four people at the Loy-Lange box company in St. Louis. 

The incident occurred when a pressure vessel catastrophically failed, fatally injuring one employee at the company. The pressure vessel launched from the building and through the roof of a nearby business, fatally injuring three members of the public.

The CSB investigated and found that an area of the failed pressure vessel had thinned over many years due to a known corrosion mechanism that was poorly controlled. The CSB also found that Loy-Lange repeatedly ignored warning signs that corrosion was causing major problems within its operations. The investigation showed that Loy-Lange ran the pressure vessel normally before its failure despite knowing that it was leaking.

The CSB determined that the cause of the explosion was deficiencies in Loy-Lange’s operations, policies and process safety practices that failed to prevent or mitigate chronic corrosion. Furthermore, the CSB determined that contributing to the incident was the city of St. Louis’ missed opportunities to identify and ensure proper inspections, identify inadequate repair and mitigate existing gaps in inspection requirements. 

Key Lessons for the Industry

In the final report, the CSB urges companies to review the key safety lessons learned from the investigation for application at their facilities — particularly companies that operate pressure vessels and steam generation systems.

1. Pressure relief devices typically are the last line of defense protecting a vessel from overpressure.

Companies must ensure that the pressure-relief devices protecting their pressure vessels are properly designed, installed and maintained, and must ensure that all pressure relief devices are set at the proper pressure. A pressure relief device with a set pressure greater than its vessel’s maximum allowable working pressure (MAWP) cannot adequately protect the vessel from high pressure process upsets. Both the American Society of Mechanical Engineers (ASME) and the National Board of Boiler and Pressure Vessel Inspectors (NBBI) Code state that a pressure vessel’s relief device shall not be set at a pressure higher than the vessel’s MAWP.

2. Leaking pressure vessels can be dangerous and should be evaluated for continued fitness for service.

When a pressure vessel leaks, its pressure-retention-ability may be compromised. The leak should be investigated, the causes should be determined, the leak should be repaired before returning the vessel to service, and the causes of the leak addressed to prevent a recurrence.

3. Pressure vessels storing a liquid at temperatures greater than its atmospheric boiling point can explode upon failure when the contents are suddenly exposed to atmospheric pressure.

The explosion results from the rapid volume expansion that occurs when a liquid suddenly vaporizes. This type of explosion is known as a BLEVE. BLEVEs and other pressure vessel failures can be catastrophic and can cause injury, fatality and significant property damage.

4. In pressure vessels and steam generation systems, ensure that damage mechanisms such as corrosion are adequately understood and controlled.

Companies should understand the damage mechanisms to which their steam systems and pressure vessels are vulnerable, the conditions that cause such mechanisms, and the means of preventing or otherwise controlling these damage mechanisms.

5. Pressure vessels must be regularly inspected, per regulatory requirements and industry guidance, by appropriately credentialed inspectors.

6. Companies can hire contractors to perform pressure vessel inspections to supplement any local or state regulatory inspections. 

Many companies exist that employ inspectors with ASME, API, NBBI and American Society for Nondestructive Testing certifications.

7. Ensure that an effective process safety management system is in place to identify equipment hazards that can lead to injury or fatality. 

Investigate incidents and near misses in which those hazards were not adequately controlled. Ensure that incident investigations are driven to uncover underlying process safety management system gaps, and that those gaps are appropriately addressed.

As a result of its findings, the CSB included recommendations to Loy-Lange, the city and mayor of St. Louis, the inspection company Arise, and the National Board of Boiler and Pressure Vessel Inspectors in its final report.