CSB Closes Recommendation to NBBI with ‘Exceeds Recommended Action’ Status

The U.S. Chemical Safety and Hazard Investigation Board (CSB) has closed its 2017 recommendation to The National Board of Boiler and Pressure Vessel Inspectors (NBBI), issuing it the designation “Closed – Exceeds Recommended Action.”

The recommendation stemmed from the 2017 pressure vessel explosion at the Loy-Lang Box Company in St. Louis, Missouri. The incident occurred when a severely corroded steam vessel ruptured during operation, killing four people, injuring three, and causing extensive damage to nearby buildings.

Following its investigation, the CSB recommended that NBBI update NB-263, Rules for Commissioned Inspectors, to “include prescriptive elements in the boiler and pressure vessel repair and alteration inspection and acceptance process that would prevent the acceptance of a non-conforming repair or alteration.”

In a letter to NBBI, the CSB confirmed that the Board voted Sept. 6, 2025, to close the recommendation after determining that the NBBI’s subsequent actions went beyond the scope of what was requested. Updates to NB-263 and related National Board Inspection Code (NBIC) provisions strengthened oversight and clarified inspector responsibilities in repair and alteration work, improving consistency and safety across the industry.

The investigation into this incident was the cover story in the summer 2023 BULLETIN.