Text For Citation: 01 Item/Group: 001 Hazard:

OSH ACT of 1970 Section (5)(a)(1): The employer did not furnish employment and a place of employment which were free from recognized hazards that were causing or likely to cause death or serious physical harm to employees in that employees were exposed to vacuum-induced differential pressure forces during manway opening: a) Heat Recovery Steam Generator (HRSG) Structure, Level 8 Drum Deck - On or about April 29, 2025, and at times prior thereto, at the Calpine Hay Road Energy Center combined cycle facility, the employer failed to protect employees performing maintenance from a sudden vacuum-induced differential pressure forces during manway removal, in that employees were directed to remove the securing bolts and lugs on an inward-swinging manway door to the LP drum of HRSG Unit 6 without confirming that internal and external pressures were equalized. The DCS (Distributed Control System) pressure display at the control panel indicated practically 0 psig, which operators incorrectly interpreted as atmospheric pressure. However, this reading did not account for internal vacuum conditions within the drum. The actual pressure remained below atmospheric, and no local mechanical gauge or vent verification step was used to confirm pressure equalization. The drum vent valve was found closed. In addition, no vacuum-relief device or pressure-equalizing valve, as described in ASME Section VIII (UG-28 and UG-35), API 510 Section 6.5.2, and NBIC Part 2, Section 4.4.3, which require vessels subject to internal or external pressure to be protected against vacuum collapse and to be safely vented to atmosphere prior to opening was provided. As the drum cooled, a residual vacuum developed inside the vessel. When the final bolts were removed, the resulting pressure differential caused a violent inrush of air that pulled the heavy manway door inward, drawing the operator toward the vessel opening. The operator sustained catastrophic blunt-force trauma to the head and torso as a direct result of the suction-force impact.