Some industries’ RAGAGEPs will call out the risk of using a butterfly valve as an energy isolation device due to its propensity to “leak by”. In this incident, the valve catastrophically failed, releasing NH3, resulting in a worker and a contractor being hospitalized. I do not know if the valve was locked out, but that does not matter in this case, as the valve internals failed, releasing the NH3.
At 9:15 p.m. on September 2, 2019, a 62-year-old employee was watching a contractor, whose age was unknown, weld on refrigeration pipes when a suction valve was pushed open by built-up pressure from a suction header. The ammonia suction gas pressure built up to 82 pounds in the suction header, forcing the suction butterfly valve to open and allowing the ammonia to exhaust. The employee and the contractor were exposed to ammonia inhalation hazards and required hospitalization.
Does your facility use “Butterfly Valves” as an energy isolation device?
Source: https://www.osha.gov/ords/imis/accidentsearch.accident_detail?id=119621.015