Pressure built inside the valve, which failed and led to a leak of toxic and flammable coke oven gas. U.S. Steel workers “for at least three years prior to the incident” had used pressurized water for the task without any formal procedure describing it. The Chemical Safety Board identified issues pertaining to procedures and hazard analysis, facility siting and process safety management systems. The affected buildings were located less than 20 feet above the coke oven gas piping that was the source of the leak, according to the report. Additionally, the CSB recommended that Nippon Steel North America develop a process safety governance program, conduct audits and promptly correct process safety deficiencies across its operations.