Abstract: On September 12, 2019, several employees were working at a petroleum refinery. This was a multiemployer site. One employer was a plumbing, heating, and air conditioning contractor. The inspection number for the contractor was 1436140. The other employer was the refinery. The inspection number for the refinery owner was 1436213. At 1:30 p.m., there was a release of approximately 523 barrels (83,150 liters) of slurry oil from the Fluidized Catalytic Cracking Unit (FCCU) at the refinery due to a broken valve. The contractor's employees were investigating lines on a structure behind a work area, doing work that was not related to the leak of the slurry oil. All told, six employees were affected. They inhaled fumes that resulted from the release of the chemical. Four of the affected employees worked for the contractor, and two of the affected employees worked for the refinery owner. Of the four contractor employees affected, two were evaluated at the site by the refinery owner's nurse practitioner, with no further medical action recommended. One of the contractor's employees was evaluated at the emergency room (ER) of a nearby hospital and released. The last of the contractor's employees was hospitalized for five days at that same hospital. The two refinery employees who were affected were also evaluated at the site by the refinery's nurse practitioner, with no further medical action recommended. The FCCU process was a process safety management (PSM) covered process, because it contained an inventory of approximately inventory 308,269 pounds (139,830 kilograms) of flammable chemicals. This was in excess of the PSM threshold quantity of 10,000 pounds (4,536 kilograms). Accordingly, the FCCU process where the incident occurred was covered under the PSM standard. One employee was hospitalized and five were treated without hospitalization.