Abstract: At 9:45 a.m. on November 26, 2021, Employee #1 was repairing the grit chain inside the pre-aeration tank #4, a permit-required confined space with atmospheric and engulfment hazards. Employee #1 and Coworker #1, both from the maintenance team, were tasked to enter the permit space to repair the plastic grit chain and bracket collection system via a confined space entry permit. They were the authorized entrants. In additional to the entrants, the employer also designated Coworker #2 (from the operation team) as the attendant/entry supervisor on this job. At approximately 8:45 a.m. after the internal atmosphere was measured, recorded, and deemed "acceptable" by Coworker #2, Employee #1 and Coworker #1 entered the permit space. At approximately 9:30a.m., they got out of the permit space for a short break and re-entered the permit space at approximately 9:50 a.m., after the internal atmosphere was measured, recorded, and deemed "acceptable" again by Coworker #2. At approximately 9:57 a.m., Employee #1 was found by Coworker #1, unresponsive and lying face down on the down-slope end of the permit space. The Honolulu Fire Department arrived the scene at approximately 10:10 a.m. After they conducted their own air monitoring of the permit space, the Honolulu Fire Department entered the permit space and retrieved the victim. The victim was pronounced dead on the scene by the EMS. According to the autopsy report by the City and County of Honolulu Medical Examiner's Office, the cause of death was natural, i.e., atherosclerotic coronary artery disease with remote myocardial infarction. The Pre-aeration tank #4 is classified as a permit-required confined space by the employer, containing engulfment hazards from the incoming wastewater (the flow rate is approximately 6.75 MGD on the day of the incident) and atmospheric hazards from the naturally occurred Hydrogen Sulfide (H2S) and methane gas (CH4) from the wastewater.