Abstract: At 10:00 a.m. on June 25, 2020, an employee working as a fire fighter for a city fire department was responding to a grass fire in a residential area a few miles away from the station. The employee was working with a crew conducting fire suppression at the site and overhaul activities back at the station. The fire crew consisted of a Coworker #1 (fire captain), Coworker #2 (fire engineer) and the employee. At the site, Coworker #2 manned the pump while the employee and Coworker #1 took a turn handling the high-pressure water nozzle. The crew was spraying at the fire burning the grass, debris and an outbuilding. Due to a radiant heat and strenuous physical exertion, the employee felt nauseated towards the end. The crew was able to contain the fire by approximately 4:13 p.m. The team returned to the fire station and prepped their equipment for the next service call. The firefighter felt worse with symptoms including dizziness, headache, nausea, vomiting, inability to keep drinking fluid down and diarrhea. He advised Coworker #1 about his symptoms and said he would feel better if he could go home. Coworker #1 allowed the employee to go home. While at home, the employee attempted to rehydrate himself but was still unable to hold anything down and he vomited. His spouse drove him to the hospital later that night where he was admitted. The ambient temperature on the day of the incident was approximately 96 degrees Fahrenheit. The firefighter stated that he had anticipated that he would have to be hydrated to perform work, so he started to hydrate himself at home before starting his shift. When he reported to work the next day, he hydrated himself more with water to Gatorade ratio of 2:1. He also diluted the drip pack in his bottled water to keep himself hydrated. The morning of the grass-fire call, the firefighter hydrated some more and while enroute to the fire zone. The treating physician indicated that the firefighter suffered a hyponatremia and severe heat exhaustion.