Abstract: Between 11:00 and 11:30 a.m. on August 17, 1989, at Pullen Park, the main circulation pump of the pool stopped for unknown reasons. When the pump stopped, the Delaval switch on the Strantrol 390 chemical monitoring unit failed to sense the loss of water pressure, thus allowing hydrochloric acid and sodium hypochlorite to be admitted to a closed, static piping system. Approximately 3 liters of hydrochloric acid and 6 liters of sodium hypochlorite were added, forming approximately 322 liters of chlorine gas. Employee #3 started the circulation pump at approximately 11:30 a.m., pushing water and chlorine gas into the pool. The gas came out of the solution, forming a vapor cloud that dissipated after approximately 20 minutes. Approximately 50 patrons, five pool staff (four lifeguards and the assistant manager), and six administrative staff were on site. The pool staff were performing their normal duties, while the others were on the site to inspect/evaluate the building's electrical system. All persons were evacuated from the pool by the locker rooms or pool office through the main entrance to the outside. Thirty-two patrons and Employees #1, #2, and #3 (two lifeguards and one administrative staff member) were treated by EMS and sent to the hospital for observation of minor lung irritation. No employees were admitted, but six patrons were hospitalized.