Swimmers doing their weekday-morning laps at Oakland's Temescal Pool ended up gasping for air and helping each other scramble out of the water on September 10 after muriatic acid and chlorine combined in the pool, sending five people to the hospital. More than 20 people were using the North Oakland facility at 371 45th Street when the chemical release began, according to three sources.
Davida Flattery, a member of the Temescal Aquatic Masters swim club, was in the pool when it happened. She told The Oaklandside she watched yellow-tinged bubbles fizzing up from the center of the pool moments before she felt like she could not breathe. Several other swimmers in the water that morning experienced the same severe coughing and breathing difficulty, and injured swimmers eventually made their way out to the sidewalk on 45th Street as 911 was called.
Muriatic acid, also known as hydrogen chloride, is added to pool water to lower its pH, while chlorine is used to kill bacteria. But when the two mix directly rather than dissolving separately into circulating water, they trigger a reaction that generates chlorine gas, a hazard that causes acute respiratory distress, severe airway irritation, and potential pulmonary edema, according to Alliance Chemical. Muriatic acid itself can also be corrosive to skin, eyes, the nose, the respiratory tract, and other bodily tissue, and ingesting it can cause severe injuries to the mouth, throat, and stomach.
Five Swimmers Hospitalized, Cause Still Under Review
Three sources say the chemical release may have been caused by either a dangerous equipment failure or human error, though that has not been confirmed. Some swimmers who were exposed contacted the state poison control hotline, and five injured swimmers ultimately went to the hospital, per the same account. All of the injured swimmers were members of the Temescal Aquatic Masters, which runs coached weekday-morning workout sessions at the pool, and club leadership has been checking in on members and providing updates since the incident.
The Centers for Disease Control and Prevention recommends that a venue be closed to swimmers during chlorine application in the first place, a standard that appears to speak directly to what went wrong at Temescal that morning. The agency's Model Aquatic Health Code provides guidance for pool operators, according to the Centers for Disease Control and Prevention.
Pool Closed Indefinitely as City Investigates
The Oakland Aquatics and Swimming Program has announced that Temescal Pool is closed until further notice due to ongoing water quality concerns, and the program says it should remain shut until Oakland Public Works addresses the facility issues contributing to that inconsistency. The Oakland City Administrator's Office is investigating the incident, reviewing policies and training, and attempting to contact injured individuals to offer support, saying the city takes swimmers' health and safety seriously. The city has not responded to questions about how many people were injured or what caused the chemical release, the report notes.
Commercial pool safety standards generally require that automated chemical dosing systems be electrically interlocked with the water recirculation pump, so chemical injection automatically shuts off if circulation stops, according to WorkSafe Victoria. A 2020 Pool & Hot Tub Alliance fact sheet describes how missing or malfunctioning interlocks can allow chemical feeders to keep running after circulation halts, potentially building up chemicals that surge into the pool once water flow resumes. Under Title 22 of the California Code of Regulations, section 65525, public pool operators are legally required to continuously run pumps, filters, and disinfectant feeders whenever a pool is open for use, according to the Legal Information Institute.
A Strained Aquatics Program Across the City
Oakland has cut its aquatics program budget in recent years, and the program now has just one full-time pool technician and half of a part-time technician, down from two full-time technicians and one part-time technician previously. Oakland's public pools have frequently been closed over the past year due to water quality issues, and DeFremery Pool is currently closed for the same reason. Live Oak Pool remained out of service throughout both the 2023–2024 and 2024–2025 school years following repeated repair failures, according to a Change.org petition calling to repair the facility.
Temescal Pool sits next to Oakland Technical High School, where it has long hosted physical education classes and local swim clubs, according to a 2021 report from KTVU. Under the California Health and Safety Code, county health officers have the authority to inspect public pool facilities, and operating one in an unsafe or unsanitary manner is a misdemeanor offense under state law, according to Digital Democracy. Nationally, pool chemical injuries send nearly 4,500 people to emergency rooms every year, according to the Centers for Disease Control and Prevention.
