A city worker died Friday after being trapped in at tank at the Honouliuli Wastewater Treatment Plant in Ewa Beach.

The Honolulu Fire Department received a 911 call at 10 a.m. requesting “a confined space” rescue at the facility. Six rescue units with about 26 workers responded to the call.

The wastewater treatment plant is used to process sewage in the Central and West Oahu regions.

Because of federal rules, a hazardous materials unit was first deployed to check the air quality in the tank to determine whether it was safe for the rescue team to enter. Once the Hazmat unit deemed the area safe, the rescue team was able to retrieve the worker from the tank.

The worker was transferred to Honolulu Emergency Medical Services at 10:39 a.m. The city did not elaborate on the worker’s condition at the point of rescue, but confirmed that the worker died.

The worker’s death is currently still under investigation. No other details were immediately available.

“[Honolulu] Mayor [Rick] Blangiardi expresses his deepest sympathy and condolences to the family in the loss of their loved one,” said a city spokesperson in an emailed statement.

“The city mourns the loss of our dedicated city employee.”