By Pool and Hot Tub Alliance Recreational Water Quality Committee

Accidental chlorine gas emissions into aquatic facilities can occur when the electrical interlock between a swimming pool water circulation pump and the pool’s chemical feeding system is lacking, improperly installed, or simply fails.

The risk of endangering pool patrons and staff by an unexpected surge of chlorine gas can be greatly reduced by designing a system to include adequate electrical interlock protection and incorporating several best practices for pool staff during pool maintenance.

When all is functioning correctly behind the scenes at pools with automated chemical control systems, chlorine based disinfectant (for pathogen destruction) and acid (for pH control) are injected into a stream of water (the “line”) being pumped into the pool following a run through the filter.

What Is The Problem?

If the pool water circulation pump stops due to an unforeseen problem or for maintenance, and the chemical feed equipment (controller) continues to add chlorine based disinfectant and acid into the line, the two chemicals may react to form hazardous chlorine gas.

Chlorine gas produced this way displaces pool water in the line, with the amount being proportional to the length of time the circulation pump is out of service and the chemical feeders are operating. When the pool water circulation pump is restarted and proper water circulation is restored, the chlorine gas is pushed through the line into the pool area where swimmers and staff may be exposed to hazardous levels.

This scenario prompted the American Chemistry Council and public health and pool industry representatives to develop a YouTube video to prevent these unfortunate events. This information and guidance is offered in the video.

Each year dozens of visitors to aquatic facilities are accidentally exposed to unintentionally produced chlorine gas.

These exposures result from a failure of the electrical interlock between the chemical feed equipment (usually involving acid and sodium hypochlorite bleach) and the water circulation pump.

This video, produced by the American Chemistry Council, presents steps that aquatic staff can take to reduce the risk of these exposures.

Download the Preventing Unintended Chemical Injection video: https://www.chlorine.org/pool-interlock-safety/