The result of this collaboration was a new, free, approximately nine-minute video titled, “Preventing Unintended Chemical Injection.” The video debuted at the October 2018 meeting of the World Aquatic Health Conference (WAHC) in Charleston, SC. The immediate response of the pool stakeholder audience was overwhelmingly positive; the general sentiment seemed to be, “where has this video been all this time?”
When all is functioning behind the scenes at the pool correctly, chlorine-based disinfectant (for pathogen destruction) and acid (for pH control) are injected into a pipeline of water being pumped into the pool following a run through the filter (Figure 1). But accidental chlorine gas emissions into aquatic facilities can occur when an electrical interlock between the pool water circulation pump and the chemical feed system is lacking, improperly installed, or simply fails.
If the pool water circulation pump stops (due to some unforeseen problem or perhaps intentionally for maintenance) and the chemical feed equipment continues to add chlorine-based disinfectant and acid into the lines, the two chemicals may react to form chlorine gas (Figure 2), which displaces pool water in the line, the amount being proportional to the length of time the circulation pump is out of service, and chemical feeders are operating. Then, when the pool circulation pump is re-started, chlorine gas is pushed through the lines and out into the pool area where swimmers or staff may be overcome by an unexpected surge of gas (Figure 3).
Electrical interlock
The video makes the point that an unintended injection of chlorine gas into a pool can be avoided by properly designing the system to include electrical interlock protection. Simply stated, electrical interlock protection ensures that if the pool pump is disabled, the chemical feed equipment will also be disabled, avoiding the development of chlorine gas in the lines.
There are various levels of interlock protection, ranging from ensuring the circulation pump and chemical feed equipment are on the same electrical circuit to installing an interlock safety switch. The video also addresses the human factors that may contribute to chlorine gas releases and the importance of good practices among pool staff, including:
- Training staff to recognize high-risk scenarios that could lead to accidental chlorine gas exposure.
- Removing all bathers and staff from the pool and deck whenever: maintenance is performed on the circulation or chemical feed systems; a ‘no flow’ condition is detected; an unexpected or manual deactivation of the circulation pump occurs; or when the interlock system is activated.
- Prohibiting re-entry into the pool until the cause of an interruption in water circulation is understood and corrected and the system is functioning correctly for at least five minutes with an appropriate free chlorine level and pH.
