Each year dozens of visitors to aquatic facilities are accidentally exposed to chlorine gas due to a failure of the electrical interlock between the water circulation pump and chemical feed equipment. For that reason, the American Chemistry Council Chlorine Division prepared an instructional YouTube video that outlines the proper steps aquatic staff can take to reduce the risk of unintended exposure to chlorine gas. The following provides the Council’s advice on interlocking chemical feeders with circulation pumps to prevent accidental chlorine overdosing.

Protecting people from exposure depends on shutting off chemical feeders when there is no water flow.

That’s because the system is safe as long as water continues to flow. Serious problems can occur if the circulation system is off and the chemical feeders continue to pump. Chlorine-based disinfectants and muriatic acid react to form chlorine gas. Dangerous levels of chlorine gas can build up in the pipes if there is no water flow. That gas will be pushed into the pool when the system comes back on. To protect people, chemical feeders should automatically shut off when there is no water flow in the plumbing at the point of chemical injection.

In order for this automatic shutdown to work, all components should be electrically interlocked together so they function as one system. There are two ways to electrically interlock a system: either through the circuit breaker or through the use of an interlock box, or safety switch. Note that basic interlock designs only react to electrical incidents, such as loss of power, and not to an inherent loss of water flow, which could be caused by something else.

The basic level of interlock protection is to ensure electrical connections to the circulation pump and chemical feeder are on the same circuit. If the circuit powering the pump is tripped, power to the chemical feeders is also lost and chlorine-based disinfectants and acid will not be added.

A more advanced level of interlock protection is to incorporate a flow or float switch in the sample stream of the chemical controller. When the sample stream loses flow, the switch signals the controller to stop the chemical feed.

The highest level of protection is to incorporate an interlock box or safety switch that monitors and controls both the circulation pump and the chemical feeders from the point of injection. The individual components are “interlocked” or dependent upon one another for operation. For example, if the pump shuts off, the interlock automatically shuts the chemical feeders down.

People get hurt due to either mechanical failures or human error. A flow switch could fail, and send a false indication of water flow when there is none, allowing the chemical injectors to continue to feed disinfectant and acid into the pool. In the case of human factors, if a pool operator bypasses the safety methods by plugging the feeder into a different circuit, chemicals could accumulate with the pump off.

The pool should be closed and bathers removed from the area whenever maintenance work is performed on circulation and chemical systems. If a flow sensor detects no flow, the pool and deck should be cleared immediately. The same is true if there is an unexpected or manual deactivation of the circulation pump.

The pool should remain closed until the cause of the interruption is understood and corrected. The system should operate correctly for at least 5 minutes, and the water should be tested for proper pH and chlorine levels before bathers are allowed to return to the area.

Be sure to install all components of the system according to manufacturer’s instructions.

The video is entitled “Preventing Unintended Chemical Injection,” and can be found on YouTube.

Preventing Unintended Chemical Injection Visit: https://www.youtube.com/ watch?v=4TjgvL8Ln18