How to Prevent Chlorine Gas Incidents in Automatically Fed Swimming Pools

When you see the term “chemical gas incident,” do you immediately assume this doesn’t apply to the commercial pools you design, build, maintain or operate?

If so, read on.

Chemical gas incidents can be difficult to describe and understand. For this reason, people misconstrue how these incidents occur.

Here, learn about what causes them and how they can be avoided.

Not what you think

Even naming these incidents is tricky business. In the increasing media coverage these accidents receive, reporters and sources sometimes called them chemical clouds or leaks. Experts, such as those in the American Chemistry Council, seem to have landed on the term “chemical gas incident.” Though probably most accurate, this term still meets with some confusion. Some assume that “chemical gas” refers to the form of sanitizer used in the pool. They believe it means gas chlorine — the type that is injected into the pool in its gas form, as opposed to a liquid or solid.

However, the “gas” in chemical gas incidents does not refer to the sanitizer used, but rather the noxious, dangerous byproduct of chemical mixing that can occurs when a circulation system with a chemical feeder malfunctions.

In these pools, chlorine and muriatic acid are injected into the plumbing at separate points by feeders such as peristaltic pumps. As water flows through the pipe, the chemicals move with it, and all is well. The problem occurs if the circulation system stops but the chemical feed continues. When this happen, water comes to a halt inside the plumbing. In this static environment, the chlorine and acid are able to make contact and mix. The chemicals react to each other, causing a toxic chemical gas to accumulate inside the plumbing.

When the circulation system turns back on, and water begins moving through the system again, it forces that chemical-gas buildup into the pool through the inlets. The gas can then take over the pool area in the form of a cloud.

Interlock solution

There currently are no statistics available regarding chemical gas incidents, partly because of public confusion about the cause. Sometimes, for instance, responders don’t know how to classify them.

While data may be lacking, they do seem to be receiving increased media coverage, as they will send some pool users to the hospital.

It’s gaining more attention in the industry, too. Besides the American Chemistry Council, which recently produced and distributed a video on the prevention of these incidents, the Model Aquatic Health Code also addresses this hazard.

The key to preventing these hazards is to ensure that chemicals cannot be fed into the plumbing lines if the circulation system is shut off. Like American Chemistry Council recommendations and most manufacturer instructions, the MAHC calls for the circulation pump and chemical feed system to be interlocked. This creates a connection between the circulation system or pump and the chemical feeder: If water stops circulating, the chemical feed similarly ceases. “I think every commercial pool should include one,” says Kevin Boyer, COO of Poolsure, in Houston, Texas.

As he sees it, this includes even wet-deck applications. “The type of the pool is less important,” he says. “If you have the potential to inject any type of chlorine and acid together into a return line of a pool, spa, catchment basin or lagoon ... then there should be interlocks installed.”

There are various types of interlocking systems that offer different degrees of protection. The most basic and economical involves electrically interlocking the feed system with the circulation pump’s power source by placing them on the same circuit. If the circuit powering the pump were to trip, the chemical feeder would shut off as well. This type of interlock is best included during design and installation of the pool, as ground fault circuit interrupters have made it more difficult to accomplish this in retrofit.

This method poses two drawbacks. First, it only protects the system in those cases when the circulation systems stops from loss of power. If flow were to stop for other reasons, such as a loss prime or pump-motor failure, the chemical feeder would continue to operate. Secondly, if the interlock does its job and shuts down the feeder, it is very easy for operators to bypass the interlock and plug the chemical feeder into another circuit.

“There’s an immense pressure on pool operators to keep the pools open and operating, whether they’re revenue-producing pools or amenities,” Boyer says. “Shutting down the pool is frowned upon, and that’s where a lot of these accidents come from.”

Matter of degrees

More protection is afforded if a flow switch — either paddle or float — is installed in the chemical controller’s sample stream.

Many controlers come with these in the bypass assembly. If the sample stream loses flow, the switch will prompt the controller to stop feeding chemicals. For this to work correctly, it is vital that the bypass line be positioned and installed to monitor flow at the point of chemical injection.

Of the methods available for interlocking the circulation and chemical feed systems, the most protection comes from a master electrical interlock box, also called a safety switch. These monitor and control the circulation pump and chemical feeders and provide a truer interlock between components, so they depend on each other to operate. These will shut down the chemical feeder anytime the flow through the system stops, regardless of the cause. They also are more error-proof to install, Boyer says.

Even if you include the latter system, the best bet comes from using multiple forms of interlocks, says Rudy Stankowitz of Aquatic Facility Training Consultants in Gainesville, Fla.

“And integration of an audible alarm sounding when no-flow or low-flow is detected, in my opinion, should be mandatory,” he says. “Many of the controllers available include this feature.”

Whichever method or combination of safeties you choose, be sure to test them before turning them over to the operator.

“You want to make sure that, when I put the filter in backwash mode, it shuts it down; when I lose prime, it shuts it down,” Boyer says. “And run through these different [scenarios].”

While standards and codes generally only specify these protections on commercial pools, those designing or operating residential pools using the same types of chemical feeders should consider it, these experts say.

Service side

Measures to prevent chemical gas incidents don’t just come during design and installation. There are things service technicians can do as well.

First of all, inspect the system every time you visit. If you see a problem, alert the operators and impress upon them the urgency. They may resist if checking or fixing the issue requires closing and emptying the pool.

Secondly, train the operators to inspect the system while you’re not there, says Terry Snow, owner of TLS Pool Service in Upland, Calif. “I changed the protocol for our city [pools],” he says. “I’ve got it to where the lifeguard comes in 15 minutes earlier, tests the water, goes over to the controller and inspects that. Then they go over to the filter controller, inspect that and write the numbers down. That way, if there is an issue, then we can address it.”

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