July 21, 2025

A maintenance employee checked the chemical room at a Millville, PA community pool last Thursday morning. He saw something leaking and immediately recognized the smell as liquid chlorine due to his background as a volunteer firefighter. The chemical room stored other pool chemicals, which led to another concern about the chlorine possibly mixing with soda ash.

Mixing liquid chlorine with soda ash is extremely dangerous, as it produces enough heat that it can create fire or explode. It also can create chlorine gas which can burn eyes, irritate the lungs and cause difficulty breathing, and in high concentrations can be fatal. Undiluted chlorine smells very different from the “pool smell” many people associate with chlorine, so it was fortunate that the maintenance employee’s background helped him recognize it and understand the hazard it posed.

As soon as he realized what was happening, he evacuated the other employees and called emergency services. The National Weather Service’s Weather Forecast Office (NWS WFO) in State College provided a HYSPLIT run to the Columbia County Emergency Management Agency. They used that information to call for evacuation of about 100 people within 350 feet from the site, including students at summer programs and people in nearby homes and churches.

HYSPLIT is the NOAA Air Resources Laboratory’s atmospheric transport and dispersion model, in use for nearly three decades. It is one of the most extensively used models of its type within the atmospheric sciences community. The HYSPLIT model can track and forecast many different hazardous materials including chemicals, smoke, dust, allergens, volcanic ash and even radiological materials. It takes into account the specific material, how it reacts and mixes in the atmosphere, current weather conditions and a multitude of other factors. This allows it to accurately predict where that material will go, how concentrated it will be in each area it travels and even how much is deposited to the ground.

Weather Forecast Offices around the country use a custom NWS version of HYSPLIT every day and frequently field requests from local emergency management agencies for runs showing where the specific hazardous material will travel through the air and at what concentrations. This helps ensure that emergency managers locate their personnel in safe areas while responding and keeps the public out of harm’s way.

Firefighters, wearing proper protective equipment and respirators, shut off the pump and did some basic containment work before a specialized clean up company and the Pennsylvania Department of Environmental Protection handled the rest of the clean-up. An estimated ten gallons of chlorine leaked from a 250-gallon tank.