Excerpts from fox32chicago.com:

A dangerous chemical spill in the western suburbs prompted a HAZMAT response Thursday evening, when a toxic and deadly gas was accidentally concocted during routine pool maintenance.

Just before 5:30 p.m., the Warrenville Fire Department responded to The Westlyn apartment complex in the 28000 block of Diehl Road and the call was soon upgraded to a box alarm, prompting a response from HAZMAT technicians in surrounding communities.

Fire officials confirmed that chlorine and muriatic acid were spilled by accident. The dangerous combination creates chlorine gas.

Hazmat technicians made entry into the building to contain, neutralize, and remove the product from the building where they discovered a hazardous vapor cloud.

A spokesperson with the complex said that a maintenance team was restocking pool supplies when there was a mixture of chemicals that caused a reaction in a mechanical room.

It led to a massive emergency response and an hours-long evacuation.

Firefighters used a large portion of the parking lot during their response, as their setup outside was just as important as it was to get inside to contain the spill.

On their way out, the HAZMAT team followed a rigorous decontamination process.

Firefighters ventilated the building, and just after 7 p.m. residents were able to return to their apartments.

Four people were treated and released by paramedics for non-life threatening injuries.

Several surrounding fire departments responded to assist Warrenville firefighters, including Wheaton, Lisle-Woodridge, Downers Grove, Boilingbrook and Naperville.

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