According to Fox31 news out of Colorado:
LAFAYETTE, Colo. â€” Firefighters did not find a spill or a leak at a Lafayette recreation center and do not know what made more than 20 people sick Saturday afternoon, says the Lafayatte fire chief.
Emergency crews transported 22 patients, many of them children…
Full Developing Story Here
This type of call is not easy for any first responder or HazMat team. Something caused people to either feel or be ill but nothing is on scene ‘taking responsibility’. As a HazMat team sometimes looking for nothing, and confirming the absence of something, is what we do. Now there is a likely scenario where whatever it was, caused the symptoms, then left without a trace. Best practice is to care for the patients, evacuate, survey, ventilate as appropriate, and do as much due diligence in the form of information gathering and monitoring as possible. Some reported a possible Chlorine leak, but this seems to have been false.
The HazMat Guys Nation Roundtable, Carbon Monoxide Response, also discusses what is often referred to as a Sick Building response and how to handle.