Three people were dead and 18 first responders were taken to a hospital Wednesday morning after police and emergency crews responded to a suspected overdose at a home in Mountainair, a small town about 65 miles southeast of Albuquerque. Two of the responders were in serious condition.

Police found four unresponsive people inside the home on Honlon Avenue. Three of them were later reported dead, and at least one person was revived with Narcan before first responders began to feel ill, according to officials familiar with the response.

The scale of the medical fallout turned a routine overdose call into a hazardous materials investigation. Albuquerque Fire Rescue HazMat teams were helping at the scene to identify what substance was involved, while state investigators tried to determine how the exposure happened and whether the danger spread beyond the home.

Mountainair police and state investigators took over the scene because the agency has hazmat capabilities. New Mexico State Police investigators believe the substance may be transmitted through contact and do not believe it to be airborne, a distinction that shaped the response as crews tried to protect themselves and treat the sick responders.

David Frazee said the responders appeared to have been exposed after entering the home. “Evidently, they must have inhaled some toxins or something from the scene,” he said. He added that the group was transported to University of New Mexico Hospital and that doctors were working to determine what chemical was used.

Peter Nieto said the responders had direct contact with the person who died and then began showing symptoms. “They had direct contact with the individual who passed, and they were feeling lightheaded, headaches, nausea, things like that,” he said. Those symptoms forced the emergency response to widen and pushed hospitals to absorb a wave of patients from a single scene.

The town of Mountainair said on social media that, based on what was known at the time, there was no sign of a communitywide hazmat issue or public danger. It also said all indications were pointing toward narcotics as a possible factor. Officials were still working Wednesday to identify the substance involved.

The unanswered question now is narrower than it was in the first hours of the incident: what exactly in that home made one person need Narcan, killed three people, and sent 18 first responders to the hospital. The answer will determine whether Wednesday’s emergency stays contained to one address or becomes a warning about a more dangerous drug exposure moving through albuquerque and nearby communities.