Authorities on Friday identified the mystery substance that hospitalized more than a dozen first responders after they responded to a New Mexico home where three people died in a suspected overdose incident.

Officials said first responders were exposed to fentanyl after arriving at a home in Mountainair, New Mexico, where four people were found unresponsive.

Two victims were pronounced dead at the scene, while a third later died at the University of New Mexico Hospital. A fourth person survived.

“Preliminary findings indicate this incident is tied to exposure to a powdered opioid substance within the home, and on-scene DEA laboratory analysis has confirmed the presence of fentanyl, methamphetamine, and para-fluorofentanyl, also called P4 fentanyl,” New Mexico State Police Chief Matt Broom said during a news conference.

“It’s a more illicit form or version of fentanyl,” he added.

Authorities said the drugs were found in powder form.

Officials said 25 people were exposed to the substance, with 20 hospitalized for treatment before being released.

Two individuals remain hospitalized after arriving in serious condition, police said.

Authorities identified two of the people who died as Micah Rascon, 51, and Georgia Rascon, 49.

Both the survivor and one of the deceased were administered the overdose medication Narcan.

Authorities said numerous first responders began experiencing symptoms including nausea and dizziness.

“These men and women responded to a dangerous situation while working to protect lives and secure the scene,” Broom said. “We especially recognize the first responders who became sick while carrying out their duties.”

Torrance County Fire Chief Gary Smith said firefighters did not enter the home wearing hazmat protection because the situation did not initially appear to require it.

He added officials would review the response procedures moving forward.

“I mean, we’re only as good as our last call, right?” Smith said. “There’ll be multiple debriefings that we’re going to be doing over the next week or two to find out where our strengths were and where our weaknesses were.”

The incident remains under investigation.