Four children died after someone at their home sprayed water on an applied pesticide, causing a reaction that resulted in toxic gas, officials in Amarillo, Texas, said.
At least five other people were hospitalized in Monday’s incident.
Fire Capt. Larry Davis said a family member used water to try to wash off the aluminum phosphide, which had been administered before by someone beneath the residence.
The incident preliminarily has been ruled an accidental poisoning.
There were 10 people inside the mobile home at the time of the incident, according to Davis.
The children ranged in age from 7 to 17, CNN affiliate KVII reported.
First responders went to the hospital for treatment of possible exposure. Several firefighters are being held for observation, according to KVII.
Aluminum phosphide is listed in the Toxicity Category I by the U.S. Environmental Protection Agency — the highest and most toxic category. Specifically, the EPA points to the “acute effects via the inhalation route.”