Loxahatchee, FL – A woman is dead and three men were in critical condition after suspected carbon monoxide poisoning from a generator near Loxahatchee Thursday evening, according to Palm Beach County Fire Rescue.

Crews responded to an unknown medical call on the 6000 block of Circle D Drive, just west of Seminole Pratt Whitney Road and north of Southern Boulevard, around 8 p.m. When firefighters approached the residence, their the carbon monoxide detectors went off, warning them of what they were stepping into. The detectors registered 300 parts per million. People start feeling symptoms at 70 parts per million, according to Fire Rescue Capt. Albert Borroto. The house had more than four times that number.

Once fire fighters put on air tanks, they found an unidentified woman dead along with three men who were conscious. It’s unclear who called 911.

Borroto said when they arrived the generator was not running, but investigators believe it had been running all day. The generator, described as a large 15,000-watt model capable of powering a home’s air conditioning, was outside near the garage. But the garage was left open just a few inches, and with the generator pointed toward it, the carbon monoxide was able to seep in, Borroto said.

It’s unclear how long the generator had been running, or how long the woman was dead. It’s also unknown exactly where the four people were in the home. The three men were flown a hospital in critical condition. Borroto noted all firefighters were OK following the incident.

Earlier Thursday, a Palm Beach County Sheriff’s deputy was overcome by carbon monoxide during a welfare check on a home that was running a generator.

Animal Care and Control officials were also at the scene Thursday evening. A neighbor said the homeowner owned several dogs. There was no official word on whether animals were found inside the home.

The neighbor said their street has been without power since Irma hit.

Though there does not appear to be any foul play at this time, because there is a death, the Palm Beach County Sheriff’s Office is investigating the incident, Borroto said.

Fire Rescue has had numerous calls for generator-related incidents since Hurricane Irma, including fires and carbon monoxide poisoning, Borroto said. It’s “not very unusual” to see since incidents after hurricanes, he said.

Tips for when using a generator:

Turn off generators and let them cool down before refueling, and never refuel while it’s on or hot.

Keep generators in a well-ventilated location outside, at least 5 feet from doors, windows and vents where carbon monoxide could get in.

Never use generators in attached garages even with the door open

Have a carbon monoxide alarm