CLEVELAND (AP) — A portable propane heater being used inside a Cleveland home caused a buildup of carbon monoxide that killed a man and left his wife and two adult sons hospitalized, authorities said.

City firefighters responded to the home around 3:15 p.m. Thursday after another relative requested a wellness check.

A 72-year-old man was pronounced dead at the scene, while his 59-year-old wife was found unconscious and incoherent. She and their two sons — ages 37 and 43 — were all being treated at a hospital, but further details on their conditions were not disclosed.

The heater was found on the home’s second floor, which authorities said had no carbon monoxide detectors. The utilities to the home had been shut off, officials said, and it wasn’t clear how long the residents had been using the propane heater.

The incident remains under investigation.