JUST IN: "It was determined there were two propane heaters inside the trailer with one of them in use. There was not sufficient ventilation which caused the individuals to succumb to what investigators believe to be Carbon Monoxide poisoning." Says Sheriff Vance Hill.

The individuals have been identified:

John glass Sr. Age 69 of Brownwood Tx

Bryan Glass age 41 of Temple Tx

Cody Glass age 13 of Troy Tx

Many are trying to keep warm with our freezing temps,

but if done wrong it could cost you your life.

Brownwood police say 3 men passed away Saturday in a trailer while hunting.

We're told this happened after being exposed to carbon monoxide from a propane heater.

Police want to caution the community about using these.

It poses the question are these types of heaters safe?

A sales representative at Lowe's says you must have proper ventilation.

And a propane heater should not be your only purchase.