(COLORADO SPRINGS) — The Colorado Springs Fire Department (CSFD) has determined the cause of a fire Monday morning, Dec. 18, in which one dog and two cats were killed and another went missing.

According to CSFD, the fire was caused by a space heater being placed too close to flammable materials.

Fire crews responded to the house fire just before 9 :30 a.m. on Monday in the 700 block of South 27th Street, near Old Colorado City.

When firefighters arrived, CSFD said they found “heavy hoarding conditions,” which prompted additional resources responding to fight the fire. CSFD said the fire spread to most of the home and inside the interior walls.

The fire was deemed under control around 11 a.m., CSFD said. One person will be displaced from the home, but no injuries were reported. One dog and two cats were killed in the fire, and another went missing for a time, but has since been found safe and reunited with its owner.

“Hoarding conditions can pose a significant risk to firefighters as fire can spread into small spaces making it difficult to locate the fire and causing the fire to spread,” CSFD said in an update. “Those conditions can also cause obstructed exits, objects falling and excessive fire loading that can, in some cases, lead to collapse.”

CSFD recommends the following tips to heat your home safely:

Keep space heaters at least 3 feet away from anything that can burn

Place the heater on a solid, flat surface

Make sure your heater has an auto shut-off so it turns off if it tips over

Plug space heaters directly into a wall, never use an extension cord

Space heaters should be turned off and unplugged when you leave the room or go to bed