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LITTLETON, Colo. — A house fire in a Littleton neighborhood that spread to neighboring homes late Friday afternoon was determined Monday to have been caused by a spontaneous combustion, according to the City of Littleton.

A tweet posted by the city said that rags used to stain a deck were left out and ignited in the 95 degree heat and two homes were a complete loss.

The homes stood directly next door to each other in the 7900 block of South Bemis Circle.

A little bit after the two homes were burning, fire was seen on the roof of a home farther down the street.

Littleton Fire Rescue said two firefighters were transported to the hospital for treatment of heat exhaustion. Crews went inside the burning homes to fight the flames and the intense heat coupled with temperatures in the mid-90s take an incredible physical toll on the firefighters.

A spokesman for Littleton Fire said the two firefighters who needed treatment were at the first two homes that burned, and then went to help put out the fire at the third home. They’re expected to be OK.

Smoke could be seen from all over south metro Denver.