Firefighters now believe a space heater caused an explosion in a Springs garage that injured two men and a child Sunday.

The 2 1/2-year-old boy and his father are both in critical condition in Denver hospitals.

Firefighters say that one of the men, who is a mechanic, was using a propane space heater Sunday as he worked on a vehicle in his garage. With his garage door down and an open flame in the garage due to the type of space hearer he was using, when the man took the fuel tank out of his vehicle it made for a lethal combination.

"When those fumes hit that heat source, those fumes become flammable and it'll cause it to flash...in some cases it'll flash and go out, in this case there was enough fuel to sustain the fire and cause a structure fire," Lt. Kenny Bradley with the Colorado Springs Fire Department told 11 News.

The explosion could be heard throughout the neighborhood near Circle and Pikes Peak. Residents living near the home on the 3000 block of Greenwood Circle also reported seeing a bright orange flame.

The fire destroyed the garage and attic at the home.

Along with the mechanic and his toddler son, a second man was in the garage at the time. The injuries he sustained were less serious, and he is recovering a local hospital.