Yakima, WA – Firefighters are still investigating the cause of an explosion Thursday night that seriously injured a West Valley man in his home.

The explosion almost certainly emanated from a 250-gallon propane tank that fueled a small heater in the man’s Bowers Road home, according to West Valley fire Capt. Darin Deccio.

“The exact cause is still under investigation, but we do know it was some type of propane explosion,” Deccio said this morning.

The victim, age 42, was taken to Harborview Medical Center in Seattle. His mother-in-law said he is in critical condition with second- and third-degree burns over 40 percent of his body.

The man’s name has not been released by authorities. The man’s mother-in-law also declined to identify him by name, saying his mother is vacationing on the Oregon Coast and hasn’t been contacted yet.

The man lived alone and was home alone at the time of the explosion, which occurred about 7:30 p.m.

His dog, a 4-year-old reddish-colored lab mix named Max, is missing. The dog has a collar with tags that say “Misha,” according to the man’s mother-in-law.