Kendall, WA – A leaky propane tank and an electric space heater are believed to have caused an explosion that injured three people Thursday.

Whatcom County Fire Marshal Bill Hewett said the property owner kept the heater in a shed to keep a family dog warm.

Propane that had leaked inside the shed was likely ignited when it combined with a rush of oxygen from the victims opening the door to the shed just before 4:30 p.m. Thursday, Hewett said.

Two of the victims were 18 and one was 19. One was airlifted to Harborview Medical Center in Seattle, while the other two were transported to St. Joseph Hospital. One of those sent to St. Joseph was released shortly after arriving, Hewett said.

Bellingham Fire Department Assistant Chief Roger Christensen said all three victims had stable vital signs when they were transported.

Officials did not release the names of the victims. They didn’t know their conditions Friday, and without the names hospitals won’t release information.

The victims called 911 from a home on the 2000 block of Clear Valley Drive, but the shed was located behind a property on the 1800 block of Boulder Valley Lane, Christensen said.