A man and his son lost their home and possessions on Thursday when fire engulfed their unit in Westsyde's Darfray Trailer Park.
Neighbours say they noticed that the man's fifth-wheel trailer was in flames just after 2:30 p.m.
"It went up so fast — wow," said Erik Hinse, who lives across the lane. "I freaked out. He was in the laundry room but I knew he has a son so I kind of lost my mind for a little while."
It turned out the son was in school.
Rick Stamm, a former Merritt Fire Department volunteer, rushed to the scene at the early stages of the fire to pull the electrical connections from the trailer.
He quickly got to a safe distance and then heard an explosion that he believed to be a propane tank.
The flames grew to at least 10 feet in height and caught a large tree behind it on fire, causing heat damage to the trailer beside it.
The man's truck, which was parked alongside the fifth-wheel, was moved before it could be damaged.
A Kamloops Fire Rescue crew quickly arrived with three engines and a rescue truck. They heard a second explosion, said acting assistant Chief Les Noel.
Firefighters found two large, undamaged propane tanks outside the unit leading them to believe it may have been a small, camper-sized container that blew.
They were able to contain the flames and had the job done in less than half an hour.
Fire inspector Arlene Ball was on scene shortly after to determine the cause, which will take a day or two, said Noel.
The resident is a new tenant to the park and "very nice man," according to manager Evelyn Yablonski, who arrived after the fire was doused.
As firefighters packed up, the upset man surveyed the remains of the trailer, which was gutted. He declined to speak to media.