The man got up to move another motorhome he had in the area, and as he was working on the engine, trying to get it started, some fuel ignited, the LBFD said.
Photos from the scene show the roof and front rooms heavily damaged.
It’s so far unclear how the fire started, but it closed the street at Orange Avenue and Del Amo Boulevard for nearly two hours.
The fire was contained to the attic, but it set of sprinklers throughout the building.
One person was sent to the hospital with burns when two separate fires charred a one-story house and clogged a beachfront high-rise with smoke.
The three fires charred about an acre of land total.
The blaze erupted early this morning at Alameda Street and Sepulveda Boulevard.
One unit was destroyed and four others sustained water and smoke damage, but no injuries were reported, fire officials said.
The latest fire was reported around 10 p.m. in the 3300 block of East 59th Street, fire officials said.
The flames sent a large plume of smoke into the air over Long Beach and prompted crews to rush to the scene.