Vallejo Fire Department spokesman Bill Tweedy said the fire started at about 5 p.m. when a man used a lighter to burn some excess propane, causing a fire flash on board the 27-foot Bayliner pleasure boat.
The man was burned over 50-60 percent of his body, and a woman on board suffered burns over 35-45 percent of her body, Tweedy said.
The woman was taken to Kaiser Permanente, Vallejo Medical Center and the man was taken to a burn center, Tweedy said. They were both in critical condition Tuesday night, he said.
The docked boat was engulfed in flames when the fire department arrived, Tweedy said.
Firefighters found one of the burn victims in the water, Tweedy said.
The fire was controlled in about 20 minutes, Tweedy said. Crews remained at the scene for more than an hour.
The blaze destroyed the pleasure boat, valued at $25,000, and caused $6,000 in damage to the roof over the boat slips, Tweedy said.