The incident happened at a shop in the 2400 block of Interstate 45, according to Montgomery County deputies.
The men were trying to repair a leaking fuel tank on their car so they emptied the tank and stored the fuel inside a container. But as the men were finishing up their welding work, sparks ignited gasoline vapors, burning both men as they tried to remove the container and control the blaze.
One man suffered burns to his upper body and the other suffered life-threatening burns to about 75 percent of his body. Both were transported to a Houston burn center for treatment. Their current conditions were not immediately known.
Firefighters from Montgomery County Emergency Services District #8 (South Montgomery County) and Montgomery County EMS then responded and quickly contained the blaze.
Both victims, ages 40 and 42, are Jasper-area residents.