A semitractor pulling double trailers caught fire on Interstate 15 in Millard County Wednesday morning, and an aggressive attack by fire crews prevented the flames from burning through the second tanker full of bisulfite, a compound that becomes dangerously unstable when heated. The incident was reported at 7:45 a.m. on I-15 southbound near mile marker 137 where firefighters found the truck fully engulfed in flames that were spreading quickly across the front trailer. The driver escaped without injury, Utah Highway Patrol Sgt. Nick Street said. Fire crews aggressively attacked the blaze and had it extinguished before it reached the second trailer containing the bisulfite, which averted a potential disaster, Street said.