Firefighters took about two hours to bring the fire under control at the DrillChem plant on the eastern fringe of Conroe, near HoustonA series of explosions rocked an oil field chemical supply company north of Houston on Friday, setting off a fire that sent a broad, dense column of thick, black smoke towering into the sky.Authorities knew of no injuries from the explosions and blaze that erupted about 4.30pm, said Conroe fire marshal Mike Legoudes.