Employers know that, despite preventive measures, accidents can happen. But accidents involving employees who might be under the influence have particular gravity, as they can indicate or lead to larger problems.

At Dura Automotive Systems Inc.’s Lawrenceburg, Tenn., facility, employees routinely assembled vehicle windows, tested products and drove forklifts. When the plant’s accident rate surpassed that of comparable plants, management suspected that drug use–illegal or legal–might be to blame.