From a recent inquiry by a customer shipping PIH drums (Poison by Inhalation), we learned that at a DOT audit, the customer was asked to provide technical information regarding the prevention of the plug Back-Off. By definition, Back-Off refers to the potential loosening of a steel plug after the required torque is reached when closing a drum (See Skolnik October 2000 Newsletter). Indeed, CFR 49, 173.227(b)(2)(ii) does state that the screw closures must be "physically held in place by any means capable of preventing back-off or loosening of the closure by impact or vibration during transportation." After contacting various plug manufacturing companies, we were told that plug back-off was taken into consideration during the product testing. Skolnik then received letter from the plug manufacturers confirming their liability. Skolnik does offer copies of these letters to PIH Drum customers that might want to keep this information in file should a compliance question arise.