The Transportation Security Administration has announced the completion of more than one million fingerprint-based background checks on truck drivers required to carry a Hazardous Material Endorsement (HME) on their CDL’s.

Begun less than four years ago, the HME Threat Assessment Program has completed a review of 1,015,660 applications, approving more than one million. Applicants who initially do not meet the eligibility requirements can take advantage of a redress program without losing their HME in the process, TSA said, and states can extend HMEs for drivers whose background assessments are still pending.

Shipments classified as hazardous materials include gasoline, explosives, radioactive and infectious substances, propane, chlorine, acids, ammonia and other poisonous gases.