The trucking company Saia Motor Freight Line has been fined by the U.S. Department of Labor's Occupational Safety and Health Administration following an investigation regarding an explosion at one of its terminals last August, injuring four employees.

Two of the employees were critically injured in St. Louis due to a forklift's ignition source and a loose coupling connection to a liquid propane gas tank, according to the investigation. It determined that two forklift operators were changing a propane tank on a liquefied petroleum gas-powered forklift inside a freight trailer when a loose coupling connection permitted liquid propane to leak, vaporize and ignite, causing a flash fire.

Both a 54-year-old lead forklift operator and a newly hired 25-year-old worker, who had used propane forklifts for about a month, received critical burns, according to OSHA. A third worker suffered burns to his legs as he helped extinguish his colleagues' burning clothing. A fourth employee, who was using his forklift near the flash fire, was also burned.

OSHA said inspectors found several powered industrial trucks with defective or bypassed safety switches being used when they were in need of repairs, resulting in a willful violation. A willful violation is one committed with intentional, knowing or voluntary disregard for the law's requirement, or with plain indifference to employee safety and health, according to OSHA.

A total of 11 serious safety and health violations were noted by OSHA, with many involving propane hazards. OSHA found that Saia did not evacuate the work area after the release of the flammable gas; require the exchange of forklift propane containers in an adequately ventilated area; mount gas containers on the cylinder indexing pin correctly; train workers on extremely flammable gas hazards; and require the use of hand and eye protection when changing cylinders. Additionally, it found hazardous chemicals in the maintenance shop were not labeled and said the company also failed to train powered industrial truck operators, and several electrical safety hazards were noted.

Based in Duluth, Georgia, Saia has 147 terminals covering 34 states and Canada. It employs approximately 8,000 workers. The company has about 150 employees at the St. Louis terminal who perform cross-dock operations.

Saia has 15 business days from receipt of its citations and penalties to comply, request an informal conference with OSHA's area director, or contest the findings before the independent Occupational Safety and Health Review Commission.

When contacted Saia for reaction to the fine it would not comment.