A Massachusets adhesives manufacturer is facing more than $900,000 in fines for 50 safety violations, following an explosion at its Middleton plant that injured four workers.

OSHA says Bostik, Inc. knew from third party and internal compliance audits conducted at the plant that its process safety management (PSM) program was inadequate.

The PSM is a detailed set of requirements and procedures employers must follow to proactively address hazards associated with processes and equipment that involve large amounts of hazardous chemicals. In this case, the chemical was acetone, used in a PSM-covered process known as direct solvation. On the day of the explosion, a valve on a transfer line inadvertently was left open, resulting in the release of flammable acetone vapors. The vapors exploded after being ignited by an undetermined source.

OSHA chief Dr. David Michaels said the requirements of the PSM standard are stringent "because the stakes are so high." 

OSHA are director for northeastern Massachusetts said it was fortunate the blast happened when there were few workers in the plant. Otherwise, the incident could have resulted in a catastrophic loss of life.

OSHA found that Bostic's analysis of hazards related to the process did not address previous incidents with a potential for catastrophic results, such as forklifts that struck process equipment, and did not address human factors such as operator error, communication between shift changes and employee fatigue from excessive overtime. In addition, the company did not ensure that a forklift and electrical equipment, such as a light fixture, switches and a motor, were approved for use in Class 1 hazardous locations where flammable gases or vapors are present.

As a result, OSHA has issued Bostik nine willful citations and 41 serious citations.