Chemical Plant Explosion Caused by Mechanical Failure
State Fire Marshal Peter J. Ostroskey and North Andover Fire Chief William McCarthy and North Andover Police Chief Charles Gray said their joint investigation into the cause of the January 7, 2016 explosion at the Rohm and Haas Electronic Materials (a subsidiary of Dow Chemical) plant on 60 Willow Street, North Andover has concluded. Investigators determined that a mechanical failure allowed air to react with a volatile chemical during a reclaiming process that resulted in spontaneous ignition and the explosion. Four employees were seriously injured. Three were transported to Boston hospitals and one was treated at a local hospital. All survived.
Over several days the Joint Hazardous Incident Response Team (JHIRT), comprised of specially cross-trained State Police bomb technicians and hazardous materials technicians, made multiple entries to make the building safe enough for the fire investigation team to enter and begin their origin and cause investigation. There were hundreds of cylinders in the room where the blast occurred that had to be examined for rupture that could cause additional explosions, and moved to safety.
The Reclaiming Process
The reclaiming process removed any residual product from the cylinders and prepared them for re-use. Using a pressurized vacuum system, the product was removed from the cylinders, heated under a hood to turn it into a vapor. The vapors entered a trap and were frozen with liquid nitrogen. When the trap was full, which could take several months, the product was removed. The chemical used in the process, trimethylaluminum, was a liquid that reacts violently to water and explodes when exposed to air.
Workers had been experiencing a pressure problem in the reclaiming process that indicated a possible leak. They were attempting to troubleshoot the problem when the explosion occurred. The investigation showed this area was where the explosion originated. The explosion occurred when air came in contact with the chemical. The fire suppression system functioned and extinguished the fire. Closer examination showed the metal chemical vessels and waste traps contained several welds and gaskets that were not regularly inspected as a part of a safety process.
The investigation was conducted by members of the North Andover Fire and Police Departments, State Police assigned to the Office of the State Fire Marshal and to the Office of the Essex District Attorney. Assistance was received from the Code Compliance Unit of the Department of Fire Services.
Occupational Safety and Health Administration (OSHA)
The federal Occupational Safety and Health Administration (OSHA) conducted their parallel and independent investigation into the workplace injuries. Their findings revealed numerous safety violations and issued three citations with fines totaling $129,200.
There had been a previous chemical explosion at this facility that killed one employee on October 9, 2013. That incident occurred during work on a different chemical process.