CSB: Overheating of Solvents Caused Danvers Blast

In preliminary findings released May 9, Chemical Safety and Hazard Investigation Board (CSB) officials determined that a November explosion that destroyed the CAI/Arnel ink and paint manufacturing plant in Danvers, Mass. – and injured 10 local residents – most likely was caused by the inadvertent overheating of solvents left stirring overnight in an unsealed mixing tank, releasing flammable vapor that accumulated and ignited.

According to CSB, the vapor built up in the facility because the solvent ventilation system was routinely turned off when workers departed the facility at the close of business each evening – an unsafe practice that investigators called the “immediate cause” of the accident.

The explosion occurred at approximately 2:45 a.m. on Nov. 22, long after all employees had departed the facility for the night. CSB said that all fuel sources for the explosion other than flammable solvent vapor – including natural gas – were ruled out.

50 Families Still Unable to Return to Their Homes

The explosion injured 10 community members, damaged or destroyed more than 100 homes and businesses up to 1 mile away and damaged numerous vehicles and boats. More than 50 families still have been unable to return to their homes, CSB investigators said. No workers were injured in the blast.

“The Danversport explosion caused the most serious community damage of any U.S. chemical accident since the CSB was established in 1998,” CSB Chairwoman Carolyn Merritt said. “But for the fortuitous timing of the explosion, nearby residents could have easily been killed by flying debris or the collapse of heavy building structures. We all have a strong stake in preventing such devastating accidents that disrupt communities.”

Facility Did Not Comply with Regulations for Flammables

According to CSB, the Danvers facility housed two independent, privately held firms that split from a single company in 1985. CAI Inc. produced solvent-based commercial printing inks, while Arnel Corp. produced solvent-based stains and coatings. Witnesses told CSB that only CAI was operating a solvent-based process the night of the explosion, when the facility was unattended.

The CSB investigation team determined that the facility did not comply with federal and state regulations concerning the storage and use of flammable liquids and solids and also lacked related permits and licenses required under the state fire code.

CSB said that the building lacked floor-level ventilation systems to prevent the spread of flammable atmospheres from process equipment, as required under the OSHA flammable and combustible liquid standard. In addition, Massachusetts fire regulations require that flammable liquid storage equipment located inside buildings must be vented to the outside and must have approved automatic shutoff valves, and fire-resistant materials must be used for attached piping. These safeguards were not in place, CSB investigators said.

Steam Heating Valves Malfunctioned or Were Left Open

Investigators said that the mixing tank likely overheated because steam heating valves either malfunctioned or were left open due to an operator error.

The steam valves evidently were destroyed in the massive fire that followed the explosion, making it impossible to confirm an exact mechanism for the presumed overheating. However, CSB determined that during the workday on Nov. 21, a 3,000-gallon mixing tank operated by CAI had been charged with powdered resin and flammable solvents – including heptane and propyl alcohol – and heated by opening two manual valves on a connected steam piping system. The mixer then was left stirring overnight.

“The operator told CSB investigators he believes he closed the steam valves before leaving for the evening, but because the valves were never recovered their actual position and functional condition cannot be determined,” CSB Supervisory Investigator John Vorderbrueggen said. “If the steam valves either leaked or remained open, 240-degree steam would have continued to heat the tank without restriction, evaporating off large quantities of highly flammable solvent vapor. During the overnight hours, vapor continued to flow out of the tank and throughout the building, eventually finding an ignition source, such as a spark from an electric device.

“By the process of elimination, that's likely to be what happened. If the ventilation system had been left on, however, the accumulation of flammable vapor would have been greatly reduced. The practice of turning off the ventilation system at night – which was unsafe in a facility that handled large volumes of flammable solvents – was the immediate cause of the accident.”

Important Safeguards Lacking

According to Vorderbrueggen, CSB noted that the companies lacked important safeguards for operating solvent-based processes.

“Such safeguards are critical to prevent a single foreseeable error or mechanical failure from leading to a catastrophic event,” Vorderbrueggen said.

For example, CSB determined that neither company used checklists or formal written procedures to help ensure the correct sequence of operator actions. There were no automatic alarms, shutdown systems or interlocks to prevent overheating of the mixing tank, CSB said.

“When hazardous processes are intended to be left running unattended, it is particularly important to use multiple safeguards, sometimes called layers of protection, to prevent catastrophic accidents,” Vorderbrueggen.

Natural Gas Ruled Out

CSB investigators ruled out all other possible fuel sources for the initial explosion, including industrial-grade nitrocellulose stored on-site; heating oil that was stored inside the building; and all potential sources of natural gas.

“We found no evidence to suggest that natural gas could have caused this accident,” said CSB Supervisory Investigator Robert Hall, PE, an engineer who formerly participated in Department of Transportation pipeline investigations. “No gas line ran into the facility, and there is no evidence of any sufficiently large gas leak near the facility prior to the explosion.”

Hall said that the nearest the gas line was at least 150 feet away from the CAI/Arnel building, and that there was no credible scenario by which gas could travel along or inside a sewer pipe into the facility.

Hall added that CSB's blast modeling confirmed the conclusion that the explosion was not fueled by natural gas.

CSB Hopes to Complete Report in 6 Months

Vorderbrueggen said that the CSB investigation will continue and that activities will include:

  • Laboratory analysis of the volatility of ink mixtures produced at the facility.
  • Further explosion modeling.
  • Analysis of opportunities to improve applicable codes, regulations, inspections and enforcement.

He said the team hopes to complete its final report within 6 months.

“We are acutely aware of how this accident affected the Danvers community,” Merritt said. “It is our hope that these preliminary findings will help inform citizens about what happened and provide information that will help other communities assure that companies handling hazardous materials are operating safely.”

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