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CSB: Solvent Might Have Fueled Boston-Area Blast

According to federal investigators, vapor from flammable solvents that were used to produce printing inks and paints likely was the source of fuel for an explosion that leveled the CAI/Arnel ink manufacturing facility near Boston.

The powerful explosion in Danvers, Mass., damaged or destroyed dozens of homes and businesses during the early-morning hours of Nov. 22 and caused a number of residents to be hospitalized. There were no injuries in the plant, which was unoccupied at the time.

"On the last workday prior to the accident, a heated mixing tank was filled with 2,000 gallons of printing ink ingredients, including flammable, volatile solvents such as heptane and propyl alcohol," explained John Vorderbrueggen, PE, lead investigator for the Chemical Safety and Hazard Investigation Board (CSB) in the CAI/Arnel probe. "Depending upon the temperature of the tank, solvents could have evaporated during the overnight hours when the facility was unattended, accumulated in the building and found an ignition source."

Natural Gas Also Is a Possibility

Vorderbrueggen noted that the agency also is examining natural gas as a possible fuel source, in addition to or in lieu of solvent fumes. According to CSB, a high-pressure gas transmission line runs underground a few hundred feet south of the facility, and other low-pressure gas lines are a few hundred feet west and north of the facility.

However, according to the agency, the CAI/Arnel building where the explosion occurred had no natural gas supply and had a concrete slab floor.

"Although there is no obvious path into the facility for natural gas, we will continue to evaluate the possibility of a leak into the building," Vorderbrueggen said.

He added that company tests detected some methane in nearby soils, at a level several hundred times below the lower explosive limit. However, CSB has found no evidence of a leak from the high-pressure transmission line, and the source of the traces of methane is not clear.

Investigators Will Interpret "Blast Markers"

A team from CSB documented at least 100 different examples of blast damage – such as shattered windows or broken beams – throughout the Danvers community. According to CSB, these "blast markers" will be interpreted using computer models in an effort to better understand the nature and the explosive force of the blast.

"We are planning to duplicate the solvent recipe that was in use on Nov. 21, and measure its volatility in the laboratory," Vorderbrueggen said. "The data will help us understand how long it might take to load the building with different flammable concentrations of solvent fumes under various scenarios, such as a leak, spill or inadvertent overheating."

CSB said it has not reached a conclusion regarding the fuel for the explosion, and Vorderbrueggen noted that a final determination is still months away.

"Both CAI and Arnel were aware that the materials they used were flammable, and for that reason had installed safe electrical devices to minimize the possibility of ignition," Vorderbrueggen said. "In any industrial facility, however, it is almost impossible to eliminate all ignition sources. Prevention efforts must focus on avoiding the accumulation of flammable vapors and gases, safely ventilating any that do accumulate and detecting any dangerous concentrations before a fire or explosion occurs."

CSB Will Examine Current National Fire Codes

According to the agency, the investigation will include an examination of whether current national building fire code provisions on handling flammable solvents are fully effective.

"Of all the accidents [CSB] has investigated since its establishment in 1998, the Danvers explosion caused the most severe damage to homes and nearby businesses," CSB Chairman Carolyn Merritt said. "This blast was considerably more powerful than might be expected from a manufacturing facility of this type. For that reason, I have asked the staff to review the guidance that is currently available to urban planners and local permitting officials on chemical facility siting to see if it can be improved.

"Better guidance and separation distances may help protect residents from accidents at new facilities, but for existing facilities the only option is improved prevention."

Focus on Flammable Solvent Safety

Merritt noted that a second serious chemical accident in 2006 – at a concrete products facility near Chicago – likely involved the flammable solvent heptane, which also was used at the Danvers plant. That accident, on June 14, occurred as an operator was heating a flammable liquid mixture in a 2,200-gallon open-top tank equipped with steam coils. A vapor cloud formed and exploded, killing a driver, injuring two other workers and causing extensive facility damage.

"Flammable solvents are among the most common industrial chemicals, and it is all-too-easy to overlook their potentially deadly hazards," Merritt said. "All companies that use flammable solvents should promptly review their operations to ensure that appropriate controls are in place. The use of closed vessels, robust ventilation systems, vapor-leak detection systems and explosion-proof electrical systems are all important for preventing disasters.

"In addition, companies should evaluate using automated or redundant temperature control systems and should follow general good safety practices, such as using written operating procedures and checklists."

Public Hearing Planned

CSB said it plans to convene a public hearing in Danvers in early April to present preliminary findings and receive comments from community members. At the hearing, the agency will consider public comments as it continues its investigation and develops its final report and safety recommendations.

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