Danvers, MA Explosion, Ventilation Analysis

The large explosion that occurred at the Danvers, MA, CAI, Inc. manufacturing facility in November of 2006 was investigated by the US Chemical Safety and Hazard Investigation Board.  Several key issues were highlighted in the investigation report (2007-03-I-MA), one of them being the safe handling of flammable liquids.

Section 5 of the report refers to the Model Fire Codes, including NFPA 30 for Flammable and Combustible Liquids.  This report states that “This code allows for flammable liquids in unsealed containers to be heated indoors as long as adequate exhaust ventilation is provided to prevent flammable vapor accumulation within the building.”
 
Although SPEC agrees with the above statement, as the explosion clearly shows, proper design of a facility is necessary to effectively coordinate “adequate” ventilation with standby power and electrical area classification. Ventilation design needs to account for several factors:
  • Air change rates or cfm/sq ft
  • Dead zones within the space
  • High and low exhaust locations
  • Pressure differentials between rooms of different uses to avoid vapor flow to unclassified areas
 
One approach that SPEC has used in the past is to install LEL monitors in the exhaust ducts to detect high concentrations of explosive vapor.  Based on the specific requirements, the high LEL can trip a fire alarm, increase air flow to make the area safe, automatically cut power to any electrical devices in the room or all of the above.
 
Although the Board concluded that CAI was a grandfathered facility and did not need to apply NFPA, a walk-through of the facility by a trained HVAC/Mechanical Engineer would have quickly revealed that simple changes to the ventilation system could have prevented the explosion.