Key Instruction Points
Flammable liquids must only be stored in refrigerators which have no internal ignition sources.
Many small tubes of petroleum ether were stored in an ordinary domestic freezer. The tubes were not sealed well and over time the petroleum ether evaporated in sufficient quantity that the concentration exceeded the low explosive limit, about 1.0 percent. A spark from an internal component caused the freezer to detonate.
Injuries and Property Damage
There were no personal injuries as the explosion took place at night. There was $11,000 damage to the room and $25,000 damage to equipment in 1982 dollars. This would be more than $250,000 in 2001 dollars. Along with the freezer, one liquid scintillation was destroyed and another was seriously damaged.
Primary Cause of the Incident
Petroleum ether, a very flammable liquid, was stored in an ordinary domestic freezer which has components (e.g., thermostat, light switch) which generates sparks. This apparently caused the vapor of the liquid to detonate.
With a flash point as low as -56 °F, petroleum ether is classified as a Class 1A flammable with an NFPA 704 fire hazard rating of 4.
Recommended Corrective Action
All materials with a flashpoint below 100° F may only be stored in a UL approved flammable materials storage refrigerator or freezer. These units do not have any internal ignition sources.
All ordinary domestic refrigerators and freezers must be labeled with the phrase, "No materials with a flashpoint below 100° F may be stored in this refrigerator/freezer."
Lab supervisors must vigorously enforce both of the above items.