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Flammable Liquid Drum Explosions

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Areas of Expertise

Michael Fox, PhD.



Flammable Liquid Drum Explosions

A laborer working for a Concrete Resurfacing Company was killed when an empty 55-gallon drum of Concrete Sealer exploded and engulfed him in flames. It is believed that the laborer was attempting to cut the empty drum open with a cutoff saw just prior to the explosion. 

The laborer was burned beyond recognition. The Concrete Sealer was 80% by weight ethanol and methanol. It is used as a treatment for concrete surfaces to make them water-repellant. On the day of the explosion, the Concrete Resurfacing Company was repairing a parking garage. 

In another incident 10 years earlier on almost the exact same Concrete Sealer product, another laborer for a Highway Repair Company was cutting the lids off of used 55-gallon drums so the drums could be used for refuse. He was using either a torch or an electric welder to cut the lids off. The procedure was believed to be inherently safe, as they would turn the drums over for several days to let any flammable liquid drain out, and then they would turn them upright and fill them with water and let them stand for five additional days before any cutting. 

In this second incident, the Concrete Sealer drum was not being cut open. However, it was standing next to another drum that was being cut open when a spark flew from one drum into the other. The drum exploded and the laborer died within 24 hours. He suffered third degree burns over 80% of his body. 

In both cases, the fuels for the explosion were ethanol and methanol vapors inside what were believe to be empty or near-empty drums. It turns out that the vapor pressure of a small amount of liquid is just enough to fill the entire 55-gallon drum with an explosive mixture of air and flammable vapors. Therefore, near-empty drums can be significantly more dangerous than drums that are full. 

The average worker perceives the risk of a near-empty drum to be less than a full drum. Because the actual risk is counter-intuitive, it is essential that drums of flammable liquids prominently warn of the high explosion risk of a partially empty drum. Additional warnings against cutting or welding are needed, as well as instructions to avoid all ignition sources and keep the drum completely closed at all times. While employee training about the risks of near-empty drums can be beneficial, used drums all to often find themselves in the hands of untrained employees or untrained non-employees. This reinforces the need for adequate and eye-catching labeling that goes beyond the usual warnings for a flammable liquid. The average, untrained layperson intuitively believes that less liquid means less risk, when the opposite is true. 

This case involved: 
The OSHA Hazard Communication Standard,
Flammable liquids, 
The vapor pressure of flammable liquids, 
  Human Factors, 
The adequacy of MSDSs, and 
The adequacy of labels.

Dr. Fox is an explosion expert, fire expert, and chemical expert with extensive experience in OSHA chemical regulations and chemical safety.