Pesticide Explosion Investigation, accident Reconstruction

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Pesticide Fire and Explosion

Two truckloads of azinophosmethyl (AZM) pesticide arrived at a repackaging plant. The trucks each contained numerous supersacks of AZM weighing 1600 pounds each. The first truckload was unloaded and placed in a storage area. A short time later, yellow fumes were noted coming from the area where the one truckload of AZM had just been placed.

The building was evacuated and the fire department was called. The yellow fumes continued to grow. The fire department asked the plant personnel if there was anything that could explode, and they were told there was not. As four firemen approached the building it exploded, killing three and injuring one.

Chemaxx was asked to investigate the underlying cause of the explosion. After considerable study, testing and analyses, Chemaxx concluded that AZM undergoes a self-sustaining exothermic decomposition beginning as low as 232°F. By the time the AZM reaches 270°F copious yellow fumes are given off that are flammable and, if in the right concentration at the time of ignition, they are explosive.

The research involved thermal gravimetric analysis (TGA), thermal-desorption-gas-chromatography-mass-spectroscopy (TD/GC/MS), differential scanning calorimetry (DSC) and modified flash point testing (due to noxious fumes given off when AZM decomposes and/or burns).

For example, in the accompanying video, AZM was gradually heated in a stainless steel pipe. There was a burning torch at the exit of the pipe. At an inside wall temperature of about 270°F, yellow fumes emerged from the pipe that were immediately ignited by the butane torch.

It was determined via witness testimony that the AZM just delivered to the plant was placed near a hot compressor pipe. This was the most likely source of heat for the early exothermic and self-sustaining decomposition of AZM that generated the yellow fumes. As the firemen approached the building, which by then contained an explosive level of the yellow fumes, others disconnected the electric power to the building. It is believed that the disconnection of power created a spark that ignited the explosion.

The manufacturer's Material Safety Data Sheet (MSDS) for the AZM incorrectly indicated that the Flammability and Reactivity ratings for AZM were both zero (F=0 and R=0). Chemaxx believes, based on testing, that anything less than 3 would be misleading but clearly the ratings should not be less than 2. Ratings of zero indicate no risk and ratings of 4 indicate very high risk. When the fire department asked if anything could explode, the plant personnel relied upon the MSDS for their response.

The underlying tragedy in this event was that the repacking plant personnel had questioned the manufacturer's ratings for flammability and reactivity, but were reassured by the AZM manufacturer that the F=0 and R=0 ratings were correct. Therefore, the repackager was not aware that the AZM was flammable or explosive. They understood it could decompose and create noxious fumes, but did not know the fumes were flammable or explosive.

Following the initial explosion there was a large fire involving many different pesticides that resulted in evacuations of nearby communities.

The issues investigated included:

Cause and origin of the explosion
Adequacy of the MSDS
Adequacy of the hazard ratings for flammability and reactivity

The experimental methods used included:

Ignition tests
Thermal gravimetric analysis
Differential scanning calorimetry
Thermal desorption-gas chromatography-mass spectroscopy
Modified flash point testing.

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