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explosion at a pyrotechnic blending facility accident reconstruction



Areas of Expertise

Michael Fox, PhD.



Pyrotechnic Explosion

An explosion at a pyrotechnic blending facility killed four young workers and severely burned one other. A photo of the site shows that the entire left end of the building was leveled and destroyed.

An explosion at a pyrotechnic blending facility
View of the Missing Building

The Blending Company was small with limited in-house expertise in chemicals or chemistry. The owner had been a housewife before forming the company and she had no education beyond high school and had never even taken high school chemistry. In fact, no one at the company had ever taken high school chemistry. The blending site was an abandoned gas station on a rural highway. Yet, it was in the business of assembling a pyrotechnic device. The Blending Company’s sole business was the assembly of a pyrotechnic device for one sole customer, a larger pyrotechnic corporation. The larger corporation retained ownership of all the mixing equipment, the chemicals and the procedures they provided to smaller blending company. In turn, the blending company supplied unskilled and low-cost labor to mix the chemicals and transform them into the pyrotechnic product. The larger company’s labor force was unionized while the smaller company’s was not. The smaller company’s employees were paid near-minimum wage in cash, were provided no medical insurance benefits and were not even provided with Workman’s Compensation benefits.

The pyrotechnic product resembled a road flare in both its appearance and function. Chemically, it was a mixture of oxidizers and fuel that were blended in an almost antique mixer (shown in photo).

One of the main chemical ingredients in the product was zinc powder.

view of the mechanical mixer
View of the Mechanical Mixer

Several weeks prior to the explosion, the workers noticed a change in the zinc powder. It had the appearance of being "wet" but in fact it turned out that it was "finer." Workers described it as "real powdery … it lingered in the air … it would be all over your face and arms."

The larger corporation approved the continued use of the "finer" zinc powder without ever inspecting the smaller company’s mixing facility to ensure that it was the correct environment for handling metal powder dusts. In fact, the abandoned gas station was not an explosion-proof environment and as might be expected, there was an explosion. Physical evidence indicated that the explosion occurred just after the finer, dustier zinc had been added to the mixer.

This investigation involved:

  • Site inspection and sample collection shortly after the explosion,
  • Energy dispersive spectroscopy of samples,
  • Detailed physical inspection of mixer and other equipment,
  • Standard analyses (EPA Methods) of samples taken from the site,
  • Differential Scanning Calorimetry (DSC),
  • Thermal Gravimetric Analysis (TGA),
  • Thermal Desorption-Gas Chromatography—Mass Spectroscopy (TD-GC-MS), and
  • Simulated test burns and explosions.

The issues in the case included:

  • Determination of the root cause of the explosion (zinc dust explosion),
  • Adequacy of Material Safety Data Sheets (MSDSs),
  • Adequancy of chemical labels,
  • Adequacy of mixing instructions,
  • Human Factors,
  • Compliance with OSHA Standards,
  • Compliance with NFPA Standards, and
  • Responsibilities of the involved corporations.

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