On August 11, 2003, a 50-year-old production worker was seriously burned and died 5 days later from a fire that resulted when stored wood flour exploded at a wood-flour mill. The employer is a wood-flour mill that grinds paper-mill waste into a fine powder, and bags and stores it as a marketable product for a variety of industrial applications. The building where the incident occurred was built to older construction standards, and not for the purpose for which it was presently used.
A structural modification violated the National Electrical Code (Class II/Div. 1) by exposing the fuse-panel room to combustible dust. In addition, a rubber seal on the fuse box intended to prevent dust from penetrating the box was not in place. Most of the electrical equipment in the factory was old and not up to code, making replacement parts difficult to obtain. The general manager, located in another state, was aware of the antiquated equipment at the mill, but was unaware of applicable safety regulations. The last documented safety inspection at the mill was in 2000.
Three employees worked at the mill, running two shifts at the time of the incident. The employees had worked together at the mill for 9 years. They did not maintain a safety program, or perform safety training or routine inspections to identify hazards related to the building, machinery, or operations. None were trained in applicable safety regulations that apply to wood-flour manufacturing. All three workers made repairs to equipment, including electrical equipment, for which they were not specifically trained or supervised.
One year prior to this incident, a worker was killed in a similar explosion and fire at an adjacent wood-products factory. Dust explosions are a known hazard in wood-products and other organic materials manufacturing that produce dust particles.
On the day prior to the incident, the production worker was shown a fuse that had been repaired by a coworker during the previous shift. Apparently, the appropriate replacement fuse was not available (or there was trouble getting it to work properly), and the coworker had taped a renewable fuse link to the outside of the melted, nonrenewable fuse cartridge. The production worker removed the rigged fuse to inspect it, and then reinserted it into the fuse holder.
A melted fuse was repaired by taping a renewable fuse link on the outside.
At 7 a.m. on the following day, the production worker started up the plant operation. Working alone, he began switching on the equipment in a standard start-up sequence. Switches were located in a large storage area adjacent to the fuse-panel room. The rigged fuse was connected to a three-phase 440-volt/30 amp electrical motor for a fan that collected dust emissions from the milling process. The motor was later inspected and found to be fully operational. The rigged fuse had evidently made good contact with the fuse holder earlier, but when removed and reinserted it remained loose enough to allow the renewable fuse link to “chatter” against the ends of the housing, due to vibrations from running equipment in the factory. When the worker hit the switch for the fan, an electric arc was generated across the poor connection between the makeshift fuse and the fuse holder. The wood dust that had accumulated inside the fuse panel ignited and exploded.
The concussion from the initial blast caused wood dust on other surfaces in the area to become airborne, creating a rapid succession of at least three explosions that combined into one very loud, superheated explosion. The required isolation of the fuse-panel room was compromised by
a large hole in the wall (1 ft x 3 ft), created during an earlier installation of an I-beam to support the main flour bin. The hole had allowed wood dust to collect on surfaces in the fuse-panel room. When the explosion occurred, the hole also allowed the blast to reach directly where the worker was standing. The upper portion of his body was severely burned, and he inhaled toxic, superheated air.
The production worker walked out of the building to an adjacent business, where he was found by emergency responders. He was awake, alert, and oriented, but had sustained second- and third-degree burns to his upper body and arms. The victim was transported to a local hospital, and transferred to the Oregon Burn Center for treatment, where he died 5 days later.
Source: https://www.ohsu.edu/sites/default/files/2019-02/ORFACE-IR-Other-Fire-WoodDust.pdf