Article Archive
Iron Dust
CSB to release findings, draft recommendations regarding three dust flash fires in Gallatin, TN
Vol. 27 Winter 2012

The U.S. Chemical Safety Board will hold a public meeting on Nov. 16 (Wednesday) in Gallatin, TN, to present the findings into three iron dust flash fires that occurred over a five month period in 2011 at the Hoeganaes facility. Two workers were killed in the first iron dust incident on Jan. 31 and the second iron dust incident on March 29 injured another employee. The third incident, a hydrogen explosion and resulting iron dust flash fires, claimed three lives and injured two others on May 27. 

At the meeting the CSB investigative team will present its findings on the circumstances of the accident to three CSB board members and the public. The Board will ask questions of the team in front of the audience and will then invite comments from members of the public. The meeting will be videotaped and an official transcript will be included in the investigative file.

Following the presentation of the CSB’s findings and safety recommendations, a panel of outside witnesses will be invited to speak on a number of issues related to the board’s findings and recommendations.  Confirmed panel members include Dr. Robert Zalosh, former professor at Worcester Polytechnic Institute and an independent expert on combustible dust; Professor Paul Amyotte of Dalhousie University in Halifax, Nova Scotia; Mr. John Cholin, P.E., who investigated a similar incident in 1992 at a Hoeganaes manufacturing facility in New Jersey; and Mr. Bruce Johnson of the International Code Council, the developer of the fire code followed in Tennessee.

At a press conference in June, CSB Chairman Rafael Moure-Eraso reported that CSB experts have done extensive testing on the metal dust from the facility. Tests show that powder samples collected from the sites of both the January and March accidents were combustible and could be exploded under test conditions. These test results largely agree with results obtained by Hoeganaes itself prior to the January accident.

Since the CSB was established in 1998, three of the four deadliest accidents we have investigated were determined to be combustible dust explosions.

A wide range of common combustible materials can explode in finely powdered form, including metals, wood, coal, flour, sugar, plastics, and many chemicals and pharmaceuticals.

Moure-Eraso displayed a sample of metal dust obtained by CSB investigators from elevated surfaces above the site of the most recent accident.

"It is a finely powdered iron dust," he said. "It is similar to material we previously tested, which was shown to cause flash fires or explode when suspended in air, confined, and brought into contact with an ignition source."

Preliminary examination of the plant showed many violations of safety practices for combustible metal powder, Moure-Eraso said. Key safety requirements from NFPA 484 were not being adequately implemented at the Gallatin plant, such as:

- Conveyors and other equipment are not adequately sealed to prevent the release of dust

- Combustible dust has been allowed to accumulate on horizontal surfaces, and housekeeping remains inadequate, particularly for elevated surfaces

- The dust collection system at the Hoeganaes plant is severely deficient, is improperly designed, and has leaks. In fact, our investigators observed combustible dust backflushing into the building more than once every minute from this system.

- The electrical equipment throughout most of the plant is only suitable for general industrial use, not for a flammable environment

- The plant has many uncontrolled potential ignition sources, including large open flames and hot surfaces from furnaces, exposed light fixtures, exposed bearings which could overheat from dust, internal combustion engines, and welding equipment.

According to CSB investigator Johnnie Banks the Hoeganaes facility employs approximately 180 workers and manufactures ?atomized iron powder that is sold to the automotive and other industries for the production of metal parts using powder metallurgy.

The plant collects scrap iron, which is then melted, sprayed into powder form, and then annealed using hydrogen gas using a large continuous furnace. This powder is then further milled, packaged, and eventually sold as a final product.

"During all three of our trips to the Hoeganaes plant my team observed alarming quantities of metal dust within close proximity to the incident locations," Banks said. "This was of particular concern as metal dust flash fires present a greater burn injury threat than flammable gas or vapor flash fires. Metal dust fires have the potential to radiate more heat and some metals burn at extremely high temperatures in comparison to other combustible materials. In addition to visible dust particles in the air, 2 to 3-inch layers of dust were observed on flat surfaces, rafters, and railings throughout the facility.

Following the May 27 accident, the CSB arrived at the Hoeganaes facility at approximately 11:00 am on Saturday May 28, Banks said.

"We documented and examined the accident site and began interviews with company personnel," Banks said. "To date we have determined the following preliminary sequence of events. According to witness interviews the incident took place on Friday, May 27, 2011, between 6:30 and 6:40 am. At about 6:10 am, two annealing operators heard a hissing sound in a trench that housed a number of process pipes carrying hydrogen, nitrogen, and cooling water. When the operators heard the hissing sound, they summoned plant maintenance personnel to lift a cover over the area where the gas leak was thought to have occurred. After several attempts to lift the cover with a pry bar were unsuccessful, a call went out to get a forklift. The cover was attached to the forklift with a metal chain and raised. As the cover was pried opened, an explosion occurred. Some witnesses saw a flash of light; some heard a muffled boom and felt the building shaking from the explosion. The building filled with dust and the lights went out. Witnesses saw burning dust raining down from above."

The initial explosion involved hydrogen gas that had been leaking into the trench from a large hole in the vent pipe, Banks said. However, the witness statements as well as the physical evidence leave no doubt that combustible iron dust was also involved in the aftermath of the explosion. Examining the scene following the incident, CSB investigators observed splatterings of burned iron dust. A hydrogen fire, described as three to four feet high, continued until an operator in the area closed a valve on the hydrogen piping.

Hoeganaes personnel called 9-1-1 and immediate medical attention was provided by Hoeganaes emergency responders. Gallatin Fire Department responders and EMTs arrived shortly afterwards and took over first aid. Three of the victims were life-flighted to the Vanderbilt Hospital Burn Unit. Tragically, two victims passed away and a third was critically injured with extensive burns.

The team examined the area of the plant where the most recent incident occurred. On this diagram, the workers fatally injured by this accident are reported to have been standing at the openings where covers of the trench were removed—north and south of the band for Band Furnace #1. The material being transported on this band, or conveyor, is the same as the material involved in the January 31st incident. The covers on the trench that were not lifted showed about a tenth of an inch of accumulated dust. Investigators also found iron dust on other surfaces in the area.

CSB investigators, along with TOSHA and company personnel examined the pipe responsible for the release of flammable hydrogen gas. A photograph showed the large, three- by seven-inch hole in the hydrogen pipe. The trench that held the pipe showed signs of dust intrusion, pipes inside in the trench showed signs of corrosion.

Immediately prior to the May 27 explosion and fire, the CSB was actively involved in ongoing testing of iron powder from the previous incidents, which were solely dust related. A small sample of just over one ounce of fine iron powder produces an intense flash fire when dropped onto a gas flame.

"If this size fire can result from just an ounce of iron powder, you can imagine the magnitude of the fire and explosion hazard from the estimated tons of dust accumulated in the Hoeganaes plant," Banks said.

The CSB is an independent federal agency charged with serious industrial chemical accidents. The agency's board members are appointed by the president and confirmed by the Senate. CSB investigations look into all aspects of chemical accidents, including physical causes such as equipment failure as well as inadequacies in regulations, industry standards, and safety management systems.

 
 

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