New System Blamed in Ink Dust Blast
A squeal, sizzle, whoosh and loud thump—not an alarm from a brand-new dust collection system—heralded a blast and flash fire that burned seven employees, three severely, at a New Jersey ink plant, the U.S. Chemical Safety Board has found.
The faulty alarm, compounded by a host of other failures, left employees no warning when the dust collection system at U.S. Ink/Sun Chemical Corp. plugged up after a few days, exploded and ignited a fire, the agency said in a newly released, highly detailed Case Study of the incident.
The accident was compounded by lack of communication, lack of training, and inadequate oversight by the facility owner as the equipment was planned, designed, installed and commissioned.
Powder Under Pressure
Those were the board's key findings from the accident Oct. 9, 2012, in the pre-mix room at Sun Ink as huge batches of bulk solid powder (kaolin, Gilsonite and carbon black) and liquid ingredients were mixed in three 10-foot-high, five-foot-diameter tanks at the plant in East Rutherford, NJ. Twenty-eight employees were on shift at the time.
The production process included the pneumatic transfer of the powder under vacuum to the tanks. Powder was also dumped from three overhead receiver hoppers into a bag dump station. As the solids dissolve in the tanks, the solution temperature increases to about 240°F. Each batch weighs about 6,600 pounds when completed.
Employees and contractors told CSB investigators later that Gilsonite dust from the bag dumping "often accumulated around the facility but particularly on flat surfaces."
"US Ink did not provide an effective means of containing fugitive dust at the bag dumping station because emptied bags were often stacked alongside the bag dump, which in turn lofted dust in to the air," the agency reported.
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A US Ink senior engineer designed the new system, but then retired, leaving no documentation or information about the installation, the Chemical Safety Board said. |
Both Gilsonite and carbon black are combustible. The formulation also included a petroleum distillate, which is flammable.
New Dust Collection
Until October 2012, the facility used a wet scrubber system to collect particulate materials during the dry material charging stages of the mixing process, the CSB said. That system had deteriorated over the years and never captured fugitive dust anyway, the agency said.
A new explosion suppression made by Fike Corp. was installed Oct. 5, 2012 (four days before the accident) to better capture the particulate materials and improve the conditions during production. The manufacturer of the dust collection system was not identified in the report.
The new system was designed by an unidentified "US Ink lead engineer" working with the manufacturer. However, the engineer retired between the design and installation phases, leaving little information or documentation about the new system behind.
The new system was commissioned the week before the incident. The explosion occurred during the first day of normal production after initial start-up.
Malfunction Ignored
On Oct. 6, a maintenance employee reported that the new system had run all night, although the mixing tanks had been turned off. US Ink managers "took no action" to address the malfunction or to shut down the system until the failure could be investigated, the CSB said.
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Duct hose material dripped and melted into the ink mixing tanks. |
On Oct. 9, when mixing resumed, a pre-mix room operator was loading Gilsonite into the bag dump station when he heard a "squealing" noise from one tank. As he left the room, he saw a flash fire break out where he had just been working. Without shutting down the mixing or dust collection systems, he went to get a supervisor.
Melting and Dripping
At that point, a "loud thump" signaled an explosion that shook the building. Employees returned to find duct hose material from the dust collection system "melting and dripping onto the tank."
Employees grabbed fire extinguishers only to hear a "sizzling" sound from the tank and see "an orange fireball erupt, advancing toward" them.
The flames engulfed seven employees.
Meanwhile, the collection system alarm panel was signaling activation of its explosion suppression system but produced no alarm. An employee in the area noticed the alarm panel, alerted workers and tried to call 911 but was knocked off his feet by the pressure from the fireball before he could do so.
"These observations are consistent with the sights and sounds of a combustible dust deflagration," the CSB noted. Workers were not wearing flame-resistant clothing as required, the CSB said.
Plugged Ducts
The CSB cited a design failure that allowed blockages in the dust collector.
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Ducts were found plugged with combustible powder in their first full day of operation. |
The hopper and dust fines chute "were filled with approximately 322 pounds of dust fines in just 2 days of system operation," the CSB said. A 10-inch-diameter chute was narrowed to four inches, and smaller ducts were plugged almost completely.
Furthermore, the CSB found that US Ink's mixing tanks had used non-conductive, rubberized flexible hoses eight to 10 feet long—hoses that became the first part of the system to fail.
Nor did the new collection system have duct cleanout doors, forcing firefighters to break into ductwork to put out the fire.
Finally, the CSB said, the company had ineffective hazard communication and a poor emergency response—failures that could have prevented injuries even after the fire.
Editor's Note: This post was updated at 5:47 p.m. ET to correct system manufacturing information. PaintSquare News regrets the error.
