DSS069: Case Study - Dust Explosion in a Fish Meal Factory in Norway in 1975

In this episode of the DustSafetyScience Podcast, we’re discussing a case study involving a dust explosion at a fish meal factory in Halsa, Norway. This study is taken from Chapter 2, Section 5 in [Affiliate] Dust Explosions In The Process Industries by Dr. Rolf Eckhoff.

Over the last number of years, there have been several incidents involving fish meal factories. In July 2018, there was a silo explosion in Halsa, Norway. Another one took place in 2017 in Florø, Norway, and in 2016, there was a fish meal explosion in Alaska. This incident took place in an open area of the building but it damaged pipes and blew out some of the doors.

Fish meal is generally reported as a low-reactivity dust but this 1975 case study shows that they can still result in a pretty large dust explosion. Two people were injured, one of them fatally. In this episode, we’re going to:

Review what the facility looked like
Show how some of the designs were inadequate
Describe the dust explosion incident
Summarize some of the technical deficiencies that led to this explosion

An Overview of the Facility

This dust explosion happened in August 1975 at a fish meal grinding plant in Halsa, a town on the west coast of Norway. In these facilities, leftover fish is ground and dried into a powdered meal used as animal feed and in agricultural settings.

The plant consisted of a wooden building about 30 meters tall, which contained several large storage and mixing silos. Unground fish meal was put on a conveyor system and conveyed into a hammer mill, which dumped its contents into the storage silos, which were three meters in diameter and 12 meters tall. The fish then went with the screw conveyor up to the bucket elevators before being brought up through the screens and back into the hammer mill.

Inadequacies in the System Design

The silos were originally used to store fish meal from the night shift in preparation for screening operations that only happened during the day, but at the time, they had a lot of issues. Inadequate design resulted in them falling out of use, although they acted like big dust collectors beneath the hammer mill by feeding collected material through the screw conveyors and back into the system.

Although the hammer mills produced large quantities of dust, there was no extraction system, so dust coated the inside of the silos and migrated into the plant. Particle sizes were very small, and on hot days, dry dust accumulated.

Another issue was that the screw conveyor bolts that connected the blades to the shaft broke often, likely due to material fatigue. The broken bolts were moved through the screens and back into the hammer mill, where they would bang around. If operators heard the noises, they would open a chute and wait for the material to work its way out.

An Overview of the Dust Explosion

On the day of the dust explosion, workers were getting ready for the night shift when they heard fugitive material in the hammer mill. One of the workers went to Mill 2 and Mill 4 and did the normal operation: open the chutes and wait for the bolts to come out. But when they opened Mill 1, they saw what was described as sparks, which was likely burning fish meal.

An explosion ejected a strong flame from the chute. Witnesses also heard a whistling sound as the event propagated through the silos below the hammer mills. Fugitive dust also dislodged and caused a larger explosion. Witnesses saw four to five-meter flames shooting out of the roof for 30 to 45 seconds. Two workers were injured, one fatally.

A Review of the Technical Deficiencies

A number of technical deficiencies contributed to the explosion. Metal from the bolts got stuck in the hammer mill and heated up after repeatedly going through the system. This, in turn, ignited the fish meal and caused combustion. When the chute opened, the explosion occurred.

Processes were obviously inadequate. The silos didn’t serve their purpose. There was no process for picking up or extracting the dust that was generated or the automatic removal of trapped metal.

Conclusion

In standard laboratory tests, fish meal generally gives a weak explosion, but that doesn’t mean it is not hazardous. When allowed to accumulate, it is highly dangerous. This 1975 explosion is a reminder that lack of attention to combustible dust safety is a hazard in all processing environments.

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