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Wednesday, December 8, 2010

Combustible Dust Case study from Allianz Risk Consulting

Case study from Allianz Risk Consulting

Explosion Hazard in a Starch Facility: Risk Management in Practice

 

Allianz Risk Consultants are trained to assess many different types of risk, including those that can pose a potential personal threat. Oftentimes, the nature of their work puts them in harm's way. Recently, Rod Greenwood, Senior Consulting Engineer, encountered just such a threat when conducting a tour of a National Starch facility in the US.

When Rod toured the plant on a recent visit, there was a coating of corn starch on just about everything in sight that was higher than 3 feet (1 m) from the floor.  Two "haze" areas were also found where corn starch suspended in the air made it difficult to see the wall on the other side of the room.

Rod realized that this plant posed a safety risk, as fires and explosions could result from the large amounts of corn starch dust.  For safety reasons, the tour was stopped and immediately recommendations for improvements at the plant were discussed.  Based on our engineering recommendations following this inspection, the severe explosion hazard presented by the accumulation of corn starch on overhead surfaces has been all but eliminated.

 

What is combustible dust?

  • A combustible particulate solid that presents a fire or deflagration hazard when suspended in air or some other oxidizing medium over a range of concentrations, regardless of particle size or shape.
  • Dusts traditionally have been defined as a material 420 μm or smaller (capable of passing through a U.S. No. 40 standard sieve).
  • Any time a combustible dust is processed or handled, a potential for deflagration exists. The degree of deflagration hazard varies, depending on the type of combustible dust and the processing methods used.
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Dust is a serious matter: The smallest spark can cause an explosion in a dusty factory.

The situation

The tour began by visiting corn starch drying and packaging areas in the plant.  It quickly became obvious that good housekeeping was not a priority.  While the floors were clean in some areas, there was a coating of corn starch on just about everything higher than 3 feet  (1 m) from the floor.

In varying thickness, it had settled on sprinkler piping, building members, production equipment, racks, lights and conduit.  [The initial introduction was in the second floor packaging area of the east hopper (which was approximately 80 x 160 feet - 24.3 x 48.6 m). Additionally, upstairs in the 30 x 70 ft. (9.1 x 21.3 m) screen room, there was a consistent 0.25 inch (0.6 cm) accumulation on everything.

As the tour continued, Rod and the risk management team from the starch company came upon two "haze" areas, where the corn starch was suspended in air, making it difficult to see the wall on the other side of the room. The first area was in the 50 x 80 ft. (15.2 x 24.4 m) hose switch room below the hoppers. As it turned out, there was a rotary valve leak, and the corn starch was being dispersed into the air, completely filling the room.

The second haze area was in the 20 by 30 ft. (6.1 x 9.1 m) dry starch east slitter room. In both areas of these, there was an accumulation of up to 3 inches (7 cm) on the floor and a consistent accumulation of 0.5 to 1 inch (1.2-2.5 cm) on overhead horizontal surfaces. Rod quickly backed out of the room with a concern for his safety due to the explosion potential.

While the housekeeping in the plant was extremely poor and totally unacceptable, no circumstances of improper electrics, improper hot work, or other sources of ignition had been identified.  Even so, this situation still posed risk. Rod determined that it was no longer safe to continue the survey in this plant. The tour of the plant was then stopped.

The survey continued at another one of the national starch company's facilities. The initial impression of these buildings was positive as they were newer and therefore were assumed to be cleaner. However, when the group entered the line 4-5 mill room, the surge hopper and cyclone air room, the conditions worsened.  These areas are 20 x 50 ft. (6.1 x 15.2 m), located above one another and separated by open grated mezzanines. Here, the group encountered another "haze" condition with up to 0.5 inch of corn starch on pipe, conduit, lighting and the grated mezzanine.

 

Conditions continued

The conditions continued into the line 4-5 packing area (a 40 x 150 ft. area -12.2 x 45.7 m) where the fiber bags are filled with starch.  The air was clear as the line was not running, however; a 0.5 inch (1 cm) coating on equipment and overhead piping was once again found. This area has roof joists that are spaced at 3 foot (1 m) on center. The lower chord and diagonal bars on each and every one through the length of the area were completely loaded with corn starch.
The group also went into a 20 x 30 ft. (6.1 x 9.1 m) packing stack-up area that had up to a 1 inch (2.5 cm) accumulation on all visible areas. Once on the mezzanine, the back side of two 'H' beams on either side of the room were checked. These hidden areas each had a 2 inch (5 cm) accumulation of corn starch the length of the beams.


At this point, Rod decided (due to the explosion potential) that the second day of the plant inspection should be cancelled. It was explained to the management team at the national starch company that the second day of the inspection could not occur due to the potentially hazardous conditions.

The Allianz Risk Consulting Engineer's comments were taken very seriously, and the management team was quite concerned and embarrassed. They pledged to do whatever was necessary to correct the issues, and to change the mindset. They planned to improve the facility right away and invited Rod back to prove to him that these changes would be made.

Allianz Risk Consultants Recommendations
  • Implement a course to educate all management on the hazards of combustible dust.  This course should include legal references and real life exposures and dangers.
  • Establish a "Stop, Fix & Run" philosophy on repairs to leaking equipment.  Operators should be instructed on immediate measures to take when exposed to leaking equipment.
  • Improve housekeeping checklists (daily, weekly and monthly) for all areas that specifically reference combustible dust exposure and prevention.
  • Engage an impartial internal quality assurance auditor to complete routine inspections to ensure site standards for combustible dust prevention and control are maintained and observed.
  • Reinforce the use of STOP walk-arounds for safety, to be used to assist in the prevention of combustible dust accumulation.  Use the success of this program to assist in identifying combustible dust.

Summary

The insured has made major improvements in the housekeeping in all areas noted. All accumulated corn starch on overhead surfaces has been vacuumed or power washed away. Management at the corn starch company has taken a strong approach toward dust exposure and housekeeping.

The intent is to help ensure that housekeeping and corn starch accumulations on overhead surfaces is never again an issue. All recommendations listed above have been completed.  The overall risk rating of the plant has been upgraded from sub-standard to above-standard and the severe explosion hazard presented has all but been eliminated.

1 comment:

  1. This is a great case study from Allianz Risk for a plant which creates combustible dust. While not typical, many times I do find plants with combustible dust problems such as this when touring plant sites for fire prevention evaluation.

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