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My Material Doesn’t Look Like a Dust, Do I Still Need to Test It for Explosibility In a Dust Cloud?

By Rachelle Andreasen, Manager, Dust Testing Operations, Earl Johnson, Lab Technician and Ashok Ghose Dastidar, Ph.D. MBA, Vice President, Dust & Flammability Testing and Consulting Services, Fauske & Associates, LLC

In an effort to help our customers understand the importance of evaluating the “dust” hazards within their facility, we have taken a current ASTM method and modified the purpose to answer the “is my material a dust” question.

yellow dust cloudASTM E2316 Standard Test Method for Determination of Particles Resulting from the Attrition of Granular Pesticides was originally authored to provide information on health hazards such as inhalation risks based on the amount of pesticide dust present within a working area. The method looks at the original size of the dust and simulates breakage from normal manufacturing and handling processes. The fines generated from this testing procedure are labeled as the “fines from attrition”.

As the amount of dust increases, the greater the risk for not only inhalation concerns, but for dust explosion hazards as well. As previously mentioned, this test procedure was modified to simulate the amount of dust that could be generated by transport via pneumatic and mechanical means within a facility or in containers on the road (i.e. sea or air).

Most recent revisions of the NFPA standards related to dust define a “dust” as a particulate with a particle size of 500 μm or smaller. For this reason, this analysis was performed by taking a sample of material and sieving the material to less than 500 μm to remove the inherent fines (i.e. the powder/dust at the bottom of the bag of cereal). Once the inherent fines were removed, the material was placed within a glass jar with an equal weight of glass beads. The material was tumbled, with the glass beads, for approximately 4500 rotations thus creating an attrition scenario. Once again, the material was sieved to less than 500 μm to remove the fines from attrition. The total quantity of fines then becomes an estimate of the amount of powder/dust that can be present in your material after transport.

As you can see from the histogram below, the commercial particle size of granulated sugar was 54% less than 500 μm (see Figure 1). After the tumbling process, the material was determined to have a particle size of 62% less than 500 μm (see figure 2). The table below also details the data generated from the analysis. The fines % was increased by approximately 8%, which is nearly a 15% increase in fines.

 Table 1 Average weight % of particles with a 500 μm diameter or smaller

Table 1 Average weight  of particles with a 500 μm diameter or smaller

 

Figure 1: “as received” particle size distribution

Figure 1 particle size distribution histogram

 

Figure 2: Particle Size distribution after attrition

Figure 2 Particle Size distribution histogram after attrition

The data generated in this analysis clearly shows that even though your material may be in granular form
(or larger), the potential for particle attrition based on your or the end users’ process should be evaluated.

There is not a definitive particle size that governs whether or not a material is explosible in dust cloud
form. The explosion characteristics can be altered based on a materials particle size distribution, moisture
content and even particle morphology. Care should be taken when operating within a facility with
explosible dust.

If you are interested in learning more about dust hazard mitigation, take a look at FAI's three step approach to dust hazard analysis below.

FAI's 3 Step Approach to DHA

 

Topics: Combustible dust, dust hazard, ASTM

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