DSS021: Understanding the Combustible Dust Testing Process with Martin Clouthier

In this episode of the Dust Safety Science Podcast, we interview Martin Clouthier, Director and Practice Lead of combustible dust testing and consulting services at Jensen Hughes, about combustible dust testing.

Dust hazard analysis has been a key feature of discussion in previous podcast episodes. In this interview, Martin talks about a fundamental first step in the process: determining the material characteristics of the dust being handled to assess how explosible, flammable, or combustible it is. This involves the understanding of the following elements:

The material properties for combustible dust and why they are important
The role played by particle size and distribution
The role played by credible ignition sources in determining the test process
The importance of working with experts to design a test screening program
The sampling process
Determining whether or not materials are actually explosible before going through an entire suite of testing
The different prevention and protection parameters involved with combustible dust testing

Martin is based out of Halifax, Nova Scotia, and has over twenty-five years of experience with industrial explosion protection. He helped build the state-of-the-art testing laboratory at Jensen Hughes and works with an extended team of subject matter experts in combustible dust hazards.

As a member of the NFPA technical committees on explosion protection and prevention (67, 68 and 69) and the ASTM Hazardous Materials Committee, Martin has valuable insight into the combustible dust challenges faced in facilities today.

The Importance of Customized Testing

Martin emphasized that every facility needs customized testing because conditions will vary from one site to the next. Particle size and distribution are variable depending on process velocity and materials used. There can also be different potential ignition sources such as:

Open flame
Electrostatic discharge
Mechanical friction
Smouldering
Foreign hot objects

For example, if a facility handles whey powder, are they with fine powders and high-energy ignition sources or course powders with minimal ignition sources? The specific characteristics define which tests should be carried out. These may include:

Minimum Explosible Concentration (MEC): Lowest concentration of a dust cloud that will allow an explosion
Limiting Oxygen Concentration (LOC): Oxygen level below which combustion is not possible, independent of fuel concentration
Minimum Ignition Energy (MIE): Minimum energy that can ignite a mixture of a specified flammable material with air or oxygen
Minimum Auto-Ignition Temperature (MAIT): The value used to assess a dust’s sensitivity to ignition from, for example, hot surfaces in dryers
Layer Ignition Temperature (LIT): The minimum temperature at which a dust layer will self-heat
PMAX: Maximum pressure that dust can generate in a closed vessel
KST: Worst-case maximum rate of pressure rise in a closed vessel under standard testing conditions

During testing, the goal is to characterize the potential violence of an explosion and what the ignition sensitivity is. Knowing the particle size distribution and ignition sources makes it simpler to come up with an appropriate program of testing

What Does the Combustible Dust Testing Process Look Like?

According to Martin, the ideal scenario is that a client calls a company like Jensen Hughes stating that they work with combustible dust, and want to identify fire or explosion hazards. Martin would then request a Piping and Instrumentation Diagram (P&ID) to help him understand the process before visiting the facility and observing how material is handled at each stage. From there, Martin collects samples that are representative of each stage of the process being examined.

With a cocoa processing facility, for example, they handle the raw cocoa beans first but, as the process unfolds, the material breaks down into powder. The dust accumulating in a bucket elevator is going to be different from the powder sampled from the dust collector at the end of the process. Martin may look to collect samples at multiple stages of the opperation.

The next step is to determine whether the material is explosible or not by using go/no-go testing. Martin said that some testers do an initial screening using the Hartmann tube but warned the results should not be treated as conclusive. Just because it doesn’t ignite in the Hartmann tube doesn’t mean that the dust won’t ignite in a 20-litre sphere or a cubic meter chamber. The size of the testing vessel is important: industrial-sized dust collectors, for example, may not be well-represented by smaller laboratory chambers.

When operators test in the only vessel available to them, either because they can’t collect enough powder or they can’t get a test done in time, they may not get the complete picture. If they find that material is explosive in the 20-litre sphere, testing it in a cubic-meter chamber could indicate that it is not explosible under some conditions.

The full procedures for testing are outlined in ASTM E1226. It is worthwhile to note that Jensen Hughes has one of the few cubic-meter testing chambers in North America, placing it in the top tier of service providers that do this type of testing.

Conclusion

Combustible dust testing is a collaborative exercise where the consultant works with the client to develop an intimate and deep understanding of their process. These insights enable them to:

Make a judicious selection of where samples should be taken
Use the right-sized testing vessel
Design a safety program that addresses all hazards

In the end, the client gets the best answers for the least amount of money, not to mention more peace of mind in the knowledge that their facility is safer for personnel and visitors.

If you would like to discuss further, leave your thoughts in the comments section below.

You can also reach Martin Clouthier directly:
[email protected]

If you have questions about the contents of this or any other podcast episode, please head to our ‘Questions from the Community’ page and submit a text message or video recording. We will then bring someone on to answer these questions in a future episode.