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Q&A: Combustible Dust Safety and Compliance

Posted on June 14, 2017

Last month, we hosted a free webinar on combustible dust safety and compliance. The goal was to clear up some common misconceptions and give health and safety professionals the tools they need to understand and protect against this hazard.

If you missed the live event, you can watch the webcast on demand here:

We got a lot of great questions about combustible dust, NFPA’s new dust testing requirements, and what type of equipment is best suited for removing combustible dust from industrial processing facilities. Here is an edited version of the Q&A.

Topic 1: Dust tests and dust hazard analysis (DHA)

How do you determine if areas are classified as hazardous environments?

The first step is to have the dust tested. The dust test is the basis for everything. Then, the dust hazard analysis (DHA) will determine if an area is deemed classified.

Can Nilfisk complete the dust test for my facility?

No. However, we can supply you with a dust test kit for you to collect the dust and provide it to a third-party testing group. Once you have the results in hand, we can help you decide on an appropriate vacuum solution.

Does my in-house dust hazard analysis (or DHA) preparer need to be qualified, trained, or certified?

NFPA 652, Appendix B, lists the requirements for a party capable of executing the DHA. It can be an in-house party, and in large corporations, the ES&H group often handles the DHA. If you don’t have the capability in-house, a consultant or third party can help. Here’s a list of companies that can conduct DHAs.

What are the best locations/areas to sample the dust for testing?

In order to properly and thoroughly test for combustible dust, samples must be taken for every step in the process in which dust is generated. For a list of dust testing vendors, please email us at questions@nilfisk.com.

Where can I find an example of the DHA form?

You can find one in NFPA 652 Chapter 7. If you do use a third-party consultant, ask them for a sample of their work. You should get a good idea based on their sample of the types of information you’ll need to be prepared to present for the DHA.

Can you define “AHJ”?

The Authority Having Jurisdiction is the party responsible for underwriting or overseeing the safety of your facility. That AHJ can be anyone, from the local fire marshal or building official, to your insurance underwriter or your ES&H group within your company. It’s whoever signs for or insures the condition and safety of your facility from a legal sense.

If I have multiple locations performing the same process, do I need to complete a DHA at each facility? Or can one DHA apply to all facilities performing the same process?

If you have multiple facilities making identical products using the same production process, you might be able to get away with one DHA. But the ultimate decision lies with the AHJ. The best plan is to check with your AHJ if they will accept one test or analysis as a sample indicative of conditions at multiple locations.

How do we deal with working at customers’ sites that don’t test their dust?

In the end it’s your customers’ responsibility to have their dust tested and determine what equipment they need based on the results. Nilfisk can advise on the best vacuum solution for their situation and will always make sure the customer is aware if the route they wish to take is non-compliant with NFPA or OSHA guidelines.

Topic 2: General housekeeping

Where does it say that dust accumulation should not exceed 1/32”?

This requirement is in the OSHA Combustible Dust National Emphasis Program (CPL 03-00-008).

Where can we find historical data for combustible dust?

There’s a lot of information available. There are many whitepapers about dust testing online, and industry associations provide historical data that you can use as resources. For example, the NFPA publishes several materials.

But, if you have specific questions or you have any combinations of ingredients or mixes of material, it’s best to have your dust tested. It’s relevantly inexpensive, and it can quickly give you an indication of the combustibility and explosive nature of your dust.

Are dust collectors required to be located outside the facility?

No. Neither dust collectors nor central vacuum systems need to be located outside of the facility. If they’re stationed in a classified environment, they must be certified to be operated in that environment. If explosion protection solutions are deemed necessary on a machine operating within the facility, then they must be designed to account for this fact.

In a non-classified environment, flameless venting can be used as long as it doesn’t vent into any other processes or working areas. Otherwise, chemical suppression can also be used to eliminate the need for venting altogether. In a classified environment, a chemical suppression system certified for that environment may be used.

If my facility has very high ceilings and we were previously using compressed air, how do you suggest we clean these areas now?

There are a variety of wand extensions and nozzles that can be used to reach up into the rafters to clean horizontal or flat surfaces and also pipes. Depending on the height in some of those areas, you might need to use a lift to shorten the distance to put less stress on the operator tasked with cleaning.

Topic 3: Industrial vacuum cleaners for combustible dust

Can I use a shop-style vacuum to collect combustible dust?

Shop-style vacuums are not recommended for combustible dust applications, for several reasons. First, most vacuum hoses on shop-style vacuums are made of rubber, which, being an insulator, will create a charge. The problem is that this charge won’t have a path to ground like it does in a true industrial vacuum. Second, most shop-style vacuums have bodies made of plastic, which is another source of static electricity. Also, when you get to the internal workings, most shop-style vacuums have a small cartridge filter, which is not antistatic. Together, this leaves you with simply too many possibilities for an incident to occur.

What are the advantages and disadvantages of a pneumatic vacuum versus an electric one?

For applications with heavier particulate, where you need a higher waterlift number on the vacuum to be able to pull that material back up into the vacuum, a pneumatic vacuum is superior to an electric one. One disadvantage is that the compressed air supply might not be available in all areas of the facility. In those cases, an electric vacuum gives you more options.

Do vacuums for combustible dust need to be pneumatic?

No, any vacuum that is compliant with NFPA standards for combustible dust may be used.

Can I use any vacuum accessories in conjunction with an explosion-proof vacuum?

The accessories should be either conductive or made of a low-sparking metal, like aluminum or stainless steel. To protect yourself and your employees, you need to make sure that any static electricity buildup has an easy path to ground. You should also try to alleviate any chance of percussion arcing, which is metal-on-metal contact with regular metal, such as steel and iron. This is why aluminum or stainless steel is recommended for accessories.

If low-sparking material construction is recommended, why are Nilfisk’s pneumatic EXP vacuums constructed from painted carbon steel?

They aren’t. Our pneumatic EXP vacuums are constructed from stainless steel. We do drop from full stainless (except for the container) for our electric and pneumatic Class II, Division 2 models (i.e., the A15DX).

By NFPA standards, the main bodies of the electric vacuums do not need to be full stainless steel to be sufficient for Class II, Division 2 environments, so we offer a painted steel version that complies with NFPA standards. The same goes for pneumatic vacuums. While this option meets NFPA standards for Class II, Division 2, if you want to upgrade to full stainless, you can still choose from our EXP line.

Do your standard filters have a wire mesh in the filter medium or around the outside of it?

All of the filters in our certified explosion-proof or NFPA-compliant vacuums have a wire mesh running through the anti-static main filter, and that filter in turn has a grounding wire that attaches to the bottom of the unit to allow for easy conductivity to ground.


We hope this information is useful as you think about the best way to protect your facility and your workers from a combustible dust incident. Have more questions? Please don’t hesitate to ask!