With NFPA 652 mandating that all facilities handling combustible dust complete a dust hazard analysis by September 7, 2020, DHAs are currently a hot topic in several industries. Everyone has questions and they’re not always finding the answers they need.
In Episode #91 of this podcast, we replayed a live Ask Me Anything session with Jason Reason from Seam Group, who answered questions about remote DHAs during a Dust Safety Academy training session. In this episode, we play the second half of the ‘Ask Me Anything’ session where Jason shares more of his knowledge by answering questions like the following:
- Can you mix mild steel from a grinding operation with mild steel from a buffing operation in the same dust collector?
- Would a foundry need separate systems for aluminum and brass, or can they go through the same system and to the same dust collector?
- Is an isolation damper needed on both the inlet and return duct of a sawdust dust collector, or just the inlet duct?
- The NFPA 664 threshold is 1500 CFM. What are the thresholds of other NFPA codes?
- Do you distinguish between a backdraft damper, a back blast damper, and explosion isolation gate?
- What about the use of water in immersion separators for 3D printing in highly combustible metal dust subject to oxidation?
- Can ATEX certification for combustible dust be recognized in lieu of CSA, UL or NRTL certifications?
- Will AHJs accept late DHAs carried out after September 7, 2020?
Q. Can you mix mild steel from a grinding operation with mild steel from a buffing operation in the same dust collector?
Jason replied that whenever metals are mixed with a metal oxide, there is always the possibility of thermite reactions.
“I had somebody combining, I think it was aluminum chips with plastic and wood in the same dust collector,” he recalled. “So that just made a complete mess, honestly. But if you’re going to combine steel and steel, you should be okay.”
He added that while they could be mixed in the same dust collector, the DHA would have to examine the possibility of a thermite reaction or any other kind of chemical reaction that could be caused by mixing different dust streams.
Q. Would a foundry need separate systems for aluminum and brass, or can they go through the same system and to the same dust collector?
Jason said that aluminum can be highly explosive, depending on particle size and how oxidized the material is. Brass is a non explosible dust, which is why it is used for non-spark producing tools. While it could potentially inhibit the explosibility of the aluminum, there are other things to be concerned about in this scenario, such as upset conditions.
“I would definitely test that mixture of aluminum and the brass in there to basically see if it’s actually explosible or not. And if you have a good lab, they can actually do a materials scan on that to figure out how much aluminum, how much brass, how much other junk is in there. So you can actually know what type of dust you’re dealing with.”
Q. Is an isolation damper needed on both the inlet and return duct of a sawdust dust collector, or just the return duct?
Before answering, Jason said, “I’m assuming they’re talking about the inlet for the exhaust duct, and then the drum, or whatever’s connected to it, for the outlet.”
He went on to say that when the air is being recycled, some type of explosion protection would be needed.
“I’ve actually had an incident, including one with OSHA, where there was deflagration inside of a dust collector. It not only went back through the facility through that exhaust duct, it went across the fan, ruined it, went up the duct, and went right back in the facility through that duct, and everyone who was hurt from it was 400 feet away.”
Although abort gates have been used to control these types of hazards, Jason recommended that facilities not recycle their air if they don’t have to. Instead, they should exhaust it outside.
“Here in the States, some people do it because it affects the clean air permit,” he conceded. “But honestly, it’s safer just to exhaust it outside. If you don’t need to return that air back in, I would not do it.”
Q. The NFPA 664 threshold is 1500 CFM. What are the thresholds of other NFPA codes?
“I think they’re talking about the exception. And if I’m wrong, they can correct me,” Jason said. “But there’s an exception in the front, and NFPA 664 is one of the only standards that has this. It says that if you have, I think it’s 5,000 square feet and 1500 CFM, the standard doesn’t apply to you.”
He explained that this exception was made for smaller wood shops. Regarding exceptions in other standards, he said, “I know NFPA 652 doesn’t apply to retail and farms and stuff like that. There are some exceptions for those.”
Q. Do you distinguish between a backdraft damper, a back blast damper, and explosion isolation gate?
“Most of the time, I’d just call it an EIV, an explosion isolation valve,” Jason said. “So that’s a backdraft damper. People call them different things, but essentially it’s the thing that flutters and then closes from pressure. There’s no sensor or anything that does it, the flap just shuts closed, if it works and it’s maintained right, and it’s tested and certified correctly.”
He added that if the party submitting the question was asking about the actual gate, it’s a device that comes down after being activated by a pressure sensor.
“It literally looks like a guillotine to me. They call that an EIV as well, an explosion isolation valve. They all operate on the same principle. There’s some type of barrier there that prevents it from going back in the facility. Some of them are passive, some of them are active. Most of the time I see the passive ones, like the backdraft dampers.”
Q. What about the use of water in immersion separators for 3D printing in highly combustible metal dust subject to oxidation?
Jason said that he has never seen somebody use different liquids inside an immersion separator for metals in additive manufacturing.
“That doesn’t mean you can’t do it,” he said. “But most people don’t.”
For those unfamiliar with the technology, he explained that it was a wet-type vac that empties out sludge. He said that he had never seen problems with titanium, but when aluminums get in water, it can release more hydrogen than titanium does.
“I have seen some potential reactions with that, including one client who actually showed me. They took a drum out of the sludge, out of the vacuum, and accidentally mixed it with titanium waste, which they probably shouldn’t have done, but they weren’t paying attention. And the 55-gallon drum was actually bubbling with hydrogen. You could see it. They put it underneath a vent so they could vent out the hydrogen, but it bubbled for four weeks. So it was actually reacting for four weeks straight, nonstop.”
Jason said that he had not seen anyone hit an LEL (low exposure limit) yet for hydrogen, but it could happen. These possibilities need to be taken into account, as well as the vacuum and how it’s constructed.
Q. Can ATEX certification for combustible dust be recognized in lieu of CSA, UL or NRTL certifications?
Jason explained that unlike United Laboratories, CSA, or FM Global, ATEX certification bodies are not considered the same as NTRL (Nationally Recognized Testing Laboratory) under OSHA.
“I don’t see that changing any time soon,” he said.
Q. Will AHJs accept late DHAs carried out after September 7, 2020?
Jason replied that despite the complications brought on by the pandemic, the September 7 deadline will remain in place. If a facility fails to complete their DHA by then, he said, “everything’s on the table. And what that means is that they could cite you. They could stop your project. They could pull your insurance. I don’t know if they’re going to do that. I have no idea. I’ve just heard they could. And so that being said… I think as long as you contact the AHJs and say, “Look, we know we have to do it. We’re taking our time with this. We’re going to get someone who’s qualified, but we may not be able to do it ’till October.” I think they’re going to be okay with that. As long as you show them you’re making an effort towards completing that DHA.
I mean, the worst thing you could do is have them test the dust and they come back saying it’s explosive. And at that point, it’s whichever compliance officer you get. You may get a lot of citations. You may get a few. It’s luck of the draw at that point. I think as long as you’re showing that you’re making an effort, the AHJ, whoever it is, is going to take that into account.”
Conclusion
Jason’s Ask Me Anything session drew a lot of interest, due to the timely subject matter and his position as an expert on the topic of DHAs. The DustSafetyAcademy regularly conducts these types of training sessions in an online form, so if you are interested in becoming a member, please check it out.
If you would like to discuss DHAs further, leave your thoughts in the comments section below. You can also reach Jason Reason directly:
Email: [email protected]
LinkedIn: https://www.linkedin.com/in/jason-reason-cih-csp-chmm-b561a148/
Website: https://www.seamgroup.com/combustible-dust
If you would like to suggest topics for future live training, you can email [email protected]. If you have questions about the contents of this or any other podcast episode, go 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.
Resources Mentioned
DustSafetyScience
Combustible Dust Incident Database
Dust Safety Science Podcast
Questions from the Community
Dust Safety Academy
Companies
Seam Group
Standards
NFPA 664
NFPA 652
NFPA 484
ATEX
Previous Episodes
DSS091: Ask Me Anything On Remote Dust Hazard Analysis With Jason Reason | Part 1
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Ask Me Anything on Remote Dust Hazard Analysis with Jason Reason | Part 2
