This interview on dust standard compliance is with Craig Froehling, manufacturing technology lead for global grain handling at Cargill, Inc., Wayzata, MN (952-742-2677). Froehling spoke July 29 on the topic of complying with NFPA 61 and NFPA 652 at CONVEY ‘20, a virtual operations workshop held online by the National Grain and Feed Association (NGFA), the Grain Elevator and Processing Society (GEAPS), and Grain Journal. Froehling serves on the National Fire Protection Association (NFPA) 61 Technical Committee, which updates that standard.
What standards does the NFPA have that cover combustible dust in the grain industry?
NFPA 61 is the industry-specific standard, and NFPA 652 is the fundamentals standard; both apply. NFPA 61 currently is in version 2020. If you do not have a copy of the 2020 version, I encourage you to purchase one at nfpa.org. This one will be much easier to follow and much easier to compare to other standards than earlier versions.
NFPA 652 currently is in the 2019 version. It often closes a year before the other standards.
The NFPA 61 Technical Committee renumbered the chapters and the bullet points to be in alignment with the NFPA 652 standard. It allowed us to see where 652 has some requirements that previous versions of 61 didn’t address.
Sometimes we would extrapolate that 652 content and put it in 61, and sometimes we would write our own content if we thought it was more applicable to our own industry. It also makes it much easier for a user to compare these two documents side by side. NFPA61-2020 addresses all of the topics required in NFPA652-2019 and was intended to be able to be used by our industry as a near standalone document.
What happens when the language differs between the two standards?
If you look at the conflict section in 652(1.4.2), it states, “Where a requirement in the industry-specific standard differs from a requirement in this standard (652), the requirement of the industry-specific standard shall be permitted to be used.”
To clarify: When you have two requirements in the two standards on the same topic, the user has a choice of which standard to follow. This conflict language is repeated in each of the industry-specific standards. That’s an important choice for users to have.
How do you make that choice? Should you use NFPA 61 for this particular scenario or NFPA 652?
If you’re handling a common agricultural dust and a common process, NFPA 61 covers that very well. So things like grain handling, dry corn milling, wheat milling, and feed milling are well-defined processes, and 61 has well-defined requirements for conveying, storage, grain dryers, dust control, etc. for those grain processes.
If you have a dust or process that is not common, 652 may be the better standard to follow. One example we have at Cargill is blending powdered sugar and cocoa powder at a cocoa chocolate plant. Both are combustible dusts, with powdered sugar being very easy to ignite.
It’s a food process, so it’s technically covered by NFPA 61, but those are pretty unique dusts, and there are no direct requirements for those in 61. So this may be a time when 652 is the right choice. That standard systematically takes the user through analysis, assessment, and hazard mitigation for those kinds of dusts.
NFPA 652 also is good for dusts that have been extracted, reacted, gelatinized, dried, or otherwise chemically altered, which happens a lot in the food processing business.
How is dust hazard analysis (DHA) addressed under each standard?
Both standards require the plant owner to do a DHA. The requirements also are the same for new processes or major modifications. If I’m going to do a project or build a new plant, I should do a DHA associated with that project.
However, there are places where the DHA requirements differ between the two standards. NFPA 652 says, “For all existing processes and facilities, DHA shall be completed by Sept. 7, 2020.” The original requirement had a three-year deadline that started in 2017.
NFPA 61 has a deadline of Jan. 1, 2022. The 61 Technical Committee provided a five-year timeline toward completion. It focuses doing DHAs on bucket elevators, conveyors, grinding equipment, dryers, and dust collection systems, which in our industry, have shown to be the “bad actors” in terms of dust explosions. At Cargill, we’re choosing to perform DHAs on all the combustible dust equipment and are going by the 2022 deadline in the 61 standard.
Are there differences in how explosion prevention and protection are handled between the two standards?
Both standards permit the use of a risk assessment to determine what level of protections are needed. A hazard is a hazard, but risk is based on the likelihood and consequences of that hazard.
You make different types of decisions based on the likelihood of this hazard occurring, the consequences if it does occur, and how much protection is needed to prevent it and mitigate it.
That’s different from prescriptive requirements, such as: “Install explosion venting of this size on this piece of equipment, and do it every time.”
So in 652, it states: “Where an explosion hazard exists within any operating equipment greater than 8 cubic feet, the equipment shall be protected from the effects of a deflagration.”
If you are familiar with country elevators, almost everything they have is larger than 8 cubic feet. So do you just put explosion venting on everything that may have an explosion hazard, or do you do a risk assessment to figure out what level of protection you’re going to need?
NFPA 61 addresses that same topic in a slightly different way: “Equipment requiring explosion protection shall be protected by one of the following ... ” Then, it goes into venting, suppression, segregation, and separation, which are all the same methods listed in 652. But the key point is that the user has to determine what equipment requires explosion protection.
NFPA 61 is very prescriptive on the need for explosion venting on bucket elevators and dust collectors. But it doesn’t talk about belt, drag, or screw conveyors. And typically in our industry, we don’t put explosion venting on those conveyors. If you do the hazard analysis, you’ll see that the likelihood of an explosion in a drag conveyor is very, very low.
A related topic is explosion isolation. NFPA 652 says, “Where a dust explosion hazard exists, isolation will be provided in accordance with 69,” which is the NFPA standard for how to “prevent propagation between equipment.”
That could be interpreted to be almost everything. If I think about my flour milling career, the whole milling process is interconnected in a flour mill. NFPA 61 states: “Where a DHA has determined that isolation is necessary, then it shall be provided in accordance with 69.”
Again, there is a determination factor of where the process really needs isolation and under what conditions does an explosion hazard exist. It’s up to the user to determine that, and the tools the user has are a DHA and risk assessment.
What potential changes are coming in these combustible dust standards?
The next potential change is a consolidation of all the standards that address handling combustible dusts.
There are seven of them:
That combined standard is anticipated to be called NFPA 660. The proposed structure for 660 is that Chapters 1 through 9 would remain the same as in 61 and 652. The 652 Technical Committee would govern and write the language for those chapters. Chapter 10 is expected to cover fire protection. And the rest of the chapters, 11 through 16, would contain the industry-specific requirements. Chapter 11, for instance, essentially would be what NFPA 61 is today.
This process will begin with the Technical Committees providing input to the NFPA 652 committee on what they felt were and were not fundamentals.
The NFPA 652 Technical Committee, through several task groups, would begin a review cycle of all this input until a single draft document (NFPA 660) can be pulled together. It’s estimated that this will take six to 12 months, because there’s an awful lot of content there.
If the NFPA Standards Council approves it, which would be sometime in 2021, the draft standard would be posted for public comment.
Then there would be further revisions based on that public input, then another round of review. It’s anticipated that it would become effective sometime in 2024.
That seems to be a long time in the future, but once it’s in the standards process, it will take time to get through all the stages. The first six to 12 months will be a lot of heavy lifting.
Who is qualified to do a DHA? Is special training required?
It’s up to the business owner to determine who is qualified. It was not intended to require that a third-party engineering firm perform a DHA, but that is certainly an option. At Cargill, we are doing ours in-house.
Individuals performing DHAs need training to do a hazard assessment, whether that’s a chlorine system, a fuel system, dust system, or a boiler system. There is training available in the market on how to do a hazard assessment.
In the back of NFPA 61, there also is a sample hazard assessment checklist for agricultural dust.
How do we know if an explosion panel is NFPA-certified?
You can ask the manufacturer of the panel what certifications they use. Actually, the panel itself doesn’t have to be certified by NFPA. You can have one designed per NFPA 68, which is the explosion venting standard.
It’s very common on bucket elevators to use explosion panels attached with breakaway bolts or specially-designed washers. You have to know what the break pressure is and determine how many bolts are needed. The manufacturer will go through those numbers. Many times it’s designed to release around 1 psi.
In NFPA 652, many requirements start with, “Where an explosion hazard exists.” What does that mean, and how would someone know if an explosion hazard exists or not?
If you have dust in suspension in its explosible range, in confinement with an ignition source, that can result in an explosion. Here’s an example: If I have a bucket elevator leg handling raw grain that’s just been harvested and I unload it into the bucket elevator, it still has all the dust in it.
I know an explosion hazard exists in the leg, because there is enough dust to exceed the minimum explosible concentration, and over the last 150 years, there’s enough history to know that grain dust is explosive. I’m going to follow the prescriptive requirements in NFPA 61 on explosion venting, materials of construction, belt alignment, and speed monitors on that leg.
In the same plant, before the wheat is milled for instance, the wheat passes through a cleaning house. The dust, chaff, foreign material (FM), and grains of other classes are removed, so all that is left is clean wheat. As part of the hazard assessment, I could take a sample, sieve it over a 500-micron screen, and measure how much dust is left in this wheat.
It could be determined that there is not enough dust left in this product to be above the minimum explosible concentration. In that case, I could conclude that an explosion hazard doesn’t exist in this bucket elevator leg. I can choose to follow the same requirements for belt alignment and speed monitoring to avoid fires, but I may not need explosion venting.
It’s similar to a drag conveyor that runs very slowly, less than 140 feet per minute. There’s generally not enough velocity for dust to be in suspension, and the drag conveyor is very full. It may be determined that there isn’t an explosion hazard inside of a drag conveyor. Each scenario needs to be analyzed.
Can the Occupational Safety and Health Administration (OSHA) cite a company for not complying with 61 and 652?
Yes and no. OSHA certainly can cite an owner under the General Duty Clause for a variety of things, including excessive dust concentrations. But the NFPA standards, at least with regard to combustible dust, are voluntary standards. They have not been adopted as code by OSHA.
OSHA does have the Grain Handling Standard that applies to grain facilities, and a facility can be cited for violations of that code.
The best approach is to be in compliance withNFPA 61, which is our industryaccepted standard, and of course, be in compliance with all of the applicable OSHA Standards.
To view Froehling’s CONVEY ‘20 webinar at no charge, go to grainnet.com/NFPA.