Q&A: Beyond Hazardous Area Classification: Mechanical Equipment Ignition Risk Assessment (MEIRA)

Powder & Bulk Solids recently presented “Beyond Hazardous Area Classification: Mechanical Equipment Ignition Risk Assessment (MEIRA) as part of its DryPro webinar series. The webinar describes a disciplined approach that identifies potential electrical and non-electrical ignition sources when conducting a DHA, including an appropriate focus on mechanical equipment ignition sources.

Kevin Jeffries, Technical Lead, Process Safety at DEKRA North America, discussed how many dust hazard analyses overlook the wide variety of ignition sources that are not electrical or electrostatic in nature. And he described a disciplined approach that identifies potential electrical and non-electrical ignition sources when conducting a DHA, including an appropriate focus on mechanical equipment ignition sources.

After the presentation portion of the webinar, a live Q&A took place. Here are the questions and answers.

Q. Will you explain the differences between Class I and Class II equipment designs and where failures could occur in both to cause ignition sources?

A. Generally speaking, if the equipment is designed for the environment, what happens —and where they become credible ignition sources — is due to lack of maintenance over time or possibly, an improper specification. So, if you look at some of those purged enclosures, if for any reason as part of a protocol you’ve got a purged system that allows you to operate in a dust environment but the seals or the gaskets aren’t in good condition, or during certain activities it’s not interlocked where somebody opens that purge, opens the cabinet up and you get dust on the inside of the equipment, when you start that air purge back up that dust will now circulate and it can actually ignite on that piece of equipment. So, the enclosures in those environments are designed to keep the material out. But if anytime the enclosure is compromised, and the dust, or vapor or whatever gets inside, those electrical systems are still firing and once that meets, you’ll have the event.

Q. Can you briefly describe assessment steps for a fan wherein bulk material is passing through the fan blades.  Example here would be an enclosure-less dust collector.

A. So, enclosure-less dust collectors, NFPA does a pretty decent job talking about the requirements including the MIE [minimum ignition energy] should be greater than 500 millijoules. So, the steps I would go through is first, look to see where I can get information on the makeup of the fan. Is it actually a non-sparking fan? Then I would see if I can do my MEC [minimum explosible concentration] calculations and see if I’m below the minimum explosible concentration, usually 25% of the MEC. With metal dust there’s more of a 10% factor. I’d look at my concentration and look to see what the makeup is of the fan. If I’m below the concentration, I then have to see if I effectively installed the dust collector because sometimes you do the concentration calculation and you’re below the MEC but it’s because the equipment is ineffective capturing the dust and you have a ton of dust on surfaces in your process. So, if the dust collector becomes more efficient you may actually exceed it. Sometimes at that point it is a matter of replacing the fan, contacting the OEM to see if they have something that is better suited. Usually what I see with enclosure-less collectors is that the wrong commodity is specified, so the enclosure-less collector may be for wood dust or something else and it’s got some other safety factors factored into it, but you want to makes sure you’re using it for the right application. Look at the minimum explosible concentration, look at the fan makeup, look at your failure rates of the fan, and from that point there are some performance-based options that are available. But the safest is to replace the fan and get something that is non-sparking.

Q. While monitoring bearings, do you suggest vibration monitoring as well as temperature monitoring?

A. It does not hurt to have that redundancy. The idea is that if you’re getting some vibration that means that there is a surface-to-surface contact somewhere that’s going to lead to overheating. The vibration is generally going to maybe give you an indication sooner than the temperature rise, so if I go through that, the temperature sensors — and there are some great folks who make some great devices — those are excellent tools but if you’re in that reliability mode as a facility and you’re into predictive maintenance and you’re using vibration, I think it’s a good indicator because you’re plant has a frequency and when you’re outside of that frequency something is wrong. There is nothing wrong with using the two, but you can get some degree of higher liability with that vibration.

Q. PHAs and DHAs can sometimes be long processes. Is there a way you have found success in creating more engagement? Usually, I find that there is one person driving the meeting, and the rest of the group is silent.

A. That’s the classic example of “What’s in it for me” and I know that it’s frustrating, because usually it’s “Hey, I want you to go sit in this meeting for 5 hours,” and nobody is giving you the “why.” In terms of an engagement from the standpoint of the group, to actively engage folks, you want to have engagement based on everyone’s area of interest and expertise. So, you want to come into it like, “Hey, from a process standpoint I want you to take a look at these items, and I need you to report out.” What I found is an effective tool if you lack engagement is to have an investigation study and then report out, and during the report out, if you give me candy during an exercise, I’m more engaged! There is nothing wrong with bribing the team based on the inputs that come out of it.

View the Beyond Hazardous Area Classification: Mechanical Equipment Ignition Risk Assessment (MEIRA) webinar on demand here.