In today’s episode of the Dust Safety Science podcast covers the second half of an ‘Ask Me Anything’ session about hazard monitoring on bucket elevators and drag/belt conveyors.
Last week, Brian Knapp, Vice President, Electronics Division for 4B Components in Illinois talked about hazard monitoring devices, types of ignition sources, common hazards, and ways of testing for and preventing them. In this episode, he goes over the following:
- What to do when the system alarms
- How to determine what’s normal for these types of sensors
- Equipment certification
- NRTL approvals
- Wireless hazard monitoring
What Should Be Done When a System Alarms?
Brian explained that when a system alarms, it could be due to a variety of reasons, including choking, and you should react accordingly, but your next steps will depend on the type of technology being used.
With rub blocks for belt misalignment, there may be a short time delay or a reduced temperature before the alarm goes off. Once that happens, your best option may be to close the gates or shut off the feed.
He identified two conditions where you would want to shut down immediately.
- Plugging, as there’s nowhere else for the material to go.
- The 20% belt slip, which is an OSHA requirement for grain handling applications. Once that much slip occurs, the belt will be damaged if it continues to run.
Brian explained that with a lot of 4B products, the temperature variation would trigger a strobe light horn alarm and, in most cases, an automatic feed shutdown. There would also be a time delay for belt misalignment and varying temperature.
“By default, we’re looking at about a 60-second time delay to shut that down but that can be reduced if it doesn’t take that long to clear a belt [and] could be extended if they’re comfortable with that,” Brian explains. “It’s all risk analysis on the part of the end user, ultimately. The 20% belt slip, the plug condition – those are immediate shutdown and then get out your shovels.
How to Determine What’s Normal for a Sensor?
Brian said that the key to avoiding so-called nuisance alarms is making sure that the sensor is the first thing the belt comes in contact with instead of sticking it two inches next to the belt, where every little movement can activate it. There needs to be a balance.
Varying temperature monitoring can also trigger nuisance alarms. You need to identify the point that’s normal for the machine. With bucket elevators, it generally runs close to ambient temperature, as the bearings aren’t typically going to heat up a lot compared to hammer mills and fans. There’s no ‘one size fits all’ approach because what’s normal temperature-wise can vary from one process to another.
How Important Is It to Use Certified and Approved Electronics?
According to Brian, this is an extremely important consideration in the dust hazard environment. OSHA has a list of nationally-recognized testing laboratories, but ATEX in Europe and IECEx in Australia have their own standards and approvals bodies.
It is important to note that in the dust hazard environment, these approvals don’t always align.“We’ve seen devices in the past that are Class 1 approved [but] will be a dust hazard in the U.S.,” Brian explains. “Some dusts have a lower ignition temperature as well. I’ve seen products that have Class I approval but they’re not even dust-tight. So you can’t necessarily use a Class I approval or a gas-approved device unless it’s concurrently approved for dust hazards. That’s important.”
What is the Equipment Certification Process?
Manufacturers that want to certify their equipment need to have an NRTL (Nationally Recognized Testing Laboratory) they work with.
“You tell them what the product is and what approvals [you] are looking to get with that product to which standards,” Brian says. “Here in the U.S., we’ve got the UL standards. In Canada, there’s the CSA standards.”
The manufacturer then sends the design information and the product itself to the lab, where its heat generation is measured and it is tested for impact and dust ingress resistance. The results go into the warnings that appear on the product.
“They’ve got to periodically come to the factory and audit things,” Brian adds. “So it’s a long-term relationship with these approval bodies. It’s not just one time.”
How Does Wireless Hazard Monitoring Work?
Brian confirmed that wireless systems are appearing in the industry, but for hazard monitoring, he recommends a hardwired system.
“To have a wire going from the sensor to the PLC or controller and then a wire from there to the motor contactor is going to be your best reliability option, I think,” he says. “Some customers are tempted to utilize wireless because it reduces the cost of installation. But you’ve got to consider reliability. We’ve had people on the coast where the wireless system works fine until an aircraft carrier comes in and swamps out all the other wireless – they can’t even use their cell phones. If they’re going to utilize wireless, [they should] consider what the backup plan is if the wireless doesn’t work.”
Conclusion
When it comes to hazard monitoring, safety should always take priority, even if it interrupts production.
“We’ve had some customers that don’t want to shut things down and they’re not going to shut down until the truck’s unloaded,” Brian says. “But by the time you get a truck unloaded and fed through the bucket elevator, there’s a lot of heat that could be generated and that’s a dangerous situation.”
If you would like to discuss further, leave your thoughts in the comments section below. You can also reach Brian Knapp directly:
Email: [email protected]
Website: https://www.go4b.com/
If you have questions about the contents of this or any other podcast episode, you can 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
Dust Safety Science
Combustible Dust Incident Database
Dust Safety Science Podcast
Questions from the Community
Dust Safety Academy
Dust Safety Professionals
Companies
4B Components
Previous Episodes
DSS146: Ask Me Anything on Hazard Monitoring on Bucket Elevators and Drag/Belt Conveyors with Brian Knapp- Part 1
Thanks for Listening!
To share your thoughts:
- Leave a note in the comment section below
- Ask a question to be answered on the show
- Share this episode on LinkedIn, Twitter or Facebook
To help out the show:
- Subscribe to the podcast on iTunes
- Leave a review and rate our show in iTunes to help the podcast reach more people
