Dust and fumes created from metalworking processes are hazardous to anyone breathing them in on a regular basis. Overexposure can lead to a variety of short- and long-term ailments and diseases.
To keep the air clear of contaminants, manufacturers must choose the right dust collection system for their particular facility. It needs to effectively handle the size of the facility’s dust particles and the concentration of dust in the air. A dust collection system that is not properly sized and set up can, in fact, introduce new hazards. A dust collector without the proper safety features can also be an issue.
In addition to preventing dust and welding fumes from being inhaled by employees, fire and explosion are the most significant hazards to address.
“Fire and explosion prevention is critical,” says Tomm Frungillo, director of sales and marketing, Imperial Systems Inc. “It affects the whole facility as well as possibly adjacent facilities. Some companies consider all metal dust and fumes as potentially flammable or combustible, and so they include safety precautions on all their equipment. Other companies look at it more by what type of dust is being created, meaning they don’t necessarily have to apply all safety precautions to each machine. For a noncombustible nuisance dust, you may not the additional equipment.”
The National Fire Protection Association (NFPA) classifies the explosibility of dusts using KST values ranging from zero to greater than 300. If the KST value is greater than zero, the dust collector must have explosion protection.
“Prevention starts before the dust collection,” Frungillo says. “We look at it from the start of the metalworking operation all the way through to the dust collector and beyond. When it comes to fire and explosion, the risk is typically a spark at the ignition source. So prior to the dust collector, a spark arrestor of some sort is critical. If there is a spark, it’s your first line of defense to knock it out of the system before it gets to the dust collector.”
He adds that sometimes if you have enough distance from the source to the dust collector, that alone could be enough to put itself out if it makes it past the spark arrestor.
At the dust collector, angle baffles in the inlet plenum can oftentimes knock the dust down into the hopper, which is where it needs to go. They can also knock sparks down, too. Imperial features this type of baffle as standard on its machines.
Filter finds
For flammable or combustible dust, a fire retardant media is used so that if there is a fire, the cartridge media itself would just smolder and not create more flame.
The best type of dust collector for fire prevention is one that uses vertically mounted cartridges. Dust can build up on the top of horizontally mounted cartridges, which creates prime conditions if a spark were to occur. Horizontal cartridges also experience problems with filter life and complicated filter changes versus vertical cartridges.
Any overburdened filter, however, can no longer work efficiently and can also present a fire hazard. Some dust collectors, including the Shadow and Cmaxx, feature pulse cleaning technology to increase filter life.
“That process can go on for months or even years in some cases, depending on the application,” Frungillo says. “However, at some point the pulse cleaning becomes ineffective. The dirtier the cartridges get, the more pressure is required to move that air through the cartridges. The media becomes so embedded that it won’t pulse off anymore. When the airflow through the system reaches the differential pressure limit the manufacturer recommends, you know it’s time to change filters.”
A high-quality filter used with pulse cleaning will last about 12 to 18 months, Frungillo says. It’s best to use filters that don’t need to be changed as often to cut down on worker exposure to dust and to be more eco-friendly with fewer filters to dispose. “We like to make sure our customers get at least a year of life from one set of cartridge,” he notes.
Newer dust collectors that use cartridges are designed in such a way that filters are easily accessible and slide in and out of the housing readily. There are a few things that can go wrong with this procedure, however. Imperial Systems designed a new Safety Pentagon program to make filter installation safer and easier. The Shadow and Cmaxx dust collectors, along with DeltaMaxx Prime filters, include these new features – some of which customers were requesting.
“To change cartridges, the operator lifts the rail system bar, it drops down and they slide the cartridges out,” Frungillo says. “Problems can arise when you have more than one cartridge in a row. In other collectors in the marketplace, when you slide the top pans back in, if you push them in from the bottom they tend to overlap, or ‘ramp.’ If there is ramping, you won’t know it until dust is coming out through that dust collector and is blowing all over the place. That is why anti-ramping is critically important.
“We have anti-ramp lift rails that prevent that from happening as you put the cartridges in,” he continues. “This stops filter pans from overlapping each other and makes sure filters always line up correctly.”
Another safety feature is the lift rail door stop that prevents the door from closing if the lift rails are not locked in the proper upright position.
“After they put the pans in properly, they have to raise the lift bar to seal the cartridge gasket to the tube sheet,” Frungillo says. “That seal forces the air through the cartridge instead of bypassing it. If you don’t lift those rails up, you won’t have that seal and will bypass the cartridge.”
A grounding tab built into the collector frame bonds the cartridge pan to the collector, providing an added level of safety.
A fourth safety check, part of the Sure-Stop system, is a channel built into the cartridge top pan that matches up with a bar on the door. It must line up with the bar for the door to close. This is just to double check that the cartridges are seated properly.
The last point of the pentagon includes double gasket top pans for an extra layer of protection to ensure a double tight seal to the tube sheet for safe operation and proper filtration.
“All of these features are vitally important to prevent employees from inhaling dust, especially a hazardous dust,” Frungillo says. “We encourage customers to provide feedback, and they have indicated these are some areas of concern, especially the pan ramping issue. We actually had a customer mention the ramping problem recently in a competitor’s collector. Unfortunately, they didn’t discover the problem until it was too late and dust was escaping.”
Imperial showed them the anti-ramping feature of the Cmaxx and they loved it along with the other Safety Pentagon features in general, and they placed an order.
Final checks
Beyond using the right equipment and safety procedures, maintenance checks are a must to ensure the equipment is consistently in good working order. Evaluating the current equipment periodically to determine any upgrades in size and capacity is good practice, as well.
Frungillo recommends checking the solenoid valves and diaphragm valves, which control the air for the pulse cleaning, on a monthly basis for most plants. He also says that it’s key to make sure dry clean compressed air is being used. Finally, keep in mind that dust disposal is an important aspect of the dust collection process.
“Maintenance should check that the hopper is in good shape and sized properly,” he says. “You don’t want any issues, especially with flammable dust.”
With the proper dust hazard analysis done prior to choosing a system and the proper safety features being included on the equipment, along with the consistent preventive maintenance, it is possible to have a very safe dust collection system.
