Avoiding the Silica Dust-up
Sometimes, it's more than throwing water on the problem.
Today, with rising concern for crystalline silica in everything from granite to quartz hard surfaces and the silicosis it can bring to workers’ lungs, the average shop has become a veritable water world with a heavy emphasis on wet fabrication.
But must a shop go all wet? Is wet fabrication the sole answer to keeping silicosis at bay? The answers to both are a spirited maybe. Water isn’t the only method for protecting workers from crystalline silica in the air, but where it is, it isn’t necessarily effective unless everyone follows good housekeeping practices. The silicosis push began in 2018 when the federal Occupational Safety and Health Administration (OSHA) adopted rules concerning the amount of permissible crystalline silica in the workplace and began enforcing them. The only way to know whether a given shop met the new mandated levels was to have it tested. And, for many companies, the best (and least-expensive) way to have a shop tested is to turn to a different branch of the regulators.
“Each state or locality has two different OSHAs,” says Mark Meriaux, accreditation and technical manager for the Oberlin, Ohio-based Natural Stone Institute. “There’s the enforcement arm – the guys that surprise you – but then there’s the consultative offices. They have different roles, and the consultative office is strictly there to do onsite consultations and help shops learn to be safer.” That means doing things like shop walk-throughs, noise monitoring and air monitoring -- all of which are free -- whether the work is done by a state government or the federal agency. Some insurance carriers also have staff hygienists and safety personnel who will do safety audits. And there are also private industrial hygienists who can be hired to do testing.
Once a shop has those numbers in hand, it can provide meaningful data when the guys that surprise you come to the door, and provide a basis for identifying troubled areas and cleaning them up. Of course, any change to the shop means more testing. “The OSHA standard says anytime there is an expected change or known change in exposures,” says Meriaux. “I read that that whenever a change is made in the shop, whether it’s a process change, or an equipment change. Many shops find it’s beneficial to them to do this annually, or every other year.” And the good news for many shops is that wet fabrication with automated equipment is a good line of defense against crystalline silica, regardless of what you’re cutting and shaping. Dr. Chaolong Qi, a professional engineer working in the Cincinnati-based Division of Field Studies and Engineering for the National Institute for Occupational Safety and Health (NIOSH), says shops using large equipment, such CNC waterjets and bridge saws, are likely not exposing their workers to dangerous levels of silicate. “They have two advantages,” notes Qi, who’s also a lieutenant commander in the United States Public Health Service (USPHS). “One is that they use a lot of water to suppress the dust, so they don’t have a lot of particles becoming airborne. And, because the computers that control these machines are stationed away from the operation, workers operating the equipment are away from the dust that is generated.” Jeff Dykstra, vice president of sales and marketing for Knoxville, Tenn.-based BB Industries LLC, puts it slightly differently. “There can still be dangerous levels [of crystalline silica] in an all-wet shop,” Dykstra says. “Water greatly helps suppress the dust and silica by turning it into a slurry that will fall to the floor. However, it’s dependent on the material being cut, the tooling being used, and the amount of water involved.”
(Graphic courtesy NIOSH)
“The best thing is to control and remove the silica dust from the source.”
Dr. Chaolong Qi
Division of Field Studies and Engineering NIOSH
Mitigating Air Quality
The material being cut certainly plays a role in the presence of crystalline silica, with some natural stones having less than 10% to quartz with up to 90% concentration. If someone is doing hand-fabrication, the tool and the amount of water also make a difference. Qi says the advantages that larger machines have in limiting exposure are missing with benchtop machines that do cutting and edge-profiling, or by using a handheld grinder or polisher, “One issue is how effective the stone is being wetted,” he says. “And the workers are very close to the source of the dust; it’s right there. That’s why the workers using handheld tools can get into dangerous levels of exposure.” He uses grinders as an example. They typically have two methods of getting water to the work surface: a spray nozzle or a central water feed. With the spray nozzle, Qi says because the tool is being moved left-and-right and up-and-down. Unless the worker is paying close attention, the water spray might not hit the entire work area. However, the central water feed is also often inadequate. “By channeling the water through the center inside the tool, you limit the water-flow rate,” he explains. “You have a small amount of water coming out, and the grinding disk works like a fan, quickly drying the spot. If the water is not wetting the spot, you end up with some dry fabrication in the process.” One option, of course, is to increase the amount of water involved in the fabrication. Qi says in preliminary tests he’s done with grinders, simply supplying additional water to flow toward the edges of the work surface gently and continuously can reduce the amount of exposure to crystalline silicate below OSHA standards. That’s not to say that everything must be done underwater, either. Long before water became ubiquitous in stone shops, many operations offered their employees some protection through enhanced air filtration. And, while an enhanced HVAC system in a large shop may do little but blow dusty air, there are other options. “Shops should help mitigate risk with air filtration, dust extractors and the correct PPE,” says BB Industries’ Dykstra. “Even with the use of water it’s imperative to maintain air quality.” Dykstra mentions solutions such as HEPA (high-efficiency particulate air) filters, dust walls or enclosed booths. Hand tools with HEPA filters have become much more common in recent years and are a must for any touch-up work done during an installation. NIOSH’s Qi isn’t a fan of ceiling mounted dust extractors, mainly because it’s difficult to get workers to use them. “It’s not user-friendly,” he says. “They’re working on a slab that’s sitting on a workbench, and as they walk around, they’re not going to drag that dust-extraction arm with them.” Getting higher marks from the researcher are things such as wet-drip curtains and enclosed booths that are going to contain airborne particulate dust within a limited area of the shop. “They work but they need some additional evaluation,” Qi says. “You have to have a certain airflow velocity to be able to move the emission into it right. The rule of thumb is 100 feet-per-minute airflow velocity. That’s not just for this industry, but for many industries, such as industrial paint booths. “And, it’s important to train the workers on using such dust control equipment, especially, especially on maintaining their position around the workbench so they are not between the dust generation source and the dust control equipment.”
Which "Wet" Covers Best?
With spray-nozzle-wetting, although a good amount of water continuously flows out of the nozzle, it can easily miss the grinding area, thus failing to keep the area wet consistently. This leads to occasional dry-grinding and higher silica-dust exposure. (Video courtesy NIOSH)
With center-water-feed-wetting, although water continuously flows out of the grinder, it isn’t adequate to keep the grinding surface wet all the time, and dust plumes from grinding are noticeable. (Video courtesy NIOSH)
Sheet-water-wetting providing additional water to form a sheet to continuously cover the grinding surface. Preliminary NIOSH research found workers’ exposure can be reduced to levels below the OSHA standard by using this method. (Video courtesy NIOSH)
Mitigating Air Quality
Keeping crystalline silica out of the air or limiting the areas where it might be airborne is recognized as the best way for dealing with the problem … and, yes, water is the best way to do that. But it’s only as effective as a shop’s housekeeping methods, and many shops don’t clean up the shop floor during work or at the end of the day. “The discharge from fabricating equipment is almost always a ‘splashdown’ event where the water and stone sludge spills onto the floor on its way to a trench system and pit, assuming the fabricator has trenches,” says Ross Perry, an engineer with Hampton, N.H.-based Water Treatment Solutions. “The failure to wash down equipment and the shop floor into the trench and pit system means the slurry will dry on the shop floor and eventually become airborne.” While Perry notes that some large fabricators in Europe have special crews to do shop housekeeping during the workday, at a minimum it’s important to commit to having someone dedicated to making sure the work gets done. It’s also critical to have a water system that’s sized properly so the pit doesn’t overflow and there’s sufficient clean – emphasis on clean – water available to do the cleanup once the equipment is turned off. “It’s a mindset that says, ‘I have to clean the shop and wash down everything at the end of the day,” he says. “I would say 90% of shops don’t do this kind of housekeeping, and they’ve not necessarily filthy, but it doesn’t take a lot of dust to create a crystalline-silica hazard.” There’s another good reason to do daily cleanup. Once that water and stone sludge is into the water recycling system, there’s little that needs to be done to get it out of the shop safely. Or, as Qi says, “Most of the water-treatment equipment used in this industry should be very effective in removing silica dust from the water.” Perry notes that filter-press systems leave a residue like potter’s clay which can easily be removed to a covered dumpster outside the shop. Other systems, which can create what he calls “a housekeeping complication” are those that leave the residue in bags which need to be dewatered before disposal. “They start with a very high level of water and the bags have to sit and weep, or drip-dry, if you will,” he says. “You can end up with multiple bags drying out and they leak. The best thing to do is put them in an area that doesn’t have high foot traffic, because periodically you’re going to have to clean that up or you’ll create another source for crystalline silica.” Sludge disposal may be one area where shops might want to evaluate and determine whether to have the employee wear a respirator for additional protection. However, NIOSH’s Qi says in the agency’s hierarchy of controls, the preference among all the tasks with potential exposure always is to control exposure levels through engineering controls – if possible. The “if” comes because a shop needs to know its numbers. “If we and the employer can document that the exposure of their workers is consistently below the OSHA standard, then they are not mandated to wear respirators,” he says. “The best thing is to control and remove the silica dust from the source.”
Vacuum-based filtration units pull loose contaminants from the shop by negative airflow. Models range from small portable units with individual-worker collection hoses to large workbench-sized structures like this Weha 13' booth. (Photo courtesy B•B Industries)
Full water-filtration systems take contaminants like crystalline silica out of the flow, but it's important to make sure that dried residue doesn't end up in the shop environment. (Photo courtesy Water Treatment Solutions)
And, yes, you can cut dry, but you'll need to enclose the cutting tool. This Ecoguard G guard from Alpha Professional Tools® needs to be connected to a negative airflow, such as a shop vacuum. (Alpha Professional Tools®)