When trying to prevent employee exposure to silica dust, recognized as a deadly hazard for nearly a century, the technology has improved and the dangers are more clearly quantified, but the National Institute for Occupational Health may have found a simple solution for cash-strapped contractors using fiber-cement siding in construction and renovation.
This comes amid a major growth period for the building material, which through just four main ingredients—water, wood pulp, fly ash (or silica sand), and cement—is more durable and more cost effective than wood.
Considering this rapid growth—from 1991 to 2010, the market share of fiber-cement siding has climbed from 1% to 13% (wood dropped from 38% to 8%)—more workers are (and will be) exposed to dust generated during the cutting process, which for optimal efficiency requires a power saw.
As explained in the 1935 study, as well as thousands since, cutting silica without proper safety measures taken is dangerous and could leave employees and employers liable for short- and long-term consequences.
Yet a recent NIOSH study may have found a practical solution: Attach a standard shop vacuum to a dust-collecting circular saw.
“Our study showed that connecting a regular shop vacuum to a dust-collecting circular saw provides a simple and low-cost solution to the problem of silica exposure from cutting fiber-cement siding,” said the study’s lead researcher, Chaolong Qi, PhD. “Implementing this intervention, with a tool these workers are already likely to have available to them, can protect workers from a potentially deadly disease.”
Through the following two-phase test, researchers were able to measure the effectiveness of the practical solution.
- First, in a laboratory setting, researchers looked at three dust-collecting circular saws connected to an external vacuum. Findings indicated that the circular saws, used in conjunction with an external vacuum cleaner that had a cyclone pre-separator and a high-efficiency particulate air (HEPA) filter cartridge, removed at least 81% of the hazardous dust even with an air flow rate lower than that found in a typical shop vacuum.
- To validate the effectiveness of a regular shop vacuum at reducing dust, researchers conducted further studies at construction sites where workers were cutting fiber-cement siding. Results of the field studies showed that a regular shop vacuum controlled the amount of silica-containing dust in the air to well below the NIOSH recommended exposure limit for crystalline silica (0.05 mg/m3).
NIOSH Recommended Controls
Of course, to actually make this solution effective, NIOSH recommended the following controls to minimize exposure:
- Effective Shop Vacuum: Use a shop vacuum with an air-flow rate of about or higher than 30 CFM.
- Adequate Hose: The hose that connects the shop vacuum to the saw should be of sufficient size (1.25-inch or greater inner diameter) to allow adequate airflow for the capture and transport of saw dust. To maximize efficiency, the hose should only be as long as necessary and be kept as straight as possible.
- Filter and Bag: A high efficiency disposable filter bag can be used as a prefilter in the shop vacuum to capture most of the dust. This will prolong the life of the filter cartridge that captures the dust that goes through the filter bag.
- Intelligent Vacuum Switch: The shop vacuum and the circular saw can be plugged into an intelligent vacuum switch. This eliminates the distraction for the operator of turning on and off a dust collection system and ensures the vacuum is running while operating the saw, avoiding uncontrolled dust release
Circular Saw and Blades
- Must Have Dust Collection Container or Hood: Use only circular saws with a built-in dust collection container or shroud that functions as a hood, partially encloses the saw blade, and can be easily connected to the LEV system.
- PCD Blades: Use polycrystalline diamond-tipped (PCD) blades designed to be used to cut fiber-cement siding. Compared to Carbide-tipped blades, they provide a cleaner cut of the siding, exhibit a longer wear life, and may reduce the dust generated.
Enhancing Effectiveness with Best Practices and Respirators
Of course, because something is labeled adequate doesn’t mean that you shouldn’t enhance the safety in your workplace. NIOSH recommends the use of half-facepiece particulate respirators with N95 or better filters for airborne exposures to crystalline silica at concentrations less than or equal to 0.5 mg/ m3 [NIOSH 2008].
Further, employers are required to follow Occupational Safety and Health Administration (OSHA) Respiratory Protection Standard (29 CFR 1910.134) if respiratory protection is used.
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