The shrouds partially enclose the bit and have a connection for a vacuum system. When a vacuum system is connected to the shroud, air is drawn into the shroud and past the bit, capturing dust and silica near the point of dust generation. These systems capture dust and silica near the source, reducing concentrations in the worker's breathing zone and his or her exposure. For continuous use, a respiratory protection program and respirators may still be required.

• Independent published studies have found a risk reduction.
• Manufacturers, vendors, or worksites have reported a risk reduction.
• Safety and health experts believe there is a risk reduction.

In evaluations of engineering controls, Shepard et al. observed, on average, a 94 percent reduction in respirable silica during the use of a Bosch rotary hammer drill with two types of hood and two types of dust extractor. While exposures to respirable dust during use of the local exhaust ventilation systems were below the OSHA Permissible Exposure Limits (PELs), they approached or exceeded the NIOSH Recommended Exposure Limits (RELs) and ACGIH Threshold Limit Values (TLVs) for respirable silica. In spite of significant reductions in respirable silica exposure while using local exhaust ventilation, a respirator may still be necessary to reduce silica exposures to less than the REL and TLV when drilling concrete.

Vacuum dust control systems can have either positive or negative effects on productivity, but definitely improve the quality of the work by capturing large amounts of airborne dust, which allows a cleaner, more efficient means of drilling into concrete.

• Manufacturers or vendors have reported an increase in productivity.
• Safety and health experts believe there is an increase in productivity.

In addition to limited information on productivity from manufacturers or independent studies, safety and health experts believe the use of these controls may lead to an increase in productivity because controls will reduce dust-related hazards and provide a cleaner work environment.

Bosch 3/4-inch SDS-plus Rotary Hammer with Dust Collection
For purchasing information visit http://www.boschtools.com or contact 1-877-267-2499 or by e-mail
Other vendors: Ace Tool, Inc., mytoolstore.com and Ohio Power Tool

Bosch Airsweep™ Wet/Dry Vacuum
For purchasing information visit http://www.boschtools.com or contact 1-877-267-2499 or by e-mail

Ventilation for construction tools is often misunderstood. There are some key concepts that can help:

• The vacuum must be located as close to the dust generation as possible to be effective. A shroud may be needed to contain the dust so the vacuum can capture it. The shroud must be kept as close to the work surface as is practical to provide adequate dust capture. The shroud should be connected to the vacuum with 2-inch, or greater, diameter tubing with a relatively smooth interior.
• The particles that can do the most damage in the lungs are small enough to penetrate the filters found on many shop vacuums. Additionally, some inexpensive shop vacuums pull the dust through the motors, which can destroy the vacuum on really dusty jobs, eliminating any initial cost savings.
• For dust containing harmful particles like silica, it is important to use as high efficiency filters as practical. The best available are called HEPA (High Efficiency Particle Air) filters because they capture 99.97% of the most penetrating particles. But HEPA filters also create a greater pressure drop and decrease in air flow rate because it is more difficult to pull air through these denser filters so capture velocity may be reduced. They also require pre-filters to extend the life of the HEPA filters, which are more expensive than other filters. Studies have shown that it may be more effective to direct the exhaust air out of the work area than to attempt to add HEPA filtration for a tool where it isn't an integral part already. HEPAs require routine cleaning or disposal of prefilters, which can cause exposures to those performing the filter maintenance.
• For operations that generate large amounts of dust, cyclonic collection units, if available, may be the best solution. Rather than require more expensive filters and bags that must be frequently changed, cyclonic units spin the particles and drop them into cheap bags that need to be replaced far less frequently because loading of the bags does not cause a pressure drop.
• Vacuum performance must be monitored on a regular basis. A vacuum with a pressure gauge allows for frequent and easy monitoring of air flow. For high dust generating tasks, dust caked on the filter may reduce flow to a level where it no longer provides adequate dust capture. Automatic and manual filter shakers, coarse pre-filters and cyclonic collections units are available with some vacuums and may help maintain the air flow rate.