Masonry dust isn't just dirty and annoying. It is laden with tiny silica particles that pose a life-threatening hazard to workers who perform dust-intensive tasks, such as tuckpointing. If inhaled into the lungs, this dust can cause silicosis, a disabling and ultimately fatal lung disease. Respirable silica scars the lungs and reduces the ability to process oxygen. The affected person always feels short of breath.
Co-author Dr. William Heitbrink, a professor in the Department of Occupational and Environmental Health, University of Iowa, Iowa City, is well aware of the grim details of silicosis. “A 30-year-old mason was diagnosed with silicosis in December 2004 after tuckpointing most of the summer before,” reported Heitbrink. “The worker was only intermittently wearing a dust mask while on the job. He ended up wearing an oxygen mask.” (See “Dust Creates Life-Threatening Situation” sidebar.)
Heitbrink researches ways of controlling workers' exposure to silica and preventing silicosis. His most recent effort, funded through a grant from CPWR (The Center for Construction Research and Training), examined four industrial vacuum cleaners, each with a hose and hood that attaches to a right-angle mortar grinder. He and grad student Javier Santalla-Elias evaluated the equipment's airflow ability and efficiency of the vacuum cleaner filters.
Industrial vacuum cleaners have two basic designs to keep most of the debris off the final filters: one has bags to collect dust and debris and the other uses the principles of a cyclone to draw air through a filter and collect debris in a bucket at the bottom. (The schematics at left show these two types of vacuum cleaners.) Both use a final filter to collect the respirable dust. The final filters should have an efficiency of at least 99.9% for the smallest particles for both types of vacuum cleaners.
Most industrial vacuum cleaners use bags, with a final filter to catch what gets through. The equipment costs $400 to $700. Bags are typically $5 each, and need to be replaced two-to-three times per shift to maintain adequate airflow.
A few manufacturers make vacuum cleaners that use cyclonic pre-separation to collect most of the debris before the air travels through the final filters. A cylindrical baffle keeps dusty air flowing directly into the filter. The baffle and tangential inlet impart a twist to the airflow that causes the larger debris to hit the vacuum cleaner walls and fall to the bottom into a plastic bag or a pail. These vacuum cleaners cost from $1500 to $2000.