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.

Two designs

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.