|
| Cab filtration and pressurization systems prevent dust from penetrating cabs reducing respirable dust exposure |
Description of Problem
Cabs on mobile equipment at surface mines, particularly older equipment, provide little, if any, dust protection. Many cabs are not properly designed for dust control in the first place. As the cabs age, the seals around the doors and at locations where controls enter the body of the cab degrade. This allows dusty air to enter the cab. In addition, for a cab to provide meaningful dust protection, positive air pressurization within the cab is needed. Few older cabs, and many new cabs, cannot maintain this positive air pressurization. Mobile equipment (such as drills, graders, loaders, dozers, and trucks) operate at surface mines and construction sites throughout the United States. Workers in the cabs are often overexposed to respirable dust and silica. For example, data from the Mine Safety and Health Administration (MSHA) have shown a 9% silicosis rate in central Pennsylvania surface coal miners. Many of these miners work in cabs.
Research and Development Activities
NIOSH began collaborating with MSHA, mine operators, and equipment manufacturers to find the most cost-effective ways to improve dust protection in cabs. While most of this work was done at actual field sites, some of it included lab studies at the Pittsburgh Research Laboratory and at cooperator facilities. In nine NIOSH field demos, economical and viable ways to improve dust protection for workers in enclosed cabs have been shown. NIOSH researchers, in partnership with mining companies and equipment suppliers of filtration systems and assisted by MSHA, showed that cabs providing almost no dust protection could show major improvements when simple changes were made to the cab. The two most important factors needed to achieve low dust levels were an efficient air filtration system (high-efficiency intake and recirculation filters) and an effectively sealed (tight) cab for positive inside cab pressurization. In most cases, the overall cost of the improvements was less than $5,000. In addition, the introduction of efficient filtration systems on the cabs was usually accompanied by putting good air conditioning and heating systems on at the same time. Miners are thus more comfortable in their cabs and are more apt to keep the cab doors closed. This further protects them from outside dust. Results of the field demos showed that a 90% reduction in respirable dust could be achieved if proper cab filtration was applied and air leaks in the cab were reasonably sealed by replacing door seals and patching up holes in the body of the cab. In most cases, the improvements yielded a cab average silica dust level below 100 µg/m3 (the silica or quartz permissible exposure limit) at moderate to high outside dust levels.
R&D Outputs and Transfer Activities
NIOSH published these findings in peer-reviewed journals, trade journals, and conference proceedings. Trade journals and conferences were selected to reach the appropriate target audience. Technical presentations were made at conferences and at mine corporate safety and health meetings A video that gives guidelines for effectively protecting cabs was also produced. The video is now available from the MSHA Catalog of Training Products for the Mining Industry (http://www.msha.gov/TRAINING/prodintr.htm). Hundreds of copies of the video have been distributed to mining companies around the world. Major unions, such as the United Steelworkers of America and the International Union of Operating Engineers, have requested copies of the video. Trade organizations such as the Industrial Minerals Association-North America and the National Stone, Sand & Gravel Association, have also asked for the video.
Description of Intermediate Outcome
One project collaborator, a filter supplier, saw an aftermarket develop for the use of its retrofit intake filtration pressurization systems for mining and related (construction) equipment cabs. While NIOSH has not been able to get any sales numbers, the supplier continues to offer the systems after several years and continues to work with NIOSH in further improving cab dust control.
MSHA dust sampling data from surface mines now show a meaningful reduction in the fraction of workers overexposed to silica. From 1991 to 2004, drill operator exposures fell by 30%, bulldozer operators by 46%, scraper operators by 75%, refuse truck drivers by 75%, and front-end loader operators by 33%. The overall reduction was 40%. While we do not have a good feel for how many cabs have been changed because of this research, we believe, based on industry and labor interest in the findings, that improved cabs account for some of the improvement. Although engineering controls developed through NIOSH research have clearly played a role in this reduction, the education of workers and the enforcement of dust standards have also been essential. This cab research, along with other NIOSH research on surface mine dust control, have provided industry, labor, and MSHA with control technologies that have contributed to this reduction. Surface coal miners and heavy construction workers can all benefit from this NIOSH-developed cab technology.