This study sought to characterize the degree to which employees in Washington state are exposed to hard metal particulates, and the degree to which exposed workers are at risk of developing asthma or hard metal lung disease (HMLD). The project involved intensive exposure monitoring and health effects tests among potentially exposed workers in 11 shops. Exposure monitoring included time-weighted average (TWA) measurements of particulates, cobalt, and chromium. Health effects were measured by questionnaires and spirometry. Cobalt exposure levels were significantly associated with the cobalt concentration in metal-working fluid, wet or dry grinding of tungsten carbide, brazing or welding of tungsten carbide, brazing or welding of stellite, and type of job.
Simcox NJ, Stebbins A, Guffey S, Atallah R, Hibbard R, Camp J. Hard metal exposures. Part 2: Prospective exposure assessment. Appl Occup Environ Hyg. 2000 Apr;15(4):342-53.
This project characterized the effectiveness of a new ventilation system in controlling worker exposures to hard metals over a one-year period. A prospective study design was employed at a hard metal tool resharpening shop, and included repeated measurements of hard metal concentrations and ventilation parameters. Before installation of the ventilation systems, cobalt exposures ranged from 10 to 707 ug/m3, with seven of eight workstations exceeding the permissible exposure level (PEL). Eighty-four personal air samples were collected after the installation of the ventilation, an average of 11 samples per worker. Study findings indicated that worker exposures to metals were controlled in most cases, especially for hoods that obtained higher airflow levels. Repeat measurements showed that variability in worker exposures was not explained by airflow measurements alone, and that hood design, worker acceptance, and use and maintenance of the ventilation system are important factors in reducing worker exposures.
Guffey SE, Simcox N, Booth DW Sr, Hibbard R, Stebbins A. Hard metal exposures. Part 1: Observed performance of three local exhaust ventilation systems. Appl Occup Environ Hyg. 2000 Apr;15(4):331-41.
Results from studies of hard metal exposure in Washington State showed that workers in tool manufacturing and resharpening shops with many machines close together, received the highest exposures. Wet grinding, dry grinding, brazing, and welding tungsten carbide led to higher cobalt exposures. Brazing and welding with stellite also led to higher cobalt exposures. Using metalworking fluids on tungsten carbide led to higher levels of airborne cobalt. The best way to reduce these exposures is to use adequate local exhaust ventilation. This booklet developed by the Field Group provides basic information on designing, installing, testing, and maintaining local exhaust ventilation systems for hard metal machining shops.