Projects - Ventilation
Body Burden of Nitrous Oxide
The purpose of this study was to determine the relationships between nitrous oxide concentration in ambient air, worker urine, and exhaled breath in dental operatories. The study also evaluated the effectiveness of a ventilation intervention in decreasing occupational exposure levels to nitrous oxide. Participants consisted of 3 dentists and 3 dental assistants with monitoring being performed both before and after intervention. A total of 46 samples were collected over a six-month period. Breath and urine samples were taken before and after the dental procedure, and passive dosimeters were worn during the entire procedure. The ventilation intervention did not result in a significant decrease in nitrous oxide exposures. There was a significant correlation between adjusted change in breath and urine concentrations, adjusted change in breath and ambient air concentrations, and change in urine and ambient air concentrations.
Hard Metal Tool Ventilation Intervention Pilot Project
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.
Ventilation Brochure: Ventilation Control for Tool Manufacturing and Resharpening Shops
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.
The Efficacy of Local Exhaust Ventilation for Controlling Dust Exposures During Concrete Surface Grinding
This study assessed the effectiveness of a commercially available local exhaust ventilation (LEV) system for controlling respirable dust and crystalline silica exposures during concrete grinding activities. Three different dust collection shroud configurations were tested during surface grinding by cement masons at six commercial construction sites. Data obtained with a direct reading respirable dust monitor were adjusted to remove non-work task-associated dust exposures and were subsequently used to calculate the exposure reduction achieved. The application of LEV resulted in a reduction in the overall geometric mean respirable dust exposure from 4.5 to 0.14 mg/m3, a mean exposure reduction of 92%. Despite the effective control of dust generated during surface grinding, 22% of the samples collected while LEV was being used were greater than the 8 hour time-weighted average permissible exposure limit, and 26% greater than the threshold limit value for respirable crystalline silica.
Croteau G., M. E. Flanagan, J. Camp and N. Seixas..The Efficacy of Local Exhaust Ventilation for Controlling Dust Exposures During Concrete Surface Grinding. Annals of Occupational Hygiene 2004 48(6):509-518.