Population based exposure assessment methodology for carbon monoxide: Development of a Carbon Monoxide Passive Sampler and Occupational Dosimeter
Two devices, an occupational carbon monoxide (CO) dosimeter (LOCD), and an indoor air quality (IAQ) passive sampler were developed for use in population-based CO exposure assessment studies. CO exposure is a serious public health problem in the US., causing both morbidity and mortality (lifetime mortality risk approximately 10-4. Sparse data from population-based CO exposure assessments indicate that approximately 10% of the U.S. population is exposed to CO above the national ambient air quality standard. No CO exposure measurement technology is presently available for affordable population-based CO exposure assessment studies.
The LOCD and IAQ Passive Sampler were tested in the laboratory and field. The palladium-molybdenum based CO sensor was designed into a compact diffusion tube sampler that can be worn. Time-weighted-average (TWA) CO exposure of the device is quantified by a simple spectrophotometric measurement. The LOCD and IAQ Passive Sampler were tested over an exposure range of 40 to 700 ppm-hours and 200 to 4200 ppm-hours, respectively. Both devices were capable of measuring precisely (relative standard deviation <20%), with low bias (<10%). The LOCD was screened for interferences by temperature, humidity, and organic and inorganic gases. Temperature effects were small in the range of 10°C to 30°C. Humidity effects were low between 20% and 90% RH. Ethylene (200 ppm) caused a positive interference and nitric oxide (50 ppm) caused a negative response without the presence of CO but not with CO.
The LOCD was used to monitor personal TWA CO exposures of 154 workshifts in a convention center during heavy use of propane powered forklifts. Performance of the LOCD was compared to an accurate standard method and against the commonly user Dräger CO diffusion tube. Exposure distributions were measured by the LOCD with a precision of about ±1 ppm. The Dräger tube was found to have a negative bias (20% at 8-hour TWA of 10 ppm, 40% below 10 ppm). Only one exposure exceeded the Cal/OSHA PEL of 25 ppm TWA for 8-hours. Workers at the loading docks had the highest 8-hour TWA exposures (50% >12.5 ppm). The LOCD is potentially valuable as a device for measurement of occupational CO exposures.