New Carbon Monoxide Sensor Developed For Occupational Use

May 17, 1999

A new lightweight, inexpensive, accurate carbon monoxide (CO) sensor and monitoring system has been developed by scientists at the U.S. Department of Energy's Lawrence Berkeley National Laboratory and Quantum Group Incorporated (QGI, San Diego).

Field testing of the new device at the Moscone Convention Center in San Francisco has shown that it is more accurate than the personal CO monitors currently available on the market.

"About 19,000 accidental carbon monoxide poisonings were reported by the American Association of Poison Control Centers in 1995," said Michael Apte, a scientist in Berkeley Lab's Environmental Energy Technologies Division, 'but very little is known about the actual extent and distribution of carbon monoxide exposures in the United States. Five hundred to a thousand accidental deaths a year are attributed to carbon monoxide poisoning, and it's the number one cause of unintentional poisoning in the United States."

Total numbers of poisonings are also difficult to estimate, according to Apte, because the effects of sub-acute CO poisoning are easily misdiagnosed as flu-like symptoms such as headaches and dizziness.

There is limited understanding about carbon monoxide exposure risks, partly because there has been no affordable way to accurately measure CO in the field. Some of the current methods of measurement require expensive, heavy equipment or unwieldy air bag samplers. Others are relatively inexpensive and lightweight, but they are not accurate or sensitive enough to provide credible quantitative results for a large number of sites.

To fill this gap in technology, Berkeley Lab and QGI worked together to develop the new CO sensor, which can clip onto a person's clothing. It can be used as an occupational dosimeter, which measures a worker's time-weighted average exposure to CO over an eight-hour period, or as a residential passive sampler measuring time-weighted average exposure in a home or office over a one-week period.

Carbon monoxide poisonings are most often caused by exposure to excessive indoor levels of the gas. Faulty combustion appliances such as gas stoves or gas-burning water or space heaters can raise CO levels into the danger zone, as can automobile exhaust in enclosed spaces. "Although carbon monoxide concentrations are regulated outdoors by national and state ambient air quality standards, most people spend 90 percent or more of their time indoors, which is where elevated CO exposures are likely to occur," said Apte.

The LBNL/QGI Occupational CO Dosimeter (LOCD) consists of a square polystyrene vial less than two inches long. The device contains a carbon monoxide sensor made of palladium and molybdenum, a diffusion tube to control the rate at which CO is sampled, and a cap to seal the system.

"When the user removes the cap, air flows into the diffusion tube at a constant rate over the sampling period, typically an 8-hour work shift," Apte explained. "CO in the air reacts with the sensor at the end of the tube, turning it from yellow to blue in proportion to CO exposure. Analysis is simple-the device is placed into a standard lab spectrophotometer which, by measuring its color change, instantly indicates how much carbon monoxide the sensor absorbed. A single LOCD can be reused many times."

To prove that the sensor works accurately in the field, Apte and his Berkeley Lab team conducted a study of the CO exposure of workers at San Francisco's Moscone Convention Center in cooperation with Crawford Risk Control Services, an Oakland (CA) firm.

During the set-up of shows in the Center's 442,000 square feet of exhibition spaces, some 40 propane-powered forklifts are active almost continuously throughout the building. Diesel trucks also drive up to interior docks from the outside.

Before the study, Moscone Center management had already put a number of safety measures in place to reduce worker and building occupant exposures to CO, including installing catalytic converters on the forklifts and modifying the building's ventilation system to reduce exhaust concentrations.

The Berkeley Lab team provided 60 workers who volunteered for the study with the new occupational sensor, which was clipped to the workers' lapels. They were also given commercially available diffusion tubes, a current method used for measuring CO exposure. The Berkeley Lab team also measured CO levels using traditional methods, including air bag samples analyzed in an EPA-approved lab procedure, and real-time CO personal monitors containing an electrochemical sensor. Exposures were measured over a three-day period.

The tests showed that the LOCD measured average workshift CO exposures accurately to within one part per million. The commercially available diffusion tube under-reported CO exposures by an average of about 3 parts per million.

"The results show that the new device represents a major improvement over current measurement technology," said Apte.

Worker CO exposures were almost all below the strict Cal-OSHA occupational standard of 25 parts per million. One worker who exceeded the standard probably received excessive exposure from operating a forklift in an enclosed semi-truck trailer, Apte said.

QGI is now looking for private-sector partners for distribution and is developing plans to manufacture and market the CO occupational dosimeter. A paper summarizing this research, "A New Carbon Monoxide Occupational Dosimeter: Results from a Worker Exposure Assessment Survey," will be published in the Journal of Exposure Analysis and Environmental Epidemiology. Its authors are Apte, Katherine Hammond, Lara Gundel and Daniel Cox.

Berkeley Lab scientists developed the diffusion tube technology used in the LOCD; the CO sensor technology was developed by QGI and validated by Berkeley Lab. The Department of Energy funded the project under an Office of Science-sponsored Cooperative Research and Development Agreement (CRADA). An early phase of the research was funded by the Office of Building Technologies, State and Community Programs.

DOE's Laboratory Technology Research (LTR) program, which sponsored the LOCD work, supports high-risk multidisciplinary research partnerships to investigate challenging scientific problems of interest to DOE and industry. In a recent LTR Industry Partner Survey involving over 100 companies, 91 percent of the companies said they had benefited from partnering with the laboratories and 97 percent of the companies said they would like to partner again with one of the labs on a future research project.
Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified research and is managed by the University of California.

DOE/Lawrence Berkeley National Laboratory

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