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Carbon Monoxide Occupational Sensor

A new lightweight, inexpensive, accurate carbon monoxide (CO) sensor and monitoring system have been developed by EETD researchers 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 on the market.

About 19,000 accidental CO poisonings were reported by the American Association of Poison Control Centers in 1995, but very little is known about the actual extent and distribution of CO exposures in the U.S. Five hundred to a thousand accidental deaths a year are attributed to CO poisoning, and it is the number one cause of unintentional poisoning in the U.S. Total numbers of poisonings are difficult to estimate because the effects of sub-acute CO poisoning are easily misdiagnosed as flu-like symptoms such as headaches and dizziness.

Limited Knowledge of Exposures

Because there has been no affordable way to accurately measure CO in the field, understanding about CO exposure risks is limited. 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.

Graphic of the carbon monoxide occupational dosimeter illustrating the various components

The LBNL/QGI carbon monoxide occupational dosimeter.

CO 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 CO concentrations are regulated outdoors by national and state ambient air quality standards, most people spend 90% or more of their time indoors, which is where elevated CO exposures are likely to occur.

How it Works

The LBNL/QGI Occupational CO Dosimeter (LOCD) consists of a square polystyrene vial less than two inches long. The device contains a CO 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, CO diffuses to the sensor at a constant rate over the sampling period, typically an eight-hour work shift. 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 CO the sensor absorbed. A single LOCD can be reused many times.

The lifecycle of a dosimeter.

When the user removes the plug, air flows into the diffusion tube at a constant rate (2). The CO in the air reacts with the sensor at the end of the tube, slowly turning it blue. The color change as measured by placing the device into a spectrophotometer, before and after use, indicates the exposure to carbon monoxide (1,3).

To prove that the sensor works accurately in the field, the EETD research 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 firm. During the set-up of shows in the Center's 442,000 square feet of exhibition space, 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 gave the 60 workers who volunteered for the study the new occupational sensor, which was clipped to the workers' lapels. They were also given commercially available diffusion tubes, used to measure CO exposure. The 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 underreported CO exposures by an average of about three parts per million. The results show that the new device represents a major improvement over current measurement technology.

Worker CO exposures were almost all below the strict Cal-OSHA occupational standard of 25 parts per million. One worker whose exposure exceeded the standard probably received excessive exposure from operating a forklift in an enclosed semi-truck trailer. QGI is now looking for private-sector partners for distribution and plans to manufacture and market the CO occupational dosimeter.

— Allan Chen and Michael Apte

For more information, contact:

  • Michael Apte
  • (510) 486-4669; fax (510) 486-6658

"A New Carbon Monoxide Occupational Dosimeter: Results from a Worker Exposure Assessment Survey," by Michael Apte, Katherine Hammond, Lara Gundel, and Daniel Cox, will be published in the Journal of Exposure Analysis and Environmental Epidemiology.

This research was sponsored by the Department of Energy under an Office of Science-sponsored Cooperative Research and Development Agreement. An early phase of the research was funded by the Office of Building Technologies, State and Community Programs.

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