Carbon monoxide is a colorless, odorless gas generated by combustion processes such as those found in heating units and internal combustion engines. Examples of workplace sources of carbon monoxide include propane and gasoline-powered forklifts, temporary heating units and gasoline-powered pressure washers, compressors, pumps, and other tools and small engines. Excessive exposure to carbon monoxide results in human tissue being deprived of oxygen. Carbon monoxide overexposure may cause chronic effects such as heart damage, acute effects such as headaches, or in extreme cases, death by asphyxiation.

The following permissible exposure limits (PEL) and more information about carbon monoxide can be found at www.osha.gov.

• OSHA PEL: The current OSHA PEL for carbon monoxide is 50 parts per million (ppm) parts of air (55 milligrams per cubic meter (mg/m³)) as an 8-hour time-weighted average (TWA) concentration [29 CFR Table Z-1].
• NIOSH REL: The National Institute for Occupational Safety and Health (NIOSH) established a recommended exposure limit (REL) for carbon monoxide of 35 ppm (40 mg/m3) as an 8-hour TWA and 200 ppm (229 mg/m³) as a ceiling [NIOSH 1992].
• ACGIH TLV: The American Conference of Governmental Industrial Hygienists (ACGIH) has assigned carbon monoxide a threshold limit value (TLV) of 25 ppm (29 mg/m³) as a TWA for a normal 8-hour workday and a 40-hour workweek [ACGIH 1994, p. 15].

Carbon Monoxide Monitoring
There are three types of carbon monoxide monitoring devices that are most suitable for determining worker exposure to carbon monoxide.

Electronic sensing instruments display a digital readout of carbon monoxide in parts per million and are the most accurate, although they are expensive and difficult to maintain. They need to be calibrated frequently to ensure their accuracy.

Colorimetric detector tubes with a hand pump can be used to sample over a time period of about 2 to 12 minutes with an error factor of plus or minus 25%. These tubes change color based on the concentration of carbon monoxide in the air and can be read in parts per million of carbon monoxide. This sampling method involves very low maintenance and is simpler to use. The detector tubes typically have a shelf life of 12 to 18 months.

Passive dosimeter tubes are similar to the colorimetric detector tube that is used with a pump. Carbon monoxide levels are indicated by a color change in the tube, and the tube provides readings in parts per million hour with an error factor of plus or minus 25%. The passive dosimeter tube is useful for determining TWA exposures and sampling over time periods of several hours. Once the seal is broken, the tube can be attached to a worker's collar or lapel. The passive dosimeter tubes typically have a shelf life of 12 to 18 months.

Propane and gasoline-fueled forklifts could be a huge factor in high levels of carbon monoxide. Forklifts should be properly tuned by a knowledgeable technician. The technician should have a good understanding of how the fuel system works and be able to decipher the readings from an accurate Exhaust Analyzer in order to reduce the levels of carbon monoxide. The analyzer should be approved for direct exhaust gas stream measurements. A common mistake is the use of an ambient air carbon monoxide detector—this type of device is not designed for highly concentrated tailpipe emissions tests and will give you very inaccurate readings.

The best way to combat high levels of carbon monoxide is to have your forklift tuned up on a regular basis. Thompson & Johnson is equipped to help you provide a cleaner air environment for your employees.