Carbon monoxide and nitrogen oxides from forklifts and other fueled equipment can create dangerous conditions

December 1996

The Department of Labor & Industries has conducted numerous inspections as the result of near-fatal exposures to carbon monoxide in industries using forklifts in warehouses and freezers.

Carbon monoxide (CO) is a colorless, odorless, tasteless gas produced during the incomplete combustion of carbon containing substances (paper, wood, and petroleum products). Forklifts powered by gasoline, natural gas, or propane may emit dangerous levels of CO. Because CO has no warning properties, employees can be exposed to high levels without realizing that there is a problem. This also applies to other gasoline, natural gas, diesel, or propane fueled vehicles, power tools, or other equipment used indoors, such as floor buffers, pressure washers, ice cleaners used to resurface ice rinks, or unvented space heaters.

In November 1994, three employees at a food processing plant were rushed to the hospital complaining of splitting headaches, blurred vision, and dizziness. An investigation by the Department revealed that the employees had been working in a freezer for one hour using a propane forklift to arrange pallets. The forklift produced levels of CO greater than the allowable exposure limit, causing CO poisoning among the workers. In a separate incident at a warehouse facility in January 1996, employees complained of nausea, dizziness, and blurred vision. An investigation revealed that a propane forklift had produced CO levels above the allowable limit. Other similar incidents have occurred throughout the state.

Exposure to CO decreases the ability of the blood to carry oxygen to the tissues. Inhalation of carbon monoxide may cause headache, nausea, dizziness, weakness, rapid breathing, unconsciousness, and death. Chronic exposures to CO have been shown to produce adverse reproductive effects, such as low birth weight. Individuals who may be particularly susceptible to the adverse effects of CO exposure include pregnant workers and those with chronic heart or respiratory disease.

High concentrations may be rapidly fatal without producing significant warning symptoms. Nitrogen oxides (NOx) are also emitted in the combustion process and high levels may cause respiratory symptoms and severe health effects at the time of exposure, as well as after the exposure.

The most effective way to keep CO concentrations below the 35 parts per million (ppm) eight hour time-weighted average permissible and 200 ppm five minute (1,500 ppm instantaneous) ceiling exposure limits established by the state is to utilize one or more of the following controls:

  • where possible, substitute equipment that doesn't produce CO or NOx (e.g. electric forklifts).
  • ensure proper maintenance of forklifts to reduce emissions
  • use and maintain catalytic converters on forklifts where applicable (the tuning of engines and installation of catalytic converters can reduce both CO and NOx emissions)
  • install feedback fuel control systems to reduce emissions
  • do not allow forklifts to idle while waiting to resume operations
  • ensure proper ventilation of work areas
  • use CO sensors or alarms; conduct periodic sampling of the work area for CO and NOx
  • provide training to employees on the symptoms, sources, and prevention of CO and NOx poisoning

These control measures should also keep NOx exposures below the permissible exposure limit. It is important to recognize that although adjustment of carburetor balance on fueled engines can reduce CO emissions to safe levels, over-adjustment can actually increase NOx emissions to hazardous levels. It is very important to establish and maintain correct carburetor balance of fueled equipment used indoors. By following the controls listed in this Hazard Alert, employers can help prevent a disaster from occurring.


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