In September 1985, workers in the cutting room of a garment-manufacturing plant in North Carolina began complaining of headache, nausea, faintness, and dizziness. The Occupational Health Branch and the Environmental Epidemiology Branch of the North Carolina Division of Health Services were asked to investigate. The results of their investigation are presented below.

The cutting room is an enclosed 20,000-square-foot building separate from the sewing operation. It has heating and air conditioning systems using only recirculated air. The furnace, which is suspended over the center of the room, directs heated forced air toward the four walls of the building and collects air for reheating as it rebounds from the walls. A propane-powered forklift was being used to unload rolls of cloth from a truck that backs up to a usually sealed garage door at the end of the cutting room.

Because the workers' symptoms coincided with the indoor use of a forklift powered by an internal combustion engine, the investigators suspected carbon monoxide (CO) poisoning. On the day of the investigation (Monday), CO measurements were taken continuously for a 5-hour period with a calibrated Gastech* tester (model EC231). The heating furnace was functioning properly and did not contribute to CO exposure in the cutting room. The plant had been closed over the weekend, and there had been no known source of CO during that time. When the work shift began, the CO level was 35 parts per million (ppm) parts of air. The forklift was started 15 minutes later, and, within 30 minutes, the CO concentration in the air had risen to 250 ppm. Spot checks taken with a Bendix Gastech* detector-tube kit while the forklift was in operation showed a CO level of 300 ppm adjacent to the continuous monitor. The level of CO was 900 ppm inside the supply truck where the forklift unloaded rolls of cloth. The current standard of the Occupational Safety and Health Administration (OSHA) for exposure to CO is 50 ppm as an 8-hour, time-weighted average; the National Institute for Occupational Safety and Health recommends a permissible exposure limit of 35 ppm and a ceiling of 200 ppm (1).

Investigators interviewed all 12 workers in the cutting room while the forklift was in use. Ten of the workers (83%) reported symptoms of headache; seven (58%) reported nausea; seven (58%), faintness; five (42%), dizziness; five (42%), irritability; four (33%), weakness; three (25%), chest tightness; and one (8%), vomiting. Two workers (17%) felt ill enough to leave work. The workers experienced these symptoms on the day of the interviews and remembered having experienced them previously, usually on days when the forklift was operating. All symptomatic workers reported feeling better after arriving home from work (median, 3-4 hours after leaving the cutting room).

Venous blood samples from five workers and one investigator showed carboxyhemoglobin (COHb) levels greater than would be expected from their smoking histories (Table 1). The cloth cutter and the forklift operator, who had the highest COHb levels, both worked with potentially dangerous machinery. Workers with COHb values less than 20% had not worked a full shift in the cutting room.

The plant managers were advised to discontinue use of the propane-powered forklift immediately and to replace it with an electrical model. Workers were informed of the risks of CO exposure and were warned of the dangers of operating heavy machinery and cutting instruments while intoxicated with CO. After the propane- powered forklift was replaced with an electrical one, workers no longer experienced the symptoms. Reported by: CD Baucom, CIH, JI Freeman, DVM, MPH, JM MacCormack, MD, MPH, State Epidemiologist, North Carolina Div of Health Svcs. Div of Field Svcs, Epidemiology Program Office; National Institute for Occupational Safety and Health, CDC.

Editorial Note

Editorial Note: Carbon monoxide is an odorless, colorless gas produced by incomplete combustion of carbon-containing materials. When there is an incorrect air/fuel mixture in an internal combustion engine, the amount of CO produced increases. In addition, CO concentration increases with insufficient ventilation of combustion gases and insufficient intake of fresh air. Inhaled CO causes hypoxia by binding tightly with circulating hemoglobin to form COHb and, thus, reduces the capacity of the blood to transport oxygen (2). Symptoms and signs of CO-induced hypoxia include headache, dizziness, nausea, vomiting, unconsciousness, and death (2,3). Persons exposed to CO may appear intoxicated as if with alcohol or other depressants of the central nervous system (4) and may not be fully aware of their degree of impairment. Therefore, employees who work with or near potentially hazardous equipment should be alerted to the dangers of CO poisoning.

When internal combustion engines are operated indoors, they are likely to produce dangerously high concentrations of CO. According to the Industrial Truck Association and the U.S. Department of Commerce, 50% of the 97,000 forklifts sold in this country in 1985 were powered by internal combustion engines, and about 75% of all forklifts are operated indoors. Other sources of indoor CO exposure include home furnaces and water heaters (5), machines for resurfacing ice skating rinks (6), and kerosene heaters (7).

Since the forklift had been operated in this plant before September, it is not clear why the onset of symptoms occurred at that time. However, since the amount of CO produced by an internal combustion engine depends on the combustion efficiency of the engine, it is possible that the combustion efficiency of the forklift had gradually declined over time. No measurements were available to confirm this hypothesis. Because there was no known source of CO in the plant over the weekend, the investigators concluded that the 35 ppm of CO at the beginning of the workshift on Monday was left over from the forklift operation of the previous week.

Although CO exposure can be reduced by local exhaust ventilation and respiratory protective devices, OSHA recommends engineering controls whenever possible to eliminate the source of CO. Public health officials should be aware of the hazards of operating internal combustion engines indoors, and plant managers should be advised to purchase electrically powered machines for indoor use.

References

1. CDC, Occupational Safety and Health Administration. Occupational health guidelines for chemical hazards. Washington, DC: US Department of Health and Human Services, Public Health Service, 1981; DHHS publication no. (NIOSH)81-123.

2. Jackson DL, Menges H. Accidental carbon monoxide poisoning. JAMA 1980;243:772-4.

3. Burney RE, Wu SC, Nemiroff MJ. Mass carbon monoxide poisoning: clinical effects and results of treatment in 184 victims. Ann Emerg Med 1982;11:394-9.

4. Winter PM, Miller JN. Carbon monoxide poisoning. JAMA 1976;236:1502-4.

5. CDC. Carbon monoxide poisoning--South Dakota. MMWR 1985;34:113-4.

6. CDC. Carbon monoxide exposures at an ice skating rink--Colorado. MMWR 1986; 35:435-6,441.

7. Anonymous. Kerosene heaters--how safe are the newer models? Consumer Reports 1985;50:74-5. *Use of trade names is for identification only and does not imply endorsement by the U.S. Department of Health and Human Services or the Public Health Service.

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