Evaluation of airborne carbon monoxide exposure monitoring program in produce cooler operations (Palm Beach County, Florida)

Carbon monoxide (CO), a colorless and odorless gas, is classified as a pulmonary asphyxiant. High level exposures can cause toxic effects or death in humans and animals (1); CO poisoning reportedly is responsible for as many as 4,000 deaths per year in the United States (2). Even low-level CO exposures can have cardiovascular, neurobehavioral, and fetotoxic effects. Smoking one pack of cigarettes a day is enough to raise carboxyhemoglobin (COHb) levels in the blood sufficiently to cause subclinical cardiovascular and neurobehavioral effects (3).

CO poisonings have been associated with the use of propane-powered lift trucks. Treated for acute CO poisoning at the F.G. Hail Hypo-Hyperbaric Environmental at Duke University Medical Center, 17 patients were found to have been exposed to CO from the exhaust of propane-fueled forklifts used in enclosed warehouses (4).

In Southern Florida, due to the warm climate, warehouses tend to be well ventilated by keeping bay doors open and running fans for the comfort of the staff. However, ventilation is not feasible in operations requiring cold storage, so there is a higher risk of exhaust build-up if propane lift trucks are used in these areas. Recently, CO poisonings occurred at a South Florida shipping operation when a propane lift truck was used instead of a hand lift in a small candy cooler (5).

Given the increased risk of CO exposure, and resulting morbidity and possible mortality, the Palm Beach County Public Health Unit, Division of Environmental Health instituted a CO monitoring program for produce cooler operations in western Palm Beach County. The purpose of this study was to evaluate the effectiveness of this program for decreasing the CO exposure from propane lift truck exhaust for the population of workers entering these produce coolers during the spring corn season. The evaluation recorded the employees' carbon monoxide exposure levels before and after intervention, measured the success of various exposure reduction strategies, and made recommendations to reduce or eliminate future risk. The success of this program and the effectiveness of various environmental control methods was demonstrated.

There were seven produce cooler operations identified in western Palm, Beach County that used propane lift trucks in coolers at the beginning of the study in 1991. Monitoring was performed annually during the heaviest spring corn harvest. Following arrival and pre-cooling, corn was loaded into the coolers with lift trucks. After storage, corn was removed and placed in refrigerated tractor-trailers.

Methods

The population studied was employees that at some point during an 8-hour shift entered the produce cooler(s). Blood testing would have been invasive and could reflect CO exposures from tobacco smoke and sources outside the workplace; therefore, the COHb (6) method was not chosen to evaluate occupational CO exposure from propane lift truck exhaust. CO levels in air were monitored using personal monitoring, grab sampling, and area sampling techniques. Personal monitoring and area sampling were performed using Gastec Passive Dosi-tubes to yield TWA CO levels over 8-hour workshifts. A CEA Model CO-7 CO detector was used to determine various grab sample CO levels. The U.S. Department of Labor, Occupational Safety and Health Administration (OSHA), 29 Code of Federal Regulations part 1910.000(a), Table Z-1-A, Permissible Exposure Level (PEL) was 35 parts per million (ppm) CO as an airborne exposure in any 8-hour shift of a 40-hour work week. The ceiling limit not to be exceeded at any time was 200 ppm. (Both of these personal exposure levels were revoked and ceased to be enforced by OSHA the last year of the three-year study. The current OSHA PEL of 50 ppm CO as a TWA was not used. There is currently no OSHA ceiling limit for CO.)

Five of the produce cooler operations needed interventions to reduce CO exposure. Each company was allowed to choose which one or combination of interventions to implement. The three basic intervention types chosen were source elimination, source reduction, and administrative control (Table 1). Company A rented electric lift trucks for use inside the cooler and trailers to eliminate the source (source elimination). Company E rotated personnel so that workers would not be performing jobs that required entering the coolers for the entire shift (administrative control). The following describes the source reduction strategies:

1. Company B purchased electric lift tracks to be used inside the coolers and used propane lift trucks only when necessary.

2. Company C installed catalytic mufflers on their rented propane lift trucks to reduce CO emissions.

3. Company D tested lift track exhausts monthly and adjusted the carburetor air/ fuel ratio for minimal CO emissions.

Data from the first visit of each year was utilized to evaluate the effectiveness of the program and reduction strategies, because in many cases the harvest diminished before interventions could be implemented. Depending on the number of employees available and the compliance record of the company, all or a representative sample of employees was monitored.

Results

The CO monitoring program was traced over three years from 1990 to 1993. All of the monitored employees were males of variable ethnicity and approximately 18 to 50 years of age. The fact that some were smokers was of concern due to the increased risk of obtaining higher COHb levels and symptoms in these individuals.

Figure 1 shows the percent of employees personally monitored that were found to be in compliance with the OSHA PEL for CO each year. Initially, in 1991, only 52% were found in compliance. After the implementation of interventions at four of the operations in 1992, 92% of the employees were found in compliance. There was evidence that the one employee with exposure over the PEL in 1992 was accidentally exposed outside the coolers, since the cooler area samples were all below the PEL. The failure of an intervention at one company and another suspected accidental exposure to exhaust outside the coolers caused the rate of employee compliance to drop to 85% in 1993. The intervention that failed after one year of use was the catalytic mufflers, possibly due to lack of maintenance.

Table 1. Company, Intervention Type, and Specific Intervention
Utilized by Second Year of Study (1992).

Company        Intervention Type         Specific Intervention

A              Source Elimination        Electric Lift Trucks

B              Source Reduction          Electric Lift Trucks/
                                         Propane Lift Trucks

C              Source Reduction          Catalytic Mufflers

D              Source Reduction          Monitoring and Carburetor
                                         Adjustments

E              Administrative Control    Rotation of Personnel

Types of interventions were compared [ILLUSTRATION FOR FIGURE 2 OMITTED] as a percentage of employees in compliance with the OSHA PEL for CO before intervention in 1991 and after intervention in 1992 and 1993. Source elimination using electric rather than propane lift trucks lead to an increase from 50% in 1991 to 100% compliance in following years. Administrative control and source reduction yielded dramatic results after the first year with increases in compliance from 0% to 100% and 90%. The second year the success of these decreased to 66% and 85% because of a possible accidental exposure outside and the failure of the catalytic mufflers.

Initial program efforts concentrated on bringing each facility into compliance with the OSHA PEL for CO of 35 ppm over an 8-hour workshift. TWA measurements account for time periods of exposure and non-exposure. The OSHA ceiling limit refers to the magnitude of any exposure. CO grab samples exceeding the OSHA 200 ppm ceiling limit were measured the third year of the program. Figure 3 shows the percentage of coolers monitored over 200 ppm by intervention type. None of the coolers with source elimination, 12.5% of the coolers with source reduction, and 50% of the coolers with administrative control were found to have CO levels above the 200 ppm ceiling limit. Source elimination was the most reliable method for achieving compliance, source reduction was less effective, and administrative control the least effective intervention.

Discussion

The objective of the CO Monitoring Program established by the Palm Beach County Health Unit was to educate produce cooler operators concerning the potential health hazards caused by using propane lift trucks in produce coolers and to provide consultation services to help the facilities lower their employees' CO exposure risk. Intervention was found to reduce significantly carbon monoxide exposure levels. The data indicated that the CO Monitoring Program needed to be continued due to the failure of some interventions to maintain consistently the employees' TWAs within OSHA compliance limits as well as the failure of various source reduction methods and administrative controls to protect against CO exposures above the OSHA ceiling limit.

The most reliable reduction strategy was the elimination of the CO source, i.e. the propane lift track. Produce cooler operators that substituted electric lift trucks reported satisfaction. Other companies were resistant to change for various reasons including the need to change batteries to extend the running time of the lift trucks (requires a hoist), the limited lifetime of the batteries, and the cost.

Administrative control was found to be a valid method for reducing overall average CO exposures but was inadequate for preventing exposure to CO levels above the OSHA ceiling limit. The other more effective interventions of source elimination through the Use of electric lift trucks and source reduction using computer-operated emissions controls should be recommended in the future.

Lift track emissions monitoring with a CO meter to determine carburetor air/fuel ratio adjustment was found to help control CO emissions. Carburetor adjustment may be needed frequently and the success of a periodic monitoring program would depend on how often the lift trucks are maintained. Operations which rent their lift trucks would need to contract with the rental companies for CO emissions monitoring and adjustment. Tune-ups for optimum engine performance (rather than minimal CO emissions) recommended by a major propane carburetor manufacturer were found to produce significant levels of CO emissions as reported by the Duke University Medical Center (3).

Catalytic mufflers were found to fail the second year of use in this investigation probably due to the inability of the company to insure adequate maintenance of rented lift tracks, Similar disappointing field experiences with catalytic mufflers on lift truck and ice resurfacer engines have been reported (7), Three way catalytic converters with oxygen sensor/ feedback fuel control systems show. greater promise and are suitable for use on propane lift trucks, The air/fuel ratio must be maintained at a critical 155,5:1 for the device to operate properly. For this reason, a computer-controlled oxygen sensor/feedback fuel control system must be used.

The Clean Air Amendments of 1990 (CAAA) extended EPA' s authority to regulate non-road vehicle emissions (8). Future outdoor air pollution control activities by the EPA and/or local governments will likely require or help encourage manufacturers to produce cleaner running engines. Stringent design criteria and exhaust emissions standards for combustion devices used indoors are necessary to reduce the risk of CO and other exhaust exposures. The colorless and odorless nature of CO can easily expose unknowing building occupants. As CO poisonings occur and public awareness increases, industry will need to design safer equipment. However, the more dangerous existing equipment will continue to be used for many years.

References

1. Kurt, T.L. (1993), "Chemical Asphyxiants," in: Rom W.N. (ed.), Environmental and Occupational Medicine, Little Brown and Co., Boston, Mass., 289-295.

2. Piantadosi, C.A. (1990), "Carbon monoxide intoxication," in: Vincent, T.L. (ed.), Update in Intensive Care and Emergency Medicine (10), Springer-Verlag, New York, N.Y., 460-471.

3. Smith, R.P., (1986), "Toxic Responses of the Blood," in: Amdur, M.D., et al. (ed.), Casarett and Doull's Toxicology, Third Edition, MacMillan Pub. Co., New York, N.Y., 263-268.

4. Fawcett, T.A., et al. (1992), "Warehouse Workers' Headache: Carbon monoxide poisoning from propane fueled forklifts," J Occup Med, 12-15.

5. "4 Treated for Carbon Monoxide Exposure," (1992), Palm Beach Post, Dec. 31.

6. Goldstein, B.D., H.M. Kipen (1988), "Hemotologic Disorders," in: Levy, B.S., D.H. Wegman (ed.), Occupational Health: Recognizing and preventing work-related disease, Second Edition, Little, Brown, and Co., Boston, Mass., 445.

7. Anderson, D.E. (1971), "Problems Created for Ice Arenas by Engine Exhaust," Am Ind Hyg Assoc J, 32:790-801.

8. U.S. 40 CFR Part 89 (1993), "Notice of Proposed Rulemaking Part 89 Control of Emission from new and in-use non-road engines for new non-road compression ignition engines at or above 50 horsepower."

Acknowledgements

This study was made possible through the support of the Palm Beach County Public Health Unit and the cooperation of the participating produce cooler operations. The Division of Environmental Health CO Monitoring Program was originally established by James Jolley and Sylvia Pfahl. Data collection and consultation was performed in cooperation with Tam Kam-Shing. The calibration of the CEA CO-7 CO detector was accomplished through the efforts of Dan Brunet of the Division of Environmental Science and Engineering. Information on vehicle emissions control and EPA regulations was obtained from At Grasso and Arlene Tanis of the Division of Environmental Science and Engineering. Dr. Lora Fleming of the University of Miami served as project advisor and supplied editorial assistance. Dr. James Garsik is responsible for editorial and graphics assistance on the manuscript.

Daryl A. Garsik, M.P.H., Environmental Specialist II, Palm Beach Co. Public Health Unit, Div. of Environmental Health, 901 Evernia St., West Palm Beach, FL 33401.