PREVENTIVE
MEDICINE
8,
Methods
369-378
(1979)
to Reduce Carbon Monoxide at the Workplace1 WALTER
Levels
M. HAAG~
Division of Physical Sciences and Engineering, National Institute for Occupational Safety and Health, United States Department of Health, Education and Welfare, Robert A. Taft Laboratories, Cincinnati, Ohio 45226 Cardiovascular disease and death attributed to the workplace exposure to carbon monoxide (CO) can be reduced. It is possible to control the removal of CO through existing engineering principles and techniques. However, it is desirable that the methods that reduce the formation of CO and prevent its introduction into the workplace be developed and utilized. Perhaps the greatest long-term tragedy of today’s standard is that future plants, which often can meet more stringent standards, are not required nor have the incentive to do so under existing Federal policies. There is a need to develop a “new source performance standard” concept as part of the implementation of the Occupational Safety and Health Act. The greatest potential to eliminate future occupational health problems rests with the opportunity to encourage new plant designs that would reduce worker exposure, thus greatly eliminating future problems. The concept of new source performance standards has existed in the control of general environmental pollution in the ambient air and in water. It is generally recognized that control of emissions from new and future plants is usually easier than control of emissions from existing older plants. What does not seem to be understood is that control of emissions in the workplace will frequently prevent general environmental contamination as well. The problem is prevented at the source. The opportunity to prevent hazardous exposure to CO exists. It must be taken by those who have a knowledge of CO, and shared with professionals, management, and employees if there really is to be a reduction of CO levels at the working place. The benefits are not only the safety and health of employees, but the conservation of energy and materials, the creation of new products and new economic opportunities, etc. This pyramiding of benefits can be the result of achieving methods to reduce CO levels at the working place.
INTRODUCTION
Cardiovascular disease is one of the leading causes of death in many industrial nations. In an effort to achieve a better understanding of this disease, increasing attention by scientists and physicians is being directed to the question of whether carbon monoxide (CO) relates to the pathogenesis of arteriosclerosis and the development of specific cardiovascular diseases. Since the industrial environment is often the primary source of exposure to many toxic materials and harmful ’ Presented at a Workshop on Carbon Monoxide and Cardiovascular Disease, sponsored by the American Health Foundation and the Federal Republic of Germany, Berlin, October 10-12, 1978. ?Address for reprints: Walter M. Haag, Director, Division of Physical Sciences and Engineering, Robert A. Taft Laboratories, 4676 Columbia Parkway, Cincinnati, Ohio 45226. 369 0091-7435/79/030369-10$02.00/O Copyright @ 1979 by Academic Press. Inc. All rights of reproduction in any form reserved.
370
WALTER
M.
HAAG
physical agents, it is appropriate that workplaces be investigated for CO exposures and those exposures be reduced. The National Institute for Occupational Safety and Health (NIOSH) recognized that CO was a serious health hazard to working men and women. As such, it produced a criteria document in 1972 for a recommended standard for occupational exposure to CO based primarily on health effects. This early criteria document was reviewed by consultants, professional societies, government agencies, and others with interest and responsibility in occupational safety and health. Most of the reviewers were of the opinion that basing the recommended standard on cardiovascular effects was justified. None of the reviewers proposed any other biologic effect of CO for primary consideration. When this document was transmitted to the Occupational Safety and Health Administration, Department of Labor, August 3, 1972, it was felt that engineering technology was available to achieve the recommended limits of 35 ppm determined as a time-weighted average (TWA) exposure for an 8-hr workday. However, at that time no study was made regarding the time necessary to achieve the recommended limits. Control of employee exposure to CO at his place of employment at the limits stated will: (a) prevent acute CO poisoning, (b) protect the employee from deleterious myocardial alterations associated with levels of carboxyhemoglobin (COHb) in excess of 5%, and (c) provide the employee protection from adverse behavioral manifestations resulting from exposure to low levels of CO. What is meant by “methods to reduce CO levels at the workplace”? The first chapter of the NIOSH criteria document contains recommendations for controlling worker exposure to CO. Are these the same? I don’t think so. To “reduce” CO levels, one is preventing hazardous exposure and thus a problem. To “control” worker exposure, one is approaching a problem as if it already existed. The line between preventive and corrective medicine is small, but the conceptual approach to the problem by the practitioners is the “great dichotomy.” NIOSH CONTROL
RECOMMENDATIONS
The NIOSH criteria document for a recommended standard (19) indicates that occupational exposure to CO shall be controlled so that no worker shall be exposed at a concentration greater than 35 ppm determined as TWA exposure for an 8-hr workday, as measured with a portable, direct reading, hopcalite-type CO meter calibrated against known concentrations of CO, or with gas-detector tube units certified under Title 42 of the Code of Federal Regulations, Part 84. In addition, no level of CO to which workers are exposed shall exceed a ceiling concentration of 200 ppm. Because employees with cardiovascular disease may not be protected by an occupational exposure to 35 ppm of CO, a medical program should be instituted consisting of preplacement and periodic examinations with special attention to the cardiovascular system and to medical conditions which could be exacerbated by exposure to CO. Such a medical program could also provide the opportunity for conducting antismoking programs for high-risk employees.
WORKSHOP:
CARBON
MONOXIDE
AND
CVD
371
Cylinders and other containers of CO shall carry a label,stating: CARBON
HIGH
MONOXIDE (CO)
DANGER COLORLESS ODORLESS GAS MAY BE FATAL IF INHALED DO NOT BREATHE GAS CONCENTRATIONS IN AIR MAY BE EXPLOSIVE
Areas where 8-hr TWA exposures to carbon monoxide exceeding 25 ppm are likely to occur shall be posted with a sign stating: CARBON
MONOXIDE (CO)
DANGER HIGH CONCENTRATIONS MAY BE FATAL PROVIDE ADEQUATE VENTILATION HIGH CONCENTRATIONS IN AIR MAY BE EXPLOSIVE SEEK IMMEDIATE MEDICAL ATTENTION IF YOU EXPERIENCE ANY OF THE BELOW SYMPTOMS 1 - Severe Headache 2 - Dizziness 3 - Nausea and vomiting GAS MASKS ARE LOCATED: (Specific location to be filled in by employer)
In the event of an emergency, the use of approved respiratory protective equipment may be necessary for evacuation purposes or during cleanup of the area. For entry into or escape from an environment containing not over 20,000 ppm, which is not deficient in oxygen, for total exposure period of not more than 30 min a Type N gas mask should be used. For work in atmospheres containing up to 100% CO, a pressure-demand type self-contained breathing apparatus should be used. For fire-fighting applications, a demand or pressure-demand type selfcontained breathing apparatus should be used. All respiratory protective equipment shall be selected so as to insure satisfactory facepiece fit. Each user shall be instructed and tested in the proper use of respiratory protective devices and each such device shall be used and maintained in accordance with the provisions of the American National Standard Practices for Respiratory Protection ANSI Z-88-2, 1969. Appropriate measures shall be implemented to assure that the release into the workplace environment of carbon monoxide in excess of the ceiling value of 200 ppm is prevented. For areas in which large amounts of CO are stored, used, or emitted, or areas within the workplace through which large amounts of CO are transported shall be provided with sufficient approved respiratory protective devices and shall be readily accessible to persons who may be located in the area to assure a timely, orderly evacuation by all persons in the event of accidental, massive release of CO. Employees who work with CO should be apprised of all hazards, be cognizant of relevant symptoms, and be familiar with proper handling procedures and ap-
372
WALTER
M.
HAAG
propriate emergency procedures. Since container leaks represent a potential for exposure, each container in which CO is stored shall be examined for leaks upon its arrival at the establishment or upon tilling and shall be reexamined periodically at least every 3 months. If the amount of CO stored has the potential of reaching concentrations of 500 ppm, an automatic visual and audible alarm should be employed in such areas. Monitoring the environmental exposure of not only the area but also the personal exposure of employees is essential to avoid medical problems. If the CO concentration is near the standard continuous monitoring should be accomplished by means of monitoring equipment capable of determining the CO concentration in the workplace environment within 5% of the actual value. Obviously, records of the personal and environmental monitoring should be maintained by employers. HAZARD PREVENTION
The control recommendations discussed can contribute to preventing hazardous exposure of employees to CO. The use of effective control technology is the only means of assuring a workplace free of exposure to harmful agents. Three of the four components of control technology were briefly touched upon previously. These three are: (a) respirators as a subset of personal protective equipment, (b) monitoring or warning systems, and (c) work practices and procedures. The fourth component is engineering controls. The lack of such technology or its application is attested to by the continual occurrence of occupational diseases and injuries. It is possible to prevent occupational health problems through the application of hazard-prevention technology in the workplace. During rule-making processes, it has frequently become evident that there is insufficient information on the availability of technology to achieve the recommended exposure limit. NIOSH is currently attempting to ensure that at least one control method (without the use of personal protective devices) exists for achieving or approaching the recommended exposure limit. In this process, NIOSH has determined that a critical unmet need exists for the documentation, evaluation, development, and application of effective control technology for limiting worker exposure to potentially hazardous agents in the workplace. Clearly, the development of procedures for minimizing or eliminating hazardous exposures which can result in occupational illness and injury requires a cooperative spirit and coordinated effort among employers, employees, academia, and government. Management needs to implement health and safety programs, provide safe and healthful working conditions, and adhere to Federal and State standards. Individual workers are responsible for complying with company requirements. Academia must educate a sufficient number of professionals and stimulate interest in occupational safety and health. The government should be the central promoter and coordinator of nationwide effort to improve safety and health conditions in the workplace environment through collation of data, research, training, and assistance. NIOSH proposes to play a key part in this government role. PRINCIPLES
OF CONTROL
Effective prevention of occupational hazards involves the design and implementation of a series of control techniques that function together as a system. The creation of an effective control system requires a detailed knowledge of the
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MONOXIDE
AND
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hazards involved, the points of origin of the hazards, routes of occupational exposure, and control options. (a) Source
Prevention of occupational exposure by control at the source of the hazard is generally the preferred means of control. One method of prevention at the source involves substitution of a nonhazardous or less hazardous material for the substance of concern. Material substitution offers the intrinsic advantage of completely removing a hazardous material from the workplace. However, the ability to find suitable substitutes for a given material is by no means certain, and the substitute materials may themselves present some (lesser) degree of hazard. The application of other control measures therefore may be necessary even after material substitution has been achieved. Process modification is a second method of controlling hazards at the source. Existing processes often were not designed to meet current occupational health standards. A reevaluation of process options with occupational health requirements included as a constraint often will identify process modification as an effective control measure. In general, processes which are continuous, as opposed to intermittent of batch, are likely to be less hazardous from an occupational exposure standpoint. Processes should be designed to contain hazardous materials within enclosed equipment to the greatest extent possible, and to minimize the potential for contamination of the workplace. Equipment modification is a commonly used means of control. Modification of pieces of process equipment which present particularly serious exposure problems is usually a less costly change than modifying an entire process. Equipment should be redesigned to contain hazards within the equipment, to avoid the generation of material or energy hazards into the workplace, and to require minimal maintenance. When maintenance is required, the equipment design should permit performance of this maintenance with minimal hazard to the workers involved. Isolation of stored materials, equipment, and the process is a fourth means of controlling hazards at the source. Isolation involves the use of a barrier between a hazard and those who might be affected by the hazard. The barrier may be provided by a physical structure or by distance. Enclosure normally requires ventilation of the enclosed area. Limiting employee access to certain areas during hazardous operations also may be an effective means of isolation. Computerized process control, automation of various maintenance procedures, and the general concept of remote processing also help to isolate processes and equipment. Potential problems involved with isolation can include accessibility of equipment for maintenance and the potential for exposure of workers during maintenance operations. A fifth means of controlling the source of emissions is local exhaust ventilation. Local exhaust ventilation involves the use of hoods that direct a flow of air across the emission point and into the hood. Sufficient air flow must be utilized to result in an air velocity at the emission source sufficient to capture and convey the chemical agent into the hood and to convey it through the ventilation system ducting. An adequate supply of air must be provided to replace the air exhausted. The make-up air, in some cases, may be used to assist in the local exhaust control.
374
WALTER
M. HAAG
General design criteria for local exhaust systems can be found in references (2, 19, 22). (b) Workplace Environment Once a chemical agent has escaped into the general workplace some degree of control still may be achieved. However, control at this stage is generally more difficult and less effective than the previously discussed control at the point of origin. General workplace control measures normally are used as adjuncts to control measures which are applied at the source. One method of general workplace control involves removal of the hazard from the workplace environment. General (dilution) ventilation and use of room filtration/air cleaning devices are examples of this concept. Geographical location of the plant (possibly permitting open construction) and environmental pollution standards will affect the applicability of these control methods. Intake air for ventilation systems should be drawn from an uncontaminated atmosphere so as to avoid the intake of contaminated exhaust air from the plant itself or other sources of contamination outside the plant. A second method of general workplace control involves the use of good work practices. Good work practices begin with the proper structuring of duties required in the worker’s job to reduce any potential exposure to a minimum. They also involve the application of common sense and good judgement by the workers during the performance of required production and maintenance functions. (c) Worker The third type of control for occupational exposure to hazards involves control measures that are implemented on individual workers. Personal protective equipment (PPE) is a means of isolating the worker from the exposure hazard. This area of protection includes respirators, supplied air and impermeable suits, gloves, goggles, safety glasses, hard hats, safety footwear, and various other types of clothing used for protection. Of this grouping, one of the most widely used devices is the respirator. The recommended use conditions for the various types of respirators are set forth in the “NIOSWOSHA Respirator Decision Logic” (15). It should be recognized that the respirators protect the worker only against certain specific types of substances and in certain concentration ranges depending on the type of equipment used. In order to have an effective respirator program it must meet the minimum requirements as set forth in 29 CFR 1910.34. This program must include proper selection of equipment, training of personnel, supervision and enforcement, and an adequate maintenance program as described in “A Guide to Industrial Respiratory Protection”( 1). Worker isolation also can be achieved through the use of physical enclosures (booths). (d) Monitoring An effective monitoring/warning program is essential to the proper function and maintenance of a control system, and is always a desirable addition to any control system. This program should consist of a monitoring/warning device, planned maintenance and calibration procedures, and a plan of action to be implemented
WORKSHOP:
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MONOXIDE
AND
CVD
375
when the monitor indicates a problem. The monitoring devices may be built into the process or control equipment in order to measure the operating parameters, or they may be installed so as to measure levels of hazards in the workplace environment. The presence of a complex control system and the lack of adequate warning properties for the substance being controlled makes monitoring/warning devices a virtual necessity. Monitoring/warning devices may indicate an emergency situation or the need for specific maintenance procedures on the process equipment, or control systems, as well as indicating the mode of operation for the control system (i.e., the use of personal protection until process/control problems can be solved). (e) Education Education in the need for and application of controls for occupational health hazards is essential to any control system. Management must be educated in the need for controls. Process and design engineers, as well as the industrial hygiene personnel, must be aware of both the principles of control and of various control options. Supervisors must be trained in the recognition of hazards related to specific processes and equipment. Finally, workers who are generally responsible for the operation and maintenance of control systems must be made aware of the occupational hazards which they face, and of the control measures which are to be followed in order to avoid occupational illness or injury both in routine and emergency operations. METHODS
TO REDUCE CARBON
MONOXIDE
EXPOSURE
Forty to sixty years ago, and even today, the approach to solving exposure to hazards was to vary the work schedule of employees. In addition, to encourage the workers to accept certain jobs in which the hazards were known, employers offered special financial incentives. This hazardous duty pay still exists. In the last 20 to 30 years, the approach used by employers relied heavily upon ventilation. The ventilation solutions were as simple as opening windows and doors to take advantage of the natural environment to the more mechanical solutions that utilized fans, air ducts, hoses, etc. In some cases, the mechanical solution was to improve the general workplace environment and as time progressed the solutions were more tailored to specific work sites. This last decade and today, the solutions are more sophisticated to take advantage of the advancing knowledge of science and engineering. There is considerable effort being directed to source prevention through improved combustion processes and catalytic conversion (3,9, 12, l&24). Although the national program to control CO emissions from motor vehicles has raised serious questions concerning the feasibility of the control program and the processes through which control policies are established, there continues to be attention focused on the CO problem (4, 8, 14, 17). Peterson (20), in the NIOSH publication, “The Industrial Environment, its Evaluation and Control,” lists the four basic principles for controlling the occupational environment as substitution, isolation, ventilation, and education. Not all of these principles are applicable to every form of hazard, but all occupational hazards can be controlled by the use of at least one of them.
376
WALTER
M.
HAAG
Substitution involves the replacement of hazardous materials, processes, or pieces of equipment with less or nonhazardous ones. Substitution may be the least expensive as well as the most positive method of controlling an occupational hazard. Usually, CO is encountered in industry as a waste product of the incomplete combustion of carbonaceous fuels. Unfortunately, nonhydrocarbon fuels are neither cheap nor readily available; therefore, substitution of alternate materials is not always feasible. Diesel fuel is being considered actively as the energy source for future automobiles. A 1973 study showed that the CO emissions were lowered when diesel fuel was used within a regenerative turbine combustor (13). Control efforts must be centered on the combustion process itself, to minimize the formation of CO (5, 6, 25). This can be accomplished through the establishment of the proper air/fuel ratios by the use of combustion monitoring equipment, and by the maintenance of adequate exhaust-stack draft through a proper supply of make-up air to the industrial building. Substitution of propane-fueled or electric powered lift trucks for gasoline-powered equipment can reduce or eliminate the CO hazard in factories and warehouses. Isolation can be achieved by the use of a physical barrier, or by the separation of the worker from the exposure source in space and time. Physical barriers can be effective for the control of CO. The barrier can be in the form of an enclosure around the worker, as is the case for crane operators or blast furnace operators, or around the process, such as an enclosed, ventilated tunnel for the cooling of foundry molds. For some workers such as toll booth operators or tunnel patrol officers, an automatic continuous CO-monitoring system and the provision of some control measure is essential. A 1972 study looked at a positive-pressure ventilation system to reduce levels of CO in the breathing zone of toll-booth attendants (21). Remotely controlled processes can isolate the worker from the hazard generation point by a distance. Special care must be taken in the design of industrial plants to isolate the exhaust stacks from combustion processes. This will prevent the inadvertent recirculation of CO into the workplace by an exhaust stack placed too close to a building-supply air inlet and can do much to prevent an unnecessary exposure. Local exhaust ventilation used alone, or in combination with substitution and isolation, is a powerful and versatile method for removing air contaminants from the workplace environment. The method is limited in that the source of the contaminant must be in a fixed location or move in a defined pattern. Perhaps the best known example of local-exhaust ventilation applied to the control of CO is the tailpipe exhaust system commonly seen in automotive service garages. There has been much research in this area over the years (11, 23). Dilution ventilation can occur naturally or by mechanical means. Mechanical ventilation is superior to natural ventilation to the extent that air currents are dictated primarily by the location and quantities of exhaust and supply air movers, rather than by weather factors. While not as desirable as the other control methods, dilution ventilation is almost always required as a supplement to those other techniques as few are 100% effective in preventing the release of CO in the workplace.
WORKSHOP:
CARBON
MONOXIDE
AND
CVD
377
Because CO is odorless and colorless and is usually present as an unwanted byproduct of the combustion process, the hazard of CO exposure is linked directly to worker awareness. An effective worker education program is necessary to instruct workers in the proper use and maintenance of combustion equipment, and continuous monitoring devices are necessary to warn of eminent hazard. A study found that in a metropolitan area, total travel by automobile resulted in a mean CO exposure nearly twice that of rail mass transit. This raises the possibility that going to and from work may be a prime exposure time to CO. The implications for alternate transportation schemes such as fast lanes, smaller engines, pooled movement, air conditioning, etc., are tremendous (7, 16). REFERENCES 1. “A Guide to Industrial Respiratory Protection,” NIOSH Publication 76- 189. 2. “ACGIH Industrial Ventilation-a Manual of Recommended Practices,” 15th ed. Committee on Industrial Ventilation, 1978. 3. Anonymous. Precipitator-cyclone combine cuts CO-boiier emissions. Oil Gas J. 75, 56 (1977). 4. Anonymous. “Reducing Pollution From Selected Energy Transformation Sources,” p. 230. Graham and Trotman, London, 1976. 5. Beale, N. R., and Hodgetts, D. Inlet valve throttling and the effects of mixture preparation and turbulence on the exhaust gas emissions of a spark ignition engine. Itrsr. Mech. Eng. (Loudon) Proc. 190, 13-21 (1976).
6. Bolton, M. S. and Taylor, D. S. Simple combustion efficiency indicator for automobile engines. Meas. Control
6, 399-400
(1973).
7. Cortese, A. D., and Spengler, D. Ability of fixed monitoring station to represent personal carbon monoxide exposure. J. Air. Pollut. Control Assoc. 26, 1144- 1150 (1976). 8. Croke, K. G., Croke, E. J., and Zerbe, R. 0. “Economic Analysis of Transportation Emission Control Strategies,” Proc. Air Pollut. Control Assoc. 69th Annu. Meeting, 1976. 9. Gilbert, L. F. Precise combustion-control saves fuel and power. Chem. Eng. (N. Y.) 83, 145- 150 (1976). 10. Gillett, J. E. Preventing emissions from manufacturing processes by suitable process design. Arms. Occup. Hyg.
19,301-308
(1976).
11. Hanna, G. M., and Butler, K. E., Jr. Design airflows for proper ventilation of service garages. Air Eng. 20-25 (October, 1967). 12. Kobylinski, T. P., Hammel, J. J., and Swift, H. E. Porous silica beads. Ind. Eng. Chem. Prod. Res. Develop. 14, 147- 150 (1975). 13. LaPointe, C. W., and Schultz, W. L. “Comparison of Emission Indexes Within a Turbine Combustor Operated on Diesel Fuel or Methanol,” SAE Paper 730669, 1973. 14. Leaderer, B. P., Stolwijk, J. A. J., and Zagraniski, R. T. Health Benefits Due to Reductions of CO Levels. Environ. Mannge. 1, 131- 137 (1976). 15. Lynch, J. R., Leidel, N. A., Nelson, R. A., and Boggs, R. F. “The Standards Completion Program Draft Technical Standards Analysis and Decision Logics,” NTIS: PB282989/AS, 1978. 16. Myronuk, J. D. Ingestion of carbon monoxide by occupants of vehicles while idling in drive-up facility lines. Water Air Soil Pollut. 7, 203-213 (1977). 17. Newhall, H. K., and El Messiri, I. A. “Combustion Chamber Designed for Minimum Engine Exhaust Emissions,” SAE Paper 700491, 1970. 18. Nicholas, D. M., and Shah, Y. T. Carbon monoxide over a platinum-porous fiber glass supported catalyst. Ind. Eng. Chem. Prod. RPs. Develop. 15, 35-40 (1976). 19. “Occupational Exposure to Carbon Monoxide,” U.S. Printing Offtce, Washington, D.C., 1972. 20. Peterson, J. E. Principles for controlling the occupational environment, in “The Industrial Environment-its Evaluation and Control,” pp. 51l-517. U.S. Government Printing Office Washington, D.C., 1973. 21. Rossano, A. T., Jr., and Alsid, H. F. “Evergreen Point Bridge Toll Booth Ventilation Study,” NTIS: PB221161, 1972.
WALTER M. HAAG
378
22. “The Industrial Environment-Its Evaluation and Control,” U.S. Government Printing Offtce, Washington, D.C., 1973. 23. Sheinbaum, M., and Stern, A. C. Tailpipe exhaust systems for garage ventilation. N.Y. Stnle Dept. Labor-Month.
Rev. 29, 25-28 (1950).
24. Sperkach, I. E., and Tumanov, G. V. Cleaning gas from the interbell space of a 1719blast furnace. Steel USSR 6, 355-356 (1976). 25. Stover, R. D. “Control of Carbon Monoxide Emissions from FCC Units by Ultracat Regeneration,” AIChe Workshop 6, 1975.
MEDICINE
8,
Methods
369-378
(1979)
to Reduce Carbon Monoxide at the Workplace1 WALTER
Levels
M. HAAG~
Division of Physical Sciences and Engineering, National Institute for Occupational Safety and Health, United States Department of Health, Education and Welfare, Robert A. Taft Laboratories, Cincinnati, Ohio 45226 Cardiovascular disease and death attributed to the workplace exposure to carbon monoxide (CO) can be reduced. It is possible to control the removal of CO through existing engineering principles and techniques. However, it is desirable that the methods that reduce the formation of CO and prevent its introduction into the workplace be developed and utilized. Perhaps the greatest long-term tragedy of today’s standard is that future plants, which often can meet more stringent standards, are not required nor have the incentive to do so under existing Federal policies. There is a need to develop a “new source performance standard” concept as part of the implementation of the Occupational Safety and Health Act. The greatest potential to eliminate future occupational health problems rests with the opportunity to encourage new plant designs that would reduce worker exposure, thus greatly eliminating future problems. The concept of new source performance standards has existed in the control of general environmental pollution in the ambient air and in water. It is generally recognized that control of emissions from new and future plants is usually easier than control of emissions from existing older plants. What does not seem to be understood is that control of emissions in the workplace will frequently prevent general environmental contamination as well. The problem is prevented at the source. The opportunity to prevent hazardous exposure to CO exists. It must be taken by those who have a knowledge of CO, and shared with professionals, management, and employees if there really is to be a reduction of CO levels at the working place. The benefits are not only the safety and health of employees, but the conservation of energy and materials, the creation of new products and new economic opportunities, etc. This pyramiding of benefits can be the result of achieving methods to reduce CO levels at the working place.
INTRODUCTION
Cardiovascular disease is one of the leading causes of death in many industrial nations. In an effort to achieve a better understanding of this disease, increasing attention by scientists and physicians is being directed to the question of whether carbon monoxide (CO) relates to the pathogenesis of arteriosclerosis and the development of specific cardiovascular diseases. Since the industrial environment is often the primary source of exposure to many toxic materials and harmful ’ Presented at a Workshop on Carbon Monoxide and Cardiovascular Disease, sponsored by the American Health Foundation and the Federal Republic of Germany, Berlin, October 10-12, 1978. ?Address for reprints: Walter M. Haag, Director, Division of Physical Sciences and Engineering, Robert A. Taft Laboratories, 4676 Columbia Parkway, Cincinnati, Ohio 45226. 369 0091-7435/79/030369-10$02.00/O Copyright @ 1979 by Academic Press. Inc. All rights of reproduction in any form reserved.
370
WALTER
M.
HAAG
physical agents, it is appropriate that workplaces be investigated for CO exposures and those exposures be reduced. The National Institute for Occupational Safety and Health (NIOSH) recognized that CO was a serious health hazard to working men and women. As such, it produced a criteria document in 1972 for a recommended standard for occupational exposure to CO based primarily on health effects. This early criteria document was reviewed by consultants, professional societies, government agencies, and others with interest and responsibility in occupational safety and health. Most of the reviewers were of the opinion that basing the recommended standard on cardiovascular effects was justified. None of the reviewers proposed any other biologic effect of CO for primary consideration. When this document was transmitted to the Occupational Safety and Health Administration, Department of Labor, August 3, 1972, it was felt that engineering technology was available to achieve the recommended limits of 35 ppm determined as a time-weighted average (TWA) exposure for an 8-hr workday. However, at that time no study was made regarding the time necessary to achieve the recommended limits. Control of employee exposure to CO at his place of employment at the limits stated will: (a) prevent acute CO poisoning, (b) protect the employee from deleterious myocardial alterations associated with levels of carboxyhemoglobin (COHb) in excess of 5%, and (c) provide the employee protection from adverse behavioral manifestations resulting from exposure to low levels of CO. What is meant by “methods to reduce CO levels at the workplace”? The first chapter of the NIOSH criteria document contains recommendations for controlling worker exposure to CO. Are these the same? I don’t think so. To “reduce” CO levels, one is preventing hazardous exposure and thus a problem. To “control” worker exposure, one is approaching a problem as if it already existed. The line between preventive and corrective medicine is small, but the conceptual approach to the problem by the practitioners is the “great dichotomy.” NIOSH CONTROL
RECOMMENDATIONS
The NIOSH criteria document for a recommended standard (19) indicates that occupational exposure to CO shall be controlled so that no worker shall be exposed at a concentration greater than 35 ppm determined as TWA exposure for an 8-hr workday, as measured with a portable, direct reading, hopcalite-type CO meter calibrated against known concentrations of CO, or with gas-detector tube units certified under Title 42 of the Code of Federal Regulations, Part 84. In addition, no level of CO to which workers are exposed shall exceed a ceiling concentration of 200 ppm. Because employees with cardiovascular disease may not be protected by an occupational exposure to 35 ppm of CO, a medical program should be instituted consisting of preplacement and periodic examinations with special attention to the cardiovascular system and to medical conditions which could be exacerbated by exposure to CO. Such a medical program could also provide the opportunity for conducting antismoking programs for high-risk employees.
WORKSHOP:
CARBON
MONOXIDE
AND
CVD
371
Cylinders and other containers of CO shall carry a label,stating: CARBON
HIGH
MONOXIDE (CO)
DANGER COLORLESS ODORLESS GAS MAY BE FATAL IF INHALED DO NOT BREATHE GAS CONCENTRATIONS IN AIR MAY BE EXPLOSIVE
Areas where 8-hr TWA exposures to carbon monoxide exceeding 25 ppm are likely to occur shall be posted with a sign stating: CARBON
MONOXIDE (CO)
DANGER HIGH CONCENTRATIONS MAY BE FATAL PROVIDE ADEQUATE VENTILATION HIGH CONCENTRATIONS IN AIR MAY BE EXPLOSIVE SEEK IMMEDIATE MEDICAL ATTENTION IF YOU EXPERIENCE ANY OF THE BELOW SYMPTOMS 1 - Severe Headache 2 - Dizziness 3 - Nausea and vomiting GAS MASKS ARE LOCATED: (Specific location to be filled in by employer)
In the event of an emergency, the use of approved respiratory protective equipment may be necessary for evacuation purposes or during cleanup of the area. For entry into or escape from an environment containing not over 20,000 ppm, which is not deficient in oxygen, for total exposure period of not more than 30 min a Type N gas mask should be used. For work in atmospheres containing up to 100% CO, a pressure-demand type self-contained breathing apparatus should be used. For fire-fighting applications, a demand or pressure-demand type selfcontained breathing apparatus should be used. All respiratory protective equipment shall be selected so as to insure satisfactory facepiece fit. Each user shall be instructed and tested in the proper use of respiratory protective devices and each such device shall be used and maintained in accordance with the provisions of the American National Standard Practices for Respiratory Protection ANSI Z-88-2, 1969. Appropriate measures shall be implemented to assure that the release into the workplace environment of carbon monoxide in excess of the ceiling value of 200 ppm is prevented. For areas in which large amounts of CO are stored, used, or emitted, or areas within the workplace through which large amounts of CO are transported shall be provided with sufficient approved respiratory protective devices and shall be readily accessible to persons who may be located in the area to assure a timely, orderly evacuation by all persons in the event of accidental, massive release of CO. Employees who work with CO should be apprised of all hazards, be cognizant of relevant symptoms, and be familiar with proper handling procedures and ap-
372
WALTER
M.
HAAG
propriate emergency procedures. Since container leaks represent a potential for exposure, each container in which CO is stored shall be examined for leaks upon its arrival at the establishment or upon tilling and shall be reexamined periodically at least every 3 months. If the amount of CO stored has the potential of reaching concentrations of 500 ppm, an automatic visual and audible alarm should be employed in such areas. Monitoring the environmental exposure of not only the area but also the personal exposure of employees is essential to avoid medical problems. If the CO concentration is near the standard continuous monitoring should be accomplished by means of monitoring equipment capable of determining the CO concentration in the workplace environment within 5% of the actual value. Obviously, records of the personal and environmental monitoring should be maintained by employers. HAZARD PREVENTION
The control recommendations discussed can contribute to preventing hazardous exposure of employees to CO. The use of effective control technology is the only means of assuring a workplace free of exposure to harmful agents. Three of the four components of control technology were briefly touched upon previously. These three are: (a) respirators as a subset of personal protective equipment, (b) monitoring or warning systems, and (c) work practices and procedures. The fourth component is engineering controls. The lack of such technology or its application is attested to by the continual occurrence of occupational diseases and injuries. It is possible to prevent occupational health problems through the application of hazard-prevention technology in the workplace. During rule-making processes, it has frequently become evident that there is insufficient information on the availability of technology to achieve the recommended exposure limit. NIOSH is currently attempting to ensure that at least one control method (without the use of personal protective devices) exists for achieving or approaching the recommended exposure limit. In this process, NIOSH has determined that a critical unmet need exists for the documentation, evaluation, development, and application of effective control technology for limiting worker exposure to potentially hazardous agents in the workplace. Clearly, the development of procedures for minimizing or eliminating hazardous exposures which can result in occupational illness and injury requires a cooperative spirit and coordinated effort among employers, employees, academia, and government. Management needs to implement health and safety programs, provide safe and healthful working conditions, and adhere to Federal and State standards. Individual workers are responsible for complying with company requirements. Academia must educate a sufficient number of professionals and stimulate interest in occupational safety and health. The government should be the central promoter and coordinator of nationwide effort to improve safety and health conditions in the workplace environment through collation of data, research, training, and assistance. NIOSH proposes to play a key part in this government role. PRINCIPLES
OF CONTROL
Effective prevention of occupational hazards involves the design and implementation of a series of control techniques that function together as a system. The creation of an effective control system requires a detailed knowledge of the
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hazards involved, the points of origin of the hazards, routes of occupational exposure, and control options. (a) Source
Prevention of occupational exposure by control at the source of the hazard is generally the preferred means of control. One method of prevention at the source involves substitution of a nonhazardous or less hazardous material for the substance of concern. Material substitution offers the intrinsic advantage of completely removing a hazardous material from the workplace. However, the ability to find suitable substitutes for a given material is by no means certain, and the substitute materials may themselves present some (lesser) degree of hazard. The application of other control measures therefore may be necessary even after material substitution has been achieved. Process modification is a second method of controlling hazards at the source. Existing processes often were not designed to meet current occupational health standards. A reevaluation of process options with occupational health requirements included as a constraint often will identify process modification as an effective control measure. In general, processes which are continuous, as opposed to intermittent of batch, are likely to be less hazardous from an occupational exposure standpoint. Processes should be designed to contain hazardous materials within enclosed equipment to the greatest extent possible, and to minimize the potential for contamination of the workplace. Equipment modification is a commonly used means of control. Modification of pieces of process equipment which present particularly serious exposure problems is usually a less costly change than modifying an entire process. Equipment should be redesigned to contain hazards within the equipment, to avoid the generation of material or energy hazards into the workplace, and to require minimal maintenance. When maintenance is required, the equipment design should permit performance of this maintenance with minimal hazard to the workers involved. Isolation of stored materials, equipment, and the process is a fourth means of controlling hazards at the source. Isolation involves the use of a barrier between a hazard and those who might be affected by the hazard. The barrier may be provided by a physical structure or by distance. Enclosure normally requires ventilation of the enclosed area. Limiting employee access to certain areas during hazardous operations also may be an effective means of isolation. Computerized process control, automation of various maintenance procedures, and the general concept of remote processing also help to isolate processes and equipment. Potential problems involved with isolation can include accessibility of equipment for maintenance and the potential for exposure of workers during maintenance operations. A fifth means of controlling the source of emissions is local exhaust ventilation. Local exhaust ventilation involves the use of hoods that direct a flow of air across the emission point and into the hood. Sufficient air flow must be utilized to result in an air velocity at the emission source sufficient to capture and convey the chemical agent into the hood and to convey it through the ventilation system ducting. An adequate supply of air must be provided to replace the air exhausted. The make-up air, in some cases, may be used to assist in the local exhaust control.
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General design criteria for local exhaust systems can be found in references (2, 19, 22). (b) Workplace Environment Once a chemical agent has escaped into the general workplace some degree of control still may be achieved. However, control at this stage is generally more difficult and less effective than the previously discussed control at the point of origin. General workplace control measures normally are used as adjuncts to control measures which are applied at the source. One method of general workplace control involves removal of the hazard from the workplace environment. General (dilution) ventilation and use of room filtration/air cleaning devices are examples of this concept. Geographical location of the plant (possibly permitting open construction) and environmental pollution standards will affect the applicability of these control methods. Intake air for ventilation systems should be drawn from an uncontaminated atmosphere so as to avoid the intake of contaminated exhaust air from the plant itself or other sources of contamination outside the plant. A second method of general workplace control involves the use of good work practices. Good work practices begin with the proper structuring of duties required in the worker’s job to reduce any potential exposure to a minimum. They also involve the application of common sense and good judgement by the workers during the performance of required production and maintenance functions. (c) Worker The third type of control for occupational exposure to hazards involves control measures that are implemented on individual workers. Personal protective equipment (PPE) is a means of isolating the worker from the exposure hazard. This area of protection includes respirators, supplied air and impermeable suits, gloves, goggles, safety glasses, hard hats, safety footwear, and various other types of clothing used for protection. Of this grouping, one of the most widely used devices is the respirator. The recommended use conditions for the various types of respirators are set forth in the “NIOSWOSHA Respirator Decision Logic” (15). It should be recognized that the respirators protect the worker only against certain specific types of substances and in certain concentration ranges depending on the type of equipment used. In order to have an effective respirator program it must meet the minimum requirements as set forth in 29 CFR 1910.34. This program must include proper selection of equipment, training of personnel, supervision and enforcement, and an adequate maintenance program as described in “A Guide to Industrial Respiratory Protection”( 1). Worker isolation also can be achieved through the use of physical enclosures (booths). (d) Monitoring An effective monitoring/warning program is essential to the proper function and maintenance of a control system, and is always a desirable addition to any control system. This program should consist of a monitoring/warning device, planned maintenance and calibration procedures, and a plan of action to be implemented
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when the monitor indicates a problem. The monitoring devices may be built into the process or control equipment in order to measure the operating parameters, or they may be installed so as to measure levels of hazards in the workplace environment. The presence of a complex control system and the lack of adequate warning properties for the substance being controlled makes monitoring/warning devices a virtual necessity. Monitoring/warning devices may indicate an emergency situation or the need for specific maintenance procedures on the process equipment, or control systems, as well as indicating the mode of operation for the control system (i.e., the use of personal protection until process/control problems can be solved). (e) Education Education in the need for and application of controls for occupational health hazards is essential to any control system. Management must be educated in the need for controls. Process and design engineers, as well as the industrial hygiene personnel, must be aware of both the principles of control and of various control options. Supervisors must be trained in the recognition of hazards related to specific processes and equipment. Finally, workers who are generally responsible for the operation and maintenance of control systems must be made aware of the occupational hazards which they face, and of the control measures which are to be followed in order to avoid occupational illness or injury both in routine and emergency operations. METHODS
TO REDUCE CARBON
MONOXIDE
EXPOSURE
Forty to sixty years ago, and even today, the approach to solving exposure to hazards was to vary the work schedule of employees. In addition, to encourage the workers to accept certain jobs in which the hazards were known, employers offered special financial incentives. This hazardous duty pay still exists. In the last 20 to 30 years, the approach used by employers relied heavily upon ventilation. The ventilation solutions were as simple as opening windows and doors to take advantage of the natural environment to the more mechanical solutions that utilized fans, air ducts, hoses, etc. In some cases, the mechanical solution was to improve the general workplace environment and as time progressed the solutions were more tailored to specific work sites. This last decade and today, the solutions are more sophisticated to take advantage of the advancing knowledge of science and engineering. There is considerable effort being directed to source prevention through improved combustion processes and catalytic conversion (3,9, 12, l&24). Although the national program to control CO emissions from motor vehicles has raised serious questions concerning the feasibility of the control program and the processes through which control policies are established, there continues to be attention focused on the CO problem (4, 8, 14, 17). Peterson (20), in the NIOSH publication, “The Industrial Environment, its Evaluation and Control,” lists the four basic principles for controlling the occupational environment as substitution, isolation, ventilation, and education. Not all of these principles are applicable to every form of hazard, but all occupational hazards can be controlled by the use of at least one of them.
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Substitution involves the replacement of hazardous materials, processes, or pieces of equipment with less or nonhazardous ones. Substitution may be the least expensive as well as the most positive method of controlling an occupational hazard. Usually, CO is encountered in industry as a waste product of the incomplete combustion of carbonaceous fuels. Unfortunately, nonhydrocarbon fuels are neither cheap nor readily available; therefore, substitution of alternate materials is not always feasible. Diesel fuel is being considered actively as the energy source for future automobiles. A 1973 study showed that the CO emissions were lowered when diesel fuel was used within a regenerative turbine combustor (13). Control efforts must be centered on the combustion process itself, to minimize the formation of CO (5, 6, 25). This can be accomplished through the establishment of the proper air/fuel ratios by the use of combustion monitoring equipment, and by the maintenance of adequate exhaust-stack draft through a proper supply of make-up air to the industrial building. Substitution of propane-fueled or electric powered lift trucks for gasoline-powered equipment can reduce or eliminate the CO hazard in factories and warehouses. Isolation can be achieved by the use of a physical barrier, or by the separation of the worker from the exposure source in space and time. Physical barriers can be effective for the control of CO. The barrier can be in the form of an enclosure around the worker, as is the case for crane operators or blast furnace operators, or around the process, such as an enclosed, ventilated tunnel for the cooling of foundry molds. For some workers such as toll booth operators or tunnel patrol officers, an automatic continuous CO-monitoring system and the provision of some control measure is essential. A 1972 study looked at a positive-pressure ventilation system to reduce levels of CO in the breathing zone of toll-booth attendants (21). Remotely controlled processes can isolate the worker from the hazard generation point by a distance. Special care must be taken in the design of industrial plants to isolate the exhaust stacks from combustion processes. This will prevent the inadvertent recirculation of CO into the workplace by an exhaust stack placed too close to a building-supply air inlet and can do much to prevent an unnecessary exposure. Local exhaust ventilation used alone, or in combination with substitution and isolation, is a powerful and versatile method for removing air contaminants from the workplace environment. The method is limited in that the source of the contaminant must be in a fixed location or move in a defined pattern. Perhaps the best known example of local-exhaust ventilation applied to the control of CO is the tailpipe exhaust system commonly seen in automotive service garages. There has been much research in this area over the years (11, 23). Dilution ventilation can occur naturally or by mechanical means. Mechanical ventilation is superior to natural ventilation to the extent that air currents are dictated primarily by the location and quantities of exhaust and supply air movers, rather than by weather factors. While not as desirable as the other control methods, dilution ventilation is almost always required as a supplement to those other techniques as few are 100% effective in preventing the release of CO in the workplace.
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Because CO is odorless and colorless and is usually present as an unwanted byproduct of the combustion process, the hazard of CO exposure is linked directly to worker awareness. An effective worker education program is necessary to instruct workers in the proper use and maintenance of combustion equipment, and continuous monitoring devices are necessary to warn of eminent hazard. A study found that in a metropolitan area, total travel by automobile resulted in a mean CO exposure nearly twice that of rail mass transit. This raises the possibility that going to and from work may be a prime exposure time to CO. The implications for alternate transportation schemes such as fast lanes, smaller engines, pooled movement, air conditioning, etc., are tremendous (7, 16). REFERENCES 1. “A Guide to Industrial Respiratory Protection,” NIOSH Publication 76- 189. 2. “ACGIH Industrial Ventilation-a Manual of Recommended Practices,” 15th ed. Committee on Industrial Ventilation, 1978. 3. Anonymous. Precipitator-cyclone combine cuts CO-boiier emissions. Oil Gas J. 75, 56 (1977). 4. Anonymous. “Reducing Pollution From Selected Energy Transformation Sources,” p. 230. Graham and Trotman, London, 1976. 5. Beale, N. R., and Hodgetts, D. Inlet valve throttling and the effects of mixture preparation and turbulence on the exhaust gas emissions of a spark ignition engine. Itrsr. Mech. Eng. (Loudon) Proc. 190, 13-21 (1976).
6. Bolton, M. S. and Taylor, D. S. Simple combustion efficiency indicator for automobile engines. Meas. Control
6, 399-400
(1973).
7. Cortese, A. D., and Spengler, D. Ability of fixed monitoring station to represent personal carbon monoxide exposure. J. Air. Pollut. Control Assoc. 26, 1144- 1150 (1976). 8. Croke, K. G., Croke, E. J., and Zerbe, R. 0. “Economic Analysis of Transportation Emission Control Strategies,” Proc. Air Pollut. Control Assoc. 69th Annu. Meeting, 1976. 9. Gilbert, L. F. Precise combustion-control saves fuel and power. Chem. Eng. (N. Y.) 83, 145- 150 (1976). 10. Gillett, J. E. Preventing emissions from manufacturing processes by suitable process design. Arms. Occup. Hyg.
19,301-308
(1976).
11. Hanna, G. M., and Butler, K. E., Jr. Design airflows for proper ventilation of service garages. Air Eng. 20-25 (October, 1967). 12. Kobylinski, T. P., Hammel, J. J., and Swift, H. E. Porous silica beads. Ind. Eng. Chem. Prod. Res. Develop. 14, 147- 150 (1975). 13. LaPointe, C. W., and Schultz, W. L. “Comparison of Emission Indexes Within a Turbine Combustor Operated on Diesel Fuel or Methanol,” SAE Paper 730669, 1973. 14. Leaderer, B. P., Stolwijk, J. A. J., and Zagraniski, R. T. Health Benefits Due to Reductions of CO Levels. Environ. Mannge. 1, 131- 137 (1976). 15. Lynch, J. R., Leidel, N. A., Nelson, R. A., and Boggs, R. F. “The Standards Completion Program Draft Technical Standards Analysis and Decision Logics,” NTIS: PB282989/AS, 1978. 16. Myronuk, J. D. Ingestion of carbon monoxide by occupants of vehicles while idling in drive-up facility lines. Water Air Soil Pollut. 7, 203-213 (1977). 17. Newhall, H. K., and El Messiri, I. A. “Combustion Chamber Designed for Minimum Engine Exhaust Emissions,” SAE Paper 700491, 1970. 18. Nicholas, D. M., and Shah, Y. T. Carbon monoxide over a platinum-porous fiber glass supported catalyst. Ind. Eng. Chem. Prod. RPs. Develop. 15, 35-40 (1976). 19. “Occupational Exposure to Carbon Monoxide,” U.S. Printing Offtce, Washington, D.C., 1972. 20. Peterson, J. E. Principles for controlling the occupational environment, in “The Industrial Environment-its Evaluation and Control,” pp. 51l-517. U.S. Government Printing Office Washington, D.C., 1973. 21. Rossano, A. T., Jr., and Alsid, H. F. “Evergreen Point Bridge Toll Booth Ventilation Study,” NTIS: PB221161, 1972.
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22. “The Industrial Environment-Its Evaluation and Control,” U.S. Government Printing Offtce, Washington, D.C., 1973. 23. Sheinbaum, M., and Stern, A. C. Tailpipe exhaust systems for garage ventilation. N.Y. Stnle Dept. Labor-Month.
Rev. 29, 25-28 (1950).
24. Sperkach, I. E., and Tumanov, G. V. Cleaning gas from the interbell space of a 1719blast furnace. Steel USSR 6, 355-356 (1976). 25. Stover, R. D. “Control of Carbon Monoxide Emissions from FCC Units by Ultracat Regeneration,” AIChe Workshop 6, 1975.
