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Thursday, 10 March 2011 17:36

Occupational Hygiene: Control of Exposures Through Intervention

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After a hazard has been recognized and evaluated, the most appropriate interventions (methods of control) for a particular hazard must be determined. Control methods usually fall into three categories:

  1. engineering controls
  2. administrative controls
  3. personal protective equipment.


As with any change in work processes, training must be provided to ensure the success of the changes.

Engineering controls are changes to the process or equipment that reduce or eliminate exposures to an agent. For example, substituting a less toxic chemical in a process or installing exhaust ventilation to remove vapours generated during a process step, are examples of engineering controls. In the case of noise control, installing sound-absorbing materials, building enclosures and installing mufflers on air exhaust outlets are examples of engineering controls. Another type of engineering control might be changing the process itself. An example of this type of control would be removal of one or more degreasing steps in a process that originally required three degreasing steps. By removing the need for the task that produced the exposure, the overall exposure for the worker has been controlled. The advantage of engineering controls is the relatively small involvement of the worker, who can go about the job in a more controlled environment when, for instance, contaminants are automatically removed from the air. Contrast this to the situation where the selected method of control is a respirator to be worn by the worker while performing the task in an “uncontrolled” workplace. In addition to the employer actively installing engineering controls on existing equipment, new equipment can be purchased that contains the controls or other more effective controls. A combination approach has often been effective (i.e., installing some engineering controls now and requiring personal protective equipment until new equipment arrives with more effective controls that will eliminate the need for personal protective equipment). Some common examples of engineering controls are:

  • ventilation (both general and local exhaust ventilation)
  • isolation (place a barrier between the worker and the agent)
  • substitution (substitute less toxic, less flammable material, etc.)
  • change the process (eliminate hazardous steps).


The occupational hygienist must be sensitive to the worker’s job tasks and must solicit worker participation when designing or selecting engineering controls. Placing barriers in the workplace, for example, could significantly impair a worker’s ability to perform the job and may encourage “work arounds”. Engineering controls are the most effective methods of reducing exposures. They are also, often, the most expensive. Since engineering controls are effective and expensive it is important to maximize the involvement of the workers in the selection and design of the controls. This should result in a greater likelihood that the controls will reduce exposures.

Administrative controls involve changes in how a worker accomplishes the necessary job tasks—for example, how long they work in an area where exposures occur, or changes in work practices such as improvements in body positioning to reduce exposures. Administrative controls can add to the effectiveness of an intervention but have several drawbacks:

  1. Rotation of workers may reduce overall average exposure for the workday but it provides periods of high short-term exposure for a larger number of workers. As more becomes known about toxicants and their modes of action, short-term peak exposures may represent a greater risk than would be calculated based on their contribution to average exposure.
  2. Changing work practices of workers can present a significant enforcement and monitoring challenge. How work practices are enforced and monitored determines whether or not they will be effective. This constant management attention is a significant cost of administrative controls.


Personal protective equipment consists of devices provided to the worker and required to be worn while performing certain (or all) job tasks. Examples include respirators, chemical goggles, protective gloves and faceshields. Personal protective equipment is commonly used in cases where engineering controls have not been effective in controlling the exposure to acceptable levels or where engineering controls have not been found to be feasible (for cost or operational reasons). Personal protective equipment can provide significant protection to workers if worn and used correctly. In the case of respiratory protection, protection factors (ratio of concentration outside the respirator to that inside) can be 1,000 or more for positive-pressure supplied air respirators or ten for half-face air-purifying respirators. Gloves (if selected appropriately) can protect hands for hours from solvents. Goggles can provide effective protection from chemical splashes.

Intervention: Factors to Consider

Often a combination of controls is used to reduce the exposures to acceptable levels. Whatever methods are selected, the intervention must reduce the exposure and resulting hazard to an acceptable level. There are, however, many other factors that need to be considered when selecting an intervention. For example:

  • effectiveness of the controls
  • ease of use by the employee
  • cost of the controls
  • adequacy of the warning properties of the material
  • acceptable level of exposure
  • frequency of exposure
  • route(s) of exposure
  • regulatory requirements for specific controls.


Effectiveness of controls

Effectiveness of controls is obviously a prime consideration when taking action to reduce exposures. When comparing one type of intervention to another, the level of protection required must be appropriate for the challenge; too much control is a waste of resources. Those resources could be used to reduce other exposures or exposures of other employees. On the other hand, too little control leaves the worker exposed to unhealthy conditions. A useful first step is to rank the interventions according to their effectiveness, then use this ranking to evaluate the significance of the other factors.

Ease of use

For any control to be effective the worker must be able to perform his or her job tasks with the control in place. For example, if the control method selected is substitution, then the worker must know the hazards of the new chemical, be trained in safe handling procedures, understand proper disposal procedures, and so on. If the control is isolation—placing an enclosure around the substance or the worker—the enclosure must allow the worker to do his or her job. If the control measures interfere with the tasks of the job, the worker will be reluctant to use them and may find ways to accomplish the tasks that could result in increased, not decreased, exposures.


Every organization has limits on resources. The challenge is to maximize the use of those resources. When hazardous exposures are identified and an intervention strategy is being developed, cost must be a factor. The “best buy” many times will not be the lowest- or highest-cost solutions. Cost becomes a factor only after several viable methods of control have been identified. Cost of the controls can then be used to select the controls that will work best in that particular situation. If cost is the determining factor at the outset, poor or ineffective controls may be selected, or controls that interfere with the process in which the employee is working. It would be unwise to select an inexpensive set of controls that interfere with and slow down a manufacturing process. The process then would have a lower throughput and higher cost. In very short time the “real” costs of these “low cost” controls would become enormous. Industrial engineers understand the layout and overall process; production engineers understand the manufacturing steps and processes; the financial analysts understand the resource allocation problems. Occupational hygienists can provide a unique insight into these discussions due to their understanding of the specific employee’s job tasks, the employee’s interaction with the manufacturing equipment as well as how the controls will work in a particular setting. This team approach increases the likelihood of selecting the most appropriate (from a variety of perspectives) control.

Adequacy of warning properties

When protecting a worker against an occupational health hazard, the warning properties of the material, such as odour or irritation, must be considered. For example, if a semiconductor worker is working in an area where arsine gas is used, the extreme toxicity of the gas poses a significant potential hazard. The situation is compounded by arsine’s very poor warning properties—the workers cannot detect the arsine gas by sight or smell until it is well above acceptable levels. In this case, controls that are marginally effective at keeping exposures below acceptable levels should not be considered because excursions above acceptable levels cannot be detected by the workers. In this case, engineering controls should be installed to isolate the worker from the material. In addition, a continuous arsine gas monitor should be installed to warn workers of the failure of the engineering controls. In situations involving high toxicity and poor warning properties, preventive occupational hygiene is practised. The occupational hygienist must be flexible and thoughtful when approaching an exposure problem.

Acceptable level of exposure

If controls are being considered to protect a worker from a substance such as acetone, where the acceptable level of exposure may be in the range of 800 ppm, controlling to a level of 400 ppm or less may be achieved relatively easily. Contrast the example of acetone control to control of 2-ethoxyethanol, where the acceptable level of exposure may be in the range of 0.5 ppm. To obtain the same per cent reduction (0.5 ppm to 0.25 ppm) would probably require different controls. In fact, at these low levels of exposure, isolation of the material may become the primary means of control. At high levels of exposure, ventilation may provide the necessary reduction. Therefore, the acceptable level determined (by the government, company, etc.) for a substance can limit the selection of controls.

Frequency of exposure

When assessing toxicity the classic model uses the following relationship:


Dose, in this case, is the amount of material being made available for absorption. The previous discussion focused on minimizing (lowering) the concentration portion of this relationship. One might also reduce the time spent being exposed (the underlying reason for administrative controls). This would similarly reduce the dose. The issue here is not the employee spending time in a room, but how often an operation (task) is performed. The distinction is important. In the first example, the exposure is controlled by removing the workers when they are exposed to a selected amount of toxicant; the intervention effort is not directed at controlling the amount of toxicant (in many situations there may be a combination approach). In the second case, the frequency of the operation is being used to provide the appropriate controls, not to determine a work schedule. For example, if an operation such as degreasing is performed routinely by an employee, the controls may include ventilation, substitution of a less toxic solvent or even automation of the process. If the operation is performed rarely (e.g., once per quarter) personal protective equipment may be an option (depending on many of the factors described in this section). As these two examples illustrate, the frequency with which an operation is performed can directly affect the selection of controls. Whatever the exposure situation, the frequency with which a worker performs the tasks must be considered and factored into the control selection.

Route of exposure obviously is going to affect the method of control. If a respiratory irritant is present, ventilation, respirators, and so on, would be considered. The challenge for the occupational hygienist is identifying all routes of exposure. For example, glycol ethers are used as a carrier solvent in printing operations. Breathing-zone air concentrations can be measured and controls implemented. Glycol ethers, however, are rapidly absorbed through intact skin. The skin represents a significant route of exposure and must be considered. In fact, if the wrong gloves are chosen, the skin exposure may continue long after the air exposures have decreased (due to the employee continuing to use gloves that have experienced breakthrough). The hygienist must evaluate the substance—its physical properties, chemical and toxicological properties, and so on—to determine what routes of exposure are possible and plausible (based on the tasks performed by the employee).

In any discussion of controls, one of the factors that must be considered is the regulatory requirements for controls. There may well be codes of practice, regulations, and so on, that require a specific set of controls. The occupational hygienist has flexibility above and beyond the regulatory requirements, but the minimum mandated controls must be installed. Another aspect of the regulatory requirements is that the mandated controls may not work as well or may conflict with the best judgement of the occupational hygienist. The hygienist must be creative in these situations and find solutions that satisfy the regulatory as well as best practice goals of the organization.

Training and Labelling

Regardless of what form of intervention is eventually selected, training and other forms of notification must be provided to ensure that the workers understand the interventions, why they were selected, what reductions in exposure are expected, and the role of the workers in achieving those reductions. Without the participation and understanding of the workforce, the interventions will likely fail or at least operate at reduced efficiency. Training builds hazard awareness in the workforce. This new awareness can be invaluable to the occupational hygienist in identifying and reducing previously unrecognized exposures or new exposures.

Training, labelling and related activities may be part of a regulatory compliance scheme. It would be prudent to check the local regulations to ensure that whatever type of training or labelling is undertaken satisfies the regulatory as well as operational requirements.


In this short discussion on interventions, some general considerations have been presented to stimulate thought. In practice, these rules become very complex and often have significant ramifications for employee and company health. The occupational hygienist’s professional judgement is essential in selecting the best controls. Best is a term with many different meanings. The occupational hygienist must become adept at working in teams and soliciting input from the workers, management and technical staff.



Read 4513 times Last modified on Thursday, 13 October 2011 20:43


Part I. The Body
Part II. Health Care
Part III. Management & Policy
Part IV. Tools and Approaches
Biological Monitoring
Epidemiology and Statistics
Occupational Hygiene
Personal Protection
Record Systems and Surveillance
Part V. Psychosocial and Organizational Factors
Part VI. General Hazards
Part VII. The Environment
Part VIII. Accidents and Safety Management
Part IX. Chemicals
Part X. Industries Based on Biological Resources
Part XI. Industries Based on Natural Resources
Part XII. Chemical Industries
Part XIII. Manufacturing Industries
Part XIV. Textile and Apparel Industries
Part XV. Transport Industries
Part XVI. Construction
Part XVII. Services and Trade
Part XVIII. Guides

Occupational Hygiene Additional Resources

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Occupational Hygiene References

Abraham, MH, GS Whiting, Y Alarie et al. 1990. Hydrogen bonding 12. A new QSAR for upper respiratory tract irritation by airborne chemicals in mice. Quant Struc Activity Relat 9:6-10.

Adkins, LE et al. 1990. Letter to the Editor. Appl Occup Environ Hyg 5(11):748-750.

Alarie, Y. 1981. Dose response analysis in animal studies: Prediction of human responses. Environ Health Persp 42:9-13.

American Conference of Governmental Industrial Hygienists (ACGIH). 1994. 1993-1994 Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. Cincinnati: ACGIH.

—. 1995. Documentation of Threshold Limit Values. Cincinnati: ACGIH.

Baetjer, AM. 1980. The early days of industrial hygiene: Their contribution to current problems. Am Ind Hyg Assoc J 41:773-777.

Bailer, JC, EAC Crouch, R Shaikh, and D Spiegelman. 1988. One-hit models of carcinogenesis: Conservative or not? Risk Anal 8:485-490.

Bogers, M, LM Appelman, VJ Feron, et al. 1987. Effects of the exposure profile on the inhalation toxicity of carbon tetrachloride in male rats. J Appl Toxicol 7:185-191.

Boleij, JSM, E Buringh, D Heederik, and H Kromhour. 1995. Occupational Hygiene for Chemical and Biological Agents. Amsterdam: Elsevier.

Bouyer, J and D Hémon. 1993. Studying the performance of a job exposure matrix. Int J Epidemiol 22(6) Suppl. 2:S65-S71.

Bowditch, M, DK Drinker, P Drinker, HH Haggard, and A Hamilton. 1940. Code for safe concentrations of certain common toxic substances used in industry. J Ind Hyg Toxicol 22:251.

Burdorf, A. 1995. Certification of Occupational Hygienists—A Survey of Existing Schemes Throughout the World. Stockholm: International Occupational Hygiene Association (IOHA).

Bus, JS and JE Gibson. 1994. Body defense mechanisms to toxicant exposure. In Patty’s Industrial Hygiene and Toxicology, edited by RL Harris, L Cralley and LV Cralley. New York: Wiley.

Butterworth, BE and T Slaga. 1987. Nongenotoxic Mechanisms in Carcinogenesis: Banbury Report 25. Cold Spring Harbor, New York: Cold Spring Harbor Laboratory.

Calabrese, EJ. 1983. Principles of Animal Extrapolation. New York: Wiley.

Casarett, LJ. 1980. In Casarett and Doull’s Toxicology: The Basic Science of Poisons, edited by J Doull, CD Klaassen, and MO Amdur. New York: Macmillan.

Castleman, BI and GE Ziem. 1988. Corporate Influence on Threshold Limit Values. Am J Ind Med 13(5).

Checkoway, H and CH Rice. 1992. Time-weighted averages, peaks, and other indices of exposure in occupational epidemiolgy. Am J Ind Med 21:25-33.

Comité Européen de Normalisation (CEN). 1994. Workplace Atmoshperes—Guidance for the Assessment of Exposure to Chemical Agents for Comparison With Limit Values and Measurement Strategy. EN 689, prepared by CEN Technical Committee 137. Brussels: CEN.

Cook, WA. 1945. Maximum allowable concentrations of industrial contaminants. Ind Med 14(11):936-946.

—. 1986. Occupational Exposure Limits—Worldwide. Akron, Ohio: American Industrial Hygiene Association (AIHA).

Cooper, WC. 1973. Indicators of susceptibility to industrial chemicals. J Occup Med 15(4):355-359.

Corn, M. 1985. Strategies for air sampling. Scand J Work Environ Health 11:173-180.

Dinardi, SR. 1995. Calculation Methods for Industrial Hygiene. New York: Van Nostrand Reinhold.

Doull, J. 1994. The ACGIH Approach and Practice. Appl Occup Environ Hyg 9(1):23-24.

Dourson, MJ and JF Stara. 1983. Regulatory history and experimental support of uncertainty (safety) factors. Regul Toxicol Pharmacol 3:224-238.

Droz, PO. 1991. Quantification of concomitant biological and air monitoring results. Appl Ind Hyg 6:465-474.

—. 1992. Quantification of biological variability. Ann Occup Health 36:295-306.

Fieldner, AC, SH Katz, and SP Kenney. 1921. Gas Masks for Gases Met in Fighting Fires. Bulletin No. 248. Pittsburgh: USA Bureau of Mines.

Finklea, JA. 1988. Threshold limit values: A timely look. Am J Ind Med 14:211-212.

Finley, B, D Proctor, and DJ Paustenbach. 1992. An alternative to the USEPA’s proposed inhalation reference concentration for hexavalent and trivalent chromium. Regul Toxicol Pharmacol 16:161-176.

Fiserova-Bergerova, V. 1987. Development of using BEIs and their implementation. Appl Ind Hyg 2(2):87-92.

Flury, F and F Zernik. 1931. Schadliche Gase, Dampfe, Nebel, Rauch-und Staubarten. Berlin: Springer.

Goldberg, M, H Kromhout, P Guénel, AC Fletcher, M Gérin, DC Glass, D Heederik, T Kauppinen, and A Ponti. 1993. Job exposures matrices in industry. Int J Epidemiol 22(6) Suppl. 2:S10-S15.

Gressel, MG and JA Gideon. 1991. An overview of process hazard evaluation techniques. Am Ind Hyg Assoc J 52(4):158-163.

Henderson, Y and HH Haggard. 1943. Noxious Gases and the Principles of Respiration Influencing their Action. New York: Reinhold.

Hickey, JLS and PC Reist. 1979. Adjusting occupational exposure limits for moonlighting, overtime, and environmental exposures. Am Ind Hyg Assoc J 40:727-734.

Hodgson, JT and RD Jones. 1990. Mortality of a cohort of tin miners 1941-1986. Br J Ind Med 47:665-676.

Holzner, CL, RB Hirsh, and JB Perper. 1993. Managing workplace exposure information. Am Ind Hyg Assoc J 54(1):15-21.

Houba, R, D Heederik, G Doekes, and PEM van Run. 1996. Exposure sensitization relationship for alpha-amylase allergens in the baking industry. Am J Resp Crit Care Med 154(1):130-136.

International Congress on Occupational Health (ICOH). 1985. Invited lectures of the XXI International Congress on Occupational Health, Dublin. Scand J Work Environ Health 11(3):199-206.

Jacobs, RJ. 1992. Strategies to recognize biological agents in the work environment and possibilities for setting standards for biological agents. IOHA first International Science Conference, Brussels, Belgium 7-9 Dec 1992.

Jahr, J. 1974. Dose-response basis for setting a quartz threshold limit value. Arch Environ Health 9:338-340.

Kane, LE and Y Alarie. 1977. Sensory irritation to formaldehyde and acrolein during single and repeated exposures in mills. Am Ind Hyg Assoc J 38:509-522.

Kobert, R. 1912. The smallest amounts of noxious industrial gases which are toxic and the amounts which may perhaps be endured. Comp Pract Toxicol 5:45.

Kromhout, H, E Symanski, and SM Rappaport. 1993. Comprehensive evaluation of within-and between-worker components of occupational exposure to chemical agents. Ann Occup Hyg 37:253-270.

LaNier, ME. 1984. Threshold Limit Values: Discussion and 35 Year Index with Recommendations (TLVs: 1946-81). Cincinnati: ACGIH.

Lehmann, KB. 1886. Experimentelle Studien über den Einfluss Technisch und Hygienisch Wichtiger Gase und Dampfe auf Organismus: Ammoniak und Salzsauregas. Arch Hyg 5:1-12.

Lehmann, KB and F Flury. 1938. Toxikologie und Hygiene der Technischen Losungsmittel. Berlin: Springer.

Lehmann, KB and L Schmidt-Kehl. 1936. Die 13 Wichtigsten Chlorkohlenwasserstoffe der Fettreihe vom Standpunkt der Gewerbehygiene. Arch Hyg Bakteriol 116:131-268.

Leidel, NA, KA Busch, and JR Lynch. 1977. NIOSH Occupational Exposure Sampling Strategy Manuel. Washington, DC: NIOSH.

Leung, HW and DJ Paustenbach. 1988a. Setting occupational exposure limits for irritant organic acids and bases based on their equilibrium dissociation constants. Appl Ind Hyg 3:115-118.

—. 1988b. Application of pharmokinetics to derive biological exposure indexes from threshold limit values. Amer Ind Hyg Assoc J 49:445-450.

Leung, HW, FJ Murray and DJ Paustenbach. 1988. A proposed occupational exposure limit for 2, 3, 7, 8 - TCDD. Amer Ind Hyg Assoc J 49:466-474.

Lundberg, P. 1994. National and international approaches to occupational standard setting within Europe. Appl Occup Environ Hyg 9:25-27.

Lynch, JR. 1995. Measurement of worker exposure. In Patty’s Industrial Hygiene and Toxicology, edited by RL Harris, L Cralley, and LV Cralley. New York: Wiley.

Maslansky, CJ and SP Maslansky. 1993. Air Monitoring Instrumentation. New York: Van Nostrand Reinhold.

Menzel, DB. 1987. Physiological pharmacokinetic modelling. Environ Sci Technol 21:944-950.

Miller, FJ and JH Overton. 1989. Critical issues in intra-and interspecies dosimetry of ozone. In Atmospheric Ozone Research and Its Policy Implications, edited by T Schneider, SD Lee, GJR Wolters, and LD Grant. Amsterdam: Elsevier.

National Academy of Sciences (NAS) and National Research Council (NRC). 1983. Risk Assessment in the Federal Government: Managing the Process. Washington, DC: NAS.

National Safety Council (NSC). 1926. Final Report of the Committee of the Chemical and Rubber Sector on Benzene. Washington, DC: National Bureau of Casualty and Surety Underwriters.

Ness, SA. 1991. Air Monitoring for Toxic Exposures. New York: Van Nostrand Reinhold.

Nielsen, GD. 1991. Mechanisms of activation of the sensory irritant receptor. CRC Rev Toxicol 21:183-208.

Nollen, SD. 1981. The compressed workweek: Is it worth the effort? Ing Eng :58-63.

Nollen, SD and VH Martin. 1978. Alternative Work Schedules. Part 3: The Compressed Workweek. New York: AMACOM.

Olishifski, JB. 1988. Administrative and clinical aspects in the chapter Industrial Hygiene. In Occupational Medicine: Principles and Practical Applications, edited by C Zenz. Chicago: Year Book Medical.

Panett, B, D Coggon, and ED Acheson. 1985. Job exposure matrix for use in population based studies in England and Wales. Br J Ind Med 42:777-783.

Park, C and R Snee. 1983. Quantitative risk assessment: State of the art for carcinogenesis. Fund Appl Toxicol 3:320-333.

Patty, FA. 1949. Industrial Hygiene and Toxicology. Vol. II. New York: Wiley.

Paustenbach, DJ. 1990a. Health risk assesment and the practice of industrial hygiene. Am Ind Hyg Assoc J 51:339-351.

—. 1990b. Occupational exposure limits: Their critical role in preventative medicine and risk management. Am Ind Hyg Assoc J 51:A332-A336.

—. 1990c. What Does the Risk Assessment Process Tell us about the TLVs? Presented at the 1990 Joint Conference on Industrial Hygiene. Vancouver, BC, 24 October.

—. 1994. Occupational exposure limits, pharmacokinetics, and unusual workshifts. In Patty’s Industrial Hygiene and Toxicology. Vol. IIIa (4th edn.). New York:Wiley.

—. 1995. The practice of health risk assessment in the United States (1975-1995): How the US and other countries can benefit from that experience. Hum Ecol Risk Assess 1:29-79.

—. 1997. OSHA’s program for updating the permissible exposure limits (PELs): Can risk assessment help “move the ball forward”? Risk in Perspectives 5(1):1-6. Harvard University School of Public Health.

Paustenbach, DJ and RR Langner. 1986. Setting corporate exposure limits: State of the art. Am Ind Hyg Assoc J 47:809-818.

Peto, J, H Seidman, and IJ Selikoff. 1982. Mesothelioma mortality in asbestos workers: implications for models of carcinogenesis and risk assessment. Br J Cancer 45:124-134.

Phthisis Prevention Committee. 1916. Report of Miners. Johannesburg: Phthisis Prevention Committee.

Post, WK, D Heederik, H Kromhout, and D Kromhout. 1994. Occupational exposures estimated by a population specific job-exposure matrix and 25-year incidence rate of chronic non-specific lung disease (CNSLD): The Zutphen Study. Eur Resp J 7:1048-1055.

Ramazinni, B. 1700. De Morbis Atrificum Diatriba [Diseases of Workers]. Chicago: The Univ. of Chicago Press.

Rappaport, SM. 1985. Smoothing of exposure variability at the receptor: Implications for health standards. Ann Occup Hyg 29:201-214.

—. 1991. Assessment of long-term exposures to toxic substances in air. Ann Occup Hyg 35:61-121.

—. 1995. Interpreting levels of exposures to chemical agents. In Patty’s Industrial Hygiene and Toxicology, edited by RL Harris, L Cralley, and LV Cralley. New York: Wiley.

Rappaport, SM, E Symanski, JW Yager, and LL Kupper. 1995. The relationship between environmental monitoring and biological markers in exposure assessment. Environ Health Persp 103 Suppl. 3:49-53.

Renes, LE. 1978. The industrial hygiene survey and personel. In Patty’s Industrial Hygiene and Toxicology, edited by GD Clayton and FE Clayton. New York: Wiley.

Roach, SA. 1966. A more rational basis for air sampling programmes. Am Ind Hyg Assoc J 27:1-12.

—. 1977. A most rational basis for air sampling programmes. Am Ind Hyg Assoc J 20:67-84.

Roach, SA and SM Rappaport. 1990. But they are not thresholds: A critical analysis of the documentation of threshold limit values. Am J Ind Med 17:727-753.

Rodricks, JV, A Brett, and G Wrenn. 1987. Significant risk decisions in federal regulatory agencies. Regul Toxicol Pharmacol 7:307-320.

Rosen, G. 1993. PIMEX-combined use of air sampling instruments and video filming: Experience and results during six years of use. Appl Occup Environ Hyg 8(4).

Rylander, R. 1994. Causative agents for organic dust related disease: Proceedings of an international workshop, Sweden. Am J Ind Med 25:1-11.

Sayers, RR. 1927. Toxicology of gases and vapors. In International Critical Tables of Numerical Data, Physics, Chemistry and Toxicology. New York: McGraw-Hill.

Schrenk, HH. 1947. Interpretation of permissible limits. Am Ind Hyg Assoc Q 8:55-60.

Seiler, JP. 1977. Apparent and real thresholds: A study of two mutagens. In Progress in Genetic Toxicology, edited by D Scott, BA Bridges, and FH Sobels. New York: Elsevier Biomedical.

Seixas, NS, TG Robins, and M Becker. 1993. A novel approach to the characterization of cumulative exposure for the study of chronic occupational disease. Am J Epidemiol 137:463-471.

Smith, RG and JB Olishifski. 1988. Industrial toxicology. In Fundamentals of Industrial Hygiene, edited by JB Olishifski. Chicago: National Safety Council.

Smith, TJ. 1985. Development and application of a model for estimating alveolar and interstitial dust levels. Ann Occup Hyg 29:495-516.

—. 1987. Exposure assessment for occupational epidemiology. Am J Ind Med 12:249-268.

Smyth, HF. 1956. Improved communication: Hygienic standard for daily inhalation. Am Ind Hyg Assoc Q 17:129-185.

Stokinger, HE. 1970. Criteria and procedures for assessing the toxic responses to industrial chemicals. In Permissible Levels of Toxic Substances in the Working Environment. Geneva: ILO.

—. 1977. The case for carcinogen TLV’s continues strong. Occup Health Safety 46 (March-April):54-58.

—. 1981. Threshold limit values: Part I. Dang Prop Ind Mater Rep (May-June):8-13.

Stott, WT, RH Reitz, AM Schumann, and PG Watanabe. 1981. Genetic and nongenetic events in neoplasia. Food Cosmet Toxicol 19:567-576.

Suter, AH. 1993. Noise and conservation of hearing. In Hearing Conservation Manual. Milwaukee, Wisc: Council for Accreditation in Occupational Hearing Conservation.

Tait, K. 1992. The Workplace Exposure Assessment Expert System (WORK SPERT). Am Ind Hyg Assoc J 53(2):84-98.

Tarlau, ES. 1990. Industrial hygiene with no limits. A guest editorial. Am Ind Hyg Assoc J 51:A9-A10.

Travis, CC, SA Richter, EA Crouch, R Wilson, and E Wilson. 1987. Cancer risk management: A review of 132 federal regulatory decisions. Environ Sci Technol 21(5):415-420.

Watanabe, PG, RH Reitz, AM Schumann, MJ McKenna, and PJ Gehring. 1980. Implications of the mechanisms of tumorigenicity for risk assessment. In The Scientific Basis of Toxicity Assessment, edited by M Witschi. Amsterdam: Elsevier.

Wegman, DH, EA Eisen, SR Woskie, and X Hu. 1992. Measuring exposure for the epidemiologic study of acute effects. Am J Ind Med 21:77-89.

Weil, CS. 1972. Statistics versus safety factors and scientific judgment in the evaluation of safety for man. Toxicol Appl Pharmacol 21:454-463.

Wilkinson, CF. 1988. Being more realistic about chemical carcinogenesis. Environ Sci Technol 9:843-848.

Wong, O. 1987. An industry wide mortality study of chemical workers occupationally exposed to benzene. II Dose-response analyses. Br J Ind Med 44:382-395.

World Commission on Environment and Development (WCED). 1987. Our Common Future. Brundtland Report. Oxford: OUP.

World Health Organization (WHO). 1977. Methods used in Establishing Permissible Levels in Occupational Exposure to Harmful Agents. Technical Report No. 601. Geneva: International Labour Organization (ILO).

—. 1992a. Our Planet, Our Health. Report of the WHO Commission on Health and Environment. Geneva: WHO.

—. 1992b. Occupational Hygiene in Europe: Development of the Profession. European Occupational Health Series No. 3. Copenhagen: WHO Regional Office for Europe.

Zielhuis, RL and van der FW Kreek. 1979a. Calculations of a safety factor in setting health based permissible levels for occupational exposure. A proposal. I. Int Arch Occup Environ Health 42:191-201.

Ziem, GE and BI Castleman. 1989. Threshold limit values: Historical perspective and current practice. J Occup Med 13:910-918.