Redefining Exposure for the Occupational Health CareProfessional

Measuring worker exposure to certain hazards is not always accurate. Exposure modeling is one method that can be used to better determine actual exposure range.

"You could barely see through the dust" "The noise was incredibly loud" "The smell was really strong" "I use my hands all day long." Traditional and occupational health care professionals (HCP) routinely ask workers questions about exposures. Information about exposures is used when performing toxicity studies, epidemiologic research, and investigations about health complaints and assessment of work-related injuries and illnesses for OSHA recordable and workers' compensation cases.

In many instances all there is to go on is the job title/description, old spot checks or as illustrated above individual worker reports. The task is certainly made simpler when extensive monitoring data is available where actual air monitoring for chemicals, noise, dosimetry or quantitative ergonomic evaluations. But even when air monitoring data is available, many factors may limit its usefulness.

Measuring the Data

Worker descriptions of exposure are rarely accurate. Workers making claims for compensation may have an interest in enhancing the level, or duration of a potential exposure whether it is chemical, a physical agent (i.e., noise, heat, vibration), biologic or biomechanical. Workers with psychosocial personal workplace concerns may also be prone to overstate exposures, while other workers may significantly under estimate workplace hazards. A recent ergonomics study demonstrated that workers in one setting consistently overestimated all levels of activity, such as hand usage, lifting and bending. During the course of the workday, while professional ergonomic assessment noted the true biomechanical activity level across the board to be 1/3 to 1/2 or more lower than that offered by the workers.

Relying on historical air monitoring data can also pose certain accuracy problems. The sampling may have been point source (right at the machine/process location) and not be reflective of actual breathing zone levels. Point source data may only reflect a few brief high bursts with virtually no exposure throughout the rest of the shift. Earlier testing results may reflect old manufacturing processes that have been since updated, or not assess the impact of newly installed local exhaust, or enhancement of general ventilation.

Workers may not be asked by the occupational HCP or volunteer their present or relatively recent use of respiratory protection. This information may be helpful for acute efforts of recent events, but not accurately represent prior exposures to agents with lung latent effects, such as asbestos, when respirators were not worn. It is just as important to assess the adequacy of the intended respiratory protection. Was the type of respirator used demonstrated to be effective for the chemical? Particulate or biologic agent? Was it carefully maintained? Were the filters changed frequently enough? And did the worker achieve an effective facial fit? It is not universally appreciated by all HCPs that even small gaps between the edge of the respirator and the face will seriously reduce or render useless the expected protection of the device.

Sampling Strategy

In the past several decades, the occupational and environmental presence of odors has created great concerns, especially in Sick Building Syndrome and those individuals claiming Multiple Chemical Sensitivities (MCS). MCS has now been designated as idiopathic environmental intolerance (IEI). However, many substances have odor thresholds (the airborne level at which individuals will first report the smell) well below the levels that result in acute or chronic adverse health effects. The rotten egg smell of hydrogen sulfide or the presence of formaldehyde are prime examples.

Unfortunately certain individuals may develop symptoms when they perceive chemical presence. In these instances, even carefully performed air monitoring may not convince the worker or their personal HCP that the workplace does not pose an actual health threat. Odor can be a protective characteristic. Its presence will alert the worker and management that there is a potential for hazardous exposure and checks for leaks and spills should be conducted. However, a number of substances have odor thresholds well above their toxicity thresholds. Thus, HCPs should have adequate informational databases to confirm these levels for individual agents.

It is important to realize that having monitoring results doesn't guarantee their utility in assessing true workplace exposure. Sampling Strategy requires careful consideration of a variety of issues including:

  • variability of production rates,
  • reliability of existing controls,
  • Nature of the chemical,
  • route of exposure (inhalation, skin absorption, ingestion),
  • proximity of work to exposure,
  • intermittent or continuos release potential,
  • potential for individual work practice variations,
  • variability of ventilation,
  • seasons,
  • what shift is sampled,
  • duration of sampling time, and
  • other work conducted in area.

The nature of the hazard will frequently impact how sampling is conducted. For example, Baker's Asthma is considered to be the result of exposure to high levels, usually brief bursts in susceptible individuals. Sampling to obtain a time-weighted average (TWA) over an eight hour day will not provide information on peaks which will help identify potentially sensitizing exposures.

Exposure Modeling

Even when exposure data is lacking occupational HCP can frequently turn to exposure modeling to help establish actual or a probable exposure range likely to have occurred. Exposure modeling takes a great deal of expertise and experience. Modeling can be performed through calculations, material testing, laboratory recreation and reconstruction sampling.

Accurate exposure assessment is critical to many of the functions of occupational HCPs. Awareness of potential gaps, and pitfalls can prevent poor decision making results in overestimates and underestimates of what really happened to workers. Working as a team with highly trained and experienced industrial hygienists is a must. But remember it frequently falls on the HCP to determine the health endpoint of concern and personal health factors. Such as facial disfigurement preventing good respiratory fit that will impact how exposure determination is measured or modeled.

Contributing Editor Howard M. Sandler, M.D. is president of Sandler Occupational Medicine Associates, Inc./OccuLink, Melville, N.Y.

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