Goelzer defines occupational hygiene as "the science of the anticipation, recognition, evaluation, and control of hazards arising in or
from the workplace, and which could impair the health and well-being of workers, also taking into
account the possible impact on the surrounding communities and the general environment."
I like this definition because it talks not only about the health of workers, but also their well- being, which the U.S. Centers for Disease
Control and Prevention, or CDC, asserts includes the presence of contentment and happiness,
the absence of depression or anxiety, satisfaction with life, fulfillment, and positive functioning.
This definition for occupational hygiene also properly takes into account not only the impact of workplace hazards on the
workers themselves, but also their impact on those living and working nearby.
A key part of the definition, highlighted in lighter blue, is the occupational hygiene framework:
anticipating, recognizing, evaluating, and controlling hazards in the workplace. This is the central work of occupational hygienists.
Let's step through what each one of these tasks involves.
Anticipation means that occupational hygienists try to identify potential exposures to hazardous agents before the exposures exist.
This incorporates the concept of pollution prevention, which may include modifying a process or work task to generate less of an
agent, using less toxic or non-toxic materials in a process or a work task, implementing conservation practices to reduce emissions so
that there will be less exposure to potentially hazardous agents, and reusing those agents
whenever possible rather than bringing more of the agent into the workplace from outside.
Another field that utilizes the concepts of anticipation and pollution prevention is the science and practice of green chemistry.
The U.S. Environmental Protection Agency defines green chemistry as "the design of chemical products and processes that reduce or
eliminate the use or generation of hazardous substances."
The 12 principles of green chemistry, defined by Anastas and Warner in 1998, are shown on the right.
These principles broadly define ways in which chemicals, processes, and products can be
made less harmful to people and the environment.
For anticipation to work effectively, occupational hygienists must be included in the design of new facilities, processes, and products.
Unfortunately, this is often not the case. Once a facility, process, or product exists, hazard recognition becomes important.
Recognition is the identification of potentially- hazardous agents in workplaces that already exist.
Harris and co-authors discuss the basic information that informs the recognition of potentially hazardous exposures.
This information includes having detailed knowledge of an industrial process and any resulting harmful emissions;
understanding the toxicological, chemical, and physical properties of potentially-hazardous emissions from these processes;
an awareness of the sites in a process that may lead to worker exposures, perhaps, for example, due to openings in enclosures or the application
of energy that may release a hazardous chemical; understanding job work patterns with energy requirements among the workers,
in other words how workers move through the workplace and interact with a process so that specific locations might be identified at which
precautions are most critical; and, finally, other coexisting stresses that may be important, including, for instance, exposures to other
chemicals that may have similar health effects or ergonomic stresses that may cause work
tasks to be performed in ways that increase chemical exposures.
Once potentially-hazardous exposures are recognized, they must be evaluated.
Evaluation is the qualitative and quantitative assessment of worker exposures to hazardous agents. This can be done in several ways.
One of the main ways in which occupational hygienists evaluate exposures is to make measurements.
This may include air sampling to measure exposure concentrations to airborne hazards.
The worker in this image is wearing air monitors on her torso, some of which are connected to sampling pumps that draw air
through the monitors. The sampling media separate the hazardous agents from the air stream for later analysis in a laboratory.
Occupational hygienists might also perform dermal or surface sampling to measure the
loading of a pollutant on the skin or on a surface.
In addition, samples may be taken from the human body – such as blood, urine, or even
fingernails or toenails – which can be used to evaluate a worker's dose to a chemical.
This type of measurement is referred to as biomonitoring.
Occupational hygienists may also potentially use models to evaluate exposures.
Exposure models are simplified mathematical representations of the real world that may be
useful for predicting or estimating exposures to hazardous chemicals.
The simple model illustrated in this image is known as the well-mixed room model in which a clean airstream with a certain flow rate
enters a room of known volume into which a hazardous chemical is being continuously generated.
As soon as the pollutant is generated, it is assumed to be distributed uniformly throughout the entire room, thus the room is "well-mixed".
Contaminated air leaves the room at the same rate in which clean air enters, and the model may include loss terms due to, for example,
adsorption of vapors to surfaces or settling of particles due to gravity.
With these parameters, concentrations inside the room can be predicted, and worker exposures can be estimated.
This method of evaluation is unlikely to be perfect, but it may be useful for prioritizing potential hazards for additional evaluation.
With both exposure models and exposure measurements, occupational hygienists must
make judgments using the information that they have received from their evaluations.
This is a critical skill for an occupational hygienist that develops with training and experience.
When evaluations indicate that an exposure is problematic for workers, then the exposure must be controlled.
Controls are interventions to reduce hazardous exposures. There is a classic "hierarchy of control" to classify various control options.
The hierarchy is illustrated in this diagram from the National Institute for Occupational Safety and Health, or NIOSH.
At the top of the hierarchy is elimination of the hazard. Elimination means physically removing the hazard from the workplace.
This is at the top of the hierarchy because exposures can no longer occur.
Next is substitution, replacing the hazard with something that is less hazardous.
Engineering controls try to separate people from the hazard or the hazard from people.
Examples include enclosures around processes, control booths, local exhaust
ventilation, laboratory hoods, and air pollution control equipment.
I consider substitution to be closely related to engineering controls because, for example, substituting one chemical for another in a
process may involve re-engineering the process or, at the very least, engineers must confirm that a change will not alter the product significantly.
Administrative controls are changes in how, when, or by whom work tasks are conducted.
Administrative controls include work practice controls, changes in the way that people perform work tasks in order to reduce exposure.
Work practice controls can be very effective, but they can get lost in the "administrative control" category.
For these reasons, I sometimes list work practice controls as a separate category.
Lowest on the hierarchy is personal protective equipment, or PPE, that is worn by individual
workers to prevent their own exposures to workplace hazards.
PPE is lowest on the hierarchy because it requires people to put on, use, and take off their equipment correctly each and every time,
whereas options that are higher up on the hierarchy of control can be applied more
broadly across a workplace to limit exposures for many workers at once.
Prevention of exposures before they happen is, of course, preferable, but that cannot always be the case.
Elimination, for example, may not be possible because a particular chemical or process may be essential for the item that is being produced.
As you move lower on the hierarchy, options often become more feasible economically and functionally, but they also become less effective.
It is worth considering that education and training are important to help workers understand the hazards that they face and to
motivate them to perform their tasks in ways that limit their exposures to hazardous agents.
In summary, the occupational hygiene framework involves anticipating, recognizing,
evaluating, and controlling hazards at work sites.
This framework leads directly to a strategy for comprehensively assessing workplace exposures to hazardous agents.