Evaluation of Hazardous Agents and Factors in
Occupational and Nonoccupational Environments
At the completion of Unit 1，including sufficient reading and studying of this and related
reference material, learners will be able to correctly:
Summarize the roles of occupational health specialists/industrial hygienists.
Name and define the categories of industrial hygiene sampling and analysis for determination of
external exposure to physical, chemical, and biological agents.
Discuss the aspect of evaluating ergonomic factors.
Discuss the aspect of evaluating hazard controls.
Discuss the industrial hygiene and medical monitoring and analysis relative to external, internal,
and effective exposures.
The occupational environment can be simply defined as any place, indoors or outdoors, where
people work in return for financial or other remuneration. The profession of occupational health,
or industrial hygiene, is based on the tetrad of anticipation, recognition, evaluation, and control of
agents, factors, and stressors related to the occupational environment that may adversely affect the
health of workers and other members of the community. All four aspects of the tetrad are interrelated.
The content of this book, however, will mostly emphasize some major instrumentation, methods,
and practices of industrial hygiene evaluation.
The occupational environment is evaluated by occupational health specialists, historically and
presently, most commonly referred to as industrial hygienists. Industrial hygienists are involved
with evaluation of the occupational environment from several different perspectives. Industrial
hygiene evaluation activities include conducting walk-through surveys of facilities and applicable
monitoring activities to gather both qualitative and quantitative data. Monitoring activities include
sampling and analysis to collect, detect，identify, and measure hazardous physical, chemical, and
biological agents present in specific areas and to which workers and others are potentially or actually
exposed. Industrial hygienists commonly interact directly or indirectly with clinical professionals,
such as physicians, nurses, and audiologists. Industrial hygienists are often familiar with some
general principles of clinical techniques to evaluate workers to determine if they reveal signs of
adverse impact from excessive exposure to agents，such as hearing loss due to prolonged exposure
to elevated sound levels. In addition, industrial hygienists evaluate control measures, including
work practices, personal protective equipment, and ventilation systems, to determine if they effec
tively reduce the potential for worker exposure. Industrial hygienists also may be involved with
evaluation of ergonomic factors to determine i f there is an appropriate match or fit between workers
and their physical workplace environments.
Industrial hygiene principles and practices often extend beyond the occupational and manufac
turing settings. For example, professional- and technician-level industrial hygienists are frequently
involved in indoor air quality (IAQ) investigations in nonoccupational settings, such as homes,
schools, and other nonmanufacturing settings. Accordingly, many of the topics presented in this
book are applicable to both occupational and nonoccupational and manufacturing and nonmanu
EVALUATION OF EXTERNAL EXPOSURE VIA INDUSTRIAL HYGIENE MONITORING
Sampling and analysis refer to the representative collection, detection, identification, and mea
surement of agents found in environmental matrices such as air, water, and soil. In occupational
and nonoccupational environments, both indoors and outdoors, air is sampled (collected) to detect
and identify physical, chemical, and biological agents and to measure related levels. The most
common matrix that is sampled and analyzed in the occupational environment is the air. Indeed,
inhalation of contaminated air by workers is considered the major mode of foreign agent entry in
most occupational environments. In addition, the air serves as a matrix for elevated sound levels,
extremes of temperature and humidity, and transfer of ionizing and nonionizing radiation energies.
The data collected and analyzed are used to evaluate both actual and potential external exposures
to agents encountered by humans. In turn, the levels are compared to established occupational
exposure limits (OELs) to determine if acceptable values for exposure have been exceeded. In the
U.S., regulatory permissible exposure limits (PELs) are enforced by the Occupational Safety and
Health Administration (OSHA) for nonmining operations and processes. Regulatory exposure limits
for the mining industry are the threshold limit values (TLVs) enforced by the Mine Safety and Health
Administration (MSHA). Other agencies have established occupational exposure limits as guidelines,
most notably the TLVs by the American Conference of Governmental Industrial Hygienists (ACGIH)
and Recommended Exposure Levels (RELs) by the National Institute for Occupational Safety and
Health (NIOSH). In some cases, a parameter will be monitored without concern necessarily for
excessive exposure. For example, illumination is evaluated and compared to recommend guidelines
to a ssure that there is a n a ppropriate, ne ither i nadequate nor excessive, quantity of lighting. Refer to
Appendix A for a summary of some related strategies for exposure assessment and calculations of
time-weighted averages (TWAs) for comparisons to established regulatory and nonregulatory occu
pational exposure limits. In relation, Appendix B is an example of an outline format of an industrial
hygiene evaluation report showing information that must be considered, documented, and reported.
Sampling and related analytical activities are divided into several categories to reflect the type
of monitoring that is conducted. Categories are based on factors that include time, location, and
methods of collection (sampling) and detection, identification, and measurement (analysis). Each
serves a purpose in evaluating the occupational environment to determine the degree of workers’
external exposure to various agents.
(i) Instantaneous or Real-Time Sampling
Instantaneous sampling refers to the collection of a sample for a relatively short period ranging
from seconds to typically less than 10 min. A major advantage of instantaneous sampling is that
both sample collection and analysis are provided immediately via direct readout from the sampling
device. The data represent the level of an agent at the specific time of sampling. Accordingly,
instantaneous sampling is also referred to as direct reading and real-time sampling. Real-time
sampling is perhaps a more appropriate designation since there are some devices already developed
and being designed for integrated or continuous monitoring (see Section ii) that provide a directreadout or instantaneous result without need for laboratory analysis and the associated delays. In
addition, the main purpose of real-time sampling is to reveal what a level of an agent is, at an
immediate point of time or during real-time.
The application of real-time sampling varies. The strategy is used when preliminary information
regarding the level of an agent is needed at a specific time and location. For example, real-time
sampling is commonly used for screening to identify agents and measure related levels. This is
important for developing follow-up monitoring strategy and determining if integrated sampling is
warranted. Real-time sampling is also beneficial for determining levels of agents during short-term
operations or specific isolated processes when peak levels are anticipated or suspected.
(ii) Integrated or Continuous Sampling
Integrated sampling refers to the collection of a sample continuously over a prolonged period
ranging from more than 10 or 15 mi n to typically several hours. Integrated sampli ng is also referred
to as continuous monit oring reflective of the extended period of sample col lection. Most work shifts
are 8 h and occupational exposure limits are most commonly based on an 8-h exposure period.
Accordingly, it is very common as well for sampling to cover the duration of the shift. Several
strategies can be followed. For example, a sample run could be started immediately a t the beginning
of the 8-h shift and allowed to run until the shift ends. Analysis of the sample would provide a
single value representative of the level of a particular agent during the shift. The single value
represents an integration of all the levels during the shift. The single value, however, does not
provide information regarding fluctuations of levels that were higher, lower, or not detectable during
shorter periods within the 8-h shift. In addition, there is no indication as to the levels at specific
times and locations during the shift. As a result, an alternative strategy could involve collection of
several samples of shorter duration during the entire shift. In turn, analysis of the individual samples
provides levels associated with specific times, tasks, and locations during the 8-hour shift. Con
centration (C) and corresponding sample time (T) data from one sample (C,) or several individual
samples (C, to Cn) can be time-weighted (C x T) and averaged, by dividing by a specific time
period (e.g., 8 h), to provide a single overall TWA for the 8-h shift (Appendix A).
A major advantage of integrated sampling is that it provides a single value for the level of an
agent over a prolonged period. The level of an agent can be determined during discrete times and
locations within a workshift to assist in identifying factors that influence elevated values of exposure
or external exposure. A major disadvantage associated with integrated sampling is that in most
cases, samples must be submitted to a laboratory for analysis prior to knowing what has been
detected in the related measurements. This frequently results in a delay between sample collection
and data reporting.
Several fundamental procedures must be followed when conducting integrated personal and
area sampling. It is important to assure that monitoring devices and/or sampling trains are properly
assembled, calibrated, and operated for the specific monitoring activity. It is equally important to
assure that field monitoring data are recorded so that samples can be associated with specific
locations，areas, individuals, dates, times, processes, equipment, temperatures, humidity, atmo
spheric pressure, and so on. Figure 1.1 summarizes a representative example of a generic integrated
Make sure that all active monitoring devices are pre-calibrated and order checked for accurate
calibration. Check batteries for charge. In addition, confirm that sampling media are not expired.
n Select a worker or area to be monitored. Briefly explain the purpose of monitoring to the worker
and/or workers in the area. Advise individuals not to tamper with the instrument or medium. Record
the worker's name or the area sampled, worker's social security number, and job title. Record date,
sampling location and sampling device and/or media identification number.
If a personal sample, attach the monitoring device and/or medium to the worker and make sure that they
do not interfere with the worker's activities. Attach the sampling medium (e.g., filter cassette) at the
worker's clavicle near the collar if a breathing zone sample is needed. If a hearing zone sample is
needed, attach the medium (e.g., audiodosimeter microphone) at the trapezius or the ear. If a flexible
hose or a cord is involved, allow enough slack to accommodate worker's range of motion when
standing, sitting, bending, and twisting and secure any excess so that it does not serve as a potential
interference or hazard.
For an area sample, position the monitoring device and/or medium approximately 4 to 6 feet from
the floor. Make sure that the medium is not in direct corttact with or too close to a contaminant (e.g.
settled or spilled particulate)
Turn "ON" an active monitoring device and record "start time". Make sure that the device is
operating. If a passive device is used, record "start time" when it is first exposed to the workplace
Document the worker's performed tasks and/or processes operating in the area during the monitoring
period. Note times when exposure may be high due to specific activities or process phases. Check
the monitoring device and medium after the first 15 minutes to half an hour, and at least two-hour
intervals thereafter. If applicable, change the medium when conditions warrant (e.g., signs of
overloading; excessive airborne concentrations of contaminant; to isolate exposure to specific time
periods or specific tasks).
Record the "stop time" when medium is changed (or sampling is concluded) and "start time" when
medium is replaced; make sure that the identification number of each sample is recorded. If applicable,
handle field blanks in a similar manner as samples (recording start and stop times in military time
makes it easier to determine sample time and convert to minutes).
Remove monitoring device and/or media from the worker or the area being sampled.
Make sure that all active monitoring devices are post-calibrated or checked for accurate calibration.
Post-calibration should be conducted prior to recharging batteries.
Figure 1.1 Example of a protocol for personal and area integrated air sampling,
(iii) Personal Sampling
Personal sampling involves direct connection of an integrated monitoring device to a worker.
The device, in turn, will collect a sample or record the intensity of an agent in the specific areas
and during specific tasks conducted by a worker. Indeed, personal sampling is frequently a form
of mobile monitoring since the sampling device travels to the same areas and at the same times as
the worker that wears it.
If inhalation is the mode and the respiratory system the route of entry of an agent, the sampling
device or related sampling medium is positioned in the worker’s breathing zone. The breathing
zone refers to an area within a 9- to 12-in. distance (radius) from the worker’s nose and mouth
(Figure l.2a). Typically, an integrated monitoring device for personal sampling is attached near the
worker’s clavicle (collar bone). Relative to evaluation and impact of sound levels, however, hearing
is the major mode and the auditory system is the route of entry. When conducting personal
monitoring for sound, therefore, the sampling device can be connected to the worker’s hearing
zone. This zone is ideally the ear itself, or the trapezius region of the shoulder 一 a region within
a 9- to 12-in. distance from the ear (Figure l.2b).
Instantaneous or real-time monitors also can be used to determine levels of a gents i n a w orker’s
breathing and hearing zones. For example, a sound level meter can be held by the individual
(a) Active-flow pump is positioned at the workers waist. Flexible tubing connects the pump to a
sample collection medium clipped to the worker’s shirt along the collar bone and positioned within
his breathing zone to collect a personal integrated sample, (b) Sound (noise) dosimeter is positioned
at the worker’s waist. Flexible wire connects the dosimeter to a microphone clipped to the worker's
shirt along the trapezius and positioned within his hearing zone to collect a personal integrated
conducting the monitoring in the auditory region of a worker. This would provide an instantaneous
assessment of sound levels in the worker’s hearing zone at the specific time of monitoring.
(iv) Area Sampling
The focus of area sampling is to evaluate the levels of agents in a specific location, instead of
evaluating levels encountered by a specific worker. Area integrated monitoring devices are typically
positioned in a stationary location (Figure 1.3a). Stationary area integrated samples are often
collected at a height of approximately 4 ft from the floor or ground. The data from a stationary
area integrated sample represent the level of an agent in the specific area during the sampling
period. Area instantaneous or real-time monitoring, however, involves area sampling in either a
stationary or mobile mode. Stationary area instantaneous monitoring may be conducted while
positioning or holding and operating a direct read instrument and standing still in a given location.
Alternatively, an instantaneous monitoring instrument can be transported via carrying it or rolling
it on a cart to various locations while intermittently checking the indicator or readout on the
instrument (Figure 1.3b).
(v) Active Flow Sampling
Presently, most monitoring techniques for actual collection of an air sample or contaminant
from the air involve active flow methods. Active flow sampling implies that energy, such as an
electronically powered (either AC or DC) device, is re quired to col lect the sa mple. Air a nd a irborne
contaminants are actively pulled through a collection medium or into a collection container. For
example, battery-powered air sampling pumps are frequently used to pull air through sample
collection media or into a sample container. Energy also can be generated manually, via physically
pumping a device for example, to conduct active flow sampling.
(a) Two-stage bioaerosol impactor is positioned on a stationary tripod. Flexible tubing connects the
active-flow pump to the impactor to collect an area integrated sample, (b) Active-flow, direct read
out instrument is carried and operated by an individual walking from area to area within a facility
to conduct mobile area sampling. Flexible tubing connects the instrument to a probe pointed in
the air to collect area instantaneous samples.
(vi) Passive Flow Sampling
Passive flow sampling implies that neither electrical nor manual energy is required to operate
the air sampling device. The method applies to the collection of diffusible gases and vapors;
collection of settling particulates; measurement of temperature, pressure, and humidity; and the
detection and measurement of forms of ionizing and nonionizing radiation. In the case of gases
and vapors, collection using a passive monitor or dosimeter (if used for personal monitoring) relies
on the movement (diffusion) of a gas or vapor from an area of relative high concentration, such as
the air, to an area of relatively low concentration, the passive monitor. There is no need to actively
move the air so that it and the contaminants flow into or through a sample collection medium. As
for other examples, although not commonly used for evaluation of the occupational environment
due to poor accuracy and precision, settleable dust can be collected passively using a pre-weighed
dust fall jar or settleable microorganisms collected passively in open culture dishes filled with agar
(vii) Surface Sampling
Surfaces that are potentially or suspected to be contaminated with a toxic or pathogenic agent
are sampled. Moistened or pre-treated cellulose (paper) sheets (wipes) and sponge-cotton-tipped
swabs are commonly used to collect a sample from a surface. The media arc then analyzed for the
contaminant of interest. Surface sampling is also referred to as wipe or swab sampling.
(viii) Bulk Sampling
Bulk sampling refers to collection of a representative portion of a matrix. For example, there
are times when actual collection of the air, not simply the contaminant separated from the air, is
warranted. Accordingly, a special glass or metal cylinder or plastic bag (e.g.，Mylar) may be used
to collect a bulk sample of air. Aliquots (subsamples) of the bulk sample can be analyzed for
specific agents. Bulk sampling also refers to the collection of a real or potential source of an agent.
For example, ...
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