Basic Calculations for Occupational Safety and Environmental Health Professionals - Mathematics and Statistics for the Environment - page 405

15.5.7 a ir m onitoring and s ampling

Air monitoring is widely used to measure human exposure and to characterize emission sources.
It is often employed within the context of the general survey, investigating a specific complaint,
or simply for regulatory compliance. It is also used for more fundamental purposes, such as in
confined space entry operations. Although it is true that just about any confined space entry team
member can be trained to properly calibrate and operate air monitors for safe confined space entry,
it is also true that a higher level of knowledge and training is often required in the actual evaluation
of confined spaces for possible oxygen deficiency and/or air contaminant problems.
In the practice of industrial hygiene, the terms air monitoring and air sampling are often used
interchangeably to mean the same thing, but in reality they are different; that is, air monitoring and
air sampling are separate functions. The difference is related to time: real time vs. time integration.
Air monitoring is real-time monitoring and generally includes monitoring with hand-held, direct-
reading units such as portable gas chromatographs (GCs), photoionization detectors (PIDs), flame
ionization detectors (FIDs), dust monitors, and colorimetric tubes. Real-time air monitoring instru-
mentation is generally easily portable and allows the user to collect multiple samples in a relatively
short sample period—ranging from a few seconds to a few minutes. Most portable real-time instru-
ments measure low parts per million (ppm) of total volatile organics. Real-time monitoring methods
have higher detection limits than time-integrated sampling methods, react with entire classes of
compounds and, unless real-time monitoring is conducted continuously, provide only a snapshot of
the monitored ambient air concentration. Air monitoring instruments and methods provide results
that are generally used for evaluation of short-term exposure limits and can be useful in providing
timely information to those engaged in various activities such as confined space entry operations.
That is, in confined space operations, proper air monitoring can detect the presence or absence of
life-threatening contaminants and/or insufficient oxygen levels within the confined space, alerting
the entrants not to enter before making the space safe for entry (e.g., by using forced air ventilation).
On the other hand, time-integrated air sampling is intended to document actual exposure for
comparison to long-term exposure limits. Air sampling data are collected at fixed locations along
the perimeter of the sample area and at locations adjacent to other sensitive receptors. Because most
contaminants are present in ambient air at relatively low levels, some type of sample concentrating
is necessary to meet detection limits normally required in evaluating long-term health risks. Air
sampling is accomplished using air-monitoring instrumentation designed to continuously sample
large volumes of air over extended periods of time (typically from 8 to 24 hours). Air sampling
methods involve collecting air samples on sampling media designed specifically for collection of
the compounds of interest or as whole air samples. Upon completion of the sampling period the
sampling media is collected, packaged, and transported for subsequent analysis. Analysis of air
samples usually requires a minimum of 48 hours to complete.
Now you should have a basic understanding of air monitoring and air sampling and the differ-
ence, though in some cases subtle, between the two. Both procedures are important and both are
significant tools in the industrial hygienist's toolbox.
To effectively evaluate a potentially hazardous worksite, an industrial hygienist must obtain
objective and quantitative data. To do this, the environmental professional must perform some form
of air sampling, dependent upon, of course, the airborne contaminant in question. Moreover, sam-
pling operations involve the use of instruments to measure the concentration of the particulate,
gas, or vapor of interest. Many instruments perform both sampling and analysis. The instrument
of choice in conducting sampling and analysis typically is a direct-reading-type instrument. The
environmental professional must be familiar with the uses, advantages, and limitations of such
instruments. In addition, the environmental professional must use math calculations to calculate
sample volumes, sample times, TLVs, and air concentrations from vapor pressures and to determine
the additive effects of chemicals when multiple agents are used in the workplace. These calcula-
tions must take into account changing conditions, such as temperature and pressure change in the