Page 71 - Plant design and economics for chemical engineers

GENERAL DESIGN CONSIDERATIONS 53
TABLE 2
Air analysis methods

Method Substance analyzed
Atomic absorption spectroscopy Metals
Gas chromatography Volatile organic compounds
Gravimetric Nuisance dust, coal dust
Particle count Asbestos
Ion-specific electrode Halogens, HCN, NH, CUCEI
X-ray diffraction Silica BIBLIOTECA CZARAI.4
Colorimetly Miscellaneous

be appropriate for the sampling media, have sufficient sensitivity, and be
reasonably free from interference. The ultimate confidence that can be placed
on an analytical result depends in part on the accuracy of the method, but to a
greater extent on how well the method has been validated for the particular
purpose and on the reliability of the laboratory performing the test.
As noted earlier, the EPA has determined that fugitive emissions from
process equipment are a large source of volatile organic compounds (VOC).
The latter are defined by the EPA as organic compounds that participate in
photochemical reactions. These reactions are of significance since the ozone
level in the atmosphere is affected by the concentration of volatile organic
compounds. Standards for ozone concentration in nonplant areas were origi-
nally one of the major concentration targets in the Clean Air Act.
In addition to the volatile organic compounds, EPA has added other
regulations controlling a number of compounds which are neither carcinogenic
agents or cause serious health problems to the public. These hazardous pollu-
tants, controlled under the National Exposure Standards for Hazardous Pollu-
tants (NESHAP), include benzene, vinyl chloride, mercury, asbestos, arsenic,
beryllium, and radionuclides. The NESHAP regulations in combination with
VOC emission-control regulations reduce exposures in the plant environment
through equipment emission-control systems. This is in contrast to the specific
objective of the Occupational Safety and Health Act (OSHA), which is the
control of occupational exposures in the workplace. This is considered in the
next section.

Exposure-Hazard Control
When it is concluded that an exposure problem exists, decisions need to be
made regarding the implementation of hazard-control measures for the purpose
of reducing exposure and correspondingly reducing the risks. However, a given
set of exposure conditions does not lead to a fixed set of control strategies.
There are many options. Since zero risk is not attainable, a,decision must be
made relative to the degree of risk reduction that is to be attained. Then a
series of choices must be made from a wide range of options available to