Chemistry Reference
In-Depth Information
Many types of respirators are on the market, from
air-fi ltering respirators of various types to self-con-
tained breathing apparatus (SCBAs), for which the
worker carries the air on a tank on his or her back.
Metal fumes require more effi cient respirators than
are needed for dust; if both are present concomitantly,
respirators designed for fumes must be used. Acti-
vated charcoal fi lters do not retain fi ne aerosol parti-
cles; therefore, combined gas and dust fi lters should be
used in spray painting. In certain operations in which
exposure is very high, for example when ships covered
with thick layers of red lead are scrapped by fl ame cut-
ting, protection may require either an air-purifying
positive-pressure respirator or an SCBA.
If respirators are used in the workplace, an intensive
program of test fi tting of the respirators to each person
and an active program of cleaning and maintaining the
respirators and replacing fi lters regularly is impera-
tive and is mandated by OSHA Standard 1910.134. For
details on respirators, their selection, capabilities, and
maintenance see Colton
et al
. (1998), Myers (2000), and
Nelson (1998).
3.3.1 Air Sampling Strategy in the Workplace
Metals usually appear in the workroom air as fumes
and solid particles and sometimes as vapor (metallic
mercury) or liquid aerosols (e.g., chromates above the
electroplating bath). Fumes are formed when molten
metal evaporates or when metal or metal compounds
are burned. The dust particles are either derived from
condensed fumes or from metal-compound dust that
has whirled up. Although the particle size distribution
varies, the respirable dust is composed of small par-
ticles that can stay in the air for many hours. Larger
particles settle but may become re-entrained as a result
of wind currents or nearby activities.
In recent decades, many new and improved direct-
reading instruments have been developed. These are
especially convenient for the real-time measurement of
concentrations of gases and vapors.
The only metal present in many workplaces pri-
marily in vapor form is mercury, and commercial
analyzers are widely used for its detection. However,
direct-reading instruments are not so helpful in deter-
mining concentrations of aerosols (fumes, particulates
and/or liquid droplets), the most common form in
which metals are present in the workplace, because
they cannot differentiate between types of aerosols.
They can, however, be used to size these aerosols by
means of optical or linked optical and electrical tech-
niques. For further information about the types, capa-
bilities, and drawbacks of direct-reading instruments,
see Todd (1998). Because metals in the workplace usu-
ally appear as fumes or particulates, we will focus
on them in the following discussion along with their
associated sampling and laboratory measurement.
Concentrations of metal in air close to a machine or
where a process is carried out are typically maximal.
They may vary considerably over a distance of a few
meters or even centimeters. For most purposes, sam-
ples should be taken in regular work areas (area air
samples) and also from the worker's breathing zone.
The number of air samples needed depends on the
purpose of the measurement. An overall picture of
workplace exposure level is obtained from sampling
carried out on a long-term basis with samples taken
from multiple, different sites. When individual expo-
sure is to be studied, personal air monitoring is the
method of choice. The samples should be taken from
the breathing zone, no farther than 30 cm from the
nose. They may even be taken from within a welding
helmet. The sampler is usually attached to the work-
er's shoulder or waist. No obstruction can be allowed
between the air sampler inlet and the worker's face,
and the equipment must not disturb the work, for
instance, by blocking sight. Workers representative
3.3 Monitoring of the Work Environment
Two complementary approaches exist for monitor-
ing metal exposure in the workplace—environmental
and biological monitoring. Measurements of airborne
metal concentrations in the work environment are
mandatory to:
1. Localize high-exposure areas.
2. Estimate individual exposure (especially when no
satisfactory biological monitoring method exists).
3. Detect engineering failures (leakages, areas of
insuffi cient ventilation).
4. Detect the effects of changes in processes or
working methods.
5. Document the impact of preventive measures.
6. Ensure that safety standards are being met.
Only a broad outline of monitoring is presented
here. For further information about environmental
monitoring for vapors and metal fumes see Burgess
(2000), Dietrich (1998), Huey (1996), Hahne (1996),
Johnson and Swift (1998), and Soule (2000b). Although
environmental monitoring provides information about
levels of the metals in air, biological sampling of levels
of metals in the bodies of workers provides a time-inte-
grated measure of cumulative exposure (Todd
et al.,
1996). For further information about biological moni-
toring see Chapter 4 on Biological Monitoring and
Biomarkers and Clarkson
et al
. (1988), LaDou (2004),
Lauwerys (1998), Levy
et al
. (2000), Que Hee (1998),
Rom (1998), Soule (2000c), and Zenz (1994).
