Environmental Engineering Reference
In-Depth Information
the location for obtaining BZ measures is deined simply by indicating that the inlet be attached
to a “lapel” (e.g., NRC, 2003). Shapiro (1990) indicates that radiation personal monitors should be
worn between the waist and the shoulders, also noting that BZ sampling should be conducted at
the lapel location. In an effort to standardize measurement methodologies, while allowing a greater
range of inlet types (many are simply too heavy to clip to a lapel), spatial deinitions are deined
for the BZ, such as “…the hemisphere of 300 mm (0.3 m) radius extending in front of the face and
measured from the midpoint of an imaginary line joining the ears” (NOHSC, 2003). Rock (2001)
similarly deines a 300 mm distance from the nose, and observes that such sampling is designated
“breathing zone,” even when a respirator is worn. While such a rigidly deined space is useful for
uniformity, limited data are available to deine the concentration uniformity throughout such a
volume, especially for aerosols. Martinelli et al. (1983) documented biases for selected elements
and suggested that resuspension of relatively large particle clothing dust was a contributing factor.
Bradley et al. (1994) reported that sampling eficiencies for respirable aerosol at various locations
across the chest and back varied from 0.45 to 0.61. Part of the chest bias was surmised to result from
the inlet being in the downwash of cleaner exhaled breath from the nostrils. This observation lends
credence to placement of a BZ inlet to the left or right rather than directly under the head. Bull
et al. (1987) generated 0.26 μm particles in 60 s releases at point locations into a chamber and found
that integrated samples collected in front of the nose and at the chest correlated to the same level
(R = 0.84) and nose versus the waist. The data suggested that within experimental error, extending
the BZ across the chest and as far down as the waist, produced essentially equivalent data for these
relatively small particles.
A continuous tracer gas plume from a point source 1 m from a manikin-mounted PEM in a
simulated indoor setting (equivalent air velocity and turbulence levels) was reported by Rodes et al.
(1995) to be only 15 cm wide at the chest, suggesting that strong, nearby sources may produce signif-
icant differences between BZ and other personal sampling methods, if suficiently long exposures
occur. This scenario is most common in occupational settings. Similarly, Coker (1981) reported that
workers handedness (left vs. right) during daily activities (in this case, paint spraying) affected con-
centrations by as much as 50% across the chest—the right lapel concentrations being much higher
than the left for right-handed individuals. Rodes et al. (2001) reported that body dander could be a
signiicant contributor to the collected mass nonoccupational BZ aerosol. Importantly, this source
and resuspended clothing dust are associated with activities and character of the person being moni-
tored, rather than external sources. The electrostatic charging of both a manikin (simulating the
body) and the PEM were found to affect aerosol collection performance in a study by Smith and
Bartley (2003). The eficiency was found to increase by ∼10% for 7 μm particles when the charge
could be effectively neutralized. Since participant clothing (e.g., sweaters) are surmised to periodi-
cally be highly charged, this may also inluence BZ uniformity for aerosols.
The listing of spatial bias scenarios provided in the previous paragraph suggest that BZ assess-
ments can certainly be substantially different from personal exposure assessment measurements
made at more distant body locations. Table 2.2 provides typical separation distances when the meth-
odologies listed are used for personal exposure sampling. Placing the inlet within 0.3 m of the
oral/nasal plane (spherical distance) is recommended to provide measurements well within 20% of
the true BZ values for gases and total mass of ine particles (<2.5) and coarse particles as large as
10 μm. Separation distances greater than 0.3 m may produce signiicant biases.
2.3.2  M onitoring  z one  l ocations
The most applicable method of obtaining personal air exposures is through sampling directly in
the BZ, and is speciically prescribed for most occupational scenarios to demonstrate compliance
with permissible exposure limits (PELs) (e.g., DOE, 2001; MSHA, 2003; NRC, 2003; OSHA,
2003). There are no U.S. regulations requiring personal exposure monitoring for nonoccupational
exposures. Personal exposure studies that integrate both occupational and nonoccupational periods
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