Environmental Engineering Reference
In-Depth Information
Table 9.2
Selected Positive Hole Correction Values
Measured concentration
(count/plate)
Corrected concentration
(count/plate)
40
42
50
53
60
65
70
77
80
89
90
102
100
115
120
143
140
172
160
204
180
239
200
277
220
319
240
367
260
420
280
422
300
555
320
644
340
759
360
921
380
1198
400
2628
Source:
Data extracted from Macher, J.,
Am. Ind. Hyg. Assoc.
J
., 50, 561, 1989.
iii. Enumeration. Enumeration of mold spores/particles on sample
slides requires the use of a suitable collection medium (e.g., Dow Corning
high vacuum grease, Dow Corning adhesive 280A, Dow Corning Silicone
spray 316), a compatible mounting medium (aniline-blue-amended Cal-
berla's solution adjusted to pH 4.2), a microscope with magnification capa-
bility of 1000
, a movable stage, and an ocular micrometer in the eye piece.
It also requires technical skill to identify mold spores and particles against
a heterogeneous mass of deposited particulate matter.
×
iv. Calibration. Total mold spore samplers require frequent calibra-
tion since they are subject to significant flow rate changes. In the Burkard
sampler, voltage has to be periodically adjusted to maintain the target flow
rate near 10 L/min. Calibrations can be conducted using bubble-type cali-
bration devices (
Figure 9.11
)
or wet test meters connected to the top of the
sampler using a specially designed rubber cork orifice.
Total mold spore/particle samplers have a major advantage over cultur-
able/viable methods in that concentrations can be determined within an
hour or so after collection. This makes them particularly suitable for sam-
