User`s guide

Sampling Techniques
333
In fact, in many cases, the mean has to be around 1/3 of the limit
before there is 95% confidence that the atmospheric concentration or
personal exposure level taken on any day would not exceed the
maximum. See insert cross-ref. In other words, at this mean
concentration, 1 in 20 results is still likely to be higher than the limit
level.
Figure 100 Probability of a Result Occurring vs. Air
Concentration (Showing Acceptable Limits)
The response to the three monitoring results illustrated in insert
cross-ref would be as follows:
1. Mean = 1/10 of the limit level, demonstrating good
compliance with the regulations.
Action required: only infrequent monitoring to
demonstrate continued compliance.
2. Mean = 1/3
of the limit level, demonstrating borderline
compliance with the regulations.
Action required: bring levels down if possible,
otherwise carry out frequent routine monitoring to
demonstrate continued compliance.
3. Mean = the limit level, demonstrating failure to comply
with the regulations.
Action required: bring levels down.
Further guidance on complying with atmospheric concentration limit
levels can be obtained from: Occupational Exposure Sampling
Strategy Manual (1977) US D.H.E.W. (NIOSH) Publication No.
77-173, Department of Health
Air Concentration (log)
(1) (2) (3)
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1/10th
Limit
Level
1/3rd
Limit
Level
Limit
Level