Odour Threshold Investigation 2012 - Bay of Plenty Regional Council

The original concept behind the testing methodology was one of using an untrained
panel of participants. However as the tests progressed panellists became well
aware of what was required and the random nature of the presentation of gas along
with the appropriate conditioning of the gas (e.g. no obvious temperature difference
between the two ports etc.) at each olfactometer port was critical. It is reasonable to
assume that during the testing the threshold value per panellist may have
decreased as panellists become more attuned to the odour. In Figure 7.15 first and
last round results are presented for a number of the Whakatāne panellists (where
each panellist attended three sessions) there is visual evidence that some of the
panellists are exhibiting this downward trend. There are however a number that
show a trend in the opposite direction. No further analysis of panellist behaviour
over sessions is undertaken at this time as a more rigorous and tailored
methodology would be required to check the hypothesis of changes per panellist
over sessions.
Figure 7.15
Trends per panellist by comparing first and last round results.
NZAAQ 7 µg/m 3 guideline analysis
There is also the ability to investigate the percentages of the dataset which are
below or above a value(s) of interest. For this exercise a value of 7 µg/m 3 has been
chosen. With the plots shown in Figure 7.16 percentage results for any value of
interest can be easily obtained. The chosen 7 µg/m 3 represents the current MfE
guideline for odour annoyance.
The percentage detection results show that most panellists in the Whakatāne and
Rotorua groups are able to recognise the 7 µg/m 3 concentration, with >95% of the
recorded detection values below this guideline. The Rotorua plot shows a slightly
lower percentage of values at which this guideline was met. The third plot shows the
results for the periods of testing in Rotorua where elevated ambient H 2 S
46 Environmental Publication 2012/06–A review of odour properties of H 2 S Odour Threshold Investigation 2012