Odour Threshold Investigation 2012 - Bay of Plenty Regional Council

At each round of the testing process the concentration of the odorous gas is
systematically increased (doubled) and re-presented to the panellists. A round is
completed when all panellists have correctly detected the presence of the odour
with certainty. The odour is presented to the panel for three rounds.
6.7 Calculation of odour concentration
The method used to determine odour concentration as calculated by the
Odourmat software is as follows. The individual threshold estimate (ITE) for a
panellist is calculated as the geometric mean of the first threshold estimate in a
series of two where the panellist correctly and with certainty, detected the odorant;
and the previous threshold estimate (see Figure 7.7 for an example of the collected
information and calculated output).
A detailed explanation of ITE calculations can be found in Sections 11 and 12 of
AS/NZS 4323.3:2001.
6.7.1 H 2 S calibration gas
A certified D-size cylinder of 5 ppm H 2 S in nitrogen gas (see Appendix 2) was used
at both locations. Each sample of H 2 S was drawn directly from the cylinder into a
Nalophan sample bag. This concentration was checked regularly using the Jerome
H 2 S monitor. The Jerome documentation states that for the concentration range 1 to
9 ppm a standard deviation of ± 0.3 ppm at the 5 ppm midpoint can be expected,
Figure 6.1 shows this to be the case with a deviation of this order being
experienced. The Jerome is also subject to thermal drift but this effect didn’t appear
to be strongly evident in the two weeks of testing.
For the purpose of calculating the final threshold the measured Jerome values were
used rather than a set value based on the gas bottle certification.
30 Environmental Publication 2012/06–A review of odour properties of H 2 S Odour Threshold Investigation 2012