Odour Threshold Investigation 2012 - Bay of Plenty Regional Council

The results generated by the olfactometer provide an odour measurement in odour
units (ou), based on the extent of dilution that resulted in 50% of the panel being
able to positively identify an odour. Dividing the known volume concentration of the
odorous gas by its measured odour concentration (ou), gives the odour threshold in
parts per billion (ppb).
6.3 Specific aspects of the methodology relevant to this study
The following aspects of the standard methodology were specifically adopted and/or
modified for this study:
• AS/NZS4323.3 was followed, except in the areas of assessor selection and
calibration, and testing room air quality.
• Assessors of all ages and both sexes were used in the study.
• The assessors received minimal training only, sufficient to participate in the
olfactometry testing. They were not pre-screened using n-butanol over a three
non-consecutive day period, and nor were any people eliminated from the
study on the basis of abnormal sensitivity (or non-sensitivity) to odour, as
required by AS/NZS4323.3.
• Competitive behaviour within each assessor panel was strongly discouraged.
A relaxed environment in the lab was encouraged, and assessors were
encouraged to talk freely (except about the testing) and not necessarily focus
entirely on the testing.
• H 2 S samples were interspersed with n-butanol samples, so as to minimise
repetition and prevent the assessors ‘looking’ specifically for H 2 S.
• The air quality in the testing room was not treated in any way to remove
odours. This was driven largely by practical considerations but has special
significance for some of the Rotorua results (see section 7.1.2).
• As required by the Standard, the TOU olfactometer is calibrated annually. This
calibration was last done in August 2011.
• A Jerome 631-X H 2 S analyser 74 capable of quantifying H 2 S in the range 2 to
50 ppm was used to measure concentration in every sample tested and for
monitoring ambient concentrations throughout this study.
6.4 Study locations
The Whakatāne session was held between 19 – 23 March using the West Wing of
the BOPRC Whakatāne office (NZMG 2861631E 6353571N). Testing in Rotorua
was initially in Scott Street at the old Department of Conservation Offices (NZMG
2795999E 6333462N) on 26 March, but due to elevated room temperatures and
ingress of ambient H 2 S, the testing was transferred to the Rotorua District Council
Redwood Information Centre located in the Redwood Reserve on the edge of the
city (NZMG 2796903E 6333228N). Testing in this latter location ran from 27 to
30 March.
74 http://www.azic.com/downloads/brochures/Jerome®%20631%20Brochure.pdf
28 Environmental Publication 2012/06–A review of odour properties of H 2 S Odour Threshold Investigation 2012