It is over. This meeting that took place in February in Trieste, was the last one on the series of the Working Group (WG) 2. The first meeting took place in Barcelona in November 2012 and after five and a half years of discussions, the first draft is here.
Some of the hot issues, that have arisen during the last meetings were brought again to the experts. Will there be finally more assessors doing the olfactometric measurement? Will the time to analyse a bag after sampling change? Will there be a new reference substance to calibrate the panel? Will there be a new design of sampler for passive sources? How will be finally uncertainty handled?
These and more questions were dealt during the very last meeting. Some of the issues have been already discussed in many meetings, like panel size. Will there be a minimum of 4, 6, 8 or more assessors participating in the measurement?
In previous discussions in former meetings, the people of the task group dealing with uncertainty showed that there is a clear improvement in the uncertainty budget if more assessors were used by the olfactometric laboratory. Regions like Ontario, Canada, use at least 8 assessors in the measurement. In the Netherlands there will also be a change in the number of assessors and it looks like a minimum of 8 assessors will be needed to perform an olfactometric measurement. A very interesting research paper presented last month by Mike McGinley at the conference of the last conference on odour management organized by the WEF in Portland, dealt with this very same hot issue.
The minimum panel size will remain being four in the coming EN 13725 standard, but that does not mean that this number is the right panel size all the time. The olfactometric measurement must meet the uncertainty requirements given by any legislation and/or competent authorities or specified in the task to be done.
Uncertainty is somehow defined in other standards. For example, the standard EN 15267-3 requires that the total uncertainty of the measured values determined in the performance test should be at least 25 % below the Maximum Permissible Uncertainty (MPU) specified e.g. in applicable regulations.
If no uncertainty is required, the sky is the limit, but at least a minimum of 4 assessors must participate in the measurement.
For example, the European Industrial Emission Directive (IED) does have some uncertainty requirements set for known pollutants (although not for odours). The IED uncertainty requirements are expressed as 95% confidence intervals and are referred to as the MPU in the standard EN 14181.
In cases were odour concentration abatement performance of equipments must be tested, a careful selection of the proper panel size must be clearly done. Panel size should be also carefully taken into account when the results of an olfactometric measurement are very close to the limit set by the regulators. Other measures to improve uncertainty such as taking replicate samples could be considered .
As for the time to analyse a sample, the maximum storage time will remain 30 hours, so no changes here either, It is clear that there is a decrease of the odour concentration in the bag through time, and this factor should be considered in order to estimate the storage time.
As it is widely known, in Germany, this time is set to be a maximum of 6 hours. In the Chilean standard Nch 3886 on static sampling for olfactometry, the time is recommended to also be 6 hours. In both the German and the Chilean standard, the storage time can be longer if proved that there is no degradation of the sample throughout time. However, among the European experts there was not much consensus on the maximum storage time, so it was left as it is now in the current text. However, some notes were included in the text to consider the proper storage time.
The discussion on new reference materials did conclude and the final text was approved. The new standard 13725 will define a new procedure to design and test any new reference odorant. The idea behind is to select better reference materials to improve the uncertainty due to panellist selection.
Last but not least, a lively discussion was hold on the use of samplers for passive area sources. Some data have shown large differences in the results obtained by flux chambers as compared to wind tunnels. A study in made in France with several devices showed differences of up to 45.000 thousand times in the odour flow rate calculated.
In order to tackle this differences, the German standard VDI 3880 defined the geometry and type of the sampler and this approach has been discussed in many meetings. However, Ms Capelli showed that some tests performed by their lab prove that results produced with the same hoods in different conditions can be very different, even by more than a factor of 10.
All in all, this last meeting of the WG2 paves the way to the new EN13725 that will hopefully be published in 2019. Stay tuned for more news!
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