Sample Numbers & Accuracy of Odour Measurement
For many people (both clients and consultants), it is not clear how many odour samples they should collect for a source.
As an sensory instrument, olfactometer has nearly no chance to reach the repeatability and accuracy characteristics of analytical instruments. The CEN standard allows a repeatability factor of 3 for odour measurement.
The study has shown that the precision can be improved when more than just one sample is taken from a source. The figure below shows the 95% confidence limits for an odour sample of 1000 OUE/m3 resulting from an increasing number of samples. There is a significant reduction in the confidence limits for sample sizes above 2, and little benefit in increasing sample numbers beyond 4.
95% confidence limits with replicate samples (after Sneath and Clarkson, 2000)
This shows that the duplicate samples are recommended if a better emission data is needed for an odour source.
|
