Unpleasant odours can cause a nuisance. But how exactly are they to be measured and what is the reliability of the measurements that can be expected if local authorities, for example, have to initiate proceedings against owners of sites which emit odours? Furthermore, the sense of smell varies between people.
A new European Standard, EN 13725, Air quality – Determination of odour concentration by dynamic olfactometry, provides a sound, scientifically objective method for assessing odours. It is the result of several years of research and inter-laboratory comparisons carried out on a European scale.
In essence, it defines a 'European Reference Odour Mass (EROM)'*. It then describes how trained human assessors working with specified apparatus (the olfactometer) are presented with the diluted gas under investigation at progressive degrees of concentration until the same threshold response is elicited as from the reference odour. From the dilution used to reach that level of stimulus, the odour concentration is calculated and expressed in 'European Odour Units per cubic metre'. That quantified unit can then be used with more confidence to report odours in the context of legal enforcement of nuisance reduction and other environmental strategies.
The reproducibility of results between laboratories has been successfully demonstrated and provides confidence that the selection of assessors (rather than trying to recruit 'representative' samples from the population), calibrated against the reference odour, provides objective information on the concentration of odour or the emission rate of odour, so that quantitative environmental criteria can be applied.
The European Commission has expressed interest in the standard and referred to it in its draft directive on biodegradable waste. The German Association of Engineers (VDI) had already adopted the draft standard as a reference method in 1999. Enquiries were received from authorities in Australia and New Zealand, resulting in a standard using the same principles.
The application of standardized tests to odour detection is just part of a larger picture. Using geographic and meteorological data, maps can be drawn up to identify levels of exposure and predict odour annoyance impacts on the population residing in those areas.
* For n-butanol as a reference odorant. One EROM evaporated in 1 m3 of neutral air is the standard olfactory stimulus, equivalent to 1 European odour unit: 1 ouE/m3.
Available for media interview:
Mr Ton van Harreveld
Phone: + 34 93 406 9061
Mobile: + 44 7785 282269
EN 13725 can be bought from the National Members of CEN from June.