A method for psychophysical screening of odorants for use in city gas based on olfactory adaptation tolerance

In many developed nations, natural gas (so-called city gas) is supplied as a utility for cooking, heating, and hot-water supply. Because natural gas is odorless, city gas must be odorized so that it can be detected in the event of a leak. Although high adaptation tolerance is an important criterion for city gas odorants, there is yet no standard method of evaluating the psychophysical suitability of new candidate odorants in terms of olfactory adaptation. In order to address this situation, we developed a method for psychophysical screening of new candidate odorants for use in city gas based on adaptation tolerance.

We used the main component of the conventional city gas odor (tertbutylmercaptan, TBM) and six new candidate odorants: cyclohexene (CH), ethyl isobutyrate (EI), isovaleric acid (IVA), 2-hexene (HEX), 1,5-cyclooctadiene (COD), and 1-methylpyrrolidine (MEP). Participants evaluated the perceived intensity of a continuously presented odor at a fixed concentration. After the time-intensity curves were quantitatively classified into fast or slow adaptation patterns, we compared the number of intensity curves classified into each pattern between TBM and each new odorant.

Our results revealed that HEX has a significantly higher adaptation tolerance than TBM, and that the other five new candidate odorants were almost equivalent to TBM in terms of adaptation tolerance.

We concluded that all of the new candidate odorants used in this study passed the psychophysical screen based on adaptation tolerance, and are therefore suitable for use in city gas.