What is mildly astonishing about smells is that in the vernacular there is no obvious means of measuring and comparing them. After all, we are surrounded by smells, some pleasant and appealing like the scent of a flower or a perfume whilst others are grossly offensive like body odour and farts. On encountering a pungent odour we register against some scale deep in our subconscious but I was hard pressed, before digging into the subject, to name a scale which gave some comparatives with which we can judge and contrast what has just hit our nostrils.
A Danish environmental scientist, P.O.Fanger, has done some work on the subject. In 1988 he came up with a unit of measure, the olf. One olf is the odour given off by a standard person, defined as someone in a sedentary occupation who takes 0.7 baths a day and has a skin surface of 1.8 square metres. I’m not sure I have considered the size of my skin surface or, indeed, anyone else’s but as I’m above the average size, vertically if not in profile, I suspect I’m slightly above that. As an Englishman I don’t bathe but have a daily shower so my cleanliness is a bit above Fanger’s standard so I’m in a bit of quandary as to whether I emit one standard olf or not. A heavy smoker, though, emits 25 olfs and an athlete, presumably after their exertions, a whopping 30 olfs.
Fanger wasn’t finished there. He came up with a decipol which he used to measure perceived air quality. A decipol is the perceived air quality in a space where there is one olf ventilated by 10 litres of unpolluted air a second. I’m not sure this is any more useful than the olf but I might just go around from time to time muttering, “just feel the decipols in this place”.
I’m not a great fan of talk shows on the radio but there are some hosts who go beyond the usual platitudinous fare and are able to riff on even the most mundane subject in an amusing and occasionally instructive way. Danny Baker is always worth a listen, I find, and one of his equivalents over the pond is Adam Corolla and his sidekick, Dr Drew, who hosted a show called Lovelines. He developed a scale called Hobo Power which ran from 0 to 100 and a standard feature on the show consisted of callers ringing in with the latest shocker of an olfactory experience and they would determine where it fitted on the scale.
A scale of sorts soon emerged. Zero meant that it didn’t whiff at all whereas the top score of 100, which has never been awarded, would result in immediate asphyxiation. A robust fart rated 13 whereas a 30 would induce someone who caught a whiff to vomit. Corolla described a smell meriting a 50 on the scale as akin to a cat that has been fed on nothing but blue cheese for a week defecating on a white-hot hibachi, a Japanese fire box.
For those who like a more scientific approach to the measurement of smells, two enterprising students from Cornell University, Robert Clain and Miguel Salas, developed a fart detector using a sensitive hydrogen sulphide monitor, a thermometer and a microphone with accompanying software. The machine would rate stench, temperature and sound – apparently, the warmer the fart, the wider it spreads – and a voice would rate it using a scale running from zero to nine. A nifty feature was that if the fart ranked a nine, a fan would switch itself on and dissipate the smell. The drawback was that unless you recruited a professional flatulist, testing was a bit haphazard which is probably why it never developed beyond a good idea.