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The release of intestinal gases (i.e. flatulence) can constitute an embarrassing problem both for the person farting and for persons in the near presence due to sound and odour. Intestinal gas may also cause physical discomfort or even pain for the person farting. When performed in a small closed environment over longer periods of time, e.g. on a spacecraft, it may even in the worst case scenario cause explosion danger.1
Flatus is gas derived from the intestines expelled by the anus. The average human produces 0.7-1 litres of intestinal gas per day.2,3 Flatus primarily consists of nitrogen and CO2, however smaller amounts of O2, H2, CH4 and other gases are also present.4 The gas components that are responsible for the unpleasant "classic" odour of flatus are sulphur-containing gases.
Studies have not been able to prove that men produce larger amounts of flatus than women, while in contrast it has been shown that women's flatulence odour is significantly worse compared to that of men.5 The average person passes gas about 10 times a day with no difference between men and women, and no difference between younger and older people.6
Flatulation could pose a significantly larger problem on commercial airplanes than on the ground due to several obvious factors:
* In airplanes many people are seated closely together in a confined small space;
* Commercial airlines have banned smoking on airlines which increases the risk of nasally detecting even small amounts of intestinal gases;
* Modern aircraft are build with increasing sound isolation which increases the possibilities of sound detection; and
* Approximately 50% of cabin air on airplanes is recirculated which keeps a great deal of the odour inside and adds to distribution of flatulence.7
It is plausible that the amount of intestinal gas produced per person is greater at airplane cruising altitude (e.g. 30,000 feet above sea level) compared with ground altitude (Figure 1). This may be surmised from a study of the elementary laws of physics: when increasing in altitude (e.g. being aboard an airplane) the pressure will fall equivalent to the increasing altitude.
Figure 1. The relationship between volume and air pressure
[Table omitted. See PDF]
The modern aircrafts are able to counteract this by the use of pressurised-cabins, but these are only...