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Use of Boyle's Law to Quantify Increased Flatulance due to Increased Altitude

by Mike Gilbert RRT, CRTT, RCP

A phenomenon that regularly plagues travelers is the increase in flatulance that occurs with the move from an area of relatively low altitude to an area of relatively high altitude. This may occur in unpressurized aircraft, pressurized-cabin aircraft, or in automobiles crossing mountain ranges. Flatus, in itself, is harmless yet leads to social ostracism and may present an explosion hazard in the presence of open flame or spark.

Free gas in the bowel consist mainly of air and methane (CH4), this mixture reacts in a predictable manner to changes in pressure and volume. The British physiscian Robert Boyle (1627-1691) is credited with the discovery that "At a constant temperature, the volume of a gas varies inversely with the pressure, and the pressure varies inversely with the volume"(1). Free gas in the bowel is affected by changes in the barometric pressure caused by changes in altitude and results in variation in the volume of said free gas.

Average barometric pressure at sea level is 760 mmHg, this decreases by approximately 3.9% for each 1000 feet increase in elevation so that the average barometric pressure at 5000 feet is approximately 623 mmHg.(2) The average commercial aircraft maintains a pressurized cabin roughly equivalent to a 5000-8000 foot elevation or a barometric pressure of 623-561 mmHg.(3)

In order to quantify this increase in volume, we utilize the formula statement of Boyle's Law: P1V1=P2V2 where P = pressure and V = volume. For ease of computation, we will assume the volume of free gas in the bowel to be 100 ml (V1) and use 760 mmHg for the barometric pressure at sea level (P1). We will use a barometric pressure of 625 mmHg (P2) for an altitude of 5000 feet and solve for V2.

760 mmHg x 100 ml = 625 mmHg x V2 ml
V2 = 121.6 ml

Consequently, a group of passengers departing from Los Angeles International Airport en route to Seattle will experience an increase of free bowel gas of approximately 20% somewhere over the skies of San Francisco. Subsequent release of this increase volume of flatus will be markedly noticible in light of regulations which have eliminated the other main intra-cabin air pollutant; cigarette smoke.

The object of this dissertation is purely to quantify this phenomenon, not to change the social mores and attitudes of our culture. Altitude induced hyperflatulencism will remain socially unacceptable until public awareness is increased through education.

Authors Note - I wrote this sometime in the late 1980's (my surviving copy was printed with a dot matrix printer )and submitted it to a few Respiratory journals but it was rejected. Now, thanks to the magic of the internet, I don't need them to be published!

1. Friel JP, et al (eds): Dorland's Illustrated Medical Dictionary, 25th Edition, Philadelphia, W.B. Saunders Company, 1974
2. Spearman CB, Sheldon RL, Eagan DF et al: Eagan's Fundamentals Respiratory Care, 4th Edition, St. Louis, C.V. Mosby Company, 1982
3. Hodgkin JE, Collier CA: Blood Gas Analysis and Acid-Base Physiology in Respiratory Care, Burton GG, Hodgkin JE (eds), 2nd Edition, Philadelphia, J.B. Lippincott Company, 1984

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