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January 1998

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By Garry K. Smith (c) Published in "Rescue Australia". December 1998, P. 11, 19, 20 65This foul air article isn't about the resulting strong aroma the morning after your best friend's feast of garlic, baked beans and cabbage. 'Foul Air', sometimes called 'Bad Air', is an atmosphere which has a noticeable abnormal physiological effect on humans. Some concentrations of gases as can occur in caves, mines, sewers, drains, buildings, ships and other confined spaces can be lethal. There are many regulations governing workers exposure to various gas mixtures and concentrations, but emergency services personnel are often exposed to much higher concentrations than are permitted in the workplace. When we talk about dangerous gases, most people instantly think of the poisonous or flammable ones such as: methane, ammonia, hydrogen sulfide and carbon monoxide, to name just a few. So often overlooked is an elevated concentration of carbon dioxide (CO2). This colourless, odourless and non-combustible gas is the body's regulator of the breathing function. The addition of CO2 from a leaking gas bottle into a poorly ventilated basement laboratory, could easily alter the enclosed atmosphere by dispersing Oxygen (O2) and Nitrogen (N2). Since CO2 is 1.57 times heavier than nitrogen and 1.38 times heavier than O2, it will have a tendency to form a layer across the floor. If left undisturbed for some time (possibly days) it will disperse, into an enclosed atmosphere, due to molecular diffusion. On the other hand, air movement from a fan or air conditioner can result in a homogenous mixture in a very short time. The edition of 10% CO2 to an enclosed atmosphere will only reduce the O2 concentration from 21% down to 19%. In other words, the introduction of CO2 into an atmosphere, dilutes other components (N2 and O2), thus it requires five percent CO2 to reduce the O2 concentration by one percent. So what you say, there is plenty of O2 to support life since we can revive a person with mouth to mouth resuscitation, when our expired air contains just 15% O2 and 4.6% CO2. - besides CO2 isn't poisonous. Well think again, because a concentration of 10% CO2 can cause respiratory paralysis and death within a few minutes even if there was 21% O2 in the atmosphere. It all has to do with red cell haemoglobin in the blood, which transports O2 and CO2 around our body. The exchange of the two gases takes place in the lungs by diffusion across the walls of the air sacs (alveoli). Oxygen from inspired air diffuses across the lining of the air sacs and enters the circulation, while CO2 moves in the opposite direction. The gases are transported between cells and the lung by the blood circulation. Diffusion occurs because a gas in high concentration will move to an area of relatively low concentration, until an equilibrium is reached. When breathing good air, this enables CO2 in the body at a higher concentration to diffuse to the inhaled air. In simplified terms, if the inspired air, "Foul Air" contains a relatively high concentration of CO2 the haemoglobin is unable to get rid of the body's waste CO2, thus the haemoglobin is not free to take on fresh O2. The result is asphyxiation and death. Open Access See Extended description for more information.

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K26-02241

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