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8 | Dräger-Tubes & CMS-Handbook

Dräger sampling tubes and systems - 20351 1.General1.1Introduction to Gas Measuring

Natural, ambient air is chemically a gas mixture that consists of 78 % nitrogen, 21 % oxygen 0.03% carbon dioxide as well as argon, helium and other rare gases in trace concentrations. In addition there is water vapor, e. g. humidity. If the concentrations of the components change, or a foreign gas is added, we no longer have natural air. When these changes occur, the potential for adverse health effects exist.The spectrum of other so-called air components can be extremely broad. It can range fromthe pleasant fragrance of a good perfume to the over powering stench of hydrogen sulfide. Likewise, the hazard of each “air pollutant” varies considerably. The type of substance, itsconcentration and duration of occurrence, as well as probable synergistic effects with certain gas compounds must all be considered. In addition, there are many air pollutants which cannot be perceived by human senses because they are colorless and odorless (e. g. carbon monoxide).If the composition of the natural air changes in any way, it should be tested, to determinethe substance which caused this change. Even substances with distinctive odors cannot bereliably assessed with the aid of the olfactory nerve in the nose. The olfactory nerve can become desensitized after a certain period of time or repeated exposure, making it impossible to smell even immediately dangerous concentrations. After a few hours we do not even perceive the pleasant fragrance of our own perfume and high concentrations of hydrogen sulfide escape from the sense of smell even after a very short while.Subjectively, one persons sense of smell may be more sensitive to certain air pollutantsthan others. In many cases substances are noticed in very low concentrations which, evenafter a long-term exposure do not necessarily cause adverse health effects. In general thesense of smell is sufficient in determining the presence of air pollutants, but the need existsfor an objective gas analysis method. Gas measurement serves as a technical aid and anassessment of the concentration is only possible with a gas measurement device. To determine the hazard potential of a gas it is necessary to measure its concentration and toconsider the duration of exposure and other parameters such as the type of work being performed.If only the concentration of an air pollutant is known it is difficult to evaluate the degree ofthe hazard. For Example, there is a degree of uncertainty regarding the health effects ofcigarette smoking. The synergistic effect of the more than 800 single substances in cigarette smoke and the physiological condition of the smoker are all factors in determining the toxicological influence to the individual.