| Gas measurement serves as a technical aid and | | | | - mass spectrometers |
| an assessment of the concentration is only | | | | - substance selective instruments with e. g. |
| possible with a gas measurement device. To | | | | electrochemical sensors |
| determine the hazard potential of a gas it is | | | | The choice of which monitor or measurement |
| necessary to measure its concentration and to | | | | method to use depends upon the objective. |
| consider the duration of exposure and other | | | | The user must evaluate the situation and |
| parameters such as the type of work being | | | | determine which substances to measure, how |
| performed. | | | | often, etc. Each of the above mentioned devices |
| Natural, ambient air is chemically a gas mixture | | | | and methods have advantages and limitations. |
| that consists of 78% nitrogen, 21% oxygen | | | | There is no universal monitor for all possible |
| 0.03% carbon dioxide as well as argon, helium and | | | | scenarios. For the selection of a suitable measuring |
| other rare gases in trace centrations. In addition | | | | device and to support the user in solving |
| there is water vapor, e. g. humidity. If the | | | | measurement problems, Draeger Safety AG & |
| concentrations of the components change, or a | | | | Co. KGaA offers competent know-how and |
| foreign gas is added, we no longer have natural | | | | technical assistance. The customer / employer |
| air. When these changes occur, the potential for | | | | should carefully train the user / employee on the |
| adverse health effects exist. | | | | use of their measurement device. Any use of the |
| The spectrum of other so-called air components | | | | measurement device without receiving prior |
| can be extremely broad. It can range from the | | | | comprehensive training can be permitted by the |
| pleasant fragrance of a good perfume to the | | | | customer / employer to the user / employees, |
| over powering stench of hydrogen sulfide. | | | | at the customer / employees own risk. |
| Likewise, the hazard of each "air pollutant" varies | | | | Photo and flame ionization detectors are |
| considerably. The type of substance,its | | | | distinguished by short response periods but they |
| concentration and duration of occurrence, as well | | | | do not offer substance selectivity. Gas |
| as probable synergistic effects with certain gas | | | | chromatographs, infrared and UV-VIS |
| compounds must all be considered. In addition, | | | | photometers are very versatile but on the other |
| there are many air pollutants which cannot be | | | | hand they are comparatively expensive and |
| perceived by human senses because they are | | | | require a specialist to calibrate the devices and |
| colorless and odorless (e. g. carbon monoxide). | | | | interpret the readings correctly. Warning devices |
| If the composition of the natural air changes in | | | | for explosion hazards like the Drager X-am 5000 |
| any way, it should be tested, to determine the | | | | are equipped with catalytical sensors to determine |
| substance which caused this change. Even | | | | explosion levels of combustible gases and vapors. |
| substances with distinctive odors cannot be | | | | They are not designed to measure lower |
| reliably assessed with the aid of the olfactory | | | | concentrations and thus are not suitable for this |
| nerve in the nose. The olfactory nerve can | | | | task. |
| become desensitized after a certain period of | | | | Draeger-Tubes with direct reading colorimetric |
| time or repeated exposure, making it impossible | | | | indication have many applications. Approximately |
| to smell even immediately dangerous | | | | 500 different substances can be measured with |
| concentrations. After a few hours we do not | | | | Drager-Tubes. Limited selectivity and the fact that |
| even perceive the pleasant fragrance of our own | | | | Drager-Tubes are usually capable of only being |
| perfume and high concentrations of hydrogen | | | | used a once may present a disadvantage. If |
| sulfide escape from the sense of smell even after | | | | repeated measurements of the same substance |
| a very short while. | | | | are to be performed daily, a measurement device |
| Subjectively, one persons sense of smell may be | | | | like the Draeger Pac 7000 CO with its |
| more sensitive to certain air pollutants than | | | | electrochemical sensor for the measurement of |
| others. In many cases substances are noticed in | | | | carbon monoxide is more economic than |
| very low concentrations which, even after a | | | | Draeger-Tubes. |
| long-term exposure do not necessarily cause | | | | When complex mixtures (e. g. solvent mixtures), |
| adverse health effects. In general the sense of | | | | are present, usually only a laboratory analysis will |
| smell is sufficient in determining the presence of | | | | suffice. The prerequisite is that the contaminated |
| air pollutants, but the need exists for an objective | | | | air is trapped in a sorbent sampling tube like silica |
| gas analysis method. Gas measurement serves as | | | | gel or activated charcoal. |
| a technical aid and an assessment of the | | | | After collecting the sample, analysis is performed |
| concentration is only possible with a gas | | | | in the laboratory with gas chromatographic |
| measurement device. To determine the hazard | | | | methods, or sometimes by the combination of |
| potential of a gas it is necessary to measure its | | | | gas chromatography / mass spectroscopy. |
| concentration and to consider the duration of | | | | Laboratory procedures of this kind offer |
| exposure and other parameters such as the type | | | | particularly high selectivity, but the analysis devices |
| of work being performed. | | | | are very expensive, requiring high maintenance |
| An important prerequisite to determining the | | | | costs and operation by specialists. |
| potential of any gaseous air pollutants is the | | | | Regardless of the gas measurement device or |
| determination of the concentration with a suitable | | | | what analysis procedure is used, it is essential that |
| gas measurement device. The kind of device to | | | | the contaminant of interest be identifiable and |
| be used depends on which gases have to be | | | | measurable. Apart from a few exceptions in |
| measured and how often. Much to the dismay of | | | | process monitoring, it is very unlikely that |
| both the user and the manufacturer, there is no | | | | concentrations of other substances can be |
| universal instrument which measures all gases or | | | | determined by subtracting the concentration of |
| vapors. The variety of substances is too wide for | | | | the gas which can be identified. For example, if |
| a single technique to measure all possible air | | | | the oxygen concentration is below the 17 or 19.5 |
| pollutants. The more chemically complex a | | | | Vol. % limit, it cannot be said which substance has |
| substance is, the more complex the gas | | | | displaced the oxygen without further investigation. |
| measurement technique. | | | | In the case of very high carbon dioxide |
| It may be that more than one measurement | | | | concentrations there is the danger of suffocation; |
| device or measurement method may be | | | | likewise if there is a leak in a gas pipeline the |
| employed, each based on different operational | | | | presence of methane poses an explosion hazard. |
| principles. The instrumentation industry offers | | | | Other contaminants present in the ppm range |
| various devices for this purpose which can be | | | | would not influence the oxygen measurement |
| used, individually or in combination on the | | | | enough to alert anyone to a potential hazard. |
| measurement task: | | | | Since many of the occupational exposure limits |
| - flame ionization detectors | | | | are in the range of 1 ppm, the measurement by |
| - photo ionization detectors | | | | difference technique is typically inadequate. |
| - gas chromatographs | | | | Before each measurement an assessment of the |
| - infrared spectrometers | | | | situation should be made as to what contaminants |
| - UV-VIS photometers | | | | are in question, at what locations, at what times, |
| - warning devices for explosion hazards | | | | and so forth, according to established safety |
| - Draeger-Tubes | | | | procedures. Monitoring according to established |
| - Draeger Chip-Measurement-System | | | | safety guidelines will help ensure safety in the |
| - laboratory analysis in conjunction with sampling | | | | workplace and effective use of monitoring |
| tubes or gas wash bottles (impinger) | | | | equipment. |