Aspiration Method

ASPIRATION METHOD, for determining the quantity of dust or gas present in the air of various, primarily industrial, premises, consists of drawing a strictly defined volume of air through using aspirators (see), which serve not only for drawing the air through but also for measuring the quantity of air passed. In cases where the drawing of air must proceed more rapidly, various pumps (manual, motor-driven, or water-jet) or electric vacuum cleaners are used for suction. Measurement of the drawn air is performed either by gas meters (see) or rheometers. When absorbing gases and vapors, the rate of suction is determined by the properties of the gases, their quantity in the air under investigation, and the specific features of the reactions used for their determination. Subsequently, either the drawn air is passed through absorbers, or individual gases are subjected to combustion, or, finally, the air is collected in receiving vessels so that the analysis itself can be performed in a laboratory. Most often, the absorption method is used for this. Aspiration of dust is performed for its gravimetric determination, for its chemical analysis, for counting and measuring individual dust particles, and, finally, for its morphological study (see Dust). The main task of aspirating dusty air is the gravimetric determination of the quantity of dust in a unit volume of air. However, the aspiration method cannot provide absolute accuracy in this regard, since it essentially measures only the quantity of dust in the absorbed volume of air, but there can never be certainty that this corresponds exactly to the quantity of dust contained in the air. The rate of suction, the degree of vacuum created, the shape and direction of the suction openings, the formation of vortices during suction that lift dust from places where it is in a state of rest after having settled from the air—all these factors can seriously influence the results obtained. From the point of view of industrial hygiene, it is important, if possible, to recreate conditions of aspiration that correspond to the physiological processes of inhaling dusty air. To this end, Recknagel proposed drawing air in a quantity of 775 liters per hour at a speed of 1.4 meters per second through a suction opening of about 1.5 square centimeters. Burshtein (Odessa) recently proposed a special device for dust aspiration that most closely corresponds to physiological conditions. In this device, the suction openings are directed vertically, like nostrils, and the air is drawn through by a pump, with the rate of aspiration set according to the inhalation conditions of the workers whose workplace dustiness is being studied at that moment. A number of authors believe that under the conditions of the commonly used suction speed, the difference in the rate of aspiration is of no essential significance. Dust aspirated by one method or another is then captured by the method of washing, filtration, sedimentation, or precipitation. Of these, the most accurate are the methods of filtration (see) and washing, although all of them are inferior to the method of electrical dust precipitation.