Directly indicating tubes

The evaluation of sampling tubes is normally done in an analytical laboratory having the appropriate equipment. In the case of directly indicating tubes, no laboratory is required, but their evaluation needs experience to avoid misinterpretations. 

Table 10.18(c) Direct-indicating Drager diffusion tubes - no pump required... 

Direct reading samplers include simple devices such as colorimetric indicating tubes in which a color change indicates the presence of the contaminant in air passed through the tube, or instruments which are more or less specific for a particular substance. In the latter category are carbon monoxide indicators, combustible gas indicators (explosimeters) and mercury vapor meters, as well as a number of other instruments. 

One problem was ensuring that the outer door was closed before the inner door was opened. Because no direct visible check was possible, a small pipe and valve were attached to the top of the torpedo tube in the torpedo room. Before opening the inner door, the valve was opened momentarily to check for the presence of pressurized water in the tube. The presence of pressurized water was a direct indication that the outer door was open. 

Lungs, brain, blood Gases (carbon monoxide, cyanide) Direct-reading colorimetric indicator tubes Head-space Microdiffusion GC... 

The tube model gives a direct indication of why one might expect the strange observations on star melts described above. Because the branch points themselves in a high molecular weight star-polymer melt are extremely dilute, the physics of local entanglements is expected to be identical to the linear case each segment of polymer chain behaves as if it were in a tube of diameter a. However, in... 

Direct Reading Colorimetric Indicator Tubes Manual, Akron, OH, American Industrial Hygiene Assoc. 1976... 

Direct-reading Measurement Techniques 6.9.3.1 Tubes with Direct Indication... 

A general precondition for a tube system with direct indication is the existence of a specific color reaction of the air contaminant with a substrate reagent The following chemical reactions are used as detecting reactions ... 

As well as direct-reading tubes for short-term measurements, tubes are also available for long-term monitoring. Here, the air sample is sucked through the tube by use of a personal-air-sampling pump (PAS-pump). These all look more or less the same and have a similar kind of indication to that of short-term tubes.Their area of application corresponds to that of PAS procedures (see Section 6.9.1.4.1). In contrast to these, the concentration can be read directly at the end of monitoring. Personal exposure is calculated based on the air volume pulled through. 

To determine an average shift concentration, a measuring time of about 8 h is usually used. Long-term tubes with direct indication are available for inorganic and organic gases, e.g. acetone, ammonia, benzene, chlorine, hydrochloric acid, nitrous gases, sulfuric acid, and vinyl chloride. 

Fig. 6.58 Long-term tubes with direct indication and direct-reading diffusion tubes, (a) Long-term tubes (b) dosimeter tubes (c) tube holder.

The basic principle of reaction papers in the form of badges is very similar to that of the tubes. An agent is applied to a substrate, and the former undergoes a color reaction with the substance to be analyzed. The intensity of the discoloration correlates to the concentration of the air contaminant. The final evaluation can take place either by visual comparison with a calibrated color scale or by photometry. Figure 6.59 shows samples of badges with direct indications. 

For many solvents and other substances directly indicating detector tubes are available. They are used for rapid assessment of emission. Since they often do not react specifically with a certain compound alone, errors have to be considered due to cross-sensitivity. 

For a few substances, direct indicating diffusion tubes are available and these devices may be used for up to 8 hours. In these cases, because the... 

These fens have an internal motor mounted on spokes or struts to centralize the unit within the housing. Electrical connections and grease fittings are mounted externally on the housing. Arrow indicators on the housing show the direction of airflow and rotation of the shaft, which enables the unit to be correctly installed in the ductwork. Figure 13.2 illustrates an inlet end of a direct-connected, tube-axial fan. 

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