Stain detector tubes

Detector tube A direct method for identifying airborne contaminants, also known as length-of-stain tube. It is a convenient tool for detecting and quantifying contaminants in field or emergency situations. 

Detector tubes A simple and relatively inexpensive measurement method involves the use of calibrated stain-length detector tubes such as those produced by Draeger, Kitagawa, Gastec, MSA-AUER, and others. CO detector tubes often rely on the reaction of CO with iodine pentoxide, which produces a purple colored iodine stain. The detector tube carries a scale calibrated in parts per million and the length of the color stain that develops after the required number of pump strokes corresponds to the concentration of CO in the sample ... 

Detector tubes As with CO, hydrogen cyanide in air can be measured conveniently with reasonable accuracy by stain-length detector tubes. A typical reagent mixture is mercuric chloride and methyl red indicator. The hydrogen cyanide is converted to mercuric cyanide with the production of hydrogen chloride, which produces a pH change and as a result the indicator changes color to red ... 

Brand name, sampling range, and expiration date of the length of stain ammonia detector tubes. The brand name and model of the sampling pump should also be recorded. If another type of ammonia detector is used, it should be identified along with its minimum detection limit for ammonia. 

D. Detector tubes—A known volume of air is drawn through a detector tube using a small hand pump. The concentration of EtO is related to the length of stain developed in the tube. Detector tubes are economical, easy to use, and give an immediate readout. Unfortunately, partly because they are nonspecific, their accuracy is often questionable. Since the sample is taken over a short period of time, they may be useful for determining the source of leaks. 

Detector Tubes for Measuring Gaseous Pollutants Detector tubes, such as stain tubes and passive sampler tubes, are simple measurement devices that are available for the gaseous pollutants—CO, CO2, NO, and NO2—and for sulfur dioxide (SO2). Detector tubes are simple and cost effective and may be useful for characterizing air quahty. However, they do not provide sufficient accuracy as a measurement technique if accuracy greater than 25% is required. 

Detection of Bromine Vapor. Bromine vapor in air can be monitored by using an oxidant monitor instmment that sounds an alarm when a certain level is reached. An oxidant monitor operates on an amperometric principle. The bromine oxidizes potassium iodide in solution, producing an electrical output by depolarizing one sensor electrode. Detector tubes, usefiil for determining the level of respiratory protection required, contain (9-toluidine that produces a yellow-orange stain when reacted with bromine. These tubes and sample pumps are available through safety supply companies (54). The usefiil concentration range is 0.2—30 ppm. 

Detector tube kits generally include a hand pump that draws a known volume of air through a chemically treated tube intended to react with certain contaminants. The length of color stain resulting in the tube correlates to chemical concentration. 

A length-of-stain detector tube and hand-operated pump are used to measure the H2S concentration in the vapor phase to the test container. The length-of-stain detector tube should be close to but not in contact with the liquid surface. 

It is a fundamental requirement that liquefied petroleum gas should not contain free water (ASTM D-2713). Dissolved water may give trouble by forming hydrates and giving moisture vapor in the gas phase. Both of these will lead to blockages. Therefore, test methods are available to determine the presence of water using electronic moisture analyzers (ASTM D-5454), dew-point temperature (ASTM D-1142), and length-of-stain detector tubes (ASTM D-4888). 

The pumps generally have a capacity of 100 ml for a full pump stroke. The sample volume taken can be controlled by the number of pump strokes taken for each tube. Pumps must be properly maintained and procedures for leak testing and for measuring the volume and flow rate can be obtained from the manufacturers. The volume of the pump should be accurate to 5 % of the value stated. Detector tubes made by one manufacturer should not be used with a pump made by a different manufacturer since the pumps have different flow characteristics and could cause different lengths of stain. Each lot of detector tubes is calibrated by the manufacturer using his specific pump design. 

Stain detector tubes are used for measuring airborne concentrations of gases and vapours. Several proprietary types are available which operate on a common principle. A sealed glass tube is packed with a particular chemical which reacts with the air contaminant. The tube seal is broken, a hand pump attached, and a standard volume of contaminated air is drawn through the tube Figure 18.1). The packed chemical undergoes a colour... 

Figure 18.1 Stain detector tube and hand pump. (Courtesy Draeger Safety Ltd)...

Stain detector tubes are available for a wide range of chemical contaminants. 

The opening created by the suit zipper or other appropriate suit penetration should be used to determine the ammonia concentration in the suit with the low range length of stain detector tube or other ammonia monitor. The internal TECP suit air should be sampled far enough from the enclosed test area to prevent a false ammonia reading. 

Any detectable ammonia in the suit interior (five ppm ammonia (NH3) or more for the length of stain detector tube) indicates that the suit has failed the test. When other ammonia detectors are used a lower level of detection is possible, and it should be specified as the pass/fail criteria. 

The tubes are sealed until ready for detection to avoid any potential contamination. At the time of detection, both ends of the tube are opened and the tube is connected to the special pump (Figure 10.3). The pump can be a manually operated suction pump or a battery-operated pump that draws air at a certain flow rate. The coated reagents will react with the targeted substances to produce the stain on the sensing surface in direct-reading types of detectors (Figure 10.2). Normally, a colorimetric tube requires a fixed volume of sample for quantitative analysis. 

Grab sampling is described here in the context of stain detector tubes. This involves taking a sample of air over a relatively short period of time, usually a few minutes, in order to measure the concentration of a contaminant. The results are illustrated in Figure 3.3.1 where the discrete measured concentrations are plotted. 

Long-term stain detector tubes are available for this purpose and are connected to a pump which draws air through the tube at a predetermined constant rate. At the end of the sampling period the tube is examined to measure the extent of staining and hence the ammmt of contaminant absorbed, from which the average level of contamination can be calculated. 

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