Sampling rate, backup

The collection efficiency of a filter sampler was demonstrated by sampling test atmospheres with a backup collector at the proposed sampling rate and time, and analyzing the collected samples. For sorbents or filter/sorbent sampling trains, the breakthrough volume was determined (to demonstrate capacity) at 80% relative humidity. 6... 

See Figure 5.) The sampling rate of the backup section is a function of the total area and length through which the contaminant must travel from the front face of the badge to the backup section charcoal strip. This sampling rate can be determined by the use of equation (3)(14). 

Since the of the backup section is 2.2 times the of the front section, the backup section should sample additional material at 46 percent of the sampling rate of the front section. (See Figure 3.)... 

Sorbent Capacity or Saturation Point. After a certain amount of substance has been adsorbed by the dosimeter the ability of the sorbent to remove vapors from the diffusion space is reduced and the sampling rate begins to decrease. The saturation point for many chemicals can be obtained from the manufacture or determined experimentally in the lab. To determine the saturation point in the lab, the dosimeter is exposed to various doses and the response or sampling rate is plotted against the dose. The point at which an unacceptable deviation in linearity occurs is taken as the saturation point. Fig. 6. Some dosimeters are designed with a backup pad which is placed behind the primary pad to measure the overload and extend capacity. 

This work has demonstrated that sorbent tubes are viable samplers for inorganic acid mists existing as vapors and aerosols. A silica gel sampling tube was developed which will collect at least a 4-hour sample of inorganic acid at a nominal flow rate of 0.2 Lpm. The optimum sampler geometry was determined to be a 7-mm O.D./4.8-mm I.D. glass tube packed with 20-40 mesh washed silica gel, 700 mg in the primary section and 200 mg in the backup. 

A glass tube (6-mm I.D. by 8-mm O.D. by 3-cm long) is packed with approximately 100 mg of sorbent in a front section and 50 mg in a backup section, each separated by glass wool plugs. Sorbents of coarse mesh size ( 20/40) are used to minimize the pressure drop across the tube. A calibrated personal sampling pump draws air through the sorbent tube at a flow rate of up to 1 liter/min. 

The rates of internal conversion from the 5Z)3 to the 5D4 states were also measured. The backup oxide in this case was yttrium. This information was obtained by determining the rise time of the 5Z)4-state green fluorescence as a function of time, when the 5Z>3 state was excited. The rise time of the 5Z)4 state is, of course, the decay time of the 5Z>3 state. It was assumed that the decay of the 5Z)3 was predominantly due to an efficient internal conversion process to the 5D4. Measurements of the decay time of the 5Z)3 state directly were not possible, since the emission from this state is very weak if not, indeed, absent. The result of this study is shown in Fig. 23, where it can be seen that the internal-conversion time remains constant at about 17 fxsec up to a terbium oxide concentration of 1 mole per cent. At higher concentrations, the internal conversion time falls rapidly, until at 10 mole per cent terbium oxide the value is about 1.7 /xsec. This is down by a factor of 10 over samples containing 1 mole per cent or less of terbium oxide. 

EXPERIMENTAL The sampling and analytical method employed in determining the various solvent vapor concentrations in air are described in detail by White etal (A)and NIOSH (2), Four Bendix National Environmental Instruments Model BDX 30 Personal Samplers were used daily (one in each laboratory) with large size charcoal tubes (SKC cat no. 226-09-100) which contained two sections of activated charcoal per tube (a 400 milligram section followed by a 200 mg backup section to indicate when "breakthrough" of the main section has occurred). The sampling pumps were operated at a rate of one liter per minute and were calibrated by means of an Environmental Compliance Corporation Model 302 Universal Pump Calibrator (a device that generates a thin film of soap which is carefully timed as it traverses a very... 

Fire-Rated Valves that handle flammable fluids may have additional safety-related requirements for minimal external leakage, minimal internal (downstream) leakage, and operability during and after a fire. Being fire-rated does not mean being totally impervious to fire, but a sample valve must meet particular specifications such as those of American Petroleum Institute (API) 607, Factory Mutual Research Corp. (FM) 7440, or the British Standard 5146 under a simulated fire test. Due to very high flame temperature, metal seating (either primary or as a backup to a bumed-out elastomer) is mandatory. 

The literature on procedures for PbB determination is abundant. Those techniques that have been shown to provide accurate and precise PbB determinations in routine use include anodic stripping voltammetry (ASV), flame atomic absorption spectrophotometry (FAAS), discrete sampling FAAS, and graphite furnace AAS (GF-AAS). The method most widely used for routine determination is AAS in its various modifications. The relatively slow analysis rate of ASV tends to limit the application of this technique to that of a backup or reference method. Whatever the technique which is applied, it should be emphasized that avoidance of contamination, careful handling of the blood samples and frequent intra- and interlaboratory checks are more important for ensuring precision and reliability than the method itself. 

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