Area samplers

ORSA 5 sampler (tube-type diffusive sampler) 400 mg of activated charcoal contained in a 0.5 cm diffusive path and 0.88 cm cross sectional area sampler OVM 500 sampler (batch-type diffusive sampler) 180 mg of activated charcoal contained in a 1 cm diffusive path and 7.07 cm cross sectional area sampler 3 M organic vapor monitor 3500 [OVM]... 

The personal sampler for respirable dust involves a cyclone preselector (see Fig. 2) operating at 1.9 + 0.1 i/min, and a parallel plate elutriator serves as a high volume area sampler (Fig. 3). 

Personal samplers are usually clipped on the workers lapel, and high volume area samplers are ideally suspended at head height away from obstructions and potential fresh air inlets. For accurate determinations, filters should be conditioned by leaving them In the balance room overnight before each weighing. Membrane filters should be passed over a static eliminator to dissipate excess charge. 

The occupational exposure standard for cotton dust is 0.5 mg/m total dust less fly, using area samplers, although personal sampling may be adopted in the near future. 

Proximity to Breathing Zone. Whereas all exposure measurement methods attempt to sample from air that is likely to be inhaled, some methods do so better than others. A sampler fixed some distance away from a breathing area is not usually accurate in measuring exposure. Even using mobile samplers that move with the worker, the few centimeters in distance from the nose and mouth to the position of the sampler, has been found to make a difference. 

Eor toxic materials, it usually is advisable to provide ventilated sampling hoods or breathing-air stations and masks, to assure that the sampler is adequately protected from toxic or flammable vapors and dusts. Special provision for access to and exit from sampling points also may be needed at elevated locations and to avoid tripping or bumping ha2ards and to ensure that the sampler does not transverse areas not intended as walkways, eg, tank covers or roofs. 

The sample area should be able to incorporate an auto-sampler which can work with both flame and furnace atomisers. Improved analytical precision is obtained when an auto-sampler is used in conjunction with a furnace atomiser. 

The regulations require three samples from the treated plot (one from each subplot) and a single sample from the control plot at each sampling interval. For foliage the preferred technique is to collect leaf punch samples. Leaf punch samplers are available in 5-, 2.5- and 1.25-cm punch areas. Common practice requires a sample of 40-5-cm leaf disks to provide a 400-cm sample using both the top and bottom of the leaf disk to calculate sample surface area. 

In most cases, if soil samples are needed, only surface samples are collected. An exception would be harvesting root crops where all residues in the top 6 in of soil would be sampled. A typical surface soil sampler is shown in Figure 2. It is the residue adsorbed on small particles (<150 o.m), which could cling to moist skin, which causes the most exposure to workers. After sampling, place a flag in the center of each sampled location to mark the area against future sampling. After the surface layer has been collected, the soil is sieved to collect the fraction <150 lam and the remainder of the soil is discarded. Maintain separate sieves and collectors for treated and control plots to prevent contamination of the control samples. 

Other paper collectors that have been used to assess droplet size and distribution patterns include cards such as Kromekote. This was one of several types of collector that provided information on spray deposition in the held, a-Cellulose samplers are fibrous in nature, and include a vertical component to their aspect. This type of collector, along with Mylar cards and other types of card samplers, are often used to provide information on spray coverage as amount of material per unit surface area. 

Collection efficiency is a measure of the amount of material collected by the sampler relative to the amount of material to which the sampler was exposed. Collection efficiencies for many types of samples can be obtained from literature references. If not available in the literature, collection efficiencies can be obtained by comparing the amount collected by the sampler with the amount collected by samplers with known collection efficiency (e.g., nominal 100% for isokinetic samplers). Alternatively, the collection efficiency can be determined by measuring the amount of material collected in a low-speed wind mnnel or spray chamber relative to the release of a known amount of material. Some samplers have collection efficiencies below 100% (e.g., wide collectors sampling small droplets), while others may exceed 100% if they sweep the air of more material than passes a given location based on sampling area alone (e.g., high-volume air samplers). 

A major problem in the sampling of surface films is the inclusion of water in the film. In the ideal sampler, only the film of organic molecules, perhaps a few molecular layers in thickness, floating on the water surface, would be removed the analytical results should then be expressed either in terms of volume taken or of surface area sampled. 

Dawson et al. [227] described samplers for large-volume collection of sea water samples for chlorinated hydrocarbon analyses. The samplers use the macroreticular absorbent Amberlite XAD-2. Operation of the towed fish type sampler causes minimal interruption to a ship s programme and allows a large area to be surveyed. The second type is a self-powered in situ pump which can be left unattended to extract large volumes of water at a fixed station. 

Bedload was sampled during competent flows at the same vertical than suspended sediment. Bedload analysis has been based upon 215 samples, 145 during 2002-2003 and 70 during 2003-2004. At SMS we used a 29-kg cable-suspended Helley-Smith sampler with a 76-mm intake and an expansion ratio (i.e. ratio of nozzle exit area to entrance area) of 3.22 (Fig. 2c). Bedload was measured at... 

Each grid area is typically sampled by taking three to four cores such as would be obtained using the sampler shown in Figure 7.3. The cores are combined and mixed to obtain the final sample for analysis. 

Toxicity end point Maehlyand Swensson 1970 No adverse effect in healthy adult humans occupationally exposed at geometric mean concentration of <1 (range 0.01-3.3 ppm, personal samplers [up to 6 ppm, area samples]) or 5 ppm mild headache in adult humans occupationally exposed at 8 ppm. The exposure duration was considered to be 8 h. 

---