Simply described, an air sampling device consists of an electrically-operated air sampling pump, sampling medium, and tubing to connect the medium to the pump. This equipment may be portable and worn on a worker, generally for an eight-hour (one-shift) period, or it may be static with long-lasting batteries or connection to a main supply of electricity. The sampling media may be a filter, solvent, or solid absorbent. Possible contact sources for names and addresses of manufacturers and suppliers of environmental monitoring equipment are listed in Appendix A. Filter media and filter holders may be purchased through suppliers and assembled in-house or can be bought pre-assembled. Personal and/or static sampling devices may be used depending upon the requirements of the sampling program, but it is important to note that static sampling frequently underestimates exposures.
A second type of device available for estimating the concentration of soluble aerosols of nickel is the detector tube with manual pump. Soluble airborne contaminants produce a color change as the pump draws the air through the detector tube. The length of the stain is proportional to the concentration. Since the typical accuracy of these readings is ± 25 percent and the lower limit of detection is 0.25 mg Ni/m3, this device should serve only as a screening tool to aid in deciding whether to conduct full shift monitoring. It should also be noted that FeSO4 interferes by producing a similar color change. A detector tube is also available for nickel carbonyl. However, as its detection limit is only 0.1 ppm, its use is limited.
Selecting the appropriate equipment depends on the goal behind sampling and any specifications established by the regulating authority. Pumps are generally interchangeable since they all have similar functions, but dust collection methods vary depending on whether particle-size-selective sampling of the dust is desired. Furthermore, some filtering media can be used to distinguish between different forms of nickel more readily than others. Therefore, the objectives of the sampling program and guidelines or regulations that apply should be determined before selecting the sampling equipment (see Section 7.2).
Manufacturers, suppliers, industry trade associations, or associations that support occupational health professionals may be sources of sampling information. Appendix A lists some possible contacts for these sources. Another alternative is to use published methods such as those prepared by NIOSH (1994a, b, c).
In addition to the air sampling device, calibration and quality control are fundamental to valid monitoring results. Equipment to calibrate the volumetric flowrate of the air sampling device is essential. Soap bubble meters, rotameters, or automated instruments may be used for such purposes and are available through equipment manufacturers and suppliers.