Rotameters and other flowmeters such as wet test meters and dry gas meters are termed secondary standards. A primary standard, as it relates to flowmeters, is one that is based on direct and measurable linear dimensions, such as the length and diameter of a cylinder, which will not change over time. As with alternative sampling methods, the employer has the obligation of selecting a method which meets the sampling and analytical accuracy and precision requirements of the standard under their unique field conditions. Most detector tubes do not meet the accuracy and precision requirements nor do they offer the specificity required to ensure measurement of exposures to a single chemical. Detector tubes are better used for screening purposes or field surveys.
Validated methods are a better choice for compliance sampling.
This will be dependent on the sorbent tube being used, the environment being sampled, and the expected concentrations. If the expected concentrations are high, the flow rate may need to be reduced to avoid overloading the capacity of the sampling device. Consult the method to determine the maximum flow rate and breakthrough volumes. Sampler capacity is a conservative estimate of the total mass of contaminant which can be collected on the sampling media with loss or overloading. For easy reference, consult the method to determine the working range of the method in ppm and in ug per sample.