These guidelines are continually open to examination by the OSHA Methods Development Team who are using them, and refinements are formally made on a periodic basis. The resulting evolution in the guidelines is apparent when comparing early methods to more recent ones. The evaluation guidelines have been effectively used and refined for more than twenty years. Revisions in this September 1999 update include the addition of evaluation tests for diffusive samplers.
Active sampling is defined as collection of an analyte using a sampling pump to draw air through an appropriate adsorbent. Diffusive sampling is a passive technique which collects the analyte without a sampling pump using the principles of diffusion.