One of the most significant developments in air sampling technology in recent years is the evolution of passive samplers. This technology was first introduced to the health and safety profession in 1973 by researchers Palmes and Gunnison. As the applications for this technology have grown and changed over the years, the number and types of passive samplers that are commercially available have escalated. Passive samplers are now a key component in the arsenal of air sampling devices.
Active sampling involves the use of an air sampling pump to actively pull air through a collection device such as a filter. Passive sampling, however, does not require active air movement from a pump. Airborne gases and vapours are collected by a physical process such as diffusion through a static air layer or permeation through a membrane. Most passive samplers used by health and safety professionals operate on the principle of diffusion; therefore, they are referred to as diffusive samplers.
There are several advantages of each system – active and passive, such as size and weight and thus worker convenience and initial cost. However, two prime factors affecting reliability (discussed later) are very important.
In the main, active sampling is pretty much independent of wind speed; diffusive samplers however do not work at all well under minimal air movement conditions or in the other extreme, high wind conditions. Most active sampling for gases and vapours is personal on sorbent tubes that have a back up section; this enables a quality and reliability check to be performed under certain defined guidelines and leads to very reliable quantification. Most diffusive samplers do not and are not capable of this.