In recent years, portable gas detectors have shrunk in size and cost while many new features have been added: automatic time-weighted average (TWA) and short-term exposure limit (STEL) calculations, data logging, man-down alarm, and wireless capabilities to name a few.

When monitoring in a duct for gas hazards, several factors should be considered, including the sampling conditions, gas characteristics and flow dimensions, in order to obtain a meaningful gas measurement. You must ensure, of course, that the sensor is not installed in conditions that will damage or hinder the sensor’s capability to detect gas. This article will weigh the merits of in-situ (localized) sampling in the duct versus pumped sampling based upon sample conditions.