Calibrations with known concentration samples of test gases and a known gas free environment should be performed to maintain the accuracy and the sensitivity of gas monitoring equipment. A gas free atmosphere or calibration cylinder of air, also known as zero air, is required to establish a clean reference for a gas free baseline against which a span or calibration adjustment can then be performed. The procedure of zeroing or air adjusting sensors to a clean baseline atmosphere is the only way of assuring the accuracy expected when performing a calibration.

The above practice will compensate for the deterioration or alteration of a gas sensor’s performance which may occur due to the aging of its materials and exposures to gas samples and environmental conditions, such as temperature and humidity fluctuations, and exposures to particulates and potential electrical or electronic influences.