Calibrations used to be very difficult but with the new monitors and multi-gas cylinders, it is relatively easy, depending on the manufacturer. The regularity of calibration is subject to great debate, as some response teams calibrate daily, others every six months. Most of the written instruction guides from the manufacturers require calibration before each use. The definition of a calibration at this point is also subject to debate, as we can verify the monitor s accuracy by exposing it to a known quantity of gas, but not perform a full calibration. The best recommendation if you are concerned with potential liability, is to bump test one monitor, use it while performing a full calibration on the second unit, then switch to verify the results of the first monitor.
All monitors have a lag time or, as it is better known, reaction time.
Sampling with or without a pump will vary the reaction time. Monitors without a pump operating in a diffusion mode will generally have a 15-30 second lag time. Monitors with a pump have a typical reaction time of 3-5 seconds, but even this can vary from manufacturer to manufacturer. Hand aspirated pumps usually require 10-15 pumps to draw in an appropriate sample. The goal is to provide a given amount of volume across the sensors.