and using discontinuous or pulsed power patterns during periods when the beads are not actually responding to gas. While this approach may result in longer battery life, it may also result in the sensor being easier to poison or inhibit. Since smaller beads contain less catalyst, it takes less exposure to poisons or inhibitors to affect the sensor. It is particularly important to verify the calibration of low power combustible sensors by exposure to known concentration test gas on a regular basis. The combustible sensor elements are usually enclosed in a robust stainless-steel housing.