Generally, gas monitors are placed in potentially hazardous areas that are damaging to monitor systems, causing degradation over time. Zero and span levels will vary as the gas sensors age and are exposed to harsh environments. All sensors have finite lifespans and must be replaced periodically, and to test that the sensors are responding correctly, each sensor needs to be exposed to the gas that it is detecting to confirm it is working and is reading accurately. This ensures safety in the workplace, preventing the frustration of false alarm conditions. Many sensors will read zero concentration, appear to be working, and read zero when exposed to gas when they are no longer working. Bump testing and calibration will confirm if the sensor in question is indeed working correctly.