Bump Testing vs Calibration

Is a bump test adequate or is calibration a better choice? A bump test is a brief exposure of the monitor to gas in order to verify that the sensors respond and the instrument alarms function accordingly. The bump test does not check the accuracy of the instrument. This is where a calibration check comes in. A calibration check is performed by exposing the monitor to a certified concentration of gas for a particular length of time to verify that it provides an accurate reading. In most applications, knowing that the instrument will respond and produce an alarm that might save your life if a threatening gas hazard is encountered is all you need. In other applications, the accuracy of the reading is also important. With the instruments available today, if you are concerned about the accuracy of your readings before you use your instrument, you are better off to calibrate it rather than do a calibration check. Common factors to consider when deciding on whether to bump test or calibrate include:

• Type of sensor
• Type of gas detector (fixed vs. portable)
• The required use and accuracy of the detector
• Manufacturer's recommendations
• Regulatory agency rules and local regulations
• How confident you are about the functioning of your instrument?

Did you go through a period of initial use in the intended atmosphere verifying accuracy on a daily basis?

• Do you keep records so you can quickly identify if a detector has a history of excessive maintenance, is prone to erratic readings or needs to be replaced?
• Whether you suspect there are environmental conditions or potential damage has occurred to the instrument that could affect the instrument's performance Considering the factors listed above, it important is to develop a regular maintenance and calibration schedule that is tailored to your specific operating and environmental conditions and reinforces your confidence in the accuracy of the device's readings. For intermittently used detectors or hand held monitors we recommend doing a bump test prior to each use. If the bump test results are not within the acceptable range, a full calibration must be performed. It generally takes the same amount of time, uses the same amount of gas, but will guarantee the accuracy of the instrument readings when it is completed.

If you are doing a calibration check, and the readings fall outside of the desired or specified accuracy, you will have to do the full calibration anyway, so you might as well do it the first time and get the guaranteed result. For continuous monitoring devices we recommend a bump test every 30 days after you have gone through a trial period and verified accurate readings on a daily basis for at least 10 days. A full calibration should be conducted if the bump test fails and every 6 months, regardless of performance or type of gas detection instrument. The only way to ensure the gas detector will accurately respond to the gases it is designed to detect is to calibrate the sensor against a known gas standard. All bump tests and calibration functions should be noted in a log book.

It is important to remember that gas detectors are life-saving devices. They are intended to measure and monitor potentially lethal gases in the workplace and other areas where people frequent. Health and safety should be of ultimate concern. Whether you choose a bump test, calibration check or full calibration, exposing the device to gas in some kind of manner allows you to decide if further action is required if you are not confident in the response or accuracy of the devices' readings. Calibration and maintenance activities should be done by appropriately qualified and trained personnel. Care and attention must be taken during the process to prevent potential error sources from degrading the results. Always use certified calibration gas appropriate to the sensors being targeted and *do not *ever use calibration gas that has passed its expiration date. The best practice is to use calibration gas, tubing, flow rate regulators, and adapter hoods provided by the manufacturer of the instrument.