Most malfunctions are discovered at the time of calibration or bump testing, meaning at some point between calibrations the gas monitor manifested a problem. Is a bump test adequate or is calibration a better choice?

We are often asked to explain the difference between calibrations and bump testing. This is a controversial subject. OHS would have you do a full calibration before each use. In practice, our customers come up with their own intervals. If the gas monitor is used infrequently, say once a month, it should be calibrated every time to give you confidence that the unit is going to respond as it should. If your company uses their detection device a few times a week, then our customers have told us they do an occasional bump test and calibrate less often.

Firstly, we would like to emphasize the importance of having the initial settings and calibration of your equipment done by the vendor or a trained technician. At CETCI, every one of our devices is calibrated in a chamber by true diffusion method prior to leaving our facility. Incorrect initial settings such as percentage can cause your meter to give false readings and some meters can be set up to use different types of calibration gas and/or different concentrations.

By most definitions, 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 the 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.  It will generally take the same amount of time, use 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. However, be aware as many of the meters on the market today require the use of a lot more calibration gas for “calibration” mode than for bump testing, which could create budget problems for those meters used frequently. That being said, health and safety should be of ultimate concern and whether you choose a bump test, calibration check or full calibration, the important thing is that before you use your gas monitor on a job where your life might be in danger, check it with gas in some manner.

In addition to using a certified calibration gas appropriate to the sensors being targeted, 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.

Once the monitor has been calibrated, it is important to maintain a written record of the results including adjustments for calibration drift, excessive maintenance/repairs, or if an instrument is prone to inaccurate readings. In closing, remember the only way to ensure worker safety is to verify the accuracy of your gas monitoring instruments on a daily basis.

For suggestions on gas detection systems, indoor air quality monitors and calibration, please visit www.critical-environment.com.

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References

Bump Test or Calibration Check? General Gas Education by Dave Wagner

http://www.askdaveblog.com/general-gas-education/bump-test-or-calibration-check/

Atmospheric Monitors: “Calibration vs. Bump Testing”

Posted on January 21, 2011 by Francelle Theriot http://rocorescue.wordpress.com/2011/01/21/atmospheric-monitors%E2%80%A6%E2%80%9Ccalibration-vs-bump-testing%E2%80%9D/

Air Monitor Calibration, Bump Testing, and Sensor Challenge

Posted on Oct 01, 2006 by James R. MacNeal http://ohsonline.com/articles/2006/10/air-monitor-calibration-bump-testing-and-sensor-challenge.aspx