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The Difference Between Bump Testing and Calibration

Bump testing and calibration are two different procedures completed to ensure the accuracy and reliability of gas detection instruments, particularly those used for monitoring hazardous gases in industrial or occupational settings. While both processes are important, they serve different purposes.

The bump test will tell you if the instrument is still reading gas levels, but it won’t tell you if those levels are correct if the instrument is not working properly; calibration will tell you that. Following is an overview of the differences between bump testing and calibration:

Bump Testing: Bump testing, also known as a functional or challenge test, is a quick verification process to check the basic functionality of a gas detection instrument. It is usually performed every day before entering a potentially hazardous environment. The main objectives of a bump test include:

Sensor Response Check: A bump test confirms that the gas sensors in the instrument respond appropriately to a known concentration of gas. It checks if the sensors are functioning properly and capable of detecting the target gases.

Alarm Verification: The bump test ensures that the instrument's alarms activate when the gas concentration reaches a predetermined threshold.

Confidence Check: Bump testing provides a level of confidence to the user that the instrument is operational and ready for use.

Bump testing involves exposing the gas detection instrument to a specific concentration of gas through a calibration gas cylinder. The exposure is to confirm the instrument's response and alarm functionality. Bump testing does not involve adjusting or correcting the instrument's settings or calibration.


Calibration is a more comprehensive process that involves adjusting and verifying the accuracy of a gas detection instrument. Calibration is usually carried out at regular intervals, based on manufacturer recommendations or industry standards, to maintain the accuracy and reliability of the gas detection instrument. The frequency depends on the type of equipment.

The primary purposes of gas calibration include:

Accuracy Verification: Calibration ensures that the readings provided by the gas detection instrument are accurate and within acceptable limits. It establishes a correlation between the instrument's sensor readings and known reference concentrations of gases.

Adjustment: Calibration allows for adjustments to be made to the instrument's internal settings or calibration factors to align its readings with the reference concentrations.

Long-Term Stability Check: Calibration provides a means to assess the long-term stability of the instrument's sensors. It identifies any deviations from the expected performance and allows for corrective measures to be taken.

Calibration is typically performed using a known concentration of calibration gas, which is traceable to national or international standards. The gas concentration is applied to the instrument, and the readings are compared to the expected values. If there are significant discrepancies, adjustments are made to align the instrument.

For both procedures, all results should be noted in a running log. This information can be helpful if troubleshooting and is often required by safety organizations. Here is more information about bump testing and calibration from OSHA.