The difference between a bump test and calibration – and why should you care?

The difference between a bump test and calibration – and why should you care?

If you work with direct-reading portable gas monitors (DRPGMs) to check oxygen levels and look for toxic or combustible gases, you’re likely to be familiar with the concepts of bump testing and calibration. But if you were given an on-the-spot pop quiz on the subject, could you tell the difference between these terms? 

The main difference between a bump test and calibration is that a bump test determines whether a DRPGM can detect if a possible hazardous gas is present, while calibration checks that equipment is accurate.

So, what’s a bump test?

The International Safety Equipment Association (ISEA) defines a bump test as a “qualitative function check where a challenge gas is passed over the sensor(s) at a concentration and exposure time sufficient to activate all alarm indicators to present at least their lower alarm setting. This is typically dependent on the response time of the sensor(s) or a minimum level of response achieved, such as 80% of gas concentration applied”. In sum, bump testing assesses function, not accuracy.

How is calibration different?

A calibration check, according to the ISEA, is a “quantitative test utilising a known traceable concentration of test gas to demonstrate that the sensor(s) and alarms respond to the gas within manufacturer’s acceptable limits”.

Calibration checks start by “zeroing” a DRPGM (resetting it to a reference point determined by the manufacturer) and testing that alarms go off after applying a high enough concentration of test gas. The resulting sensor reading should match the concentration listed on the test gas container. The ISEA says that a device is accurate within an acceptable range that’s “typically ± 10 to 20% of the test gas concentration applied unless otherwise specified by the manufacturer, internal company policy, or a regulatory agency”.

The ISEA guideline describes full calibration as “the adjustment of the sensor(s) response to match the desired value compared to a known traceable concentration of test gas”.

This adjustment accounts for naturally occurring drifting and other environmental factors. Specially trained, qualified personnel are the only people permitted to perform full calibrations.

Bump up your bump test knowledge and avoid calibration frustration

Perform a bump test and calibration check every single day before anyone uses the DRPGM that day (and according to manufacturer’s instructions). You can perform a full calibration twice, but after two “fails” the device must be pulled from use. Full calibrations should also take place after the following types of exposures:

  • Different operator or working environments;
  • Extreme environmental, storage and operating conditions;
  • Highly concentrated target gases and vapours;
  • Solvent vapours and corrosive gases;
  • Poisons and inhibitors; and
  • Testing best practices.

When testing a device, use the following guidelines:

  • Perform the calibration in fresh air. Choose a test environment with conditions that match your workplace;
  • Check the gas’s expiry date: refer to your product manual for specifics;
  • Keep a record: it’s essential that you keep records of all device testing and maintenance. Should a user experience a reportable event with one of your devices, the Occupational Safety and Health Administration (OSHA) needs to see a history of all bumps and calibrations during the year prior to the incident. But even without an incident, recording keeping is very valuable.

Digital tracking and remote monitoring are just some newer technologies that automatically track and allow you to manage your fleet’s bump tests and calibrations from wherever you are. Some can even be paired with GPS devices to alert you on man-down and detect a health emergency.

Interested in simplifying the management of your gas detection fleet with automated calibration? Learn more about the Galaxy GX2 automated test system here.

For more information or enquires visit or give the company a call on 0860 543 356.

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SHEQ Management

SHEQ MANAGEMENT is the definitive source for reliable, accurate and pertinent information to guarantee environmental health and safety in the workplace.
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