If your industry requires the use of direct-reading portable gas monitors (DRPGMs), chances are you are familiar with bump testing and calibration practices. But can you tell the difference between bump testing and calibration?

If you want to understand the difference between bump testing and calibration, then our guide is for you. It breaks down the differences between the two so that you can better choose the test that is right for your product. This guide will teach you everything you need to know – let’s get started:

1. The main difference between Bump Test and Calibration

After research, the difference between bump testing and calibration is that bump testing is used to determine if the DRPGM is able to detect potentially harmful gases. Instead, calibration will determine whether your bump test machine is overall accurate.

However, things don’t stop there. There are two main types of calibration, with bump testing providing more detail to analyze. But the reality is a bit more complicated than that, and we recommend that you learn more about crash testing, the two types of calibration, and related best practices. This will help you keep these distinctions in mind and use them correctly.

Bump Test and Calibration guide

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2. Define the difference

In fact, direct-reading portable gas monitors fall under the purview of the safety equipment trade group International Safety Equipment Association (ISEA), which issued a statement in 2010 to promote consistency in how people use, test, and maintain DRPGMs. In the statement, the organization carefully fleshes out the differences between bump testing, calibration checks, and full calibration, and recommends how and when to use each method for testing.

1) What is a crash test?

ISEA defines bump testing as

“During a qualitative functional test, a challenge gas is passed through the sensor at a concentration and exposure time sufficient to activate all alarm indicators. […] This is usually determined by the sensor’s response time or a minimum response level achieved, such as 80% of the applied gas concentration.”

This checks that the sensors and alarms are working as expected, failure may indicate a blockage. In conclusion, crash tests evaluate functionality, not accuracy.

2) How is calibration different?

Did You Know Part of the confusion between bump testing and calibration is that calibration checks and full calibration are two different things? Both types of calibration test the accuracy of the DRPGM, but they are used differently.

According to the ISEA, calibration checks are

“Using a known and traceable concentration of a test gas, quantitative testing is performed to ensure that the sensor and alarm response is within the manufacturer’s specifications.”

The calibration check begins by “zeroing” the DRPGM (resetting it to a manufacturer-determined reference point) and testing whether the alarm will sound when a sufficiently high concentration of test gas is applied. The sensor reading should match the concentration listed on the test gas container.

ISEA says the device’s accuracy is acceptable, “typically ±10-20% of the concentration of the test gas used, unless otherwise specified by the manufacturer, internal company policy, or regulatory agency.”

The ISEA guide will describe the full calibration

“Adjust the sensor response to match the desired value compared to a known traceable test gas concentration.”

This adjustment takes into account naturally occurring drift and other environmental factors. Specially trained and qualified personnel are the only ones allowed to perform a full calibration.

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3. Importance of bump testing

So why crash test? If your gas detector is used in harsh and difficult conditions, it is frequently dropped, exposed to the elements, and clogged with sediment, all of which can affect its ability to test for gases. For these reasons, we encourage gas detectors to be crash-tested each time they are required to be used to ensure they work when required. Essentially, the crash test evaluates the capabilities of the DRPGM, not the precision of the machine.

4. Improve your bump test knowledge and avoid calibration failures

Now that you understand the difference in definition, let’s look at some tips and tricks for using crash testing and calibration. Before anyone uses the DRPGM (and according to the manufacturer’s instructions), perform bump testing and calibration checks.

The manufacturer’s guidelines (plus internal policy and regulatory recommendations) determine how and when a DRPGM should be calibrated. You also need a full calibration if the bump test or calibration check fails. You can perform two full calibrations, but after two “failures”, the device must be taken out of service. Full calibration should also be performed after the following types of exposure :

  • Different Operators or Work Environments
  • Extreme environmental, storage, and operating conditions
  • High concentrations of target gases and vapors
  • Solvent vapors and corrosive gases
  • Poisons and Inhibitors

Bump Test and Calibration guide

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5. Testing Best Practices

When you test your device, follow these guidelines :

  • Calibrate in fresh air
  • Choose a test environment that matches your workplace conditions
  • Use recommended gas mixtures that meet National Institute of Standards and Technology (NIST) requirements
  • Check the expiry date of the gas
  • Always refer to your product manual for specific information

6. How often do we need to bump test and calibrate portable gas detectors

Here are some suggestions for how often you need to bump-test and calibrate your portable gas detector.

1) Collision (or span) checking

The bump check involves exposing the instrument to a known concentration of a test gas in order to verify calibration.  The instrument reading is then compared to the actual amount of gas present (as indicated on the cylinder).

If your instrument’s response is within the acceptable range of actual concentrations, its calibration is verified. A bump test should trigger an instrument alarm if the test gas concentration is high enough.  A full calibration is required if the bump test results are not acceptable.

2) Instrument calibration

Second, whether your instrument issues warnings and/or alarms at the appropriate time depends on its ability to convert detected gas quantities into accurate readings. “Calibration” refers to the measurement accuracy of an instrument relative to known gas concentrations.

Gas detectors perform relative measurements: instead of independently assessing the amount of gas present, they measure the concentration of a sample of air, which is then compared to the known concentration of the gas sampled by the instrument configuration. This “known concentration” is used as the measurement scale or reference point for the instrument.

3) Full Calibration

Third, full calibration is the adjustment of the instrument’s readings to coincide with known concentrations of zero and span gases (usually certified standards) to compensate for calibration drift. An instrument requires a full calibration only if it fails the bump test (or after repair).

4) Calibration frequency

Ultimately, the frequency of calibration depends on how long the sensor has been in operation, conditions of use (including chemical exposure), and the user’s experience with the instrument.

New sensors should be calibrated more frequently until calibration records demonstrate sensor stability. As a result, the frequency of calibration can be reduced to a schedule determined by the safety officer or plant manager.

However, portable gas detectors need to be bump tested daily or before you use them, and if your detector fails the bump test, it will need to be recalibrated. Most test machine manufacturers recommend recalibration at least every six months or 180 days.

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