Bump Test vs Calibration: What's the Difference?

Anyone responsible for portable gas detectors will hear two terms constantly: bump test and calibration. They are often used interchangeably, but they are different checks with different jobs. This article sets out bump test vs calibration in plain terms, explains how bump testing a gas detector fits into daily routines, and shows how the two work together to keep your monitors reliable.

Bump test vs calibration: the short answer

A bump test checks that the detector responds to gas. Calibration checks and adjusts how accurately it responds.

In a bump test, the sensors are briefly exposed to a known test gas at a concentration high enough to trigger the alarms. If each sensor responds and the audible, visual and vibrating alarms activate, the instrument passes. Nothing is adjusted.

In a calibration, each sensor is exposed to a certified concentration of gas and the instrument's reading is adjusted so that it matches the known value. Calibration corrects the gradual drift that every gas sensor experiences over time.

Why bump testing a gas detector matters

Gas sensors can fail without warning. An electrochemical sensor can dry out, a sensor inlet can become blocked by dust or water, and LEL sensors can be poisoned by substances such as silicones. A detector with a failed sensor may still power up and display normal readings in clean air.

A bump test is the simplest way to catch this before someone relies on the monitor. Most manufacturers recommend a bump test before each day's use, and many sites build it into their pre-use checks, particularly for confined space entry.

How to carry out a bump test

The exact procedure depends on the instrument, so follow the manufacturer's instructions. In general:

• Switch the detector on in clean air and let it complete its start-up checks

• Apply the correct test gas using the recommended regulator and calibration cap or docking station

• Confirm that each sensor responds and every alarm activates

• Record the result, either on paper or through the instrument's datalog or docking station

• If any sensor fails, take the detector out of service and arrange calibration or repair

Why calibration is still essential

Passing a bump test does not mean a detector is accurate. A sensor can respond enough to trigger an alarm while still reading noticeably low. Over months, that drift can become significant, and an under-reading monitor could fail to alarm at the right level in a real hazard.

That is why most manufacturers recommend calibration at least every six months, in addition to daily bump testing. Calibration should also be carried out after a failed bump test, after exposure to high gas concentrations, after a sensor replacement, or if the instrument has been damaged. You can read more about our gas detector calibration service.

What a calibration includes

At 7 Solutions, calibration is carried out by manufacturer-trained engineers and every instrument is returned with a calibration certificate. As part of the service the detector is checked, each sensor is tested and adjusted against certified gas, and any faults are reported to you before further work is done.

Bump test vs calibration at a glance

• Purpose: a bump test confirms the sensors and alarms respond; calibration confirms and corrects accuracy

• Frequency: a bump test is typically recommended before each day's use; calibration is typically recommended at least every six months

• Adjustment: a bump test changes nothing; calibration adjusts the sensor readings

• Paperwork: bump test results are usually logged on site; calibration should come with a certificate

For more background, see our earlier article on calibration and bump testing.

Getting your detectors calibrated

We calibrate single gas, 4-gas, multi-gas and PID instruments from Honeywell (BW and RAE), Crowcon, Dräger, MSA, Industrial Scientific, WatchGas, GMI, Oldham and more. See the brands we calibrate and repair.

Calibration prices (plus VAT) start at £40 for a single gas monitor and £50 for a 4-gas confined space monitor, with multi-gas instruments at £90 and PIDs at £140. Instruments can be posted to our Hampshire service centre in Waltham Chase, Southampton, or serviced on site, and our Northern Service Centre covers the North East and Yorkshire.

Frequently asked questions

Can a bump test replace calibration?

No. A bump test only proves the sensors respond and the alarms work. It does not check or correct accuracy, so periodic calibration is still needed.

What gas do I need for a bump test?

Use the test gas mixture specified by the detector's manufacturer. For a typical 4-gas monitor this is a mixed cylinder containing methane (or another LEL reference gas), CO, H2S and a reduced oxygen level.

What should I do if a detector fails a bump test?

Remove it from service straight away and do not use it for gas monitoring. It will usually need calibration, and sometimes a replacement sensor.

Do I need to bump test a brand new detector?

Yes. Most manufacturers recommend a bump test before first use and before each day's use thereafter.

Need calibration or a replacement monitor?

Book calibration through our calibration and service page or our customer portal at portal.7solutions.co.uk. If you need cover while your instruments are away, take a look at gas detector hire. Call 01489 326031 or email info@7solutions.co.uk.