Short answer: A bump test briefly exposes the detector to a known test gas to prove the sensors respond and the alarms go off. Carry one out before each day's use, and if it fails, do not use the detector until it has been recalibrated.
What is a bump test?
A bump test, also called a function check, is a quick qualitative test. You pass a test gas over the sensors at a concentration high enough to trigger the alarms. It confirms two things: gas can reach the sensors, and the audible, visual and vibrating alarms all work.
It does not prove the instrument is accurate. That is the job of a calibration check or a full calibration.
How is it different from calibration?
| Check | What it proves | Typical frequency |
|---|---|---|
| Bump test (function check) | Sensors respond and alarms activate | Before each day's use |
| Calibration check | Readings fall within the manufacturer's tolerance of a known gas | As the manufacturer or your company policy specifies |
| Full calibration | The sensor response is adjusted to match a traceable gas | At regular intervals, and after any failed check |
The definitions above follow the position statement from the International Safety Equipment Association (ISEA). Many UK safety bodies refer to the same statement.
What does HSE say?
HSE safety bulletin guidance notes that the operating instructions for most gas detectors recommend a function check, often called a bump test, before each day's use. This is in addition to periodic calibration. If you use the detector with a sample tube, HSE recommends doing at least the first bump test for a new job or set-up with the tube attached and, where practicable, with the substance you are actually testing for.
HSE's confined-space guidance (INDG258 and L101) also says that atmospheric testing should be done by a competent person using a suitable, correctly calibrated detector. Continuous monitoring may be needed where conditions could change.
What do you need?
- The detector, charged or with fresh batteries
- A test gas cylinder that matches the detector's sensors, for example a four-gas mix of methane or pentane (%LEL), oxygen, carbon monoxide and hydrogen sulphide. Check the cylinder is in date.
- A regulator suited to the cylinder and detector, either fixed-flow or demand-flow
- The manufacturer's calibration cap or adaptor and tubing, or a bump-test docking station
- A record sheet or logging software
How do you carry out a bump test step by step?
- Inspect the detector. Look for cracks, a blocked sensor grille, damaged clips or a missing filter.
- Switch on in clean air. Let the detector complete its start-up self-test and warm-up. Check that oxygen reads about 20.9 % and the other gases read zero.
- Check the cylinder. Confirm the gas mix matches the sensors, the cylinder is in date and there is enough pressure left.
- Fit the regulator and cap. Attach the regulator, then connect the tubing to the cap and fit the cap over the sensors. If you will be using a pump and sample tube on the job, test through that tube.
- Apply the gas. Open the regulator. Readings should rise quickly. Toxic and flammable readings go up and oxygen goes down if the mix contains reduced oxygen.
- Confirm the alarms. Every alarm (sound, light and vibration) should activate within the time the manufacturer specifies.
- Stop the gas and clear the detector. Close the regulator, remove the cap and let the detector return to clean-air values. Silence or reset the alarms.
- Record the result. Note the date, the detector's serial number, the cylinder batch number, whether it passed or failed, and who did the test. Docking stations do this automatically.
Most bump tests take less than a minute.
What should you do if it fails?
- Don't take the detector into the work area.
- Check for simple causes: an expired or empty cylinder, the wrong regulator, a badly fitted cap, or a blocked filter.
- Repeat the test once. If it fails again, carry out a full calibration following the manufacturer's procedure. If calibration also fails, take the detector out of service and send it for repair.
When should you bump test more often?
Extra checks are sensible after:
- A drop or impact, or the detector getting wet
- Exposure to gas levels above the sensor's range
- Use in extreme temperatures, high humidity or dusty conditions
- Possible contact with substances that poison sensors, such as silicones, or with solvent vapours
- Handing the detector to a different person, or changing the job conditions
FAQ
Is a bump test a legal requirement? UK law requires work equipment to be suitable and properly maintained, and confined-space testing must use correctly calibrated equipment. Daily bump testing is the manufacturers' and HSE's recommended way to show this.
Can I bump test with a lighter or exhaust fumes? No. These give uncontrolled concentrations and can damage the sensors. Use the correct certified test gas.
Does a docking station count as a bump test? Yes, as long as it is used as the manufacturer intends.
How long does test gas last? Check the expiry date on the cylinder. Reactive gases such as hydrogen sulphide have shorter shelf lives.
Sources
- HSE safety bulletin, "Failure to detect dangerous gas/vapour due to incorrect specification of sample tube": https://www.hse.gov.uk/safetybulletins/failure-to-detect-dangerous-gas.htm
- HSE, "Confined spaces: a brief guide to working safely" (INDG258): https://www.hse.gov.uk/pubns/indg258.pdf
- HSE, "Safe work in confined spaces" (L101): https://www.hse.gov.uk/pubns/priced/l101.pdf
- HSE, "The selection and use of flammable gas detectors": https://www.hse.gov.uk/PUBNS/gasdetector.pdf
- ISEA, statement on validation of operation for direct-reading portable gas monitors: https://safetyequipment.org/wp-content/uploads/2022/12/calibration_statement-2010-Mar4.pdf
- BSIF, "Bump test every time" guidance: https://www.bsif.co.uk/wp-content/uploads/2019/01/Bump-Test-Every-Time-0318.pdf
Related products: Gas & Environment Detectors
