“A recent calibration does not prove that your portable gas detector will respond correctly today.”
A bump test and a calibration are not the same procedure.
Calibration checks the accuracy of a portable gas detector against a known concentration of test gas and allows the instrument to be adjusted where necessary.
A bump test is a quicker functional check used to confirm that gas can reach the sensors, the sensors respond and the detector’s alarms activate.
Portable gas detectors may therefore need both periodic calibration and bump testing before each day’s use.
Quick Answer: What is the difference between a bump test and calibration?
A bump test confirms that a gas detector responds when exposed to test gas and that its alarms activate. Calibration checks the detector’s response against a known gas concentration and makes any necessary adjustment in accordance with the manufacturer’s procedure. A successful calibration does not remove the need for subsequent bump testing.
Learn more about Velocity Safety’s gas detector calibration services.
Key Takeaways – Gas Detector Bump Testing
- A bump test is not a calibration.
- Most portable gas-detector instructions recommend a bump test before each day’s use.
- A bump test checks sensor response and the operation of audible, visual and vibration alarms.
- Calibration checks the instrument’s response against a known gas concentration and allows adjustment where required.
- A detector can develop a fault or suffer sensor contamination after its most recent calibration.
- A detector that fails its bump test should not be used until the fault has been investigated and resolved.
Jump to:
Gas Detector Bump Test vs Calibration
Bump testing and calibration both involve exposing a gas detector to test gas, but they serve different purposes.
| Check | Bump Test | Calibration |
|---|---|---|
| Main purpose | Confirms that the detector responds to gas and activates its alarms. | Checks the detector’s response against a known gas concentration and permits adjustment where required. |
| Typical frequency | Before each day’s use, subject to the manufacturer’s instructions and site procedure. | At the interval specified by the manufacturer and the employer’s maintenance programme. |
| Does it adjust the detector? | No. | The calibration procedure can include adjustment where the response is outside the permitted tolerance. |
| Does one replace the other? | No. | No. |
Sending a portable detector away for calibration every few months does not confirm that it remains functional on every day between calibrations.
Why Is Bump Testing Important?
Portable gas detectors are used to warn workers about potentially dangerous atmospheres, including toxic gases, flammable gases and oxygen deficiency or enrichment.
Their sensors can be affected by:
- Exposure to high gas concentrations
- Sprays, solvents, paints, vapours or greases
- Sensor poisons or inhibitors
- Dirt, dust or blocked sensor openings
- Impact or physical damage
- Incorrect storage or unsuitable environmental conditions
Some faults may not be identified by simply switching the detector on.
The display, lights and audible alarm might appear operational while a damaged, obstructed or inhibited sensor fails to respond correctly to the target gas.
A bump test challenges the detector using actual test gas. This provides a practical check that the gas reaches the sensor and the detector responds.
Calibration only confirms the detector’s condition at the time it was calibrated
A detector could be calibrated successfully and then suffer contamination, impact or sensor damage before its next scheduled calibration. Regular bump testing helps identify a loss of function before the monitor is relied upon in a hazardous atmosphere.
How Often Should a Portable Gas Detector Be Bump Tested?
HSE notes that the operating instructions for most gas detectors recommend a function check—commonly called a bump test—before each day’s use.
The correct procedure should be based on:
- The detector manufacturer’s instructions
- The gases and sensor types involved
- The employer’s risk assessment
- The safe system of work
- Site conditions and potential contaminants
- Any impact, unusual exposure or suspected equipment fault
Additional testing may be appropriate after the detector has been dropped, exposed to a high gas concentration or subjected to substances that could affect its sensors.
For guidance on periodic calibration intervals, see our article explaining how often gas detectors should be calibrated.
How Is a Gas Detector Bump Test Performed?
The exact method depends on the detector and its manufacturer’s instructions.
A typical manual bump test uses:
- A suitable cylinder containing the required test gas
- The correct fixed-flow regulator
- Compatible tubing and a detector adaptor
- A safe and suitably ventilated testing area
The detector is exposed to test gas so the operator can confirm that the relevant sensors respond and the audible, visual and vibration alarms operate correctly.
Automatic test stations can also apply gas, assess the detector’s response and create an electronic record of the outcome.
Only compatible gas, regulators, adaptors and test procedures should be used. The applicable manufacturer’s instructions must always be followed.
What Happens If a Gas Detector Fails a Bump Test?
A portable gas detector that fails its bump test should not be relied upon for confined-space entry or other hazardous-atmosphere work.
The instrument should be removed from use and investigated in accordance with the manufacturer’s instructions.
Depending on the result, this may involve:
- Checking that the correct test gas and equipment were used
- Checking the gas cylinder’s concentration and expiry date
- Inspecting tubing, adaptors and sensor openings
- Completing a full calibration
- Replacing a failed or contaminated sensor
- Sending the detector for servicing or repair
If the detector cannot successfully complete the required checks, it should remain out of service.
Final Takeaway
A calibration certificate does not replace a pre-use bump test.
Calibration checks whether a gas detector responds accurately against a known standard. Bump testing checks whether the detector can respond and alarm when it is needed.
Portable gas detectors can be affected at any point between scheduled calibrations, which is why bump testing forms an essential part of a properly managed gas-detection procedure.
Need help with portable gas detector calibration or testing equipment?
Velocity Safety provides gas detector calibration support and can help businesses understand the difference between periodic calibration and routine functional checks.
Send us the manufacturer, model, quantity and gases monitored, and we’ll confirm the support available.
📞 Call: 01254 933486
📩 Email: info@velocitysafety.co.uk
🌐 Or contact Velocity Safety online.
Frequently Asked Questions
Is a gas detector bump test the same as calibration?
No. A bump test confirms that the detector responds to gas and activates its alarms. Calibration checks its response against a known gas concentration and allows adjustment where required.
Does a calibrated gas detector still need bump testing?
Yes, where required by the manufacturer’s instructions or the employer’s testing procedure. A detector can become damaged, obstructed or contaminated after calibration and before its next scheduled service.
Should portable gas detectors be bump tested every day?
HSE states that most gas-detector operating instructions recommend a function check before each day’s use. Employers should follow the applicable manufacturer’s instructions and establish an appropriate testing procedure for the equipment and risks involved.
What should happen after a failed bump test?
The detector should be removed from use and investigated. It may require another correctly performed test, full calibration, servicing, sensor replacement or repair before being returned to use.
Can a detector pass its self-test but fail a bump test?
Yes. A start-up self-test may check the detector’s electronics, display and alarms without proving that its sensors can respond correctly to the target gas. A bump test exposes the sensors to test gas.
