Bump Test vs Calibration: Gas Detector Checks Explained
Short answer: A bump test briefly exposes a gas detector to a known test gas to confirm the sensors respond and the alarms work. It is a function check, not a measure of accuracy. Calibration adjusts the instrument's readings against a known concentration. Follow the manufacturer's instructions for how and when to do each.
A gas detector only protects people if it still responds when a hazard is present. Two different checks are used to keep portable monitors trustworthy: a bump test and a calibration. They are often confused, but they do different jobs. This guide explains the difference, how manufacturers such as Dräger describe each check, and how to match calibration gas and accessories to the instrument.
What's the difference?
The International Safety Equipment Association (ISEA) distinguishes these checks in its statement on validating direct-reading portable gas monitors:
- A bump test (also called a function check) is a qualitative check. A challenge gas is passed over the sensor at a concentration and for a time sufficient to activate the alarm indicators. ISEA says the purpose is to confirm that gas can reach the sensor and that the alarms work. The check is not intended to measure calibration accuracy. (Source: ISEA, Validation of Operation for Direct-Reading Portable Gas Monitors)
- A full calibration adjusts the sensor response so it matches a known, traceable concentration of test gas, in accordance with the manufacturer's instructions. (Source: ISEA)
Dräger, whose portable detectors and test equipment Keyline Safety carries, describes the same split in practical terms: a bump test checks that the detector is functioning correctly and should be performed before each use; calibration evaluates the response against a known standard and adjusts the device to maintain accuracy. If a bump test fails, the instrument must be recalibrated before use. (Source: Dräger, Gas Detector Calibration and Bump Test)
Dräger also offers more than one bump-test mode on some instruments: a quick bump test that checks whether an alarm threshold is crossed, and an advanced or extended bump test that checks whether the reading stays within a defined tolerance. Check the manual for the detector and test station you use. (Source: Dräger Pac 6x00/8x00 Technical Manual)
When to bump-test and when to calibrate
ISEA recommends that a bump test or a calibration check of portable gas monitors be conducted before each day's use, in accordance with the manufacturer's instructions. Any monitor that fails a bump test or calibration check must be adjusted by a full calibration before further use, or removed from service. A full calibration should be done at the intervals the manufacturer, a workplace policy or a regulator specifies. (Source: ISEA)
Dräger likewise treats a regular bump test as the basic pre-use check, and says prescribed calibrations remain essential because environmental conditions and ageing can change sensor sensitivity. (Sources: Dräger; Dräger, Regular testing of mobile gas detectors)
Canadian guidance does not replace those manufacturer instructions. CCOHS states that confined-space atmospheric tests must be done with equipment that is appropriate and calibrated according to the manufacturer's instructions. Always follow the manual for the specific detector, and any occupational health and safety rule that applies to your site.
Matching calibration gas and accessories
Both a bump test and a calibration depend on the right test gas reaching the sensors. Match the cylinder's gas mixture and concentration to the sensors in the monitor and to the values in the manufacturer's specification. Use a compatible regulator or adapter, and do not use expired or incorrect gas. Dräger notes that expired or incorrect test gas can produce an improper check or calibration.
Accessories have to fit the instrument family. A bump-test station, docking station, adapter or regulator listed for one Dräger series may not fit another. Confirm the part against the detector model before you order.
Why this matters before a confined-space entry
If a monitor is used to test the air before someone enters a tank, pit, vault or other confined space, a failed or skipped check can hide an oxygen, toxic or flammable hazard. Our guide to confined-space air testing and rescue planning covers when to test, what to record, and why the rescue plan has to be ready before anyone goes in. The detector still has to be checked and maintained as the manufacturer requires.
Keyline Safety's stand
Do not treat a bump test as a calibration, and do not skip either check the manufacturer requires. A detector that has not been function-tested, or that failed a bump test and was not then calibrated, should not be relied on to clear a space or warn a worker. Match the test gas and accessories to the instrument, follow the manual, and take a failed instrument out of service until it is corrected.
What Keyline Safety does
Keyline Safety is a PPE and safety supplier in London, Ontario, serving Canadian workplaces since 1968. For gas-detector checks, our live range includes:
- Collection: Calibration Gas and Gas Detection Accessories
- Collection: Gas Monitor Bump Test Stations
- Collection: Gas Monitoring and Detection Equipment
- Collection: Single Gas Monitors
- Collection: Multi-Gas Monitors
- Product: Dräger X-am 2800 (Ex, O2, CO, H2S)
- Product: Dräger Bump Test Station for X-am 1/2/5x00
- Product: Dräger 58 L calibration gas (CH4, CO, H2S, O2)
- Product: Dräger X-dock 5300
Need help matching calibration gas, a regulator or a bump-test station to a monitor? Ask Keyline Safety through our safety assistant chat.
Frequently asked questions
What's the difference between a bump test and calibration?
A bump test is a function check: it confirms the sensors respond and the alarms activate when exposed to a known test gas. Calibration adjusts the instrument's readings against a known concentration so the measurements are accurate. They are not interchangeable.
How often should I bump-test or calibrate a gas detector?
Follow the manufacturer's instructions for that instrument, and any workplace or regulator rule that applies to your site. Dräger says bump tests should be performed before each use. ISEA recommends a bump test or calibration check before each day's use, in accordance with the manufacturer's instructions. (Sources: Dräger; ISEA)
What should I do if a bump test fails?
Do not use the detector. Dräger and ISEA say an instrument that fails a bump test should be calibrated before further use. If it fails calibration, remove it from service and follow the manufacturer's service instructions.
What calibration gas do I need?
Use the gas mixture and concentration specified for your monitor's sensors in the manufacturer's documentation, with a compatible regulator or adapter. Do not substitute a different gas or an expired cylinder.
Keep reading
- Before anyone goes in: confined-space air testing and rescue planning
- The crucial role of gas monitors in workplace safety
