A bump test is a quick functional check that confirms your gas detector responds to the gases it is designed to detect and that its alarms activate. It is the single most important daily habit for anyone who relies on a portable gas monitor — and it is different from a full calibration. This guide explains what a bump test is, how it differs from calibration, how often to do one, and which calibration gas to use.
What is a bump test?
A bump test (also called a functional test) briefly exposes a gas detector's sensors to a known concentration of test gas that is above the instrument's low-alarm set point. If the detector reads the gas and goes into alarm, it passes. If it does not respond — or does not alarm — the instrument fails and must be removed from service and recalibrated or repaired. A bump test answers one question: will this monitor warn me if I walk into danger right now?
Bump test vs. calibration: the key difference
People often use the terms interchangeably, but they are not the same:
- Bump test — a fast pass/fail check (typically under a minute) that verifies sensor response and alarms. It does not adjust the instrument.
- Calibration — a longer procedure that exposes the detector to a precise concentration of calibration gas and adjusts the readings so they match the certified value, correcting for sensor drift.
Think of a bump test as checking that the smoke alarm beeps when you press the button, and calibration as re-tuning it so it triggers at exactly the right level.
How often should you bump test?
Industry guidance from OSHA and the safety equipment association (ISEA) is clear: a bump test or calibration of direct-reading portable gas monitors should be performed before each day's use, following the manufacturer's instructions. If a detector has not been bump tested, the safest practice is to test it before sending a worker into a potentially hazardous atmosphere. For the full calibration schedule, see how often you should calibrate a gas detector.
How to perform a bump test
- Confirm the detector is on, warmed up, and reading a normal/fresh-air baseline.
- Attach the calibration cap and connect tubing to a cylinder of test gas through a fixed-flow or demand-flow regulator.
- Apply the gas for the manufacturer-specified time (usually 30–60 seconds).
- Confirm each sensor responds and the instrument goes into alarm.
- Record the result. Pass → return to service. Fail → calibrate or remove from service.
What gas do you use for a bump test?
For a standard 4-gas monitor, you use a 4-gas mix containing carbon monoxide, hydrogen sulfide, a combustible (methane or pentane) and oxygen — for example 100 ppm CO / 25 ppm H2S / 50% LEL CH4 / 18% O2. Always use gas that is within its expiration date; an expired or out-of-spec cylinder can cause a false pass. See calibration gas shelf life for details. Not sure which mix your detector needs? Find it on our calibration gas by detector page.
Shop 4-gas bump test cylinders →
NIST-traceable, ISO 17025 certified, 15–30% below OEM pricing — ships in 48 hours from our Florida facility, CoA included.
Frequently asked questions
Does a bump test replace calibration?
No. A bump test is a pass/fail functional check; it does not adjust the instrument. You still need periodic full calibration to correct sensor drift.
How often should I bump test my gas detector?
OSHA and ISEA guidance is to bump test (or calibrate) before each day's use, per the manufacturer's instructions.
What happens if a detector fails a bump test?
Remove it from service and perform a full calibration. If it still fails, the sensor may need replacement or repair.
What gas is used for a bump test?
A test gas above the low-alarm set point — for a 4-gas monitor, a CO/H2S/LEL/O2 mix. Always use in-date, NIST-traceable gas.