What a bump test checks
A functional test, commonly called a bump test, exposes the detector to suitable test gas to confirm that gas reaches the sensors and that they respond by activating the intended alarms. It is a qualitative operational check. Switching the instrument on and hearing its start-up signal does not replace this test: an electronic self-check does not necessarily establish that gas can reach the sensing element.
How it differs from calibration
OSHA distinguishes a bump test from a calibration check and from full calibration. A calibration check compares a reading against a known concentration using the manufacturer’s specified tolerance. Full calibration adjusts instrument response. A detector may pass a response test while still requiring investigation of its accuracy. Procedures, records and user training should preserve these distinctions so a completed functional test is not reported as a complete calibration.
What the test requires
Use the gas, regulator, adapter and procedure appropriate to the detector and its sensors. The cylinder must be identifiable, suitable and within its valid use period. Follow the precautions for handling test gas. An incorrect or expired mixture can produce misleading results. Perform the test under controlled conditions; do not substitute an improvised exposure for specified test gas or assume a mixture intended for another instrument is equivalent.
Frequency and exceptional events
OSHA’s bulletin cites ISEA’s recommendation to check instruments before each day’s use, following manufacturer instructions. This is not a universal legal rule for every instrument and country. Impacts, overexposure, contamination or extreme environmental conditions may require additional verification. The maintenance programme should define intervals and responsibilities from the actual equipment, risk and applicable instructions, including how to respond when an instrument has experienced an unusual event.
If the detector fails
Failure is not resolved by ignoring an alarm, repeating the test without investigation or treating another channel as a substitute. Follow the required checking, calibration or service procedure, and do not use the detector to protect a person while its operation is uncertain. OSHA states that instruments failing calibration should be removed from service until corrected. Instrument verification is part of the preventive control system.
Keep a useful record
Record detector identification, date, tested channels, gas identification, result and action taken after failures. Automatic records should also be traceable to the unit issued to the user. Passing a bump test does not make an atmosphere safe: subsequent gas measurement still requires an appropriate procedure, interpretation of all relevant hazards and work decisions consistent with the results. A functional detector is one necessary component, not the complete assessment.
