The closest thing to an official definition of “bump test” appears in an OSHA Safety and Health Information Bulletin (SHIB 09-30-2013) entitled “Calibrating and Testing Direct-Reading Portable Gas Monitors.” We have posted a Knowledge Base article providing some commentary on that Bulletin.
Here is what the Bulletin says about Bump Testing (DRPGM = Direct Reading Portable Gas Monitor):
Bump Test (or Function Check)
This is a qualitative function check in which a challenge gas is passed over the sensor(s) at a concentration and exposure time sufficient to activate all alarm settings. The purpose of this check is to confirm that gas can get to the sensor(s) and that all the instrument’s alarms are functional. The bump test or function check does not provide a measure of the instrument’s accuracy. When performing a bump test, the challenge gas concentration should trigger the DRPGM’s alarm(s).
When to Perform a Bump Test and When to Perform a Full Calibration
In the past, there has been some confusion regarding proper calibration procedures and frequency. To clarify this issue, ISEA updated its position statement on instrument calibration in 2010, stating, “A bump test . . . or calibration check of portable gas monitors should be conducted before each day’s use in accordance with the manufacturer’s instructions.” If an instrument fails a bump test or a calibration check, the operator should perform a full calibration on it before using it. If the instrument fails the full calibration, the employer should remove it from service. Contact the manufacturer for assistance or service.
Let’s unpack this a bit. Before each day’s use, you should hit your gas detector with some concentration high enough to set off the alarms, to test its gross functionality. If it fails this bump test, then you should go ahead and try to perform a full calibration, now using an appropriate gas standard. If the unit cannot be calibrated, it must be taken out of service.
Fair enough, except if the instrument passes the bump test, and depending on the gas in question and the range involved, the actual calibration could still be off—perhaps significantly. How useful, then, are the measurements obtained that day? Indeed, if regulations are to be followed, isn’t accuracy of vital importance?
While we link to United States Department of Labor Occupational Safety and Health Administration regulations, there are similar statutes and guidances in many other countries, as well. cf. UK Health and Safety Executive.
For the common toxic gases, how much longer would it take to perform a real calibration—compared to a bump test?
Further to regulatory matters, and as a wake-up call to some in the gas detection industry, standards have been promulgated for more than 600 substances, and in virtually all cases are based on 8-hour time-weighted averages. Thus, there is far more to best practices toxic gas detection than instantaneous alarms.
Should you not expect more—day to day—from your gas detector than it only being grossly functional?
Here is a follow-up article, entitled “More on bump testing in gas detection.”