When to Test the Detector
Determining the frequency of gas detector testing will depend on a suitable risk analysis of
the protected area. For example if the consequences of a leak are small, then checks every 6
months or a year may be acceptable. If the consequences of a leak are severe, then it is good
practice to check the detector calibration regularly.
While the gas sense detectors are not currently intended for hazardous area use, the extract below gives an idea of
the sort of practice required when the consequences of a leak are severe.
The International Safety Equipment Association
recommends, at a minimum, verication of sensor
accuracy before each day’s use. Additional testing of
instrumentation should be carried out before each
new conned space entry – after the crew’s lunch
hour, for example.
The only way to guarantee an instrument will detect
gas accurately and reliably is to test it with a known
concentration of gas. Exposing the instrument to a
known concentration of test gas will show whether
the sensors respond accurately and the instrument
alarms properly.
There are two methods of verifying instrument
accuracy: a functional or bump test and a full
calibration. Each is appropriate under certain
conditions. A bump test veries calibration by
exposing the instrument to a known concentration
of test gas. The instrument reading is compared
to the actual quantity of gas present, as indicated
on the cylinder. If the instrument’s response is
within an acceptable tolerance range of the actual
concentration, then its calibration is veried.
It is recommended that users check with the
gas detection equipment manufacturer for the
acceptable tolerance ranges.
Instruments should be “zeroed” before the bump
test to give a more accurate picture of the bump test
results.
Also, the test should be conducted in a clean, fresh
air environment. When performing a bump test,
the test gas concentration should be high enough
to trigger the instrument alarm. If the instrument
fails a bump test, it must be adjusted through a full
calibration before it is used.
During a period of initial use of at least 10 days in
the intended atmosphere, calibration should be
veried daily to ensure nothing is in the atmosphere
to poison the sensors. The period of initial use
must be of sufcient duration to ensure the sensors
are exposed to all conditions that might adversely
affect the sensors. If the tests demonstrate that no
adjustments are necessary, the interval between
checks may be lengthened, but it should not exceed
30 days.
If the instrument fails a bump test, it must be
adjusted through a full calibration before it is used.
When calibrating an instrument, always follow the
manufacturer’s recommended calibration frequency
and procedure.
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