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MAN0585.P65
Issue 01 - 11/99
2987M5023
the aspirator bulb at a rate of approximately ten per
minute. If using the electric pump, sample for five
minutes. If the Minigas Mk5 gives an alarm indication,
note the hazardous condition and refer to supervisory
personnel.
WARNING
Because of the difficulties of transferring chlorine or
sulphur dioxide via rubber tubing, drawing a sample with
an aspirator (hand or electric) is not a suitable method for
these gas checks.
When using the aspirator attachment to test for toxic gases,
account must be taken of the effect of adsorption, particularly
in a wet environment, of the atmosphere toxic content - see
Section 3.2.3.
If no alarm has occurred during the above checks, remove the
aspirator (if fitted) and enter the work area ensuring that the
Minigas Mk5 is worn with the sensor grill facing outwards
towards the breathing zone.
3.2.3
Adsorption of Toxic Gases
Instead of passing freely along rubber tubing, molecules of
certain gases can stick onto the tubing wall, thereby reducing
their concentration at the end of the tubing. This effect is known
as adsorption and is most noticeable with chlorine and sulphur
dioxide, to the extent that, as stated above, the aspirator should
not be used for toxic gas checks with these toxic gases.
Typically, with 5mm diameter neoprene tubing the reduction in
hydrogen sulphide or carbon monoxide concentration is
approximately 1ppm/metre. Because of the lower alarm level
setting, this is particularly significant with hydrogen sulphide
measurements. The effect is aggravated if the inside of the
tubing is wet, when the resulting reduction in the hydrogen
3. USE AND TRANSFERRING DATA AFTER USE
