5.1 After a tank has been cleaned, ventilated
and prepared for entry, it should be tested for oxygen content, and
finally, as appropriate, for toxic gases at various levels from top
to bottom.
5.2 The atmosphere can only be accepted as suitable
for entry when all the relevant hazards have been identified and removed.
5.3 Appropriate testing of the atmosphere of a
tank should be carried out with properly calibrated equipment by persons
trained in the use of the equipment. The manufacturers' instructions
should be strictly followed. Testing of the tank should be carried
out before any person enters the tank, and at regular intervals thereafter
until all work is completed. Where appropriate, the testing of the
tank should be carried out at as many different levels as is necessary
to obtain a representative sample of the atmosphere in the tank. In
some cases, it may be difficult to test the atmosphere throughout
the tank without entering the tank and this should be taken into account
when assessing the risk to personnel entering the tank. The use of
flexible hoses or fixed sampling lines which reach remote areas within
the tank, may allow for safe testing without having to enter the tank.
5.4 All ventilation must be stopped prior to and
during the atmosphere tests and resumed prior to any person entering
the tank.
5.5
Criteria for Tank Entry
5.5.1 For entry purposes, steady readings of all
the following should be obtained:
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.1 21% oxygen by volume by oxygen content meterfootnote;
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.2 not more than 1% of lower flammable limit (LFL)
on a suitably sensitive combustible gas indicator, where the preliminary
assessment has determined that there is potential for flammable gases
or vapours; and
-
.3 not more than 50% of the occupational exposure
limit (OEL) of any toxic vapours and gases.footnote
5.5.2 A responsible person should ensure that
all measuring instruments in use have been properly calibrated and
are maintained in accordance with the respective manufacturer's instructions.
5.5.3 If these conditions cannot be met, additional
ventilation should be applied to the tank and re-testing should be
conducted after a suitable interval.