Underground Petroleum Storage Tanks and Related Wastes - Code ...

11.5 above). This in turn determines the cutting method selected. The preferred
method of opening up tanks is by cold cutting, as even products that are normally
nonvolatile can produce explosive vapour when heat is applied.
A report on the condition of the tank, including the size and location of any holes
that may be found, must be recorded in the form required by the principal and as
advised by the project engineer.
Oxygen under pressure is not safe with petroleum products or other hydrocarbons.
Spontaneous combustion will occur in certain conditions. Do not use high
pressure oxygen to clean scale or dirt from areas of tanks to be cut.
11.11 Method
At the time of processing, no more than one tank will be permitted on the disposal
pad. The tank should be stripped of all fittings, and vents and manhole covers
removed allowing the tank to vent. It should be lifted slightly at one end and any
product and sludge air pumped or vacuumed out into prepared drums/containers.
Tanks in storage and tanks on the disposal pad shall be regarded as dangerous
goods Class 3(a) and the particular rules requiring an isolation distance of 15
metres from any source of ignition shall be followed.
The tank shall then be rendered inert by either filling with water or by one of the
other methods outlined in sections 11.4 and 11.5. If the tank is not filled with
water, it is essential to have to hand an approved intrinsically safe vapour tester
and certified operator during the processing, to monitor the status of the tank. It is
also essential to allow the tank to cool before testing for vapour — most
explosimeters only operate satisfactorily at normal temperatures.
An opening of 1 m2 minimum should be cut in the top side of the tank, or the
whole of one end removed.
Always work from outside and on the top side of the tank — never from inside,
and never from the end. If the tank explodes it will almost invariably blow the
ends out. It is not acceptable to crush tanks even when the ends have been cut out.
Experience has shown that explosive cavities can be formed which cause dangers
to the on processor. It also makes it impossible to deal with the scrap metal as
specified in Octel Instruction Publication No. 5 — 01/92.
A Lower Flammable Limit reading will only be given from a Class 3(b) or 3(c)
tank (e.g. kerosene, diesel or fuel oil) after it starts to fume. Where a Class 3(b) or
3(c) tank is badly holed and cannot be filled with water it should be purged with
steam. The expelled air from inside the tank should be monitored at the time of
hot cutting.
11.12 Tank Entry
Before anyone enters a tank or other confined space a competent person must
inspect and test the confined space and issue a Confined Space Entry Permit
listing any specific precautions that must be taken. These will include full breathing
apparatus where there is any possibility of oxygen deficiency or petroleum or
other toxic vapours, and personal protective equipment to suit the circumstances.
See also section 13 Special Hazards.
Transport and Disposal of Petroleum Storage Tanks 21