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15 LADDERS, STEPS AND PLATFORMS

15 LADDERS, STEPS AND PLATFORMS

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S E C T I O N

5
U N D E R G R O U N D
I N S TA L L AT I O N S

AS/NZS 1596:1997

TA N K

5.1 APPLICATION An underground tank installation shall comply with the requirements
of Section 3 and Section 4, together with the additions or qualifications given in this Section.
Where any requirements of this Section (5) differ from a similar requirement of Section 3,
this Section (5) shall take precedence.
A tank which is partly or wholly above the general ground level but is wholly covered with
soil, or a tank within a sand-filled chamber, shall be treated as an underground tank.
The exposed portions of tank shells excluding an access hole or inspection pit that are partly
buried or mounded shall be treated as above-ground tanks. For separation distances and fire
protection, the capacity of the tank shall be used. Water supply for fire protection shall be
based on the exposed area.
5.2

CORROSION CONTROL

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5.2.1 General Each tank shall be provided with a method of corrosion control that
provides protection for the tank from the effects of the corrosive nature of the surrounding
soil.
A cathodic protection system shall be designed and installed under the supervision of a
specialist in cathodic protection systems. (For guidelines on the design, installation, and
operation of cathodic protection systems, see AS 2832.2.)
5.2.2 Testing of coating The electrical resistance and the continuity of the coating of the
tank shall be spark-tested over the whole surface in accordance with AS 3894.1. The potential
shall be suitable for the characteristics of the particular coating, as specified by the coating
supplier. Any flaws detected in this test shall be repaired and retested. The coating shall be
spark-tested again at the last possible stage prior to final placement and burial, and any
handling damage shall be rectified and re-tested.
5.3
5.3.1

LOCATION AND INSTALLATION
Tank location

Tanks shall be located as follows:

(a)

Separation distances for underground tanks shall comply with Table 5.1.

(b)

Tanks shall not be located beneath the bunded area of flammable or combustible liquid
storages.

(c)

A tank shall be not less than 3 m from an underground tank for flammable or
combustible liquids unless the two installations have compatible corrosion protection
systems specifically designed to cater adequately for the area between the tanks in
which case the separation may be 1 m.

5.3.2 Tanks in groups Tanks may be arranged in groups with no limitation on the number
of tanks in a group, provided that —
(a)

tanks shall not be buried one above another; and

(b)

the standard filling level of all inter-connected tanks shall be in the same horizontal
plane unless the piping and valve system prevents uncontrolled levelling of the liquid.

5.3.3
(a)

Tank covering

An underground tank shall be covered as follows:

The tank shall be set on not less than 150 mm of clean inert sand and —
(i)

be surrounded with not less than 150 mm of clean sand; or

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AS/NZS 1596:1997

(ii)

44

be supported by a concrete anchor, which shall be separated from the tank
surface by a material offering adequate protection to the tank coating and
preservation of cathodic protection to the total tank surface, and then covered
with 150 mm of clean inert sand.

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NOTE: The correct conductivity and pH levels are critical to cathodic protection.

(b)

If vehicles can pass above the tank, it shall be covered by not less than 300 mm of
sand superimposed with reinforced concrete not less than 150 mm thick, but also
adequate to support any likely superimposed loading, and extending not less than
300 mm in all directions, beyond the outline of the tank. If traffic access is prevented,
a covering of not less than 600 mm of sand or earth may be substituted.

(c)

Where tanks are wholly or partly above ground level, that part above ground level shall
be entirely covered to a minimum radial thickness of not less than 600 mm with either
additional sand or suitable earth. For mounds without retaining walls, the slope of the
cover shall be not steeper than the angle of repose of the material.

(d)

The covering for a tank shall be resistant to erosion by wind or rain, by water streams
during firefighting or by nearby tank cooling systems. The covering shall be
maintained.

TABLE 5.1
SEPARATION REQUIREMENTS FOR UNDERGROUND STORAGE SYSTEMS
From

Tank shell

Tank fitting, e.g. valve,
flange, ullage gauge

To

Minimum requirement

Public place boundary
Adjacent property boundary

As illustrated in Figure 5.1

Protected place (on or off site)

No specific requirement, limited
by other requirements

Adjacent LP Gas tank

1m

Public place

3m

Adjacent property

6m

Protected place

6m

Pump

See Clause 4.12.5

Filling connection

For a wet hose delivery* and inward flow only, distances are as for
tank fittings; otherwise for remote connections as per Clause 4.7.7(b)
to (e) and requirements as for Clause 4.7.3. For direct connections,
Clause 4.7.2 shall apply.

Safety valve discharge

See Clause 5.5.2

* This term refers to a hose assembly design which limits the loss of LP Gas liquid on
disconnection to 1 L or less.

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45

AS/NZS 1596:1997

NOTE: These illustrations should not be interpreted as setting limits to the type of installation allowable. Their
purpose is to indicate boundary locations only.

FIGURE 5.1

TANK DISTANCES FROM BOUNDARIES

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5.3.4 Anchoring The tank shall be installed in such a manner as to prevent movement in
excess of the system design. Any steelwork associated with the anchoring system shall not
make electrical contact with the tank or the piping system unless included in the cathodic
protection system.
5.3.5 Tank branches and tappings The provisions for tank tappings for filling, draw-off
and similar use shall comply with the following requirements:
(a)

Direct filling is permitted only where liquid is discharged into the vapour space of the
tank.

(b)

Where an access hole and cover projects from the tank shell to above ground for the
attachment of piping, the portion that is above ground shall be heat-protected by some
means having a fire resistance level of not less than — /120/120.

(c)

Where a pipe is connected to a tank shell rather than to such an access hole and cover,
the protective valves shall be arranged at the first pipe joint from the tank shell,
provided that —

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(d)

(i)

the joint is not more than 400 mm from the point where the pipe emerges from
the ground; and

(ii)

a manual shut-off valve or a flanged or screwed joint, shall not be buried. (For
illustrations of possible arrangements, see Figure 5.2.)

Any connection for loading a tanker shall be a remote connection.

5.3.6 Gas storages other than LP Gas The distances specified in Clause 4.2.5 shall
apply, but only from the connections to the underground LP Gas tank.
5.4

ACCESS, PROTECTION, FITTINGS AND ACCESSORIES

5.4.1 Access Each component or fitting which may be required to be accessible, e.g. a
filling connection, gauge, safety valve or access hole, shall be located within an access pit,
or within a dome or housing mounted directly above such an access pit, or on or within a
nozzle or branch extending from the tank to above ground level.
5.4.2 Protection for above-ground equipment Any part of, or accessory to, a buried tank
which projects above ground level shall be designed, located, or protected so as to be not
liable to accidental damage.
5.4.3

Access pits

Any access pit shall comply with the following requirements:

(a)

The pit opening shall be covered by an above-ground dome or housing, or by a flush
cover, capable of preventing the entry of water.

(b)

A flush cover that is subject to traffic shall be of sufficient strength to withstand
normal traffic loads.

(c)

Pit walls shall be of low carbon steel not less than 6 mm thick, or reinforced concrete
not less than 75 mm thick, or masonry not less than 100 mm thick, or an alternative
material of equivalent performance, and shall extend from the tank to the ground
surface in such a manner that traffic loads are not transmitted to the tank shell by the
pit wall.

(d)

A pit shall have a horizontal cross-sectional area of not more than 2 m 2, and shall be
not more than 1 m deep.

(e)

The access pit shall be provided with a means of limiting, or of detecting and
dissipating, any buildup of vapour prior to access.

5.4.4

Contents gauging

The following requirements apply:

(a)

Where the contents gauge is obscured by the filling connection, a means of remote
gauging system shall be used.

(b)

Any contents gauge within an access pit shall be capable of being read at all times,
without the aid of a portable light source.
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5.5

AS/NZS 1596:1997

DISCHARGE FROM SAFETY RELIEF DEVICE

5.5.1 Discharge rate The rate of discharge of a safety relief device on an underground
tank may be reduced to not less than 30% of that required for an above-ground tank as
specified in Clause 3.4.1(d).
5.5.2 Point of discharge The discharge from a safety relief device shall be directed
vertically upwards, and the discharge point shall terminate not less than 3 m above the
ground. The discharge point shall be not less than 2 m from any opening in a wall or
structure which could permit vapour to enter a building, a cavity wall, a roof space, or a
similar enclosure.
NOTE: Particular care should be taken to recognize such potential entry paths as weatherboards and
roofing tiles.

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A shear point shall be fitted downstream of the safety valve to ensure that impact or high
wind loads cause failure at the shear point so that the safety valve remains in the tank
maintaining containment.

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