Oil Storage Tank Base Requirements

If you are installing or replacing an oil storage tank, it is always wise to seek advice from an OFTEC-qualified technician, as they will be able to carry out a fire and environmental risk assessment and ensure you comply with current regulations.  However, below we have outlined some key areas you need to take into consideration when thinking about Oil Storage Tank Base Requirements

While many of these regulations cover the design and construction of the tank itself, it is important that the base on which the tank stands is fit for purpose. One factor is the weight of a full tank; as a guide, fuel oil weighs approximately one tonne per 1000 litres, plus the weight of the tank itself. As domestic heating oil tanks can have a capacity of up to 3500 litres, the total weight could be 3.5 tonnes.

The base must therefore be stable and solid enough to take this weight regardless of potentially changing ground conditions such as soil erosion. If an unstable base is unable to maintain uniform structural support across the full footprint of the tank, this could result in leakage and even fracture of the tank or pipes.

The base should be level and constructed of a non-combustible material such as solid concrete, paving stones or stonework, on a properly prepared bed and extending by a minimum of 300mm beyond the perimeter of the tank. If pre-cast concrete slabs are used, these must be at least 50mm thick and laid on a compacted and blinded hardcore base. If a concrete base is cast, this must be at least 100mm thick. The base should also offer a degree of impermeability so that in the event of a minor spillage, the soil will not be contaminated.

Another factor that must be taken into consideration is the siting of the tank, and this is particularly important if an existing tank is to be replaced, as the present location may no longer meet regulations. The tank must be placed where there is a minimal risk of fire spreading to the tank from nearby structures, and even the lesser risk of a fire starting at the tank and spreading outwards.

A minimum clear space of 1.8 metres must be maintained between the tank and the following:

  • non-fire rated eaves of a building
  • any non-fire rated building or structure (for example, a garden shed)
  • openings (such as doors or windows) in a fire rated building or structure such as a brick-built house or garage
  • liquid fuel appliance flue terminals

The tank must also be sited at least 760mm from any non-fire rated boundary such as a wooden fence, and 600mm away from screening such as trellis and foliage that does not form part of the boundary. This is important to remember when planning to conceal an unsightly tank that may be visible from a house’s windows.
If there is insufficient space on the site to meet these regulations, a fire protection barrier with a minimum rating of 30 minutes may be used with a reduced gap of 300mm between the tank and the fire barrier, subject to the approval of the tank’s manufacturer.

Location of a fuel oil tank within a building such as a garage or outhouse is generally undesirable due to the unpleasant odour of fumes as well as increased fire risk, but if this is unavoidable the tank must be fully enclosed within a 60-minute fire rated chamber.

Steel Tank Installation
  • To limit corrosion, we recommend
    raising the tank on two or more pillars to keep the base clear of groundwater (bunded tanks are supplied with additional base support runners for installation on a ground-level platform)
    inserting a bitumen-type strip material underneath the tank contact points
  • On single skin tanks only, inclining the tank slightly towards the drain socket end to allow rainwater to drain from the top of the tank
    If the tank is placed on pillars, these should extend beyond the sides of the tank to support them from beneath (see Figure 1).
  • Atlantis Single-skin steel oil tanks are supplied with:
    • two 2” BSP top female sockets (fill & vent)
    • one 1.5” BSP top female socket (tank gauge)
    • one 1” BSP bottom outlet socket
    • one ¾” BSP plugged drain socket.
  • Atlantis Bunded steel oil tanks are supplied with:
    • two 2” BSP top female sockets (fill and spare)
    • one 1” BSP plugged top suction drain
    • one 2” BSP tank-to-bund vent
    • one 2” bund vent with vent cap
    • one 1.5” BSP top female socket (bund gauge)
    • one 1.5” BSP top female socket (tank gauge)
    • one 1” BSP bottom outlet socket
Plastic Tank Installation
  • A bunded plastic tank may be installed on pillars (see Figure 2). Raising the tank so that the bottom outlet is higher than the boiler inlet will allow gravity to feed the fuel directly to the boiler.
  • If placed on pillars, a bunded plastic tank will need a full flagstone base to bear its weight across the full diameter of the tank, supported by concrete lintels.
  • A bunded plastic tank may also be placed directly onto a ground-level non-combustible base (see Figure 3). This is preferable if the location has limited headroom, or to minimise visual impact.
  • If located at ground level, a bunded plastic tank will require an internal flexible suction pipe to draw the fuel oil up to a top outlet, which is factory fitted within the outer bund. It will also require a de-aeration device to be fitted between the tank and the boiler to ensure no air bubbles reach the boiler.
  • Atlantis plastic single skin oil tanks are supplied with:
    • one 2” top male socket (fill)
    • one 2” vent
    • one 1” bottom outlet or 1” top outlet socket
    • one 4” inspection cap
    • one gauge port
  • Atlantis plastic bunded oil tanks are supplied with:
    • one 2” top male socket (fill)
    • one 2” vent
    • one 1” bottom outlet or 1” top outlet socket
    • one 4” inspection cap
    • one gauge port
    • one outer bund locking lid
Steel Oil Tank Installation

Figure 1

Plastic Bunded Oil Tank Installation

Figure 2

Plastic Oil Tank Installation

Figure 3

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