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Abandoned underground tanks

When a person conducting a business or undertaking (PCBU) intends that a underground storage and handling system will no longer be used, the system so far as is reasonably practicable, must be removed (section 366 of the Work Health and Safety Regulation 2011. If this is not possible, the person must ensure that, so far as is reasonably practicable, there is no risk to health and safety.

It may not be practicable to remove an underground tank due to its close proximity to surrounding structures (e.g. adjacent underground tanks of building foundations) or extensive system of pipe work existing in the subsurface above the underground tank. In such cases, the tank may need to be decommissioned 'in-situ' which means that the tank is left in its existing position and made safe.

Hazards

Any work on existing or abandoned underground tanks or associated pipework is potentially dangerous where residual levels of flammable gases, liquids and vapours are present. Introducing an ignition source (e.g. activities such as grinding, hot cutting or welding) may cause an explosion or other dangerous occurrence unless suitable procedures are adopted.

Tar-like deposits and sludge may have accumulated in the tank and pipe work. Flushing with water may not remove them and vapour testing may not detect this. Exposure of these deposits to air and sunlight under normal temperatures, or work involving heat (e.g. use of grinders or oxy-acetylene cutting), may release vapours creating a potential explosion hazard.

By following the steps listed below, the likelihood of dangerous occurrences can be minimised or even eliminated:

  • Remove the tank from the ground and transport to a disposal area and arrange for the tank to be decommissioned.
  • Decommission the tank in-situ by removing its residual contents including purging vapours, and filling the tank with an inert solid material like concrete or sand.
  • If it is intended that the tank be used again (within two years), you can fill the tank with water and a corrosion inhibitor and conduct appropriate maintenance to maintain the system's integrity.

Who is responsible?

The PCBU for the workplace is responsible for ensuring that the tank is abandoned in a safe manner. If no work activity is being conducted on the site under a PCBU, then the property owner in their capacity as the owner of the underground tank system will be responsible for the abandonment.

Decommissioning

When decommissioning an underground tanks that has been used to store a flammable gas or liquid (includes those combustible liquids with a flash point equal to or less than 93°C), a PCBU must notify WHSQ.

As LP gas, petrol and diesel are the main types of hazardous chemical preferentially stored in underground tanks (to reduce the inherent risk of fire and explosion), this requirement mostly affects fuel retailers and depots.

The PCBU must also ensure that the associated risks for the underground storage and handling system are managed and controlled while the tank is waiting to be decommissioned.

After a tank is decommissioned

Having decommissioned an underground tank, the PCBU should:

  • amend relevant documentation including emergency plans and the emergency service manifest and site plan for the workplace
  • update the notification for a manifest quantity workplace using Form 73 – Notification of a manifest quantity workplace (Smart Form)
  • retain all relevant documentation for their records
  • provide these records to any new owners if the property changes hands.

Notification

When a PCBU has an abandoned underground tank that has been used for storage of flammable liquids, Categories 1-4, (e.g. petrol, resins, ethanol, diesel) or flammable gases (e.g. LP gas), WHSQ must be notified as soon as practicable after the tank is abandoned (refer to section 367 of the WHS Regulation).

Why do I have to notify?

The notification is to ensure that abandoned underground fuel tanks are made known to the regulator and that decommissioning occurs in accordance with AS4976: The removal and disposal of underground petroleum storage tanks to make the location safe.

More information

More information on the removal and disposal of underground tanks is available in Australian Standards, for example AS4976: The removal and disposal of underground petroleum storage tanks.

This standard also provides guidance for managing a tank that is temporarily out-of-service.

Last updated
11 July 2018

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