Instead, the process analyses a number of underlying indicators which are significant for assessing the chances of such incidents.

A complicated formula, where these factors are weighted in accordance with their contribution to the overall position, yields a composite indicator for major accident risk.

Viewed over a series of years, this in turn provides a clear picture of the trend – which has been declining over the past decade so that the risk has roughly halved over the period.

The annual Trends in risk level report (RNNP) from the Petroleum Safety Authority (PSA) uses risk indicators to measure the status of so-called “defined hazard and accident conditions” (DFUs). But what are these DFUs? And which of them comes with a potential for causing major accidents?

A company responsible for pursuing oil and gas activities acceptably must identify the occurrences it needs to guard against – known as “defined hazard and accident conditions” (DFUs).

Defined hazard and accident conditions (DFUs)

The annual RNNP report uses one or more risk indicators to measure the status of most DFUs. All data acquired through various channels are processed in a statistical model. This shows how the various contributors to risk are developing, both collectively and for the individual DFU.

DFUs with a potential for causing major accidents in the petroleum industry include the following:

  • Leaks of flammable gas or liquids:
    A distinction is drawn between ignited and non-ignited leaks. A non-ignited leak, for example, could allow gas to spread over large areas so that later ignition causes an explosion and a major accident.
  • Well control incidents:
    Loss of well control could lead to a blowout. Such an incident has the potential to cause substantial harm to people, the environment and material assets.
  • Fire/explosion in other areas:
    An example of such incidents is a fire in the living quarters with the potential to develop into a major accident.
  • Collisions and other structural damage to a facility:
    A distinction is drawn between collisions by vessels (supply ships, shuttle tankers or the
    like) manoeuvring close to the facility, and by vessels not related to the activity or drifting objects (such as barges).

    Platforms and rigs are designed to withstand minor collisions. But being struck by a big vessel, possibly at high speed, could cause damage which leads in the worst case to complete collapse of the support structure.

    Damage can also occur in extreme weather conditions. This type of hazard involves loss of stability or mooring/positioning system failures on floating units, resulting at worst in a total loss.
  • Leaks from subsea production facilities with pipelines and associated equipment:
    Installations on the seabed can be damaged by objects dropped from above. Fishing gear may also cause substantial harm.

    The major accident potential of damage to subsea facilities relates primarily to pollution from possible oil spills. Any nearby surface facilities could also be threatened.

Other DFUs

Other DFUs also exist which have no major accident potential but nevertheless form part of the overall picture. These include personal injuries, occupational illness and diving.