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Appendix 1

OSD process integrity initiative

As indicated in the executive summary and elsewhere in this report, OSD has undertaken an initiative to deal with Process Integrity concerns as a result of the reporting plateau (see earlier comments) shown by recent offshore hydrocarbon release statistics, and by trends identified from these statistics.

The initiative is aimed at increasing the awareness of the current unsatisfactory situation, to identify root causes to bring greater emphasis on the necessity to reduce offshore hydrocarbon releases, and to influence those people in the best position to bring that about.

The Process Integrity initiative has three strands:

  1. OSD has investigated all RIDDOR reportable hydrocarbon releases which occurred during the planning year to 31 March 2001, which included offshore visits by Inspectors for all major and some significant releases. The results of this work are documented in offshore technology report OTO 2001/055 - OSD Hydrocarbon Release Reduction Campaign - Report on the hydrocarbon release incident investigation project 01/04/2000 to 31/03/2001.
  2. Process integrity inspections of all manned production installations, will be phased in over a three year period, i.e. 2000 to 2003.
  3. Regular joint HSE/Industry Workshops on hydrocarbon releases will be held, at least annually, and the first two of these were held on 9 November 2000 at Ardoe House near Aberdeen, and on 7 November 2001 at Brittannia Hotel, Aberdeen.

Proceedings for these seminars are available from UKOOA.

Appendix 2

Severity classification

As indicated in the introduction to this report, there have been discussions with the offshore industry on a classification system for hydrocarbon releases. The consensus reached is that all reported releases can be classified as minor, significant or major by applying agreed definitions and provisional classification criteria.

Definitions: The definitions were agreed as follows:

Major: "Potential to quickly impact outwith the local area, e.g. affect the Temporary Refuge (TR), escape routes, escalate to other areas of the installation, causing serious injury or fatalities."

A major leak, if ignited, would be likely to cause a "major accident", i.e. it would be of a size capable of causing multiple casualties or rapid escalation affecting TR, escape routes, etc.

Significant: "Potential to cause serious injury or fatality to personnel within the local area and to escalate within that local area, e.g. by causing structural damage, secondary leaks or damage to safety systems."

A significant leak, if ignited, might have the potential to cause an event severe enough to be viewed as a "major accident" or be of a size leading to significant escalation within the immediate area or module.

Minor: "Potential to cause serious injury to personnel in the immediate vicinity, but no potential to escalate or cause multiple fatalities."

A minor leak, even if ignited, would not be expected to result in a multiple fatality event or significant escalation, but could cause serious injuries or a fatality local to the leak site or within that module only.

Any offshore hydrocarbon release reportable under RIDDOR 95 can be classified under one of the above definitions, using criteria reported on the OIR/12 form. It was also decided to group all releases of hydrocarbon liquid under one category of "liquids", since oil, condensate, and non-process liquids (diesel, helifuel, glycol, etc.) share the common characteristics of flammable fluids.

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The simplest criteria for classification is to use inventory released. This can be further refined by taking into account hole size and duration, pressure, congestion factors and a variety of other mitigation factors. At the time of preparation of this report, the preferred criteria were based on quantity released, release rate and duration. It should be noted, however, that discussions with industry on further refinement of the criteria are still ongoing. (See 'Implementation' at the end of this Appendix.)


  1. Gas Releases:

    • Either [Quantity released > 300 kg]
    • or [Mass release rate>1kg/s and Duration >5 mins]

    This could result in a jet fire of over 10 metres length (>1kg/s) capable of causing significant escalation after 5 minutes duration, or a flash fire/explosion on reaching LFL. Where 300 kg equates to approx. 3000 m3 explosive cloud at NTP, enough to fill an entire module or deck area, and to cause serious escalation if ignited.

  2. Liquid Releases (Oil/Condensate/Non-process):

    • Either [Quantity released > 9,000 kg]
    • or [Mass release rate>10kg/s and Duration >15 mins]

    This could result in a pool fire over 10 metres in diameter (>10kg/s) filling a module or cutting off a deck, hindering escape and affecting more than one person directly if lasting for over 15 minutes duration.

  3. 2-Phase Releases:

    • Either [Quantity of liquids released > 300 kg]
    • or [Liquids mass release rate>1kg/s and Duration >5 mins]

    Combinations of the major gas and liquids scenarios described above are possible, depending on the gas to oil ratio (GOR) involved.


  1. Gas Releases:

    • Either [Quantity released < 1 kg]
    • or [Mass release rate <0.1 kg/s and Duration < 2 mins]

    This could result in a jet fire of less than 5 metres length (< 0.1 kg/s) which is unstable (< 2 mins duration) and therefore unlikely to cause significant escalation , or a flash fire/explosion on reaching LFL. Where <1 kg equates to <10 m3 explosive cloud at NTP, probably insufficient to cause a significant hazard if ignited.

  2. Liquid Releases (Oil/Condensate/Non-process):

    • Either [Quantity released < 60 kgs]
    • or [Mass release rate <0.2 kg/s and Duration < 5 mins]

    This could result in a pool fire smaller than 2 metres in diameter (< 0.2 kg/s) unlikely to last long enough to hinder escape (< 5 mins), but could cause serious injury to persons nearby.

  3. 2-Phase Releases:

    • Either [Quantity released < 1 kg]
    • or [Liquids release rate <0.1 kg/s and Duration < 2 mins]

    Combinations of the gas and liquids scenarios described above are possible, depending on GOR involved.

Significant: (Those between major and minor.)

  1. Gas Releases:

    Capable of jet fires of 5 to 10 metres lasting for between 2-5 minutes, or release rates between 0.1 to 1.0 kg/s lasting 2-5 minutes giving explosive clouds of between 10 and 3000 m3 in size.

  2. Liquids Releases (Oil/Condensate/Non-process):

    Pool fires between 2 and 10 metres in diameter, lasting for between 5 and 15 minutes.

  3. 2-Phase Releases:

    Combinations of the gas and liquids scenarios described above are possible.

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All current and future releases will be classified according to the above agreed criteria for the types of hydrocarbons involved, and the results used in HCR statistics reports.

Any further refinement of the criteria will be retrospectively applied, and the severities adjusted where necessary.

It is important to note, however, that those releases with a hole size labelled N/A are special cases where the release rate is not applicable to the mode of release (e.g. open topped vessels such as shale shakers, or where carry-over of hydrocarbons from one system to another was involved). All such releases were classified by inspection of the amount released only.

Updated 2009-09-06