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Offshore hydrocarbon release – investigation policy


OG status:
Fully open
Author unit / section:
OSD 2.4
Target audience:
All OSD Inspectors
Version No:


1 This document replaces SPC/TECH/OSD/38 Version 1 and provides instructions and guidance on investigations into offshore unintentional hydrocarbon (process and non process) releases, in particular those releases which require mandatory investigation by OSD Inspectors. It describes:

2 If a hydrocarbon release gives rise to HSE declaring a major incident offshore, OSD’s Major Incident Response Plan will supersede this SPC.


3 Hydrocarbon releases are a key indicator of how well the offshore industry is managing major hazard risks and the integrity of installations. Figures have gradually declined from a level of 139 major and significant releases in 1999/2000, but have plateaued to around 70 to 80 each year from 2005/2006 onwards.

4 Reducing the number of hydrocarbon releases requires the industry to improve its performance in the safe production and processing of hydrocarbons by preventing uncontrolled releases.  HSE needs to ensure that operators learn the reasons for any releases which do occur and take effective action to reduce the likelihood of further releases. So, part of OSD’s strategy to improving the industry’s performance is to ensure that we undertake thorough investigations of hydrocarbon release incidents so that:

Reporting of hydrocarbon releases

5 Unintentional hydrocarbon releases are required to be reported to HSE forthwith by the quickest practicable means under Regulation 3 of the  Reporting of Injuries, Diseases and Dangerous Occurrences Regulations (RIDDOR). The OIR9b form has to be sent to HSE within 10 days.

6 Since 1992 details of each release have been recorded on a database, as recommended by the Cullen inquiry into the Piper Alpha disaster. It includes releases of non-process hydrocarbons, such as diesel, hydraulic oil, methanol and glycol. The data includes statutory information reported under RIDDOR and additional voluntary information supplied on form OIR12. The OIR12 should be submitted to HSE within 4 weeks after a hydrocarbon release, though in practice it may take longer.  Oil and Gas UK have issued guidance  to operators on submission of OIR12 data. 

7 Hydrocarbon releases are classified into three categories of Major, Significant and Minor. These classifications are based on information in the OIR12 reports, which are checked by the process integrity team (OSD3). They assign the severity category of Major, Significant or Minor to each release in accordance with potential consequence descriptions agreed with the offshore industry. These are broadly classified as:

Agreed Severity Classification criteria can be found on the HCR system HELP facility.

Technical judgement is applied by OSD 3 in assigning the final category or severity of the release. For example, a 450kg gas release may be categorised as a significant and not major due to the duration of the release (say several hours) because it represents a lesser hazard from that of a say a 320kg release over a much shorter time.

Action by Inspectors

Deciding to Investigate

8 It is OSD’s policy that hydrocarbon releases which fall within the Major or Significant categories are for mandatory investigation. However the exact categorisation of such a release may only become apparent when the OIR12 has been submitted and scrutinised by OSD3, which may be some time after the event. This SPC therefore gives advice on investigation decisions and practises for hydrocarbon releases both before the formal categorisation is available, and subsequently.

9 Once an IMT has been notified “forthwith” by telephone etc of a hydrocarbon (process and non process) release the Team Leader is to decide, at the earliest, if a full investigation is to be pursued.  They are not to wait for the OIR12 or OIR9B notification as it is often too late for a rapid response. It is recognised that the initial information may not be accurate, or be scant. However, the IMT Team Leader or focal point inspector is to seek further information at the earliest from the dutyholder and use any local or Divisional knowledge, including Specialist Inspector advice to enable the best initial assessment of whether to investigate or not.

10 Immediate or timely (eg 1 to 5 days or when it is safe to do so) offshore full  investigations are to be pursued where the release has given rise to:

  1. An emergency evacuation/escape;
  2. Casualties;
  3. An ignition (see para 22 for further guidance); or
  4. a precautionary downman of the installation

11 On occasions there may be minor ignitions. These usually arise from lube oil / utility systems which may not warrant deployment of resources in a full offshore investigation. Careful judgement should be exercised considering source of ignition, type of substance ignited, escalation issues, emergency response and history of similar ignitions on the installation and across the industry. If the IMT leader decides not to investigate such an ignition refer to para 17.

12 Where a release does not meet the above criteria the IMT Leader will make the judgement to pursue a full offshore immediate or timely investigation based upon:

13 Advice on the scope/depth of any hydrocarbon release investigation is given in Annex 2.

Resourcing an Investigation

14 Full investigations are best resourced using multidiscipline teams comprising IMTs and appropriate Specialist Inspectors. However, this ideal may not be realised in the initial response to a release requiring an offshore full investigation. 

15 The IMT Team Leader should endeavour to mobilise, at the earliest, the best resourced Investigation Team that can be achieved in the first instance. Other specialists can join the initial Investigation Team later, if needed or are not available immediately. Those who participate in the early stages of investigations must be able to take statements, gather evidence, make initial enforcement decisions, and recognise when and what Specialists Inspectors are best deployed to aid the investigation.

16 When an IMT Team Leader has difficulty resourcing the Investigation Team they are to inform the Operations Manager so that they can deploy Inspectors from other IMT Teams. If a timely investigation (within 1 to 5 days) cannot be commenced then a judgement should be made when realistically this can happen. If the projected date of commencing a full investigation is too far into the future such that the scene of the incident may be unrepresentative of the conditions at the time of the incident, witnesses become dispersed, and other evidence may become difficult to obtain then the IMT Team Leader should discuss this with the Operations Manager. If the Operations Manager is unable to change priorities or make suitable resources available from across the Division then the incident will be classed as “no immediate offshore investigation”. Only when this approach has been exhausted is the Operations Manager able to record that there are no suitable resources available for pursuing an immediate or timely offshore investigation.  The reasons should be carefully recorded on the Decision Recording Form (DRF) and then saved on COIN.  In this event an onshore investigation is to be pursued.

Using the Decision Reporting Form

17 The DRF form can be used for recording a number of reasons when a Team Leader decides to deviate from this SPC (i.e. not to pursue a full offshore or an onshore investigation when the investigation criteria are met). These include:

18 When completing a DRF the details of why any part of this SPC, relating to investigation decisions, are not to be followed should be carefully recorded including any actions to be pursued (if any) in part D of the form. The DRF must be signed by the relevant Operations Manager. All DRFs are to be attached to the relevant section of COIN and a copy sent to the IMT administrator.  

Investigating releases onshore

19 If the only practicable alternative due to resource constraints, is to pursue an onshore investigation this should be undertaken at the dutyholder’s head office at the earliest opportunity. This will be recorded in part D of the DRF. This type of investigation should be more than simply discussing matters with a dutyholder’s safety adviser/manager or asset manager etc. Inspectors should be more intrusive, endeavouring to speak to witnesses when they return from offshore or via telephone when they are offshore. The information/evidence collected will be what is currently available without waiting until the dutyholder’s investigation is complete. Any additional information/evidence can be obtained at a later date. Having undertaken an onshore investigation the IMT Leader should not rule out pursuing a full offshore investigation. In making this judgement the IMT Leader will consider:

  1. the factors listed in paragraphs 10 and 12;
  2. the quality of the dutyholder’s own investigation, findings and recommendations;
  3. lack of progress in implementation of any of the dutyholder’s own recommendations for preventative measures; or
  4. the time passed since the incident.

20 Resourcing the offshore investigation should follow the principles described in paras 14 - 16 above.

21 Decisions as to any future Inspection of dutyholders’ measures taken to prevent recurrence should be recorded in the installation’s intervention plan.

Acting on the subsequent OIR12 Notification

22 When the IMT Team Leader receives information from OSD 3 on the severity of the release following submission of an OIR12, any past decisions on the investigation of the release should be reviewed. Where a full investigation has not been pursued offshore, so far, but the severity has now been classed as Major or Significant, the IMT Leader must decide if an offshore investigation is now a practical course of action. Alternatively, the IMT Leader is to arrange for an onshore investigation if one has not been carried out already (see paras 19 - 21). Depending on the time passed from the date of the release, new information acquired by Inspectors, the lack of a suitable dutyholder investigation, or lack of progress by the dutyholder implementing further preventive measures, the IMT Leader should not rule out pursuing a full offshore investigation and/or taking enforcement when it is appropriate to do so. This is particularly important where the release quantities equal or are above 25kg for gas or two phase fluid, or more than 250kg of liquid. If the IMT Team Leader decides that an offshore full investigation is warranted the resourcing of the investigation should follow the principles described in paras 14 - 16 above.

23 If a Major or Significant hydrocarbon release is not to be investigated for any reason, then the IMT Team Leader must seek formal approval from the relevant Operations Manager and the reasons carefully recorded on the DRF (see paras 17-18).

Incidents classed as non-mandatory investigations

24 Hydrocarbon releases categorised as Minor do not require mandatory investigation. However, IMT Team Leaders may choose to follow them up onshore or offshore at the next planned inspection to check how the dutyholder has responded to the incident. This may require assistance from Specialist Inspectors. The follow up visit will check how the dutyholder has investigated and responded to the incident.  Inspectors will assess the breadth, depth and suitability of the dutyholder’s own investigation, lessons learned and measures put in place to prevent recurrence. This type of intervention is classed as an inspection. Inspectors are to document their findings in their normal Inspection Reports. Depending on the time passed from the date of the release, new information acquired by Inspectors, the lack of a suitable dutyholder investigation, or lack of progress by the dutyholder implementing further preventive measures the IMT Leader should not rule out pursuing a full offshore investigation and or, taking enforcement when it is appropriate to do so.

Investigation Reports

25 For all offshore investigations inspectors are to complete an investigation full report,. It is important that the report records the immediate and underlying causes of the release based on the evidence collected, and have any relevant documents attached.

26 Reports should use the templates TRIM folder A copy of the completed report, and any other relevant documentation, should be forwarded by email to the IMT administrator.

COIN Recording

27 Releases that meet the mandatory investigation category (see paragraphs 8 - 12 above) must be recorded on COIN as such. If a release for which notification has been initially recorded as non-mandatory on COIN this must be changed to mandatory when the OIR12 notification and assessment by OSD3 categorises the severity as major or significant.

28 All investigation reports, DRFs are to be uploaded to COIN. Copies of dutyholder reports are not to be uploaded to COIN.

Analysis of Immediate and Underlying Causes

29 OSD’s Process Safety Team will review all OSD Investigation Reports to further analyse release causation: immediate and underlying. The conclusions will be published internally on a regular basis and will be used to inform the Process Safety Topic Strategy and other OSD interventions.

Release Quantity

30 Guidance on calculating release quantities is in the attached spreadsheet  ‘Offshore hydrocarbon releases - ready reckoner’. It includes user notes and a unit converter. To use it, more information may be required than is on the form OIR9, so it may be more effective to phone the offshore installation manager directly for an estimate of the release quantity.

31 Annex 1 contains additional guidance on estimating the severity of a release, in advance of severity being assigned by the process integrity team.

Further Information

Further information can be obtained from OSD 3.1 or OSD2.4.

Annex 1: Severity classification of major and significant hydrocarbon releases

This guidance is intended to help identify major and significant releases for investigation, if the form OIR/9b data is insufficient and the installation manager cannot give an adequate estimate. The additional data on the form OIR/12 may take some time to receive and process before a severity can be assigned, so this guidance may be used in an initial assessment. It is not a definitive guide to classification.

Investigation ready reckoner

The form OIR9/b may not provide data such as hole size, duration of release or operating pressure for the ready reckoner, but it may be possible to deduce it from the event description. Approximate operating pressures may be obtainable from the safety case or other references. For example:

Gas releases

Descriptions of gas releases that suggest the following are possible candidates for at least a significant classification:

Oil, condensate and non-process liquids

Descriptions of liquid releases that suggest the following are possible candidates for at least a significant classification:

Two-phase releases

Two-phase releases can vary from low gas/high oil to low oil/high gas, depending on the gas-to-oil ratio for the field and/or the location of the leak. Such releases may need to be modelled as predominantly liquid or predominantly gas releases. If the description of the event suggests that the release is largely liquid in nature, treat as for oil releases above. If the description suggests that the release has large quantities of gas, treat as for gas releases. 

Annex 2: HCR Incident Investigations

HSE definitions

1 HSE defines investigation as a reactive process which includes all those activities carried out in response to an incident or a complaint to:

2 An investigation may range from an enquiry by a single inspector about a minor incident or complaint to a large enquiry involving a team of inspectors.  Preliminarily enquiries asking for more information is not classed as an investigation.

3 HSE considers a dangerous occurrence with the potential for directly causing the death of anyone or major injuries to a number of people as a serious concern.  This reflects the view of the public at large and not just those of an individual(s).

4 HSE’s Enforcement Policy sets out the broad factors that it takes into account in selecting which incidents to investigate and the level of resource to be used. These include the:

5 Incidents and accidents have immediate and underlying causes. HSE defines these as:

6 HSE defines a major incident when events occur that require HSE’s attention and which meet either of the following criteria.

When HSE declares an offshore event to be a major incident, OSD’s Major Incident Response Plan will be evoked. This will change OSD’s initial response to the incident and some aspects of any subsequent investigation.

Scope and types of OSD investigations

7 For the purposes of this SPC and in the context of regulating a major hazard industry OSD’s hydrocarbon release policy has been framed in the context of HSE’s definitions and its Enforcement Policy quoted above.

8 In this SPC the term full investigation is used.  A full investigation is defined as an intervention where Inspectors pursue all reasonable lines of enquiry to establish what happened, identify immediate (or direct) and underlying (or root) causes, ensure steps are taken to prevent recurrence, assess how effective any emergency response arrangements put into effect were, and check compliance with relevant statutory provisions by:

9 Inspectors undertaking investigations are to make use of all relevant internal and external published information and advice or participation from Topic Specialists in pursuing lines of inquiry.

Published information includes such things as:

Topic Specialists team participation or advice from, but not limited to:

Using Analytical Investigative Methods (AIMs)

10 HSE’s policy on the use of AIMs in investigations is available on the intranet. In summary it says that AIMs should be used when investigating all potential major incidents (as defined by HSE) and fatal incident investigators. However, Inspectors should consider using AIMs in a full investigation even when the incident does not meet the minimum criteria of the policy. Such occasions are where the:

Updated 2016-06-30