Streamlining the regulatory journey for offshore oil and gas decommissioning

HSE info

Decommissioning and dismantlement, the final stages of an asset’s natural lifecycle, bring with them a number of challenges for both Duty Holder and Regulator. The following information aims to provide an insight into the health and safety regulatory requirements for these activities. This information does NOT replace statutory guidance and Duty holders should ensure they are aware of the regulatory obligations associated with their activities.

Health and safety regulations which are applicable will be dependent on the size and complexity of the decommissioning and dismantlement project being undertaken. For this reason, early engagement is key for both parties to ensure the duty holder fully understands compliance expectations and can plan their work accordingly.

All contact with the HSE in relation to decommissioning should go via the appointed Focal Point Inspector (relevant to current Operators). Where a company does not have an appointed Focal Point Inspector then they may use this or the HSE website to contact the Offshore Decommissioning Team.


Health and safety associated with decommissioning and dismantling offshore Oil & Gas installations is regulated by the HSE as part of the Offshore Safety Directive Regulator (OSDR). The competent authority is a partnership between the Health and Safety Executive (HSE) and the Offshore Petroleum Regulator for Environment and Decommissioning (OPRED).

Offshore safety is regulated via a suite of offshore specific major accident regulations underpinned by the Health and Safety at Work etc. Act 1974 and its relevant statutory instruments. The Application Outside Great Britain Order extends these obligations to offshore oil & gas operations within the UK Continental Shelf (UKCS).

Health and Safety within offshore oil & gas activities are regulated as part of a permissioning regime and as such every installation operating within the (UKCS) is required to have an accepted safety case. Operators must literally make a “case for safety” which is assessed and accepted. The safety case must provide an adequate demonstration of the duty holder’s arrangements for identifying and managing the risks arising from their planned activities. The safety case should demonstrate to owners, workers and the regulator that the duty holder has the ability and means to manage and control major accident hazards (MAH) effectively.

The installation safety case must be submitted to, assessed and accepted by the competent authority before the installation can be operated. The safety case then remains in place throughout the lifecycle of the asset until it ceases to be an installation as defined in Regulation 3 of the Offshore Installations and Pipeline Works (Management and Administration) Regulations 1995 (MAR). In simple terms the safety case remains in place from first oil until final cut and lift.

The Offshore Installations (Offshore Safety Directive) (Safety Case etc) Regulations 2015 (SCR2015) detail the mandatory contents of an offshore safety case.

Late Life and Preparation for Decom Activities
As an installation transitions towards decommissioning and dismantlement, Regulation 24 of SCR2015 requires the accepted safety case to be continually updated to ensure that it reflects the current state of the installation and its operations. Significant updates, either physical modifications and/or operational management changes that change the basis on which the original case was accepted would likely be seen as a material change to the safety case.

If a revision to the safety case is considered to be a material change then the updated case must be submitted to the competent authority for assessment and acceptance. There are a number of criteria which may trigger a material change - during late life operations duty holders should ensure they understand these criteria in the context of the decommissioning and dismantling work they plan to undertake and how this will be managed to ensure compliance with the safety case process

Paragraphs 287-298 inclusive of SCR2015 guidance document (L154) provide further detail on material changes to a safety case.

The duty holder must decide how they plan to manage their case through their decommissioning and dismantlement journey. HSE require a clear transition from an operational safety case to a dismantling safety case. This can be done via one, or a number of, material changes that detail how late life operations and decommissioning work will be undertaken and lead through into the dismantling safety case submission. Alternatively, the duty holder may choose to go directly to a dismantling safety case. The complexity of each installation and the associated work scope will likely influence which approach is more appropriate.

Duty holders should recognise that long term complex work scopes may change as the project develops thus making an adequate safety case demonstration in a single submission very challenging. It should be noted that variations from the work scope as detailed in the accepted safety case may require an unplanned material change submission that can lead to a project delay. For this reason there is merit in approaching safety case submissions on a phased basis.

Duty holders should consider identifying key project milestones / phases of work and align material change submissions to mirror these key phases. Such a phased approach would enable the duty holder to plan decommissioning activities in a structured fashion and identify all work which may trigger a material change whilst the work is still in the planning stage, which in turn enables more effective and efficient safety case management.
An early stage strategic overview meeting between the HSE and duty holder will make this process easier. A timeline document to indicate how they plan to manage material change submissions and the extent of activities to be covered in each submission would help understand how each work phase interacts with the next. This information will encourage the duty holder to fully consider which activities will be covered by each submission and will enable the HSE to plan for assessment.


Well Plug and Abandonment
Once an installation has ceased production the wells will need to be plugged and abandoned to prevent any uncontrolled release of hydrocarbons into the environment. Plug and abandonment of wells is a specialised activity and regulated by the Wells group within HSEs Energy Division. Guidance and requirements for well notifications and how wells are regulated by OSDR can be found here:


Cleaning and Making Safe
Once an installation has ceased production it will need to be cleaned, made safe and engineered down before main dismantlement activities commence. Duty holders should ensure that any safety case submissions made during this phase of work clearly demonstrate how hydrocarbons in the topsides, pipework and risers will be managed through the decommissioning process. Consideration should be given to drain down, flushing, purging and isolation arrangements and the potential for unintended hydrocarbon release during these activities.

Currently there is no industry agreed definition of what constitutes hydrocarbon free. Duty holders must demonstrate that they have given due consideration to potential levels of hydrocarbons that may be left after flushing and purging activities to ensure the risks during subsequent decommissioning or dismantling activities, e.g. hot working, are ALARP. The Dutyholder should also detail their definition of hydrocarbon free and how attainment of this status will be demonstrated, for example - certification by an Independent Competent Person (ICP).

As an installation is cleaned and the hydrocarbon inventory reduced, the major accident profile will also change. It is important that duty holders recognise that being hydrocarbon free does not mean an installation is major accident free and attention should be given to the remaining major accident risks. It should be recognized that, although a platform may be hydrocarbon free, there may be a rise in other major accident scenarios as a result of the planned scope of work eg increased helicopter activity or an increased collision risk due to greater marine activity.

As the MAH profile changes the duty holder should review the relevance of Safety and Environmental Critical Elements (SECEs) regularly in cooperation with the Independent Competent Person (ICP) and the verification scheme. During this decommissioning phase SECEs will change or be retired altogether. Changes to the major accident hazards, SECEs and performance standards need to be documented and included within the safety case for assessment as part of any material change submission.

Material change submissions must demonstrate a link with the existing safety case and that changes to major accident scenarios, mitigation measures, SECEs etc. are appropriate. Material change submissions which cover the downgrading or removal of safety systems must adequately explain why a reduction in protection standards is acceptable – failure to do so may lead to an extended assessment process. SCR2015 Regulation 16 covers management and control of major accident hazards and further guidance on what should be included in an adequate demonstration is given in paragraphs 210-222 of associated guidance document L154.

Duty holders may choose to undertake large scale decommissioning work themselves, subcontract and manage a number of third party contractors or they may opt for a hands-off turnkey approach which sees the duty holder engage an independent consortium to provide a complete decommissioning service. Irrespective of how the work is being carried out HSE would usually expect a number of material changes to the existing safety case to cover the change of status through to submission of a dismantling safety case.

Clear, early and frequent engagement between duty holder and regulator will ensure issues are identified and that the regulators can involve relevant topic specialists at an early stage if appropriate. Earlier engagement will lead to a better understanding between regulator and duty holder and as a result a smoother assessment process.


Offshore Dismantlement and Removal
Dismantlement of a fixed installation will usually take one of three forms – piece small, reverse installation / modular removal or single lift. Regulation 20 of SCR2015 talks of a specific dismantling safety case. In practice this is simply a final revision of the existing safety case to cover dismantling activities and the specific major accident hazards and risks involved. This submission can accommodate final dismantlement methods on-board the installation and those undertaken from separate attendant vessels or installations.

Regardless of the chosen method, final dismantlement and associated preparations are considered to be connected activities as defined in SCR2015 Regulation 16 and Article 4 of the Health and Safety at Work etc Act 1974 (Application Outside Great Britain) Order 2013. As such the duty holder is required to account for that activity in the safety case to ensure that all the relevant MAHs have been identified, explicitly described and suitable mitigation presented to enable assessment of the case. Equally, although specialist contractors will likely be used for this work the legal responsibility lies with the Dutyholder and they should assure themselves that adequate control measures remain in place for each stage of the work.

In order for this process to begin a dismantlement safety case must be submitted and accepted by OSDR as the competent authority. The case must fully detail the intended dismantlement and removal method and provide timescales for the operations to be undertaken.

The specific requirements needed to address pipeline aspects in an offshore safety case are given in the pipelines safety case assessment template. Guidance regarding offshore pipelines and how they are regulated can be found here:

Again, as with other aspects of the decommissioning and dismantlement journey, early engagement between the duty holder and regulator will enable any possible issues to be identified and resolved on a timeous basis.


Onshore Dismantling and Removal
The onshore stage of decommissioning may be undertaken at one of the UK decommissioning receiving bases. Upon receipt into a decommissioning receiving base it becomes the regulatory responsibility of HSE’s onshore Divisions. It is likely that installations brought onshore in one piece or large modular sections would meet the definition of a structure and that the Construction Design Management (CDM) Regulations may therefore apply, those brought in piece small would likely be classified as waste. Where UK facilities are to be used then Operators will benefit from speaking to appointed onshore Inspectors to ensure compliance expectations are understood prior to landing. Onshore Inspectors can be accessed via the Offshore Decommissioning Team in the first instance.


Other Links and Resources
Details of applicable offshore legislation and associated guidance can be found here: