November 2015

Process Safety Analysis versus HAZOP

Colin McWhirr

Colin McWhirr

Operators are facing costly and time consuming production and regulatory challenges that require a clever approach to managing technical safety and risk.

2015 has seen a shift change in attitudes and actions across the oil and gas industry as the oil price crash forced unprecedented ‘belt-tightening’ across all aspects of the sector. With the quandary of low barrel price and spiralling lifting costs likely to continue for some time, there is a mounting need to re-examine risk management approaches to avoid complacency and cut backs in this crucial area.

Oil and gas production facilities are inherently highly hazardous. The critical element in any risk management process is the prevention of loss of hydrocarbon containment or equipment damage given the outage and capital costs, and the escalation consequences of energy release. Through its evolution, the oil and gas industry has developed a number of methodologies and processes to analyse, assess and ultimately improve process safety offshore to assure the robustness of the process plant and its personnel.

As part of a facility’s five yearly Safety Case Thorough Review process, the Process Hazard and Operability Study (HAZOP) is the predominantly used process safety assurance technique in the United Kingdom Continental Shelf (UKCS). It is one of the most widely used hazard identification methods and has found applications in many aspects of the offshore industry.

By dividing each process system or operation into nodes, this is a highly structured and systematic examination to identify all potential 'deviations from design intent'.

It also assesses the resulting impacts on Personal, Environment, Asset and Reputation (PEAR). These studies can typically take around four to six months to complete for a single offshore facility.

A targeted, time-saving approach
Developed by Xodus, Process Safety Analysis (PSA), on the other hand, is a more focussed and time-effective approach and is applied to the process design integrity of existing assets to identify credible loss of containment or release of energy scenarios. The outcome of such analysis is to fully understand the consequences and the need for remedial measures. It takes into account real operational experience, including any variations from design intent and reviews each process system in the plant (i.e. separation, compression, etc.) in sequence. The review can also be used to identify significant asset damage/production outage threats. The intent is to focus on major accident hazards or major asset impacts only, with less focus on operability.

Though the PSA process delivers the same worksheet output as HAZOP, the main difference is that PSA uses coarser nodes than full detailed design HAZOP – i.e. a production separator system is reviewed as a complete element rather than sub dividing into five or six nodes. The HAZOP process uses deviation guidewords such as No Flow, More Flow, Less Flow, Reverse Flow, More Pressure etc., whereas the PSA starts with a hazard issue or hazard condition which is selected from a process hazard checklist.

The PSA uses detailed hazard checklists which have been derived from many years of HAZOP study and are tailored to the type of system being scrutinised. Developed by Xodus HAZOP chairs – most of whom have more than 30 years of HAZOP chairing experience – these checklists help to condense out the typical issues experienced with the various types of offshore systems. They have also been developed and extended to give guidance and best industry practise on the optimal way to manage the specific hazards and standard LOPA (Layers of Protection Analysis) templates have been prepared in response to this.

This is an important development in offshore process safety design guidance and is beneficial for engineers to improve their understanding of the process hazards associated with typical process plant offshore and the best way to mitigate these hazards. At present, guidance and international codes of practice such as API 14C (a recommended practice for analysis, design, installation and testing basic surface safety systems on offshore platforms) are limited in this area.

Smarter working for improved safety
The main factor which supports the PSA approach is that offshore plant is relatively simple and the design arrangements and configurations between platforms are by and large the same. If a facility had a unique design configuration, the PSA would recommend that section be subject to traditional HAZOP scrutiny. Similarly, PSA is not appropriate for midstream and downstream plant due to their increased process complexity.

Implementing a PSA approach can deliver significant time and financial savings as the majority of significant process hazard issues can be identified and assessed in around three workshop days for a typical large UKCS offshore facility.

This is opposed to between 40 to 60 days for a full detailed design re-HAZOP. Though PSAs require greater preparation time, usually between 10 and 15 days of the chair’s time as opposed to five days for a HAZOP, this is still around a third of the chair’s resource commitment needed for a full process HAZOP study.

The PSA therefore offers clear pragmatic benefits to operators to achieve a robust process safety assessment at a minimal cost, resource and schedule impact. Though this approach has been adopted by a number of operators in the UKCS, the uptake has been limited due to lack of familiarity and understanding.

It is a hard fact that risk management does have a price. In this era of cost containment, industry leaders and decision makers must look at working more effectively and efficiently to ensure that the best process delivers the best results. The industry must continue to review and scrutinise its own procedures to ensure these are robust and economic whilst still maintaining the safety of its invaluable workforce.