Deep in thought

Paul Boughton

When a robust Process Safety Management (PSM) audit programme finds no issues, it does not always mean that improvements cannot be made. Conrad Ellison explains

The purpose of a Process Safety Management System (PSMS) is to provide a framework of high level procedures (or risk control systems), in order to maintain protective equipment and operations in a healthy state.

So, on face value a PSM audit, which shows year-on-year improvement, can be cause for celebration, but what if it is just an indication that performance has reached a plateau? A serious accident could be just around the corner. There are always more improvements that operators could be making to improve process safety performance even further.

Often, little thought is given as to whether the issues explored as part of the audit year after year are even the right ones. If not, you will not see improvements in the number of process safety incidents (PSIs). You are likely to find that leading process safety performance indicators are not consistent with the audit performance, and the lagging indicators are showing a worrying trend with the number of process safety incidents remaining the same or even increasing.

One limitation of PSM audits is that they are constructed around distinct generic elements, which are audited in turn without considering how they interact with each other. This potential interaction between barriers is often not visible at the PSM audit level. It’s likely that interactions are missed in accordance with the ‘Swiss Cheese Model’ of accident causation. This illustrates that although many layers or barriers of defence lie between hazards and accidents, there can be flaws in each layer, which when aligned can allow accidents to occur.

Why dive deeper?

With this in mind, auditing PSM system elements may not actually identify the potential for a process safety incident. Instead an assessment of specific accident scenarios and verification of specific barriers is required.

It’s for this reason that ABB Consulting advises opting for a Deep Dive audit as it can provide assurance that process safety is being managed appropriately.

This type of audit does not aim to replace conventional PSM audits but complement them. PSM audits are still needed to illustrate that the overall systems are being well managed. The Deep Dive audit just takes the process to the next level. It involves making major accident scenarios and their associated barriers the sole focus of the audit. This type of audit is designed to:

* Establish all major accident scenarios;

* Confirm the basis of safety (BoS) is robust;

* Check that the design of barriers allows for the required risk reduction and that they are installed correctly;

* Ensure barriers are appropriately maintained and tested; and

* Confirm workforce competency with barrier management.

A Deep Dive audit therefore provides rigorous assurance that each identified scenario has sufficient barriers which are working effectively. Essentially it provides an overview of the process safety ‘vital signs’ and ensures that best practice in management systems is being achieved.

What does a Deep Dive audit entail?

Stage 1 - Understanding: Hazard analysis reports such as HAZID and HAZOP reports must be reviewed to identify major accidents and the required barriers.

From this a range of high-risk scenarios for the detailed Deep Dive audit can be established. A broad range of event types need to be selected to enable the assessment of different types of prevention, control and mitigation barriers.

Stage 2 – Verification and field visit. Verification is then sought for the effective functioning of each scenario and its associated barriers. There are three foci to this stage: barrier verifications; processes and the people operating them.

Experience has shown that the best results can be obtained by deploying two process safety specialists as assessors; one with a PSMS and operations background and the other with a plant engineering and asset integrity management background.

It’s also important to tap into the knowledge of onsite process engineers, operating managers and maintenance engineers.This helps with the understanding of major accident scenarios and ensures that the audit team can efficiently locate key information.

An essential part of this process is conducting a field visit, which focuses on verifying specific barriers. To begin with, the barriers are visually checked to ensure that they are in good condition and have been installed as per design. We find photographs of any deficiencies are an excellent way of providing high-impact evidence to site management.

Following on from this are discussions about the barriers with operators and maintenance technicians. This tests their understanding of the potential for major accidents on the site and their role in maintaining the barriers. It can be an indication of complacency when you find that operators are unaware of the emergency procedures necessary for preventing the escalation of incidents.

Stage 3 – Reporting. The audit report provides details of the assessment for each barrier, along with a decision on whether the barrier is working effectively or whether a related weakness needs to be addressed. This could relate to the plant, processes or people involved.


A prime concern in process safety management is to prevent process incidents from occurring. Therefore it makes sense to devote some assurance effort directly to the scenarios themselves, focusing on the specific risks and layers of protection.

A Deep Dive audit of key process incident scenarios can be a very direct and cost-effective way to provide assurance that process safety is being managed appropriately. It complements traditional audit-based assurance processes and enhances an organisation’s process safety management audit and review program. That is not to suggest that auditing of the PSMS is not a necessary or effective tool. It just needs to be accompanied by an approach that takes process safety even further and provides operators with a high degree of confidence that barriers are working as effectively as possible.

Conrad Ellison is Principal Safety Consultant at ABB Consulting UK

Recent Issues