Breaking Conventional Thinking: Hazard Study Selection
1 August 2023 | Hazard Analysis
The decision-making process that precedes process safety hazard studies is an important step in the overall process. Typically, a project-driven stage-gate approach is used, where a Hazard Identification (HAZID) study is performed before a Hazard and Operability (HAZOP) study. This approach is widely accepted and provides a logical structure for the process. This stage-gate approach may be widely accepted, but it is not the only approach. Other decision-making processes may provide a more effective approach to process safety hazard studies and selection is highly dependent upon the wider context. This article is focused upon HAZID and looks further at selection criteria with examples of where breaking conventional thinking, and altering our approach, could be beneficial provided that specific studies are not mandated by legislation.
Conventional Thinking – Hazard Study 2 (HAZID) and Hazard Study 3 (HAZOP)
There are a range of questions often asked about HAZID and HAZOP centred around what each study is, how to perform them, when they should be used, and even which study is better. Stock answers will refer to the 6-stage hazard study process where HAZID is the quick, low detailed, early-stage study designed to quickly identify issues before they become costly problems. HAZOP, on the other hand, is more detailed, deals with complex plants and processes well and is performed later in the project. While these answers hold validity, adhering faithfully to them will limit other alternatives and the key to understanding this is found in one of the questions typically asked.
HAZID or HAZOP – Which is better?
This is like asking which tool is better for a job, a hammer, or a screwdriver? Just like a craftsperson, the type of tool you choose will depend on the situation. The same goes for selecting a technique to perform a hazard assessment. The best option will depend on the context and goals of the assessment and a competent professional would decide, taking into consideration the most suitable tool for the job. All such decisions come back to the same basic question – why are we performing the study in the first place?
Study selection, risk management and the wider context.
Hazard studies are performed to identify the hazards in which a qualitative or quantitative risk assessment can then be performed on. Once the risk is assessed, adequate measures are put in place. At a macro level however, risk assessment and risk management need to be understood more broadly and in the context of the whole site or organisation. Effective study selection is dependent upon a range of factors such as.
- Is this an existing plant and if so, what hazard studies are already present?
- Is this a new project and, if so, what stage is it at, how complex is the system and is the technology well understood?
- Resourcing – do we take all plants and processes through to a full HAZOP or do some not warrant it?
- How mature is the organisations existing risk assessment and management systems?
Are greater benefits derived from across-the-board improvements or from specific and highly focussed improvements?
Consider the following examples.
Hazard Study selection – a simple bulk storage tank.
A project is initiated to install a single bulk storage tank within a bunded area which will contain flammable materials and vents direct to atmosphere. It will be filled from road tanker and the storage tank will contain a pump to transfer to a process area. A standard project approach would see us conduct a low detail HAZID study followed by a HAZOP study on the detailed design. The HAZID guide words would include the following (not exhaustive):
- External Fire
- Internal Explosion
- Vapour Cloud Explosion
- Acute Exposure
- Noise
The HAZID methodology, however, does not need to be low in detail and can be easily modified to a hybrid approach by including some additional guidewords. In this instance, it would be possible to create a HAZID study which is also a suitable and sufficient qualitative risk assessment without the need to conduct an additional HAZOP. This resource efficiency frees up time for the completion of actions and leads to a “real world” reduction of risk – an activity which is so often performed poorly.
The only real objection to this hybrid approach could be that the study would need to be conducted when more detail was available, thus removing the advantage of early identification of issues. This is easily countered by the fact that a simple, well understood, and codified design is unlikely to yield such surprises. On balance, the benefits would seem to outweigh the negatives in this instance.
Hazard Study selection – a complex bulk storage tank.
Now, let’s consider the case of an existing bulk storage tank that is heated and agitated, with vents into a common vent header and liquid inlets via a common manifold and various filling sources. Conventionally, HAZOP would be the technique of choice for a situation like this, but it may be wise to consider the bigger picture. What if the site had an incomplete set of hazard studies or they were of a poor quality? Or if the company is at the beginning of a process safety management journey with likely significant gaps in safeguards and compliance?
A HAZID study applied across the multiple systems and areas could quickly find the common issues and generate actions that would have a much larger, and more immediate benefit. For example, if asset integrity management of pipework or hoses is inadequate or missing, it’s probably a common issue across the entire site and not just on a specific plant or process. So, while the extra detail of a HAZOP will be needed at some point, the breadth of a HAZID study would be the faster and more effective way to reduce the site risk at this specific moment in time.
