Created on August 7, 2014

It’s been quite sometimes that I am not sharing something related with Process Safety Management. So, today I’ll write a bit about it… just for the purpose of sharing. I am sure, many of you are master about it so please take it as refresher and please feel free to add something to it. For you who is new to this subject, you may find it useful.

I am quoting it from the PSM book that I am now preparing with the help and contributions from some other LebSolution consultants. The book is planned to be launched in a complete set sometime in late 2015. It is about approaches that are commonly used by many people in the industry when we start talking about process safety.

The two approaches commonly used in approaching the topics to be discussed, are: “Two Lenses Concept” and “Swiss Cheese Models”. These two approaches are used to give us a better but simpler way in understanding “process safety” and its management. And today, we will talk about the later one, “Swiss Cheese Models”. We will talk about the first one in another opportunity.

Following some past major incidents, James T. Reason, a professor of psychology from University of Manchester, in 1990 introduced a new conceptual model in analyzing the incident causations, called “Swiss Cheese Model” in his book titled as “The Contribution of Latent Human Failures to the Breakdown of Complex Systems”. The model analyzes causes of systematic failures or accidents. It describes accident causation as a series of events which must occur in a specific order and manner for an accident to occur, which it compares to the holes of some unique pieces of Swiss cheese lining up as shown in the below figure.

This model is represented by Christopher Hart (2003) as a set of spinning disks with variable size holes, suggesting that relationship between hazard & barriers is dynamic, with the size and type of weakness in each barrier constantly changing, and alignment of the holes constantly shifting.

The prevention and mitigation barriers (protection layers) can be in the form of “Human, Facilities, Business Process, Procedure, Software, etc”. “Human” is one of the most important protection layers because it always exists in any other layers. In some cases, when other protection layer is not effective, the “human” factor of that layer will make it works. While in some other cases, the “human” factor can make a good conditioned protection layer becomes not-effective.

In the context of Process Safety Management, the following approach are applied:

  • The hazards can be flammability, explosivity, toxicity, reactivity, etc of the materials or energies being handled.
  • The undesired events can be loss of primary containment (leaks, etc).
  • The consequence can be injury or casualty to people (employee contractors, communities), damaged to environment, loss of asset, and degraded company reputation.
  • The prevention and mitigation barriers, which if happened to be effective, then process safety incident is unlikely to happen.


Swiss Cheese Model in Our Daily Life

It may be better to understand principle of the Swiss Cheese Model by applying it to one of our daily activities. The below figure shows the result of Swiss Cheese Model application into “Safe Driving” activities which is self-explanatory.

One important barrier in the context of “safe driving” is the “braking systems & turning lights”. Do you want to drive your car without braking system? I am sure we don’t. This car braking system is equivalent to the Emergency Shutdown System in our industry, and the turning light is equivalent to the alarms appear in the control room.

But, why many of us still take for granted existences of ESD and Alarm system in our plant?
Why still so many critical safety devices are left in NOT ACTIVE condition either purposely or un-purposely? And
Why many of us still acknowledge critical alarm in our console without even look at it?

Key Message:

Understand your hazards and your protection barriers, and make sure it is sufficient, active and effective to protect you, your colleagues, your family, and your community.



Lukmanul Hakim


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