The Process Safety Professional. Process Safety Fundamentals (Part 3)

We are working on the book The Process Safety Professional. The current Table of Contents is available here. We are gradually releasing the contents of the book to paid subscribers. This is the fourth release. The topic is ‘Risk’.

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Risk Analysis

Process Safety Management involves an understanding of risk, and determining what levels of risk are acceptable in different situations. Risk analysis is challenging because risk is itself both objective and subjective.

Components of Risk

Risk, which always implies some type of negative outcome, is made up of three components: hazards, consequences and predicted frequency.

A hazard is a situation that has the potential to cause harm or loss. When climbing a ladder, the hazard is falling off the ladder. On a process facility, a hazard could be ‘Tank T-101 Overflows’.

Each hazard has consequences — safety, environmental and economic. If someone falls off a ladder the consequence could be severe injury, or even death. If a chemical storage tank overflows, the consequences could be safety (fire or exposure to toxic fumes), environmental and economic.

Each hazard also has a predicted frequency of occurrence (not probability). In the case of the ladder, someone may fall off it say once in a thousand uses; the predicted frequency of tank overflow could be say once every twenty years.

These three terms can be combined as shown in Equation (2.1).

Risk(Hazard) = Consequence * Predicted Frequency (2.1)

Equation (2.1) shows that risk can never be zero — a truth not always grasped by members of the general public or the news media. Hazards are always present within all industrial facilities. Those hazards always have undesirable consequences, and their likelihood of occurrence is always greater than zero. The consequence and likelihood terms can be reduced in size, but they can never be eliminated. The only way to achieve a truly risk-free operation is to remove the hazards altogether (or, with respect to safety, to remove personnel from the site).