What is risk?

Definition

Risk in the field of safety refers to the likelihood and severity of hazardous events that can cause harm to people, the environment, or property due to the processing or handling of hazardous substances. These risks are typically associated with chemical plants, refineries, and other industrial processes with the potential for large-scale accidents or catastrophic failures.

When discussing the accidental release of hazardous chemical substances, risk typically refers to the probability of fatal injury due to exposure to the release of a hazardous chemical substance. It is a value that we can quantify (e.g. 10^-6 /year). Within RISKCURVES, this is the most common definition. However, risk can also encompass other aspects, such as the probability of non-lethal damage, operational issues, or environmental pollution, which can also be calculated and expressed after a Quantitative Risk Assessment (QRA).

Components of risk

Risk is quantitatively defined as the product of the probability of an event occurring and the consequences of that event. This can be expressed as:

This formula highlights that both the likelihood of an event and its potential severity are crucial for assessing risk.

Chance​

Chance is a combination of failure frequency and probability damage​.

Failure frequency of the incident​:

• Base failure frequency is the number of failure events per unit time.

• For one point release, it is expressed per unit of time (e.g., per year or per million years) [1/year]​. Example: 1 release every 10,000 years is the same as  1·10^-4 releases per year.

• For transportation routes it is expressed per unit of length and time [1/(km∙year)]​. Example: the number of releases over a 1 km natural gas pipeline every 10,000 years.​

Probabilities:

It is always a number between 0 and 1 (no units). Examples include probability of various effects such as:

• Exposure (wind direction, statistics)​

• Negative health effects (lethal injury)​

• Weather conditions (statistics)​

• Environmental conditions (temperature, solar radiation)​

• Direct or delayed ignition, BLEVE fraction. etc.​

• Protection (shelter and evacuation)​

• Damage (Probit function)​

• Presence of people (population data)​

Effect​

The “lethality effects” are the consequences of an undesired outcome. Software tools such as EFFECTS or FLACS can provide valuable assistance in this analysis, helping to quantify the potential impact of hazardous events.

By understanding and calculating risk, chance and effect, organizations can better assess and manage the potential dangers associated with the handling and processing of hazardous substances.