Everyone working in the chemical industry will probably avoid talking about associated risks simply because it scares people. After all, no one likes to be reminded about a potentially negative outcome of a process.
While we love to discuss opportunities to obtain a profit, maybe even gamble a bit on winning a lottery, our mind somehow seems to reject focussing on potential losses. Due to this mechanism, the concept of risks is poorly understood.
Unfortunately, this is a side of the bargain that we should also consider, and it is one of the main reasons to perform safety studies. We simply need a “number” or a “value” to be able to judge acceptability. Yes, we can make a profit by producing a chemical, but what will be the potential loss for us if an accident happens?
For that reason, we introduce risk as the probability of a negative outcome, where several safety-related criteria have been established. To provide some insights on safety, we should try to answer: “What can go wrong?”, “What are the consequences?” and “What are the risks?”.
Introducing the Coloured Books: Consequence and Risk Analysis
We have illustrated the required steps in the scheme below, and fortunately, there are standard guidelines available for every step in the so-called Coloured Books.
Consequence Analysis
The left block of this scheme is commonly called consequence analysis and consists of three steps leading to the determination of CONSEQUENCES belonging to potential accident scenarios. We can use techniques such as HAZID (HAZard Identification), HAZOP (HAZard and OPerability Study), or FMEA (Failure Modes and Effects Analysis) to identify essential and critical accident scenarios typically described as “Loss of Containment” scenarios.
Once we know what might go wrong, we need to evaluate the resulting phenomena of the potential release of hazardous material. Can we have a fireball, a vapour cloud explosion, or a toxic cloud? And if this happens, what distances will be reached?
The Yellow Book describes methods that can be used to determine these effects. As a next step, the Green Book describes methods to translate physical effects like heat radiation, overpressure levels or toxic exposure to resulting damage in terms of destruction level, injuries or lethality. These highly relevant steps of evaluating the consequences of potential accidents have all been incorporated within the Gexcon EFFECTS software.
Risk Analysis
Once we know what an accident might cause, it is equally relevant to derive the associated risk. In this case, risk is translated to “Chance x Consequences”. We need to subsequently define the chance of an accident happening (e.g., how often can we have a leak), the chance of an exposure happening (e.g., the chance that a flammable cloud reaches a nearby installation) and the chance of damage occurring (e.g., the chance that we will have 50% lethality due to radiation levels). This allows putting a risk number to a specific level of damage. For instance: What is the risk of escalation to other equipment? What is the risk of dying at that location? Or, what is the risk of many people getting injured? These risks are typically expressed as a “chance” of having this specified degree of damage. To give an example: for “lethality” we hope to reach a range of “once in a million years”.
While internal safety studies might focus risk of “onsite risk” (i.e., the chance of having product losses, production capacity losses or escalation risks), typical governmental regulatory requirements often focus on “external risk”. They might require expressing an “Individual Risk” (also known as LSIR Location Specific Individual Risk), the chance of people dying when located at a specific location in proximity to dangerous activities. Some countries use criteria like “Societal Risk”, which expresses the chance of having an accident leading to a certain number of victims.
Risk analysis helps us identify high-impact, low-probability from low impact, high probability types of accidents because it tells us how often we might expect a specific level of damage. Such risk evaluations are often presented in a risk matrix. The Societal Risk criterium which uses a Frequency vs Number of victims, is nothing more than a typical risk matrix approach to be able to judge impact (see figure below).
Introducing Gexcon RISKCURVES
Gexcon's RISKCURVES tool, which combines the consequence models of EFFECTS with a complete risk calculation tool, is specifically designed to derive criteria like “Individual Risk”, “Escalation Risk” or “Societal Risk”. It is based upon Purple book methodology, allowing us to perform a full Quantitative Risk Assessment (QRA) for all potential accident scenarios that might occur on a chemical site.
