Industrial Accidents 2.1 Accidents
2.6 The Role of ‘Uncertainty’ and ‘Risk’
2.2 foresee the next incident, performance indicators assume a key role.
Examples of some methods related to the probability of occurrence (like the Fault Tree Analysis or the Event Tree Analysis) are described in Chapter , where the broad topic of the human factor effects is also discussed. Some of the hazard identification techniques (deeper described in Chapter ) are:
“What if” Analysis. It is the simplest technique, based on the repetitive question “What will happen if” a certain component or procedure related to the examined process does not work properly;
Hazard and Operability Analysis (HAZOP). It is a structured method to identify the hazards related to a process, analysing all the possible deviations from the normal operating conditions; and Failure Modes and Effects Analysis (FMEA). It is used to identify potential failures in equipment or system design, analysing the effects on their selves.
Qualitative techniques are used by the experienced team to evaluate the hazards of an existing technology, with documented long past experience. This book does not intend to discuss such qualitative approaches because differently from the above mentioned methods, they do not generally allow the conceptual link between risk
assessment and incident investigation.
In Chapter , the transition between two ways of understanding the world has been briefly mentioned referring to [50]. On the one hand, there is the deterministic approach, son of the scientific method where everything is rigorously obtained from logic processes in a complete and satisfactory way. It is the method of the time reversibility where the objects – intended as physical reality – are put in the centre of the reasoning. On the other hand, there is the probabilistic approach, son of the complex theory where certainties drop in favour of a likelihood of occurrence, of a limited knowledge because relations among objects are now preferred rather than their physical reality. As a consequence, the concept of “uncertainty” strongly imposes itself and leads to another important related concept: the one about “risk”. The risk can be defined as a measure of economic loss, human injury, or
environmental damage or reputation regarding both the incident likelihood and magnitude of the loss, injury, or damage. To establish
the likelihood, a frequency assessment is performed, while the definition of the magnitude requires consequence assessment. The consequence is the ultimate result of an initiating event, deviations or multiple deviations, intended as a change in a state beyond specified limits, conditions or status (whose boundaries are monitored by the performance indicators).
It is interesting to note how the perception of risks may be different from how they actually are [35]. Most people fear the trivial risks and underestimate the significant dangers of the everyday life. Probably, this happens because risk perception is driven by emotions, being the human response guided by survival. To have an idea, according to the United States Department of Labor (Bureau of Labor Statistics), it is safer to work in a US chemical plant than at a grocery store. Indeed, the chemical industry established excellent safety records in the last decade. It can be impressive to know how dangerous is to be a timber cutter, a fisher, or structural metal workers. In conclusion, the
approach to industrial risks requires an open mind, free from
prejudices. This is especially required to a forensic engineer, in order to carry out a correct investigation.
The risk acceptability is a criterion intimately connected to both the company policies and the compliance with the national laws and the technical standards recognised worldwide. Thus, different companies may accept or not the same risk, depending on their own managerial choices, even if a minimum level of risk acceptability comes from the compliance with standards.
The risk matrix is a great tool to have a graphical visualization of risks and their combination of magnitude and frequency (Figure 2.46).
It is particularly used when a semi quantitative risk analysis is performed. This type of analysis uses a numerical approach, which is typical of full quantitative risk assessment (discussed in Chapter ), together with simplifying and conservative assumptions regarding the consequence severity assessment, the frequency assessment of the initiating events, and the effectiveness of safeguards. The results of a semi quantitative risk analysis are generally expressed in orders of magnitude. However, a risk matrix is also generally used with a qualitative risk analysis, like in the example of Figure 2.46. Here,
both the probability and the severity are expressed in qualitative terms, that need to be evaluated from an experienced team to assign the proper risk level, given by the combination of a determined class of severity with a specific one for probability. Instead, in a semi
quantitative risk analysis, probability is usually expressed in occasion per year (yr−1) while the consequences are identified through a
progressive level from 1 (the less severe) to 5 (the most severe), depending on the severity of the foreseen consequence. In the
example, the black regions define the most severe risks. A risk in this region often requires the immediate stop of the industrial process, being absolutely not acceptable. The light grey area of the matrix
usually identifies a particular region where the risk could be accepted.
Risks in this region require an “As Low As Reasonably Practicable”
(ALARP) study. Briefly, it is a cost benefit analysis of the potential intervention required to mitigate the risk to the acceptable region.
Since the mitigation may require an economic effort which is not justified by the reduction of the risk category, a risk falling into the ALARP region may be accepted as such: managers will take the
accountability of this justified cost based choice. When performing an ALARP study, two key questions must be addressed:
Which alternatives are available for eliminating, reducing or managing the risk; and
which factors determine the practicability of each risk mitigation alternative.
Figure 2.46 Example of a risk matrix.
Source: Courtesy of CGE Risk Management Solutions (NL)).
Finally, the dark grey region regards the acceptable risks, so no further mitigation or ALARP study is required.
Risk mitigation is possible thanks to the Individual Protection Layers (IPLs). They are instrumented safety functions, or mechanical devices, or administrative controls that guarantee whether a reduction of the frequency of occurrence or a decrease in the level of severity of the event.
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