Industrial Accidents 2.1 Accidents
2.3 Process Safety
2.3.1 Management of Safety
In recent decades, the quality management programs changed
substantially, continuously improving themselves. Many companies applied the same emphasis to process safety management, being aware that a stationary strategy would have been dangerous, badly affecting performance and global competitiveness, not reaching the full satisfaction of the society's safety expectations. This is the moment where companies raised the bar, in a proactive approach about how to learn from experience. But this kind of strategy actually also fails if performance indicators, named lagging indicators, are low frequency and high consequence past events. This leads to the currently most used risk based process safety management. In this approach, companies continue to be compliant, adherent to well established technical standards, valorise their experience applying the lessons learnt, and continue using the lagging indicators. What makes the difference in a risk based process safety management is the use of leading indicators. In other words, independently of any loss events, risk information is used to predict the performance, in a full
prevention based approach. The adoption of this strategy requires an accurate understanding of the risks, a proper selection of the
performance indicators, an adequate discipline to monitor them, a developed organization integrity to review performance, and a powerful and flexible management system, capable of applying the corrections suggested by the predictive metrics. It is a performance based approach, in opposition to the prescriptive one. A risk based process safety management simply answers the following questions:
What can be wrong? (Hazard identification);
how bad could it be? (Consequence evaluation); and how often might it happen? (Frequency evaluation).
Understanding hazards and risks, managing them, and learning from experience are three important pillars of a risk based process safety, but a fourth one needs to be introduced: commitment to process safety. Commitment to process safety, as reminded by [34] and [12], means:
Developing and sustaining a Process Safety Culture;
identifying, understanding and being compliant with standards;
constantly improving the managerial skills and competencies; and ensuring an adequate workforce and stakeholders involvement.
It is difficult to define uniquely what Process Safety Culture is. A useful definition is given by [34]: “the combination of a group of values and behaviors that determine the manner in which process safety is
managed”. The best way to ensure a successful Process Safety Culture is to apply the requirements of conventional safety culture, since the two topics share many concepts. The topic is extensive, thus the interested reader is invited to consult the references cited in this Paragraph together with the suggested further readings, to study in depth this pillar of Process Safety. For the scope of this book, it is sufficient to present the key principles that should be addressed when developing, evaluating, or improving a management system and its Process Safety Culture:
Maintain a dependable practice. It means that the implementation of good practice is ensured over time. It generally requires strong leadership, establishing process safety as a core value, written procedures and documents, establishing high performance goals;
develop a sound culture and implement it. It means that the organization should maintain a sense of vulnerability and be
modest with respect to its capability of managing risk. An open and effective communication must be ensured, together with a constant training for both groups and individuals. A questioning and
learning environment, mutual trust, and a prompt response to process safety issues are also other important elements; and guide and monitor the culture, continuously monitoring the performances.
Learning from case histories is a good option to gain an immediate outline about process safety and how it reflects on both daily activities and unwanted incidents. [35] and [12] show many examples of
chemical process safety incidents. The attention to Process Safety is quite recent, as Figure 2.23 shows. Similarly, the evolution of the
safety culture is shown in Figure 2.24. Today, industrial accident analysis, strongly based on the Process Safety concepts, has widely accepted the Swiss Cheese Model by Reason, whose details are discussed in Chapter .
Figure 2.23 Contributing factors in improving loss prevention performance in the process industry.
Source: Adapted from [1]. Reproduced with permission.
Figure 2.24 The evolution of safety culture.
Source: Adapted from [36]. Reproduced with permission of Fiorentin.
Dealing with process safety also requires a multidisciplinary approach:
mechanics, physics, chemistry, metallurgy, industrial process
engineering, and thermodynamics are only some of the main topics that a process safety engineer handles on a daily basis. The required approach is an important link with the attitude and the skills that a forensic engineer spends when dealing with industrial accidents. This point of contact is crucial since it shows a first connection between the context of the process industry and the forensic discipline. Following this observation, some of the main important arguments related to the
“process safety” are now presented. The approach used is by choice a smooth path.
Plants and units of an industrial company are equipped with the Basic Process Control System (BPCS). It consists of all instrumentation, including the Distributed Control System (DCS), for process
measurement, display, and regulation installed to support normal process operations. The DCS does not perform any safety
instrumented functions with a claimed Safety Integrity Level (SIL) ≥ 1 (this concept will be discussed in depth in Chapter , where the Layer Of Protection Analysis is introduced). The DCS is a computer based control system which divides process control functions (display, control, communication and data storage) into discrete subsystems interconnected by communication channels (data highways). The SIL indicates the degree of risk reduction allocated to a Safety
Instrumented Function (SIF): they range from 1 (lowest integrity) to 3 (highest integrity). A SIF is an instrumented function with a specified Safety Integrity Level (SIL) necessary to achieve Functional Safety, i.e.
part of the overall safety related to the process and the Basic Process Control System, which depends on the correct functioning of the
Safety Instrumented System (SIS) and other protection layers. Finally, an SIS is an instrumented system used to implement one or more Safety Instrumented Functions. An SIS is composed of any
combination of sensors, Logic Solvers, and Final Elements. The Logic Solver is that portion of either a BPCS or SIS that performs one or more predefined functions as a result of the condition of the input
data. The logic solver may be pneumatic, hydraulic, electrical,
electronic or programmable electronic. Sensors and Final Elements are not part of the logic solver. Indeed, the Final Element is the part of an SIS that implements the required physical action to achieve a safe state. Simple examples are on off type valves and motor control
starters. An automated instrumentation system or subsystem that performs a discrete action in response to Process Variables (i.e. a measured characteristic of a process such as pressure, temperature, flow, level or concentration) or physical conditions outside a
prescribed limit is named Interlock. The affected device shall stay in the safe state until the condition which caused the action is corrected.
An interlock may be designated to prevent hazards related to safety, environmental, asset protection/mechanical integrity or product quality excursion and may protect against one or more hazards (i.e. a chemical or physical characteristic that has the potential to harm people, property, or the environment).
A simple way to indicate the general flow of plant processes is the
Block Flow Diagram (BFD). It is a schematic representation of the flow process through blocks. An example is shown in Figure 2.25. To have a first reference to the associated equipment, the Process Flow Diagram, also known as Process Flow Sheet (PFS), is consulted. It is a diagram commonly used in the process engineering that displays the
relationships among major equipment of a plant facility. Figure 2.26 shows an example. Major information, like pipings and designations, are shown in the Piping and Instrumentation Diagram (P&ID), a detailed diagram where the piping and all the items in the process flow, together with the instrumentation and control devices, are shown. An example is in Figure 2.27.
Figure 2.25 Example of BFD for the production of benzene by the HydroDeAlkylation of toluene (HDA).
Figure 2.26 Example of PFS for the manufacture of benzene by Had.
Figure 2.27 Example of P&ID for the production of benzene by Had.
Process Hazard Analysis (PHA) is one of the available tools to identify, analyse and control the industrial hazards. Its results can be seen as an organised effort to face the consequences associated with deviations in process and operations, equipment or in handling the hazardous
chemicals. A Process Hazard evaluation uses Risk Assessment (RA) techniques to determine the magnitude and frequency of
consequences, assessing whether adequate safeguards are in place and developing recommendations whether additional safeguards are
required. A safeguard is defined as any device, system or action which would likely interrupt the chain of events following an Initiating Event (IE). Finally, an IE is an event or deviation that results in a sequence of events that could lead to an undesired consequence.
The interested reader can find a rich literature about Process Safety, in the “Further reading” section of this Chapter.