Evaluating Safety Competencies Through a Risk-Based Design and Process Safety Elements Approach

Summary

In preventing process accidents, the identification and analysis of process hazards—including equipment failures (such as design and assembly errors), improper maintenance and repair, misuse, material defects, and human error—form a fundamental principle of the process safety management system, with all possibilities being evaluated during the design phase. When production is targeted, process details are not emphasized, and design work typically begins with determining product specifications and production capacity based on market data and customer requirements. Minimum production cost is the objective in determining the production route. Beyond operating costs, safety measures are included among cost inputs, along with measures required by legal restrictions. Risk assessment conducted during the design phase establishes how safety can best be achieved at each stage of the process lifecycle. In determining the production route and creating process flow diagrams, the identification of chemicals to be used, equipment selection, and planning of construction methods should be accompanied by risk evaluation across the entire process lifecycle. Hazard identification and risk assessment work determine the behavior of process chemicals and the likelihood of equipment deviating from its design purpose. Critical equipment identification through effective hazard analysis methods during the design phase will govern the determination of risk control procedures. Manufacturing safety is ensured through the identification and implementation of technical measures, while safety-related measures are established through the use of technical standards and other tools that comply with legal regulations.

Introduction

Any activity or operation that takes inputs and transforms them into an output is called a process. The output of a process can be either a finished product or the input to the next process. The complete set of operations in which raw materials are transformed into finished products at various process parameter values through different energy inputs within equipment can also be termed a manufacturing process. Manufacturing processes are facilities in which, in addition to risks arising from process parameters dependent on the properties of chemicals present in the process, flue gas emissions from the process, liquid waste, and solid waste are discharged. In establishing the design foundation, the effects of technical operating parameters on these risks also hold significant importance. These risks stem from uncertainty arising from variability in process conditions and lack of information. While protective measures to prevent accidents are planned in the design of a chemical unit, despite all these measures, accidents cannot be completely eliminated. Although accidents are by definition neither tolerable nor acceptable, when they do occur, harm should be avoided to the greatest extent possible.

Process Safety

The fundamental objective of process safety management is to prevent accidents that could harm employees, other people, and the environment, or to minimize their effects, as well as to prevent devastating economic losses. Aside from natural disasters and other initiating causes, accidents result from deficiencies in process safety. In preventing accidents, the identification and analysis of process hazards—including equipment failures (such as design and assembly errors), improper maintenance and repair, misuse, material defects, metal fatigue, corrosion, welding defects, and human error—form a fundamental principle of the process safety management system. Process safety begins with the design concept and is evaluated in detail in sustained design calculations. Design problems are poorly defined and do not offer a single solution. When production is targeted, process details are not emphasized, and design work typically begins with determining product specifications based on "market data and customer requirements." Product specification is one of the most important external constraints limiting the designer's selection flexibility.

While production capacity is determined through proper market research, no information exists regarding the production route. Determining the production route requires simultaneous evaluation of technology-capacity relationships, while waste specifications set by law form another external constraint defining the boundaries of design work.

By evaluating the effects of these constraints, the determination of which production route will be used, what the process units will be, and the completion of working conditions and material flow paths between equipment leads to the engineering calculations phase of the design. In this selection, the behavior of process chemicals limiting equipment performance (physicochemical, thermodynamic, phase, and kinetic data), as well as limitations in equipment designs, act as internal constraints. The main objective in design work is to achieve economical production costs through the creation of a technically operable process flow diagram by evaluating all constraints. It should not be forgotten that the inputs affecting production costs are not limited to expenditures necessary for process operation alone. Cost effects of measures taken to ensure process safety can have variable percentages. Hazard information such as flammability-explosion tendencies and toxic properties of chemicals act as external constraints in establishing process safety. When operating parameters are selected in accordance with these constraints, process efficiency may be low. In this case, at high efficiency values, measures targeting safety and environmental constraints are implemented with additional costs.

Creating Flow Diagrams with a Safety Approach

The development of the entire facility design involves evaluating many different subjects. The economic picture generally determines whether the proposed facility receives management approval. In facility design, the application of engineering principles in a safe and environmentally acceptable manner relates to whether previously set economic objectives can be met. Designers should consider how safety can best be achieved at each stage of the process lifecycle. Safe design is defined as a process of integrating hazard identification and risk assessment methods at the beginning of the design process to eliminate or minimize accident risks throughout the designed process's lifetime. In conducting safe design, the properties of process chemicals and hazard information play an important role as external constraints. Safe design, from the concept phase, requires determining the chemicals to be used, equipment selections, and planning of construction methods, as well as considering requirements across the entire process lifecycle simultaneously. Throughout the process lifetime, in addition to operation and maintenance activities, decommissioning, demolition or dismantling, and disposal methods at the end of the lifecycle should also be considered. Safety constraints related to chemicals are of great importance in determining flow diagrams and operating conditions. Therefore, process safety requirements for the entire lifecycle must be evaluated at the stage of creating process flow diagrams. Safe facility operation requirements include keeping process variables within known safe operating limits, detecting hazardous conditions that arise, providing alarm and automatic shutdown systems, and establishing connections and alarms to prevent hazardous operating methods. Risk assessment conducted during the design phase, together with the determination of risk control procedures, guides how safety can best be achieved at each stage of the process lifecycle, in addition to evaluating cost effects. The basis of risk assessment begins with hazard identification. In identifying hazards, in addition to chemical properties, the process conditions to which they are exposed—which can lead to risk transformation—are also important. Possible changes in process conditions can lead to deviations in temperature, pressure, pH, etc. within equipment, causing changes in phase or reaction stoichiometry, as well as sudden changes in the mentioned process parameters that go out of control.

How long and under what conditions an equipment can fulfill its function is itself a design output, and the reliability values of equipment can be defined during the installation phase.

Regarding "Functional Safety" work aimed at preventing risks from equipment hardware and software failures and likely operator errors causing malfunction, the evaluation of deviations from design intent can be considered during the design phase itself. Depending on process operating conditions and designed equipment characteristics, preliminary information about "Condition-Based Maintenance" for operational reliability and "Risk-Based Maintenance" for failure correction can be obtained. When the above points are considered, the identification of "Critical Equipment" or equipment becomes of great importance. The identification of critical equipment guides the facility layout plan to prevent domino effects. The evaluation of what possible failures of critical equipment could be, how frequently they could occur, and their impacts will illuminate "Risk-Based Inspection" planning, which determines necessary control activities in the process lifecycle. The basis of critical equipment identification lies in predicting what possible deviations could lead to and their severity. This selection may require not only simple risk determination methods evaluating failure probabilities but also realistic approaches such as the "Dow Fire and Explosion Index" (Dow-Fire Index) that consider the chemical content and quantity of equipment. Through "Hazard and Operability" (HAZOP) hazard analysis conducted for critical equipment, process deviations can be identified properly. Evaluation of the "Basic Process Control System" (BPCS) to address deviations from parameter values leads to the creation of "Piping and Instrumentation Diagrams" (P&ID).

After the concept process design is completed, the adequacy of BPCS for process safety is questioned, and the necessity for additional measures is determined accordingly.

Through Process Hazard Analysis (PHA)—ranging from simplified screening to rigorous HAZOP engineering work—process weaknesses are identified during the design phase, and based on accident scenarios created, "Layers of Protection Analysis" (LOPA) reveals the need for risk-reducing measures to prevent Loss of Containment (LOC) in the process and mitigation actions in case an accident occurs. If additional safety requirements are needed, Safety Instrumented System (SIS) design is conducted for SIS implementation. The implementation of SIS is based on the principle that an unwanted hazardous condition that could arise during any determined operation is detected, and the necessary safety elements are activated to prevent this condition. With the determination of SIS elements and their locations in the process, P&ID is completed. P&ID automatic control circuits include level, flow, pressure, temperature, speed, and similar controls for deviations from design values. Following detection, the elimination of parameter deviations is carried out through the implementation of appropriate control elements (P, PID, fuzzy control, etc.) and computer control routines and other controllers. The identification of risk-reducing measures to prevent or reduce the frequency of accidents and mitigation actions in case an accident occurs through the elimination of deviations causing loss of containment is the final stage of design.

Safe Design Work Tools

In designing process units, many protective measures must be included to minimize hazards resulting from toxic emissions, fire, explosion, or other unintended events. Mandatory emissions from process operation, material and waste handling, leak emissions from equipment connections, and maintenance work are the primary sources of toxic and flammable-combustible emissions. However, protective design against fire or explosion is often not technically always possible. In such cases, measures aimed at mitigating effects come into play. Legal regulations, operational rules, and standards to be followed throughout the process lifecycle play compulsory or guiding roles in shaping process safety. Many different standards have been developed to ensure safety conditions in the installation, operation, and maintenance of industrial facilities. It begins with compiling information about the hazards of chemicals in the process. Material Safety Data Sheets (MSDS) may be insufficient for physical properties, toxicity, reactivity, and flammability-explosion tendencies. In such cases, it is necessary to utilize internationally recognized systems such as CAS (Chemical Abstract Service) and ESIS (European Chemical Substance Information System). While health risks are controlled through the application of regulations regarding permissible exposure information, the evaluation of dangerous effects of process parameter deviations out of control and different chemicals inadvertently mixed due to foreseeable human error should also be considered. To prevent flammability-explosion tendencies from leading to unintended accidents, proper calculations in accordance with relevant regulations should be performed using accepted standards.

Conclusion

In safety design conducted with technical design, consideration is given to how safety will be established throughout the entire lifecycle, and planning occurs as early as possible. Safe design and installation are achieved through the integration of hazard identification and risk assessment methods in the design process. At this stage, the evaluation of chemical hazard information and process deviations is important. Sound risk assessment and achievement of safe design, like many engineering problems, also require answering relatively straightforward questions. "What am I investigating?" provides system clarification; "What could go wrong?" identifies hazards and failure conditions; "How bad could it be?" provides consequence and impact analysis; "How often?" estimates frequency; "What is the risk?" performs risk calculation and risk assessment; "What should I do?" establishes the roadmap for risk management during the design phase. With the contribution of these questions, manufacturing safety is ensured through the identification and implementation of technical measures, while the determination of measures necessitates the use of technical standards and other tools that comply with legal regulations. The use of standards compatible with the system is the strongest aid for risk management. Prof. Dr. Suna Balcı Gazi Üniversitesi / Gazi University Mühendislik Fakültesi Kimya Mühendisliği Bölümü   Sources • Lipton, S., Lynch, J., "Health Hazard Control in the Chemical Process Industry," Wiley, New York, 1987. • McKinnon, G.P., Tower, K., "Fire Protection Handbook," National Fire Protection Association, Boston, MA, 1986. • Peters, M.S., Timmerhaus, Klaus D., West, Ronald E. "Plant Design and Economics for Chemical Engineers," 5th ed., McGraw-Hill, New York, 2003. • Seider, W.D., Seader, J.D., Lewin, D.R., Widagdo, S., "Product & Process Design Principles", 3nd ed., Wiley, New York, 2010. • Sinnott, R.K. "Coulson & Richardson Series: Chemical Engineering Design", 6th ed., Butterworth-Heinemann, Oxford, 2005. • Turton, R., Bailie, R.C., Whiting, W.B., Shaeiwitz, J.A., Bhattacharyya, D., "Analysis, Synthesis, and Design of Chemical Processes", 4th ed., Pearson, New Jersey, 2013.