Inherently Safer Design (ISD)

The concept of Inherently Safer Design (ISD) pertains to the aspect of process safety that prioritizes the prevention of hazards or the mitigation of their probability and impact, as opposed to depending on supplementary equipment and protocols. The system of controls known as the hierarchy of controls relies on the principles of ISD as a fundamental component of risk management. Its purpose is to mitigate or eliminate hazards that have been identified.  As illustrated in the below figure, the hierarchy of controls—in order of increasing effectiveness—is comprised of the following categories:

  • Administrative
  • Active engineered
  • Passive engineered, and
  • ISD
Hierarchy of Controls (ISD)

In process safety, the ISD study methodology focuses on identifying and implementing design solutions that inherently reduce or eliminate process hazards. The goal is to minimize risks associated with the process by considering inherently safer options from the early stages of design.

Methodologies for conducting an ISD study in process safety:

  1. Define Study Objectives: Clearly define the objectives of the ISD study, such as reducing process hazards, improving safety performance, or complying with regulatory requirements.
  2. Identify Process Hazards: Identify and understand the process hazards and potential accident scenarios. This can be done through process hazard analysis techniques like Hazard and Operability (HAZOP) studies, What-If analysis, Fault Tree analysis, or other relevant methods.
  3. Inherent Safety Principles: Inherent safety principles are a set of guidelines or strategies that aim to design processes, systems, and facilities in a way that reduces or eliminates hazards at their source. These principles help to minimize risks and enhance overall safety by addressing potential hazards during the design stage. Familiarize yourself with inherent safety principles and apply them during the study. These principles include minimization, substitution, moderation, simplification, and inherent protection. Each principle focuses on reducing hazards at the source or eliminating them entirely.

Commonly recognized Inherent safety principles:

  1. Minimization: Minimization involves reducing the quantity of hazardous materials used or generated in a process. This can be achieved by using smaller quantities of hazardous substances, optimizing process conditions, or minimizing inventories. By reducing the amount of hazardous materials present, the potential for accidents and their consequences is significantly reduced.
  2. Substitution: Substitution involves replacing hazardous materials or processes with less hazardous alternatives whenever possible. This can be achieved by selecting less toxic, less reactive, or more stable substances or by adopting alternative technologies or processes that inherently pose fewer risks.
  3. Moderation: Moderation focuses on reducing the severity or impact of a hazard. This can be accomplished by modifying process conditions, such as temperature or pressure, to reduce the potential for accidents or mitigate their consequences. For example, operating at lower pressures or temperatures can make a process inherently safer.
  4. Simplification: Simplification aims to reduce the complexity of a process or system to minimize the potential for errors, failures, or accidents. By eliminating unnecessary process steps, equipment, or control systems, the overall complexity and associated risks can be reduced. Simplification also helps improve operability, maintenance, and troubleshooting.
  5. Inherent Protection: Inherent protection involves designing systems or incorporating safety features that provide passive protection against hazards. This can include features such as pressure relief devices, fire-resistant materials, or physical barriers that automatically activate or prevent the escalation of incidents, even in the absence of human intervention.

These inherent safety principles are not mutually exclusive, and multiple principles can often be applied together to enhance the overall safety of a process or facility. The goal is to implement these principles during the design stage to reduce the reliance on procedural mitigation measures, such as alarms, safety instrumented systems, or operator intervention, which may be less reliable or prone to failure.

It is important to note that the application of inherent safety principles requires careful consideration of process-specific factors, regulatory requirements, and economic feasibility. Multidisciplinary collaboration among engineers, process safety professionals, and designers is crucial to effectively implement inherent safety principles and achieve optimal safety outcomes.

  1. Identify Design Alternatives: Brainstorm and identify alternative design options that could provide inherent safety benefits. Explore various design parameters, such as materials, process configurations, equipment selection, layout, and operating conditions.
  2. Evaluate Design Alternatives: Evaluate the identified design alternatives using a systematic and structured approach. Assess their potential for hazard reduction, risk mitigation, and overall safety performance. Consider technical feasibility, reliability, operability, maintainability, and environmental impact.
  3. Quantify Risk Reduction: Quantify and compare the risk reduction potential of each design alternative. This may involve using risk assessment techniques like quantitative risk analysis (QRA), consequence modeling, or other appropriate methodologies to estimate and compare risks associated with different designs.
  4. Select Optimal Design: Based on the evaluation and risk reduction assessment, select the design alternative(s) that provide the highest level of inherent safety. Consider factors such as feasibility, cost-effectiveness, operability, maintainability, and regulatory compliance.
  5. Implementation and Monitoring: Develop an implementation plan for the selected design alternative(s). This may include engineering modifications, procedural changes, training programs, or other necessary actions. Monitor the effectiveness of the implemented measures and make adjustments as needed.
  6. Documentation and Communication: Document the findings, recommendations, and decisions made during the ISD study. Communicate the outcomes to relevant stakeholders, including management, engineering teams, and process safety professionals.
  7. Continuous Improvement: Continuously review and assess the implemented design changes. Collect feedback, track performance indicators, and identify opportunities for further improvement. Incorporate lessons learned from the ISD study into future design projects and process safety initiatives.

Remember, process safety is an ongoing effort, and the ISD study methodology should be integrated into the overall process safety management system of the organization. The involvement of multidisciplinary teams, including process engineers, safety professionals, and design experts, is crucial to ensure a comprehensive and effective ISD study.

When conducting an ISD study as part of a safety study, the following input documents are typically required

  1. Process Description: A detailed description of the process under study, including process flow diagrams (PFDs), process and instrumentation diagrams (P&IDs), and other relevant process documentation. This information is crucial for understanding the process and identifying potential hazards.
  2. Hazard Identification Study Reports: Previous hazard identification studies, such as Hazard and Operability (HAZOP) studies, Process Hazard Analyses (PHA), or other relevant studies, provide valuable insights into identified hazards and risks associated with the process. These reports help identify areas for improvement and guide the ISD study.
  3. Safety Data Sheets (SDS): SDSs provide detailed information on the properties, hazards, and safe handling procedures for chemicals and materials used in the process. They are essential references for understanding the inherent hazards associated with the substances involved and exploring safer alternatives.
  4. Incident Data: Historical incident data, including records of past accidents, near misses, or process upsets, provide valuable information on the vulnerabilities and potential hazards of the process. Analyzing incident data helps identify recurring issues, root causes, and areas for improvement in the ISD study.
  5. Regulatory Standards and Guidelines: Relevant regulatory standards, guidelines, and best practices specific to the industry or jurisdiction provide important benchmarks for safety requirements and considerations. They help ensure compliance and provide a framework for evaluating the inherent safety of the design.
  6. Engineering Design Documents: Detailed engineering design documents, such as equipment specifications, layout drawings, equipment datasheets, and instrumentation details, are essential for evaluating the feasibility and potential impact of proposed design alternatives. They provide the necessary technical information to assess the inherent safety aspects of the design.
  7. Existing Safety Systems Documentation: Documentation related to existing safety systems, including safety instrumented systems (SIS), emergency shutdown systems (ESD), fire protection systems, and others, helps evaluate the effectiveness of these systems in providing layers of protection and identifying potential areas for improvement.
  8. Operational and Maintenance Procedures: Operational and maintenance procedures provide insights into how the process is operated, controlled, and maintained. These procedures help identify potential hazards and risks associated with routine operations and maintenance activities.
  9. Multidisciplinary Expertise: Inherent safety studies require input from various disciplines, including process engineers, safety professionals, chemical experts, mechanical engineers, and others. The knowledge and expertise of these professionals are vital for conducting a comprehensive ISD study and identifying suitable design alternatives.

It is important to note that the specific input documents required may vary depending on the nature of the process, the organization’s internal procedures, and the regulatory environment. Collaborating with relevant stakeholders and subject matter experts is crucial to ensure that all necessary input documents are identified and accessed for the ISD study.