Using concept stage HAZOPs as an opportunity to implement inherently safer design options
Updated: Dec 3
Hazard and Operability (HAZOP) workshops are, together with other Process Hazard Analyses (PHA), an important tool for understanding hazards inherent in a process design, and ensuring that the process design includes means for proper and effective monitoring and control of these hazards, as well as barriers preventing them from being realized as hazardous consequences for people, environment or asset.
Traditional HAZOPs are based on the concept of using a pre-defined set of parameters (such as pressure, temperature, and flow) and combining these with pre-defined guidewords such as (“More”, “Less”) to identify ways in which the given process design as represented on the Piping and Instrumentation Diagrams (P&IDs) might deviate from the desired design intent. After the causes of such deviations are identified, and the consequences assessed, the safeguards in place preventing these consequences from being realized are evaluated. If the HAZOP team agrees that safeguards are inadequate, actions are raised.
While a properly conducted HAZOP remains one of the most effective ways of evaluating a given process design with regard to safety and operability, it seldom explores inherently safer design solutions in-depth, often due to the fact that at the time of the HAZOP the process design has to be more or less “frozen” in order to provide a meaningful basis from which to explore possible deviations from design intent.
A “Concept-HAZOP” performed at a suitable time during a project's concept design stage allows for “designing on paper” and the exploration of alternative solutions. If P&IDs are not yet available, Process Flow Diagrams and related mass and energy balances can be used together with information about the intended operating and design envelopes, and, if available, plant layout / GA drawings. A “Concept-HAZOP” is hence a perfect opportunity to do a thorough and documented review of the inherently safe design options available. This can be performed by utilizing the “traditional” HAZOP methodology (a multi-disciplinary team systematically reviewing the process design, node per node), but with guide words and parameters modified to reflect the focus on inherently safer design:
Inherent Robustness: Designing systems with inherent resilience to deviations from normal operation. E.g. ensuring that the design envelope is such that e.g. temperature and pressure deviations cannot credibly be exceeded, ensuring that structure and supporting account for excessive level in vessels, using materials that are tolerant/resistant against degradation effects such as e.g. corrosion, ensuring a layout that prevents escalation of hazards, etc.
Minimization: Minimizing the use, production, or storage of hazardous materials. This principle emphasizes reducing the quantity or concentration of hazardous substances in the process, e.g. through smaller storage tanks, improved treatment/neutralization of hazardous by-products or waste products etc.
Moderation: Modifying process conditions, such as temperature, pressure, or flow rates, to reduce the severity of potential hazards or their likelihood of occurring. E.g. can the process be operated in a way where there is less inherent energy (lower temperature, lower pressure, etc.)
Simplification: Simplifying process designs, configurations, or operations to minimize potential points of failure and human error. Simplification aims to reduce complexity and increase reliability while maintaining safety. E.g fewer moving parts, passive systems vs. active systems, etc.
Substitution: Identifying and substituting hazardous raw materials, intermediate products, and auxiliary systems with safer alternatives whenever possible. This may involve selecting less toxic, less environmentally harmful less flammable, or less reactive substances to reduce risks. Substitution principles can also be used to evaluate different processes, or technologies to allow for safer operations (e.g. less maintenance, fewer start-up/shutdowns, etc).
In addition to the increased safety directly achieved through applying ISD principles in the design, benefits from a systematic review of inherently safe design options in a “Concept-HAZOP” includes:
Decision support and transparency: By systematically exploring ISD options for a process design, and recording this in a HAZOP worksheet, a list of potential ISD options should hopefully be available for the later project stages. Together with ALARP and cost/benefit analysis of these options, the project gains valuable documentation of the evaluations performed at the early stage of project execution, including why / why not specific design options have been chosen.
Early risk reduction: By addressing and removing hazards at the conceptual stage, engineers can mitigate/eliminate risks before they become “inherent” in the process design, and later require additional safeguards such as trips and relief devices to be engineered in.
Potential lifecycle cost savings: While the ISD options may sometimes be more expensive from a CAPEX perspective, these solutions many times reduce OPEX for the asset, as it often leads to fewer items requiring maintenance (through “simplification” or “substitution”) and potentially less wear and tear (through “moderation” and “inherent robustness”)
