Abstract

Post implementation of the UK Safety Case Regime, UK designers have tended to apply a risk based approach to the management of major accident hazards when designing new facilities. Although meeting the intent of goal setting, risk based design is subject to numerical uncertainty and can be challenged in terms of effectiveness in ensuring actual risks to personnel are as low as reasonably practicable (ALARP). This paper describes how a project has taken a different approach using the principles of inherently safer design to concentrate on avoidance and prevention of major hazards.

The vision of an inherently safer design is one which has:

  • Fewer inherent hazards

  • Reduced probability of unwanted events

  • Reduced inventory and damage potential, leading to reduced severity of the event

  • Fewer activities on the plant and thus less people exposed

  • Reduced scope for smaller incidents to escalate and overwhelm the facilities

  • Clear focus on simplicity, reliability and longevity to reduce exposure

The outcome of implementing an inherently safer design process is a robust concept in which the risks from major accident hazards have been minimised with emphasis on elimination of hazards and use of passive safety systems and measures. The management of residual risk from major hazards can then effectively achieved by the application of:

  • Safety Critical Design Measures (SCDM) that can be readily taken through into construction and maintained in operations and;

  • Procedures to reduce the risks from safety critical tasks

By starting the hazard management process with the mind set of elimination of hazards, rather than using risk analysis techniques to aim for an ALARP solution, it is maintained that the risk profile achieved is lower than would have resulted from a traditional risk based approach. In addition the facility is simpler in design and construction with lower maintenance and inspection requirements.

1 Introduction

Post implementation of the UK Safety Case Regime [Ref 1], UK designers have tended to apply a risk based approach to the management of major accident hazards when designing new facilities. Although meeting the intent of goal setting, risk based design is subject to numerical uncertainty and can be challenged in terms of effectiveness in ensuring actual risks to personnel are as low as reasonably practicable (ALARP). This paper describes how a project has taken a different approach using the principles of inherently safer design to avoid and prevent major hazards, and to reduce residual risks to personnel through control and mitigation of those hazards.

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