I. Introduction

In the hierarchy of controls, designing the hazard out of the process is the preferred method. Although this approach makes sense, designers do not always apply this concept to the fullest extent. The only way to ensure that accidents do not happen is to apply the principles of inherent safety (IS) throughout all life cycles of the process. Administrative practices, such as requiring PPE or shielding personnel from hazards, will only be effective as long as all other factors that could affect safety are perfect. Unless a process is inherently safe, accidents will likely happen if enough time is allowed. In addition to preventing accidents, IS principles will also protect processes and the general public from deliberate attacks on manufacturing facilities, such as acts of terrorism. This paper discusses the principles of IS, and discusses case studies where application of these principles would have prevented catastrophe.

II. Background: Principles of inherent safety
2.1 Introduction

To make a facility inherently safe means to remove hazards so that accidents will not happen. The hazards can be in the form of toxic or flammable chemicals, unsafe process conditions, design flaws that lead to injuries, or work processes that can introduce hazardous situations.

At its core, IS involves analyzing risks and challenging the premise that the hazard should be there. This approach is contrasted with accepting that the hazard exists and deciding how to "work around" it. When safety practitioners consider how process, work practice, or workplace design issues can cause undesirable consequences, they should always examine why the hazard has to be present.

Although the preferred method is to design the hazard out of the system, IS principles may involve making the process inherently "safer" rather than absolutely safe. On the continuum, the safety professional should always be pushing to go to the next level, from using administrative procedures to protect workers, to using active measures such as interlocks, to using passive measures, to the ultimate solution of designing the hazard out completely (Figure 1).

Figure 1. Preferences in Protections from Hazards (available in full paper).

The progression of questions that can be asked during a review for inherent safety include:

  • What is the hazardous material, situation, or procedure?

  • What administrative and hardware controls are in place?

  • Are controls passive such that they will never fail? (e.g., dikes to collect spills)

  • Do the controls require that hardware or a person take an action?

  • Does the hazard even need to be present, or can it be eliminated?

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