The Design Process: Process Safety – Keep the Stuff in the Pipe

Article by Tom Baxter CEng FIChemE

In the third in a series of articles aimed at giving new graduates a better understanding of the current design process, Tom Baxter argues that inherent safety should be at the forefront of hazardous chemical plant design

TREVOR KLETZ, often described as the father of process safety, suggested the most effective approach to risk management was to first eliminate the hazard then utilise layers of protection to manage the hazard. When designing a plant, he said you should ask yourself if there is a safer reaction route, question the need for large inventories of hazardous material and high temperatures and pressures, and see if the process can be simplified.

Kletz produced a paper “What you don’t have can’t leak”. It is a concept that underpins one of the key tenets of inherent safety – eliminate. The pillars of inherent safety are outlined in Table 1.

Table 1: The pillars of inherent safety

Figure 1 illustrates that inherent safety thinking at the front end of the design process can have a massive impact on plant safety.

Figure 1: Effectiveness in risk reduction across project phases

Clearly, we want to avoid a loss of containment from the process plant that will release hazardous/polluting substances.

The new graduate should consider the causes of loss of containment:

  • overpressure
  • underpressure (vacuum)
  • high temperature
  • low temperature
  • corrosion
  • erosion
  • vibration

Other causes include incorrect operating procedures, flawed maintenance practices, and human error.

Should a loss of containment occur, the focus moves from prevention to mitigation – fire and gas detection, passive fire protection, fire water, escape and evacuation, competence training etc.

The chemical engineer is tackling risk by managing both probability and consequences.

There are a raft of risk identification techniques that are used at various stages from concept through detailed design and into operations. Some of the common techniques are summarised in Table 2.

Article by Tom Baxter CEng FIChemE

Retired senior lecturer at Aberdeen University, visiting professor of chemical engineering at Strathclyde University, and retired technical director, Genesis Oil and Gas Consultants

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