How Safe and Available Is Your Plant Actually?

• André Fijan

Keywords: Safety, Availability, Tolerable risk, Accumulative risk, Safety instrumented function, MTTFS

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Abstract:

Engineering contractors are designing the plants, which are being build everywhere in the world. These plants have to meet the safety and availability requirements from the end-users. The safety is an important factor to obtain the permit from the authorities to operate the plant. The availability is an important factor to obtain the investment approval for the plant. Effective safeguarding of a plant is reducing the inherent risks in the process to an acceptable level, while the achieved availability provides the best return on investment. In most discussions, one factor is usually neglected: the number of Safety Functions within a certain process unit. Safety Functions can be operational procedures, mechanical devices (e.g. relieve valves, dykes, bursting disks), and/or Safety Instrumented Functions (SIF’s).

The objective of this paper is to give the reader a better understanding how the number of Safety Functions affects the actual safety and the actual availability of a process unit. The paper will first discuss tolerable risk criteria. Secondly, it will discuss the impact of the number of Safety Functions on the actually achieved safety. Thirdly, the paper will discuss the impact of the number of Safety Instrumented Functions on the availability of the plant. Finally the concluding remarks are presented. © 2009 Inside Publishing. All Rights Reserved.

Volume: 2009   Issue: 2

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