Human Factors and Risk Assessment
Authors: Al-Minhali Ahmed Ali Nasser 
Published: December 2007

A case study was presented in the 1994 Abu Dhabi International Exhibition and Conference (ADIPEC, 94) which discussed the importance of investigating human factors in the design of a high integrity protection system (HIPS) to be installed on an offshore high pressure gas platform, (SPE reference ADSPE 80).

This paper will follow up on the design changes, installation and operation of the HIPS with emphasis on practical implications as a result of improper integration of human factors in the system reliability and risk assessment studies.

Introduction

The importance of investigating human factors in the design and management of petrochemical plant has developed rapidly in the last ten years, Mainly following the implication of human error as a contributor to recent disasters in high technology/high risk industrial sites. Technology had made it easier to design more complex systems to improve efficiency, productivity and control of processes in the oil industry.

However the safety and reliability of these systems are dependent on humans in varying complexity of organisational structures and in different environmental conditions.

This implies that designers and managers must ensure that sufficient consideration is given to human factors at all stages of plant life and it is encouraging that such considerations are being legislated in many parts of the world.

In a previous paper we demonstrated the technique and methodology for incorporating human factors in risk assessment (Fig. 1) and provided an examination of the deficiencies in the traditional approach to design and operation of relief protection in an offshore environment with emphasis on the need for designers, project managers and engineers to conduct a systematic risk assessment of identified hazards.

The process system in the case study presented comprises installation of three satellite wellhead towers (Fig. 2) with three wellheads each producing high pressure sour gas routed to a nearby offshore treatment and export platforms. In this presentation, we concentrate on the sequence of events from design to full operation of these towers with respect to application of sound safety principles for protecting against overpressurisation.

The hydrocarbons produced are very sour and extremely toxic to humans. Gas flows from each well through a choke valve into a common production header for the three wells (with by-passes to either the test separator or to the pig launcher) and then into subsea lines to collection and production platform (Fig. 3). The choke valve is set at the percentage required to control flow and pressure. The shut in pressure of the producing wells is up to 5700 psig, whilst the piping downstream of the choke valves are designed at a much lower pressure i.e production header and downstream is up to 900 psig (ANSI-900) and test header up to 2500 psig (ANSI-2500). This piping and equipment need to be protected against possible over pressurisation. This is to be achieved by a combination of pressure control, a high integrity shutdown system and instrumentation.

The decision to install a modern HIPS instead of a standard pressure safety valve (PSV) was taken during the Coarse Hazop by the Project team on the basis of the following options:all pipelines and associated equipment to be designed for full close in pressure 5700 PSI.

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