Evacuation Performance
Authors: Ré António Simões , Veitch Brian 
Published: October 2008

Evacuation system performance deteriorates as weather conditions worsen. A research program based primarily on model scale tests of several different types of evacuation system has quantified how prevailing weather affects performance. To do this, several measures of performance were proposed and their utility confirmed. The most recent phase of the research program investigated performance in extreme weather conditions. Results are presented and discussed in the context of goal-based decision making.

Introduction

Evacuation of an offshore installation is a process that begins with embarkation of personnel, followed by lowering or delivery to the sea, followed by departure from the splashdown point to a place of safety removed from the immediate hazard that precipitated the evacuation and where a rescue can be attempted. This might be expressed as a goal: In circumstances that necessitate a marine evacuation, personnel must have access to an evacuation system, be able to embark and launch safely, clear the installation, and survive until rescued, and to have a reasonable expectation of successfully escaping harm in the environmental conditions that can reasonably be expected to prevail during operations.

Regulations in the offshore and maritime industries in many jurisdictions are moving away from specification-based standards and towards goal-based standards, a move that has prompted debate in both industries. To add to and help inform the debate in the arena of evacuation, a research program has been investigating the performance capabilities of several types of evacuation system, including conventional twin falls davit launched lifeboats, the same system modified by the addition of a flexible boom, and free fall systems [e.g. 1,2].

These investigations have been based on model scale experiments and have focused on quantifying how weather conditions and various evacuation station design parameters affect the performance of evacuation systems. In order to quantify performance, it has been necessary to define performance measures and demonstrate their utility.

Recently, the performance of the conventional twin falls davit launched totally enclosed motor propelled survival craft (TEMPSC) was tested in extreme weather conditions with the aims of determining the upper operational weather limit of such a system, the role of wave steepness, and the effects of launch orientation. The results of these experiments complement earlier work and have led to a conceptual framework for assessing performance capabilities and designing to meet safety goals. The framework is presented here along with experimental results.

Evacuation Zones and Performance Measures

It is useful to consider the evacuation area as consisting of several zones, illustrated in Figure 1 and named here as splash-down, clearing, rescue, and exclusion zones. One measure of the system's performance is how closely the evacuation system delivers the lifeboat to the target launch point, which for the conventional system considered here is vertically below the lifeboat in its deployed position. The closer the actual splash down is to the target, the better. The distance between the target launch point and the installation is the clearance and this can be expected to have an important influence on the likelihood of a successful evacuation, particularly in terms of avoiding collisions after launching.