Blast Loading From Gas Explosions Onto Nearby Structures
Authors: Bailey P. , Chynoweth S. , Friis J. , Louca L.A. , Rhodes T.C. , Shirvill L.C. 
Published: October 2008

This paper describes a joint industry funded project that studied the blast loading onto nearby structures as a result of gas explosions in modules on offshore facilities. Although much effort has been directed at understanding the generated overpressure from gas explosions, the prediction of the received loading onto nearby structures caused by the resultant blast wave has been given less attention. This is of course a crucial aspect in evaluating, for example, the integrity of safety critical barriers protecting the temporary refuge, and for assessing the vulnerability of escape routes.

Large scale experiments were carried out to investigate the interaction of the blast wave from a vented gas explosion with a target structure. The cubic target was comprehensively instrumented to measure the pressure load on its surfaces and the dynamic response of the structure. The study resulted in a large amount of unique data and the results are presented, discussed and compared with model predictions.

The project described in this paper has resulted in guidance to structural and safety engineers to ensure that offshore facilities are sufficiently robust to accidental explosions without being overly conservative.

Introduction

This study forms the final part of the joint industry project on Gas Explosions in Offshore Modules Following Realistic Releases. It addresses an important area in the evaluation of the hazards posed by gas explosions; the blast loading onto nearby structures. Although much effort has been directed at understanding the overpressure from the source explosion, the prediction of the received loading on structures caused by the blast wave propagating out from a gas explosion has received less attention. This is of course a crucial aspect in evaluating loading on safety critical barriers, protecting for example the temporary refuge.

The joint industry project known as Phase 3B has been undertaken in order to gain information on the explosion load generated in more realistic conditions1. The project has been sponsored by BG Group, BP, Enterprise, ExxonMobil, HSE, Institute of Petroleum, Marathon, Norsk Hydro, Shell, Statoil, Talisman and TotalFinaElf.

The blast loading study has two parts; experiments to investigate the interaction of an external blast wave from a vented explosion with a target structure, and analysis of the results derived from the experiments. The large scale experiments used an existing facility at Advantica Technology's Spadeadam Test Site to generate the explosion and blast wave, thus enabling the resources to be concentrated on building and instrumenting the target, carrying out the experiments, and analysing the results.

In this paper we describe the test facility used, the testing campaign conducted, the analysis of the measured data (both pressure and structural response) and compare those data with appropriate theoretical analyses.

Test Facility and Testing Campaign

Explosion Chamber.

The Spadeadam explosion chamber was chosen to provide a well characterised, repeatable explosion source that could be used to provide both shocked and unshocked pressure pulses at a remote target location.