Geologic mapping and structural analysis in the Bannock Range, SE Idaho, indicate that the bulk of Cenozoic extension in southeast Idaho was accommodated by slip on the low-angle Bannock detachment system. The Bannock detachment system consists of lowangle normal faults with a likely N-S extent of >130 km. It was active from ca. 10.3 Ma to ca. 3-4 Ma and accommodated >15 km of top-to-the-WSW extension. The master low-angle detachment fault cuts steeper, older normal faults and extensional folds in its hanging wall.Crosscutting relationships and prior work show that the hanging wall to the detachment system began as a cohesive block that later broke up along normal faults that either sole into or are cut by the master detachment fault. After breakup began, the master detachment fault was folded isostatically by a NNW-trending extensional anticline, the Oxford Ridge anticline. The folding produced a new listric low-angle normal fault east of the Oxford Ridge anticline to replace the back-tilted portion of the detachment fault. This new low-angle normal fault excised part of the hanging wall, cut hanging-wall structures, and served as a secondary breakaway for the detachment. West of the Oxford Ridge anticline, the master detachment fault initiated and slipped at a low angle, is the youngest low-angle normal fault of the system, and has not been rotated to a low-dip angle through time.The exhumed Bannock detachment system, although somewhat smaller, shorter lived, and more disrupted by younger Basin and Range normal faults, is similar to the buried Sevier Desert detachment system beneath central Utah. Both top-to-the-west systems formed near the transition between the Sevier thrust belt and its hinterland, collapsed broad thrust-related culminations eroded to Cambrian rocks, are paired with partly coeval top-to-east metamorphic core complexes ~100-160 km to the west, lie east of major thrust ramps, formed and slipped at low angles in the most extended part of the system, and exhibit a translation and breakup phase of deformation. Both are late Cenozoic in age and have voluminous lacustrine synrift deposits that record saline and alkaline conditions during early extension. Similar processes likely produced both detachment systems.

In 1992 Interim Guidance Notes were issued in the UK to provide guidance for the design of offshore topsides for fires and explosions. This Guidance was one consequence of the Piper Alpha Tragedy in the North Sea. Since 1992 a great deal of further research and technology has been developed in order to improve understanding of the characteristics of fires and explosions and the response of the structures and equipment to these events. In order to collate this new information in a readily useable format, the United Kingdom Offshore Operators Association (UKOOA) and the Health and Safety Executive (HSE) commissioned the MSL Consortium to update the existing Interim Guidance Notes and produce Part 1 of the new Guidance. The MSL Consortium consisted of the organisations represented by the authors with contributions from WS Atkins (Houston) and Beth Morgan Safety Solutions. The project manager was Minaz Lalani of MSL. The new Guidance is being developed in three parts. The first two parts deal with the philosophy for the avoidance and mitigation of explosions and fires respectively, which together establish the background for Part 3 which will provide detailed guidance on design practices for fire and explosion engineering. This paper describes the first document. Specific issues which are discussed include installation risk screening, nominal explosion loads, inherently safer design, hazard management, and the derivation of Design Explosion loads. This paper also describes the recommended method for explosion response assessment given in the Guidance.

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