In the space of a fortnight covering the period 29th May to 10th June 2000 three separate incidents occurred on site. Each of the individual incidents is considered in further detail below.
For a general introduction to the basic design of power distribution systems and the power distribution system at the Complex see Appendix 1.
Construction of a new facility (known as E4 – Ethanol plant) began early in 2000. As part of the project to supply electrical power to the E4 facility it was necessary to dig a 700m long trench for the installation of new high voltage (11kV) cables between electrical sub-station No.5 and the E4 plant. At an early stage existing underground services, including the 33kV feeder which ran between electrical sub-stations No.1 and No.5, were identified as being in the vicinity of the new trench which ran from the Oil Refinery area into the Chemicals area of the Complex.
The overall project was organised and managed by BP Works Projects Group. Personnel from the BP Power Distribution Group were also involved in the design concept for the provision of the 11kV electrical power supply to service the E4 plant and were to be involved later at the commissioning stage. They were however not actively involved at the detailed design stage and a member of the BP Works Project Group produced the scope of work and the health, safety and environment plan for the project.
BP Oil Grangemouth Refinery Limited was the client for the works and also the principal contractor. They engaged a term contractor, who had been present on-site for many years, as the main sub-contractor for the groundwork. The groundwork contractor in turn sub-contracted the actual excavation work to an excavation contractor who supplied the manpower with the groundwork contractor responsible for the supply of other items including tools, facilities, plans and a level of supervision. The groundwork contractor carried out a risk assessment and produced a method statement for the excavation work to be carried out.
BP Oil Grangemouth Refinery Limited also engaged a main electrical sub-contractor for the electrical & instrumentation work to be carried out. The electrical sub-contractor in turn sub-contracted the laying of the cable in the excavated trench to a cable-laying contractor.
Supervision of the trench work was provided by representatives from the excavation contractor, the groundwork contractor and by a supervisor from the BP Construction Group. See below for a schematic showing the relationship between the different groups.
Due to the route of the trench, which ran across areas controlled by different business streams (Oils and Chemicals,) the involvement of operatives from the different areas in the day to day operation of the Complex permit-to-work systems was required. Since the excavation and cable-laying activities were carried out in areas under the control of the Oils and Chemicals businesses, authorisation from these business areas for the work to be carried out in their areas and the safety requirements specific to each of these individual areas had to be sought on a daily basis by the excavation teams.
Prior to the start of the excavation, operatives from the excavation contractor were given a "toolbox talk" which identified the correct tools and their manner of use for the excavation work to be carried out. Instructions were given to dig down to 900mm or until cable tiles covering existing cables were discovered. It was permitted to break the ground surface to a depth of 300mm using a compressed air power tool known as a clayspade and then to excavate the remaining depth only using special non-ferrous tools.