Application of a probabilistic basis when determining the capacity and extent of dropped object protection can be challenging. In particular, this is a concern when defining safe distances for lifting and load handling activities during rig operations. Delivering to-the-point assistance within load handling risk to a large number of operators, ORS subject matter experts share their advice on the matter.
The facilities team should liaise with the drilling and well (D&W) team to make sure that all relevant activities are considered and to understand the required load handling and lifting flexibility needed by D&W.
Relevant company requirements and industry standards should be identified and embedded in the study.
All potential dropped object hazards should be accounted for. This could be done based on existing hazard or risk identification evaluations in the project. Typical hazards are load handling to/from the subsea template, lifting to/from supply vessel, and handling of the mooring system.
Risk acceptance criteria and methodology for evaluating the risk (i.e. determination of hit probability and consequence) need to be clearly defined for all relevant assets. This is not necessarily limited to assets with hydrocarbon inventory. Note that the acceptance criteria could be different before and after production start-up (e.g. relevant for production drilling).
Dropped object protection is often achieved by other considerations, e.g. overtrawlability. Such considerations and resulting impact capacities should be taken into consideration.
Establish requirements for dropped object protection and safe distances:
A clearly defined risk acceptance criteria should be used as a guiding principle when establishing the design requirements for dropped object protection as well as safe distances for load handling and lifting activities. This should be an iterative process that combines the engineering expertise of the facilities team with the required flexibility requested by the D&W team. The result should be a set-up with fit-for-purpose protection for all relevant activities.
The safe distances should as far as possible be robust with regards to small variations in e.g. drilling schedule and lifting plans. The resulting lifting and load handling charts used by the rig need to be fixed to avoid too much complexity. A key measure for determining safe distances successfully is to determine suitable distances commensurate with object characteristics.
Safe distances should be defined for all credible dropped object hazards.
Two sets of safe distances should be established if required. One considers activities prior to production start-up (cold system) and one considers activities after production start-up (hot system).