Guidelines for isolation and intervention: Diver access to subsea systems

Summary

This guidance document is primarily aimed at project managers, project engineers, offshore construction managers, diving supervisors and safety personnel, all of whom have a responsibility for developing safe schemes of isolation and intervention for divers accessing subsea systems. Additionally, engineering personnel involved with the design of such systems should also use this document to ensure that all new (or being modified) subsea systems incorporate adequate isolation facilities.

This document sets out what is considered to be good practice for ensuring a safe degree of isolation is established prior to conducting diver intrusive works on any energy-conveying system in which pressure differentials, electrical power or laser power may exist at levels which – on loss of containment – would be harmful to personnel or cause damage to the environment or equipment.

The guidelines are applicable for use when preparing workscopes, procedures, reviews and risk assessments for any diver related work.

These energy sources (pressurised liquid, pressurised gas, electricity and laser light) may be found as a conveyed product or service utility within either or both of the following two major subsea equipment categories:

• flowline/manifold/tree and wellhead systems (containing any of – oil, gas, condensate, water injection, chemical injection – either separately or in various combinations)
• subsea control and umbilical systems (containing any of – hydraulic fluid, high and low voltage powered equipment, communication signals, instrumentation signals, optical data signals, power transmission and distribution, chemicals, gas – each within dedicated sub-systems).

The general principles of isolation philosophy and isolation practice, as applicable to such systems, are given in Section 3, whilst detailed guidelines regarding isolation and intervention are given in Sections 4 and 5 respectively.

Adequate planning is essential for an effective isolation, not only to ensure awareness of the task requirements and ready availability of all materials, tools, etc., before work begins, but also to identify and assess the isolation options and their associated hazards and effects.

Safe standards of isolation are primarily determined by the size and nature of the potential hazards associated with the equipment to be worked on. Other fundamental factors which should be addressed are:

• an understanding of all the parameters associated with the energy source being isolated
• status, condition and accessibility of available isolation hardware
• identification of adjacent live systems which may influence or be affected by the isolations, and
• the anticipated duration of the actual intervention work.

Occasionally, the requirement may arise to utilise divers to conduct work on items of hardware which have been specifically designed for ROV installation, operation or recovery. In such instances, the isolation and intervention guidelines set out in this document should still be applicable.

Whilst it is not possible for these guidelines to account for the detailed and specific complexities of each and every subsea system encountered, the principles set out in this guidance should be applicable.

Contents

• Introduction
• Glossary
• Principles of Isolation
• Flowline/Manifold/Tree and Wellhead Systems
• Subsea Control and Umbilical Systems
• Isolation Flowchart and Isolations Summary Table
• Typical System Drawings
• References