Page 29 - Offshore Electrical Engineering Manual

16 CHAPTER 2 The Offshore Electrical Environment

Whatever further means of ensuring the survival of the particular installation and
its personnel are considered in each installation Safety Case, it is certain to influence
the design of the electrical system and equipment, particularly in minimising the risk
of electrical ignition sources and in the provision of emergency secure electrical sup-
plies, completely independent of normal platform supplies.
As an important means of minimising risk of ignition sources, the hazardous area
boundary drawings produced during the platform process design stage are discussed
in PART 5 Chapter 4 and represent the situation during normal operating conditions.
However, it is also necessary to consider the situation during a major outbreak of fire
or after serious gas leak; the so-called ‘post red’ situation.
There are three electrical systems which normally monitor, control and mitigate
the extent and spread of oil and gas leaks and hence the safety of the platform:

1. the fire and gas monitoring system
2. the emergency shutdown system
3. safe and hazardous area ventilation systems.

These systems and devices are defined as the ‘Safety Critical Elements’ (SCEs)
in the statutory regulations, the definition being

such parts of an installation and such of its plant (including computer pro-
grammes), or any part thereof–

(a) the failure of which could cause or contribute substantially to; or
(b) a purpose of which is to prevent, or limit the effect of, a major accident.

Emergency power, and the various communication systems, and on floating
installations the ballast control system may also be included as electrical SCEs. All
these systems will have some bearing on the design of the platform electrical system,
either because they may include the facility to shut all or part of the electrical system
down, or because a secure, or at least a more reliable electrical supply is needed to
operate them. Every installation is different, and non-oil and gas installations such
as offshore wind farm substation platforms will need their own safety cases at every
stage including decommissioning and abandonment.

FIRE AND GAS MONITORING
Every installation must have, as a statutory requirement, a designated control point
located in a nonhazardous area, capable of overall management of the installation
and manned continuously.
All pertinent information from the production processes, drilling, utilities
and firefighting systems need to be monitored at this control point, and emer-
gency controls associated with these systems have to be available there to enable
sufficiently effective control to be exercised in all operational or emergency
conditions.