Page 191 - Offshore Electrical Engineering Manual

178 CHAPTER 17 Telecommunications – Internal and External

A duplicated, Public Address/General Alarm (PA/GA) system, fully certified
for use in hazardous areas is provided to advise personnel of an emergency and
the actions to be taken. Each system can be accessed from the control room, radio
room, helideck and lifeboat stations. The PA/GA systems on bridge-connected
platforms should be fully integrated to ensure all personnel are aware of the
current situation and can be contacted individually. The PA/GA system should
be able to carry routine and emergency speech and alarm on both halves of the
system simultaneously. It is a statutory requirement that in an emergency, the
PA system can broadcast a tone indicating the nature of the emergency (muster
and prepare to evacuate) and to issue instructions to all areas where personnel
may be present, including lifeboat, cabins and muster stations (Please refer to
Reference 1).

REDUNDANCY, DIVERSITY, SURVIVABILITY AND
SAFETY ISSUES
1. The internal communications must all be provided with secure battery-backed
supplies to ensure that they will work if the main power systems have been
disabled. The two (main and standby) UPS supply batteries and their chargers
should be rooms located in geographically separate rooms. Chargers should be
supplied from separate switchboards.
2. Cables for alternative telecom systems and their electrical supplies should be
routed separately in order to minimise the possibility of common mode-failures.
3. All internal communication equipment requires to be suitable for operation
in at least zone 2 hazardous areas, so that the risk of igniting uncontrolled gas
releases is minimised.
4. Public address and telephone systems on bridge-connected platforms will
require fall-back modes of operation to cater for scenarios such as loss of the
bridge. Damage due to fire or explosion on one platform should not take out the
whole system (For further guidance, please refer to the Bibliography).

EXTERNAL TELECOMMUNICATIONS
The normal and emergency roles of the external communications system installed
on an offshore installation are to provide the necessary facilities to safely operate
the installation in normal conditions, and also to supervise and inform personnel for
control of emergencies by:

1. Communicating with shore-based incident rooms
2. Communicating with external emergency support personnel (coast guard, heli-
copters, rescue vessels, etc.)
3. Communicating with the neighbouring installations