1 FIRE AND GAS DETECTION SYSTEM: GENERAL REQUIREMENTS
The purpose of the Fire and Gas Detection System is to early detect gas releases and fires that could arise on Platform and initiate automatic actions of shut-down, depressurization and firefighting Systems activation case by case.
The Fire Detection System has been designed to:
• detect a fire as early as possible;
• initiate preventive shut-down actions (ESD) at an early stage in order to mitigate the consequences;
• alert any personnel on board via PA/GA System;
• alert personnel in NA/Q-PI Platform Control Room;
• isolate electrical equipment except the essential safety Systems electrical equipment.
The Gas Detection System shall be designed to:
• detect flammable gas releases at an early stage;
• allow preventive actions intended to isolate leakage (ESD);
• isolate electrical equipment to minimize ignition sources except the essential safety Systems electrical equipment;
• alert personnel on board via PA/GA System;
• alert personnel in NA/Q-PI Control Room.
The Platform Fire and Gas Detection System will comprise:
• IR point Gas Detectors (hydrocarbon, methanol and hydrogen);
• Fire Detectors (smoke, flame and temperature detectors);
o UV/IR flame detectors;
o Optical smoke detectors;
o Rate of rise heat detectors;
o Fusible plug networks (pneumatic, not welded) and linear heat detector cables;
• Manual ESD push-buttons;
• Manual Alarm Call point (MAC);
• Abandonment shut-down Alarm push-button;
• Man Overboard Alarm push-button;
• Flashing Red Lights for ESD and Fire Detection alarms;
• Flashing Blue Lights for Gas Detection alarms;
• Acoustic alarms;
• System status alarms for closed areas protected by clean agent Systems (visual/acoustic).
All F&G equipment are suitable for installation in Zone 1, Gas Group IIB, Temperature Class T3 hazardous area and have been manufactured for marine (saline) environment; the selection has been made according to Hazardous Area Classification study. Moreover, detectors shall be installed with sufficient weather protection (e.g. wind protection hoods, etc.).
Status of F&G Detectors installed on NA/Q-PIII Platform is monitored by NA/Q-PI SCADA System; moreover, manual activation of NA/Q-PIII safety and firefighting Systems shall be possible from NA/Q-PI Control Room in case of incidental event on NA/Q-PIII and automatic activation failure.
Manual activation to be possible only during unmanned conditions; during manning periods (limited to maintenance operations) no manual intervention is possible from NA/Q-PI Control Room and Total Saturation Firefighting System shall be excluded with dedicated selector key-locked to avoid dangerous situation for personnel.
The presence of confirmed fire or gas in any area of the Platform will cause shut-down of NA/Q-PIII Platform.
No H2S is expected in the fluids treated on the Platform, thus no toxic gas detection is required.
Detectors to be installed on NA/Q-PIII Platform shall be selected among the following types on the basis of predictable hazardous scenario:
• Heat Detector
o Fusible Plugs (TSE);
o Linear Heat Detector Cables (LHD);
o Rate-of-rise (HD) (with ambient temperature compensation).
• Smoke Detector
o Optical (YE).
• Flame Detector
o Ultraviolet / Infrared (BE).
• Flammable Gas Detector
o IR Point type (CGD).
F&G System components are self-monitoring and any fault that makes unavailable the System or any part of it shall be clearly indicated at the NA/Q-PI Platform Control Room (“fault” alarm).
Moreover, the System has been designed so that maintenance, function testing, etc. can be carried out without disabling it. All detectors have been positioned in a way that they are easy to reach for maintenance, testing and inspections.
The selection of the fire and Gas Detectors type depends on the characteristic phenomena of combustion and on the predictable initial leak in the monitored zone.
F&G detectors cabling shall be arranged and specified to reduce the risk of loss of fire and gas detection functionality in the event of an incident, in particular:
• cables connecting fire and Gas Detectors to the fire and gas junction box shall be diversely routed as possible;
• fire and gas junction box will be positioned to reduce its exposure to potential fire and explosion events;
• the F&G marshalling and System cabinets shall be located in a protected area outside process area;
• F&G cables shall be specified as fire resistant type to IEC 60331.
The shut-down logic governing executive actions in response to fire and gas detection is described in the ESD/PSD Block Diagram (doc. n° AN3-B-HSE-DG-11004