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Fire and Gas (F&G) System

Consists of

· Manual fire call points

· Fire detectors

· Flammable gas detectors

· Toxic gas detectors

· Local Fire alarm panels

· F&G PLC

· Alarms

Alarms

· Loud speaker – For unit

· Optical Beacon

· Motor siren

· Strong sound

· For fire only

· Local Bell – Use in building

Local fire alarm panels

· Has a mimic panel to know where the fire originated

· Only for buildings, for plants, we rely on DCS.

· Purpose

· For fire brigade

· Because buildings are common alarm we need to know where fire is

· Types

· Addressable

· More diagnostics

· Chain loop topology. If 1 detector fails, the other detectors can till work

· Conventional

· One loop per room

· If 1 detector fails, all other detectors won’t work

Fire and Gas Voting

· A method to ensure robustness against failure

· Do IPF study for fire and gas – to be implemented

· Normally use 1oo2D

· Originally 1oo2, If 1 fault become 1oo1. Unlike safeguarding if 1 fault, fail safe

· For automatic, 2oo2

Fire Detection System

Type of fires are

· Flaming – From hydrocarbons

· Smoldering – Fire burning without flame

· Flash

For early detection one need to detect

· Smoke first

· Flame Second

· Heat last

Fire is detected by looking at

· Flame

· Smoke

· Heat

· Human visual

Type	Advantage	Disadvantage	When to use
Flame	Fast detection
Smoke	Early warning		Closed areas, for early warning
Heat	Hazard specific, less nuisance alarms, reliable	Cannot function test, damage replace, Slow response	When rapid fire spread is unlikely,
Person

Human Visual

· Manual Call Points

· In process area Installed at side of roads every 100 meters

· In offsite area installed at side of roads every 200 meters

Flame based fire detectors

Type	Principle	Advantage	Disadvantage	When to use
Infrared	Detect IR from flame flickering	Open fires	Cannot detect smouldering fires, Cannot detect H2 based fire, Solar radiation interference	Preferred technology for hydrocarbon
Ultraviolet		Extremely Fast detection, open fires	Heavy smoke will foul the lens. Welding, flare, black body interference.
UV-IR		Expensive		The best
IR multiple Freq
Visual CCTV

Smoke based fire detectors

· Smoke detectors provide the earliest warning for fires.

· From critical buildings, a concept called VESDA(Very early smoke detection apparatus) is utilized. In our plant, the system is called USSD (Ultra sensitive smoke detection). The concepts of USSD is

· Aspiration units are installed throughout the building. Installed normally on ceilings

· The smokes are sucked and brought to a central unit

· The central unit hosts an optical type smoke detector

Type	Principle	Advantage	Disadvantage	When to Use
Optical / Scattered light type	Smoke deflects beam of light	Good for smouldering fires,		Preferred choice, most common
Ionization	Smoke particles reduce current created from ion flow of radioactive materials	Sensitive to small smoke particles	Must be applied together with heat detectors	Only when ionization type cannot be used. Use in printing workshops, highly flammable places

Heat detector types

· Most commonly used inside plants since it’s hazard specific

Type	Principle	Advantages	Disadvantages	When to use
Fusible	Heat will melt a tube containing pressure	Cheapest	False alarms, easily
Continuous-line	Heat will cause insulators to melt and 2 conductors come in contact
Bimetallic	Heat causes metal to bend

Control is the art of keeping a measured variable at a desired level
How to determine where to put fire detectors?

· Best is use of F&G mapping software

· No standards, just based on principle (owner) study

· Installed at most likely place for leaks

· Mechanical seals

· High pressure Flanges

· If gas tend to go up, the detector should be place on top and vice versa

Gas Detection System

Flash point is the lowest temperature at which a liquid can form an ignitable mixture in air
Installed normally at

· Analyzer house

· Pit

· HVAC air intake for buildings in plant

Flammable gas detectors

Type	Principle	Advantages	Disadvantage	When to use
Electro Catalytic	Combustible gas oxidizes and produces heat	Robust, detects any combustible gasses, Cheaper	Catalyst can be poisoned, Single point detection, fail-dangerous	Use when hydrogen detection is needed
Electro Chemical	Electrolysis of gas creates voltage	PPM Level, Good repeatability,	Cannot be used at high temperature and low humidity, Must change electrolytes, Not fail safe, Gas specific (H2S, SO2,CO2,NO2, CL2)	Old technology, typically avoided, used mainly for toxic gas (see below)
Point type Infrared Gas Detector		Long service life, background gas does not effect service life, has diagnostic, fail safe	Cannot detect hydrogen	Preferred choice for HC plants.
LOS Infrared Gas detectors		Larger coverage	Expensive, high prone to nuisance alarms	Unit of measure is PPM Meter

Control is the art of keeping a measured variable at a desired level
The most common control algorithm used is the PID control

Hazardous Gas detectors

· 2 categories

· Category 1 – Immediate health effect gasses (H2S, CO, HCL)

· H2S < 10 PPM, more than that is dangerous. 1000 PPM = dead

· HCL < 5 PPM

· Category 2 – Long Term (Vinyl Chloride, benzene, toluene)

Type	Principle	Advantages	Disadvantage	When to use
Electro Catalytic H2S gas detector	Combustible gas oxidizes and produces heat	Robust		For H2S detection
Electro Chemical	Electrolysis of gas creates voltage	PPM Level, stability, immune to environment change	Must change electrolytes, Not fail safe, Gas specific (H2S, SO2,CO2,NO2, CL2)	Preferred choice
Semiconductor

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