· Manual fire call points
· Fire detectors
· Flammable gas detectors
· Toxic gas detectors
· Local Fire alarm panels
· F&G PLC
· Alarms
· Loud speaker – For unit
· Optical Beacon
· Motor siren
· Strong sound
· For fire only
· Local Bell – Use in building
· 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
· 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
· Flaming – From hydrocarbons
· Smoldering – Fire burning without flame
· Flash
· Smoke first
· Flame Second
· Heat last
· 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 |
· 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
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 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 |
· 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 |
· 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
· Analyzer house
· Pit
· HVAC air intake for buildings in plant
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 |
· 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 |
||||