Fire Suppression System.

The purpose of a fire suppression system is to either put out a fire or stop it from propagating. These systems are often used together with fire alarms and smoke or heat detectors to safeguard people and physical structures. The three main fire suppression system categories use water, inert gases, or various chemical agents to suppress a fire. These systems can also be automatic or manual, depending on whether they require outside intervention to activate. Some fire suppression systems can be hazardous to anyone in the general vicinity, including the danger of asphyxiation associated with pumping inert gases into an area to starve a fire of oxygen.
Water tends to be one of the most commonly used types of fire suppression, and is typically utilized in a sprinkler system. This type of fire suppression system can be either wet or dry. A wet sprinkler system is constantly charged, meaning there is always water in the pipes. This type of fire suppression system can be automatic, and it will activate if the system senses smoke or an excessively high temperature. Dry sprinklers are manual systems that can only be activated after a water source is connected to a stand pipe.
Another method of fire suppression involves filling an area with inert gas. Since fires require oxygen to burn, this can have a smothering effect.These fire suppression systems are commonly used in sensitive areas where water could potentially damage items such as computer equipment or documents. Computer server rooms are one area where inert gas, such as argon, is often used to suppress fires.
Inert gas can suppress a fire without damaging electronics or other equipment, but it can also pose other health and safety hazards. In some cases, an inert gas fire suppression system can lead to asphyxiation. Most of these systems come equipped with alarms to warn personnel to leave the area before the gas is released. Another potential issue with these systems is pressure, since the sudden introduction of a previously compressed gas into a small space can potentially blow out windows or walls.
Both wet and dry chemicals can also be used in fire suppression systems. These systems are typically automatic, though they can also have manual controls to activate the release of fire suppressing chemicals. Some materials can react poorly to the presence of water or inert gases, in which case a dry or wet chemical fire suppression system is often the safest option. Since these chemicals may be hazardous to human health, a delay is often built in

Heat Detector

The heat detector operates by using a matched pair of thermistors to sense heat. One thermistor is exposed to the ambient temperature, the other is sealed. In normal conditions, the two thermistors register similar temperatures, but, on the development of a fire, the temperature recorded by the exposed thermistor will increase rapidly, resulting in an imbalance of the thermistors and causing the detector to change to the alarm state.
                 Rate of Rise detectors are designed to detect a fire as the temperature increases, but they also have a fixed upper limit at which the detector will go into alarm if the rate of temperature increase has been too slow to trigger the detector earlier.
Fixed heat detectors only change to the alarm state at a preset temperature.

UV/IR (Ultraviolet/infrared) Flame Detector.

UV/IR Detector, which makes use of an ultraviolet radiation sensitive phototube in addition to an infrared detector. This combination provides a flame detector which is highly immune to false alarms. The UV portion of the detector, as described in the previous section, is combined with an infrared detector, which responds to changes in the intensity of infrared radiation. By sensing very specific wavelengths in both the UV and IR spectra and then processing these Signals with a microcomputer, a very high degree of discrimination is achieved. Incorporated in the IR circuitry is a flicker discrimination circuit. This permits the detector to ignore steady IR sources such as hot objects. The inherent flickering of a flame provides the necessary modulation to activate the IR circuit. Since a flame is a copious source of both ultraviolet and infrared radiation, discrimination is provided when both UV and IR emissions are detected. If only UV is detected, as in the case of arc welding, no alarm is given. If only IR is detected, such as a large modulating hot object, no alarm is given. However, if both conditions are met in the correct combination and intensity, as determined by an algorithm in the microcomputer, a fire is identified and the alarm outputs are activated. 

Current Level          Detector status
        0mA                           Fault
        2mA                           Optical Integrity (io) Fault.
        4mA                            Normal Operation
        8mA                            IR Alarm Only
        12mA                          UV Alarm Only
        16mA                          Pre-Fire Alarm
         20mA                         Fire Alarm


UV ( Ultraviolet) Flame Detector.

Flame Detector which contains an ultraviolet photo tube that responds to radiation in the 185 to 260 nano meter region when radiation from a flame strikes the cathode plate within a UV detector tube, electrons are ejected from the cathode plate. These electrons are accelerated towards the positively charged anode of the tube. They collide with molecules of an ionization gas, with which the tube is filled. This emits more electrons and produces an avalanche condition. More   electrons are released which creates a momentary electron flow from the cathode to the anode. This momentary current (pulse) recurs at a rate proportional to the intensity of the UV radiation. This output converted to standard mA  output.

IR GAS DETECTOR

The infrared (IR) method of gas detection relies on the IR absorption characteristics of gases to determine their presence and concentration. IR gas detectors consist of an IR light source (transmitter) and light detector (receiver) to measure the intensity both at the absorption wavelength and a non-absorbed wavelength. If gas is present in the optical path, it will affect the intensity of light transmitted between the light source and the detector. This change in intensity provides the data for determining that a specific gas or type of gas is present. This method works only for gases that can absorb infrared radiation. Most hydrocarbon based gases absorb IR radiation at around 3.4 micrometers, which is transparent to both water and carbon dioxide vapors.Combustible IR gas detection can take one of two forms: either the point detector or the open path detector. The primary difference between point detectors and open path is the size of the IR path and its relationship to the gas/vapor sample source. The self-contained point detector has a smaller IR path than the open path detector, and is used to monitor fixed areas of space. The open path detector usually consists of a separate transmitter and receiver, which monitor much larger areas of space. Consequently, in some instances a single open path detector serves the function of multiple point detectors.

Working Principle of Combustible or Flammable Gas Sensor

Many gases and vapors are combustible. The catalytic bead converts the combustible materials to heat. A change in heat is then converted to a change in resistance, which can be measured.
Taking a matched pair of catalytic beads and coating one so that it does not respond to the presence of combustible gases can compare the change in resistance between the two beads. The bead that is coated is called the reference bead and the other is called the active bead. Because the beads are a matched pair, they will respond equally to changes in ambient temperature, humidity, and pressure. This makes the sensor virtually immune to changing environmental conditions.
  By connecting one end of each catalytic bead together, a series circuit is formed. This circuit is supplied with a constant current. The voltage drop across each of the beads will be identical in the absence of combustible gases. As combustible material is converted to heat, the resistance of the active bead increases and causing a voltage drop across each bead to be different. This difference is proportional to the amount of combustible gas that is present.
 The voltage from the sensor is amplified and fed to an Analog to Digital (A/D) converter and then made available to the microprocessor. The baseline and the gain for the amplifier are set using digital potentiometers. They are adjusted by the microprocessor during calibration.

OPTICAL SMOKE DETECTOR

In one type of photoelectric device, smoke can block a light beam. In this case, the reduction in light reaching a photocell sets off the alarm.
 In the most common type of photoelectric unit, however, light is scattered by smoke particles onto a photocell, initiating an alarm. In this type of detector there is a T-shaped chamber with a light-emitting diode (LED) that shoots a beam of light across the horizontal bar of the T. A photocell (light receiving cell), positioned at the bottom of the vertical base of the T, generates a current when it is exposed to light. Under smoke-free conditions, the light beam crosses the top of the T in an uninterrupted straight line, not striking the photocell positioned at a right angle below the beam. When smoke is present, the light is scattered by smoke particles, and some of the light is directed down the vertical part of the T to strike the photocell. When sufficient light hits the cell, the current triggers the alarm.



Auto Ignition Temperature

Auto ignition temperature is the minimum temperature at which a substance will spontaneously ignite in air without any external source of ignition, such as spark or flame.

              Ignition Temperature of common liquids and gases.
Name
Ignition Temperature(OF)
Acetaldehyde
347
Acetic acid
867
Acetone
869
Acetylene
581
Ammonia
1204
Benzene
928
Butane
788
Carbon
1292
Carbon monoxide
1128
Cyclohexane
473
Diethyl ether
320
Ethane
882
Ethyl alcohol
685
Ethyl benzene
810
Ethyl ether
356
Ethylene
842
Hydrogen
932
Gasoline
536
Iso-butane
864
Iso-pentane
788
Isopropyl alcohol
750
Methane
999
Methyl alcohol
867
Naphtha
550
n-Butane
550
n-Heptane
399
n-Hexane
437
n-octane
403
n-pentane
500
Propane
842
Styrene
914
Toluene
896
Xylene-m
982
Xylene-o
867
Xylene-p
984

IONIZATION SMOKE DETECTOR

A typical ionization chamber consists of two electrically charged plates and radioactive source (typically Americium 241) for ionizing the air between the plates .The radioactive source emits alpha particles that collide with the air molecules and dislodge their electrons as molecules loser electrons ,they become positively charged ion. As other molecules gain electrons, they become negatively charged ions. Equal numbers of positive ions and negative ions are created. The positively charged ions are attracted to the negatively charged electrical plate, while the negatively charged ions are attracted to the positively charged p[late. this creates a small ionization current that can be measured by electronic circuitry connected to the plates.(normal condition in the detector)
Particles of combustion are much larger than the ionized air molecules. As particles of combustion enter an ionization chamber, ionized molecules collide and combine with them. Some particles become positively charged & some become negatively charged. As these relatively large particles continue to combine with many other ions, they become recombination centers, and the total number of ionized particles in the chamber is reduced. This reduction in ionized particles results in decrease in the chamber current i.e. sensed by the electronic circuitry monitoring the chamber. When the current is reduced by a predetermined amount, a threshold is crossed and alarm condition is established.










ABBREVIATIONS


A
AC                   Alternating Current
ACR                 Air Circuit Breaker
AGA                 American Gas Association
AHU                Air Handling Unit
ANSI                American National Standards Institute
API                  American Petroleum Institute
ATEX               Atmosphere Explosibles
B
BASEEFA        British Approvals Service for Electrical Equipment in
                        Flammable Atmospheres
BDV                Blow down Valve
BMS                Building Management System
BSI                  British Standards Institution
BVQI               Bureau Veritas Quality International
C
CCR                 Central Control Room
CEN                 Committee European de Normalization (European Committee for
                         Standardization)
CENELEC        European Committee for Electrotechnical Standardization
CFL                 Compact fluorescent Lamp
CMS                 Condition Monitoring Systems
COMP              Continues optical monitoring path
CRT                 Cathode Ray Tube
CRU                 Condensate Recovery Unit
CSA                 Canadian Standards Association
CSP                  Collector and Separation Platform
D
DACR              Digital Alarm Communicator Receiver
DACS               Digital Alarm Communicator System
DACT              Digital Alarm Communicator Transmitter
DBUS              Data Binary Unit System
DC                   Direct Current
DCS                 Distributed Control System
DPT                 Differential Pressure Transmitter
DYNPOS          Dynamic Positioning (of rigs and ships)
E
E&P                 Exploration and Production
EC                    European Communities
EECS               Electrical Equipment Certification Service (UK)
EEPROM         Electrically Erasable Programmable read only memory.
EL                    Explosive limit
ELCB               Earth Leakage Circuit Breaker
EOL                 End of Line
EOR                 Enhanced Oil Recovery
ESD                 Emergency Shutdown System
ESDV               Emergency Shutdown Valve
ESP                  Electric Submerged Pump
EU                   The European Union
F
F&G                 Fire & Gas System
FACP               Fire alarm control panel
FCV                 Flow Control Valve
FD                   Filament Detector
FD                   Fire/Flame Detector
FID                  Flame Ionization Detector
FM                   Factory Mutual
FM                   Frequency Modulation
FPD                 Flame photometric Detector
FPSO               Floating Production Storage & Offloading
FT                   Flow Transmitter
G
GB(S)              Gravity Base Structure
GC                   Gas Chromatography
GDF                 Gas Detector Flammable
GDT                Gas Detector Toxic
GOR                 Gas Oil Ratio from the well
GOSP               Gas Oil Separation Plant
GTP                 Gas Treatment Platform
H
HART              Highway Addressable Remote Transducer
HD                   Heat Detector
HID                 High Intensity Discharge
HIPPS              High Integrity Pressure Protection System
HIPS                High Integrity Protection System
HMI                 Humane Machine Interface
HP                   High Pressure
HPS                 High pressure sodium
HPU                 Hydraulic Power Unit 
HVAC              Heat Ventilation & Air Conditioning
I
I/O                  Input/Out put
I/P                   Current to Pneumatic
IEC                  International Electro-technical Commission
ILD                  Instrument loop diagram
IP                     Ingress Protection
IR                    Infra Red
IS                     Intrinsically safe
ISO                  International Standards Organization
J
JB                    Junction Box
L
LAN                 Local Area Net Work
LCD                 Liquid Crystal Display
LCV                 Level Control Valve
LED                 Light emitting diode
LEL                 Lower Explosive Limit
LHD                Linear Heat Detection Cable System
LNG                 Liquefied Natural Gas
LP                    Low Pressure
LPG                 Liquefied Petroleum Gas 
LT                   Level Transmitter
LVDT              Linier Variable Differential Transducer
LVDT              Linier Voltage Differential Transformer
M
MBFU              Mercury vapor
MBTF              Blended mercury vapor
MCB                Miniature Circuit Breaker
MCC                Motor Control Centre
MCCB              Molded Case Circuit Breaker
MICC               Mineral Insulated Copper Cable
MODEM          Modulator & Demodulator
MOS                Metallic Oxide Semi-conductor
MSDS              Material Safety Data Sheet
MTBF              Mean Time between Failure
N
NAC                 Notification Appliance Circuit
NEMA             National Electrical Manufacturers Association (US)
NFPA              National Fire Protection Association
NGL                Natural Gas Liquids 
NRTL              Nationally Recognized Testing Laboratories (US)
NRTL              Nationally Recognized Testing Laboratory 
P
P&ID               Piping instrument diagram
P/I                   Pneumatic to Current
PAGA              Public Announcement General Alarm
PCP                 Progressive Cavity Pump
PCV                 Pressure Control Valve
PD-Meter        Positive Displacement meter
PGP                 Power Generation Platform algorithm
PID                  Proportional Integral Derivate control 
PIMS               Production Information Management System
PLC                 Programmable Logic Control
PMT                photo multiplier tube
POC                 Pimp of controller (for artificial lift)
POSMOR         Position mooring for a floating facility
PPB                 parts per billion
PPE                 Personal Protection Equipment
PPM                parts per million
PROM              Programmable read only memory
PSD                 Process Shutdown System
PT                   Pressure Transmitter
PV                   Process Variable
R
RAM                Random Access Memory
RF                   Radio Frequency
ROM                Read Only Memory
ROV                 Remote Operated Vehicle (for subsea work over)
RTD                 Resistance Temperature Detector
RTU                 Remote Terminal Unit
S
SAP                 Systems Applications and Products
SAS                  Safety and Automation System
SCADA            Supervisory Control and Data Acquisition
SD                   Smoke Detector
SDI                  Smoke Detector ionization
SDO                 Smoke Detector Optical
SHE                 Safety Health Environment
SIL                   Safety Integrity Level
SOLAS             Safety of Life at Sea (convention)
SP                    Set Point
SRU                 Sulfure Recovery Unit
SWL                Safe Working Load
T
 Ta                   Tamb Ambient Temperature
TCD                 Thermal conductivity detector
TCV                 Temperature control valve
TDSA              Time Domain Signal Analysis
TIP                  Tie in Platform
TLP                 Tension Leg Platform
TT                   Temperature Transmitter
TWA               Time Wait Average
U
UEL                 Upper Explosive Limit
UHF                 Ultra High Frequency
UL                   Underwriters Laboratory Inc.
UMS                Unmanned Machinery Space Classification (marine =E0)
UPS                 Uninterrupted Power Source
USM                Ultra Sonic Meter
UV                   Ultra Violet
V
VCB                 Vacuum Contact Switch
VCR                 Vacuum Circuit Breaker
VESDA            Very Early Smoke Detection Apparatus.
W
WHP               Well Head Platform