Fire and Gas Detection System Requirements for the Oil and Gas Industry. Offshore Platforms are also applicable for onshore plants/terminals. Safeguarding and Protective System to ensure oil and gas facilities are safe to operate.

1. Fire and Gas Detection System
(Offshore Facilities)
(Part 2 : Block Diagram (Philosophy), Signal Types and Redundant
Failure)
Chun Chet Gan (Ir.)
MSc Operations Management
[Manchester School Management]
University of Manchester Institute of Science and Technology (UMIST),
United Kingdom.
BEng (Hons) Mechanical Engineering
[Simon Building]
University of Manchester, United Kingdom

2. Fire and Gas Block Diagram
• A block diagram shows the source and destination of the signals.
• It is a general overview of the entire detection system (including signals to/from
other F&G sub-system or other panels)
• The arrows show the direction of the signals.
• This is the representation the entire fire and gas detection system.

3. Fire and Gas Block Diagram
• Drawing Format :
- Reference drawings,
- Drawn By/Checker/Approver,
- Notes,
- Legend (symbols and descriptions of the field devices or panel, etc.)
• Drawing Areas can be segregated :
- by area,
- hazardous and safe area,
- indoor and outdoor area,
- interfaces with other platforms (or other drawings)

4. FGS
FIELD DETECTORS
ALARM STATUS
(FROM PANELS)
ALARM
SHUTDOWN
POWER ISOLATION
ACTIVE SUPPRESS
SYSTEM
CLOSE DAMPERS
INDICATION (CONSOLE)
PUSHBUTTONS/
KEYSWITCHES
OFFSHORE PLATFORM – SIGNALS

5. FGS
FIELD DETECTORS
FIELD DETECTORS
• These are input devices (e.g. gas, flame, manual call points, smoke
or heat detectors).
• It detects whether there is a gas leak or a fire.
• Signals will be sent from individual devices to the system panel.

6. FGS
ALARM STATUS
(FROM PANELS)
ALARM STATUS (FROM PANELS)
• Status signals from other panels are sent to the fire and gas panel FGS
to monitor the conditions of the sub-system).
• The alarm conditions will activate appropriate outputs from the fire and
gas panel.
• Fault signals from these panels are sent to the FGS panel when there is
a fault in other panel or sub-system.

7. FGS
ALARM
SHUTDOWN
POWER ISOLATION
ACTIVE SUPPRESS SYSTEM
CLOSE DAMPERS
TO OTHER SYSTEM (PANEL OR FIELD DEVICE)
• These include signals to activate the output devices via the FGS
panel.
• For example PAGA alarm panel will activate the alarms and ESD
shutdown panel will close the shutdown valve or open the blowdown
valve when this output signals are sent from the FGS panel.
• This action can be used to isolate power from the power feeder at the
Motor Control Centre MCC/Switchgear Room.
• The solenoid valve attached to the deluge system is activated from
here.
• The HVAC panel that closes the gas tight dampers is also originated
from this signal.

8. • Indicators are located on a console. Indicators are also located in the
graphic screen.
• These are required to show whether there is a gas leak or a fire in a
designated area.
FGS
INDICATION (CONSOLE)
TO INDICATOR (CONSOLE/GRAPHIC SCREEN)

9. FGS
PUSHBUTTONS/KEYSWI
TCHES
FROM CONSOLE (HUMAN MACHINE INTERFACE HMI)
• Pushbuttons/keyswitches are located on the console. It is also
located in the graphic screen.
• The function is to start or stop the shutdown system, enable
maintenance, reset, etc.
FGS
FIELD DETECTORS
ALARM STATUS
(FROM PANELS)
ALARM
SHUTDOWN
POWER ISOLATION
ACTIVE SUPPRESS
SYSTEM
CLOSE DAMPERS
INDICATION
(CONSOLE)
PUSHBUTTONS/
KEYSWITCHES

10. TYPICAL BLOCK DIAGRAM – OFFSHORE
(FOR REFERENCE ONLY)
(this slide is from previous internal lecture)

11. I/O and Signal Types (and Its Application)
• The type of signal to/from the FGS panel are as follows:
1) Digital Input, Digital Output
2) Analogue Input.
• Digital Inputs
- Volt Free Contact, normally from panel (e.g. alarm signals)
- Supervised, and volt free (manual call points, panel fault signals)
• Digital Outputs
- Powered type (to a solenoid of a deluge valve, supervised for line-break)
- Volt free type (to panel, e.g. PAGA to activate the alarm, contact normally close
during normal operation, or ESD to shutdown the platform)
• Analogue Input
- 4 – 20 mA signal (field devices from gas detectors or flame detectors) (some
times, smoke detectors or heat detectors uses this input card)

12. Fire and Gas Detection System -
Signal Type
Analogue
I/O Type Description Device
AI Analogue Input Pressure Transmitter (4 – 20mA)
Smoke Detectors (0 – 25mA)
Heat Detectors (0 – 25mA)
AI3a Analogue Input, 3 wire Flame Detectors
Point Gas Detectors
AI3a Analogue Input, 3 wire Line-Of-Sight Detectors (Receiver)

13. Fire and Gas Detection System -
Signal Type
Digital
I/O Type Description Device
DIF Digital Input, Volt Free Contact ESD pushbutton (normally closed)
HWC (Hardwired Console) Maintenance
Override Keyswitches
Fire water pump status
DIS Digital Input , Volt Free Contact, Manual alarm callpoints
Supervised Valve limit switches (monitoring)
Turbine generator fire and gas status
FM 200 extinguishant system status
HVAC panel status
Addressable system status
HWC Pushbutton (start fire water pump,
activation deluge)

14. Fire and Gas Detection System -
Signal Type
Digital (con’t)
I/O Type Description Device
DO Digital Output, powered HWC (Hardwired Console) Indicator (3 watts)
Fail safe solenoid (10watts)
DOS Digital Output, supervised Non-fail safe solenoid (10 watts)
powered Shunt relays (10 watts)
DOF Digital Output, volt free contact Fire water pump start, inhibit start
Diesel generator pump, inhibit/stop
SDS sub-system (Fail safe)
PAGA system (Fail safe)
HVAC panel
Addressable system

15. Fire and Gas Detection System -
Signal Type
Addressable
I/O Type Description Device
AAI Analogue Addressable Input Field Addressable Devices
(smoke detectors, heat detectors, manual
alarm call points, volt free signals from
panel – via contact module, pressure
switches input signals – via contact module)
AAO Analogue Addressable Output Field Addressable devices (door release unit
- via relay module)

16. Fire and Gas Detection System -
Signal Type
Others
I/O Type Description Device
- - Line of sight detectors (receiver)
Remote LED Detector (Smoke Detector)
Remote Terminal Unit (Point Gas Detectors and
Line of Sight Detectors)
Contact module
Relay module

17. Failure Rate and Mean Time Between Failure
• Failure rate can be applied here. It is the number of detectors that failures in
operation.
• It is calculated based on percentage or fraction. If there are 10 failures in a hundred
(100), then, the failure rate is 10%. This figure is important to apply in calculating
the probability of failures.
• Mean Time between Failure MTBF is the time between two failures, the first and
the second failure (if it is start to first failure, it is the operating time before the first
failure). If there are several failures, the average is calculated. (The problem arise
when there is a coincident failure).
• This calculation is known as the time between failures is determined. If a gas
detector MTBF is 15 years, then, the time between failure is 15 years on average.

18. A Paper on Reliable and Safe Detectors
• I’ve written an article on this. Visit IEM website, under publication. Refer to
Jurutera, May 2008 issue, in the features section.
• The article writes on the factors that would assure the performance of the detectors.
These are (1) Good Operation Performance, (2) An Assured Built-in Quality, and
(3) Best Possible Suppliers.

19. Suppliers Performance Factors
• (1) Good Operation Performance –
the performance is calculated using
quantitative equation by considering
the number of days in operation. A
good number will indicate that the
performance is at optimum condition.
Also note that it is impossible to have
a total pass. Thus, an acceptable level
will show the required performance of
the detectors in the field.
• (2) An Assured Built-in Quality – A
system of management of the product
or service quality. This can be either
policy/procedure in place or
interpersonal skill(s) of the supplier.
This assures the quality that is built
into it, and
• (3) Best Possible Suppliers – a choice
of suppliers, to meet the required
specification is considered. The best
supplier will be awarded.

20. Redundant Failure
• Take note of failure rates of individual detectors. A coincident failure occurs when
both the detectors protecting the area fail to operate at the same time.
• Similarly, redundant failure, the spare or second detector, fails will cause a
failure/distruption in a particular area.
• This is a very unlikely occurrence. A theoretical reliability calculation is shown on
the next sheet which shows mathematically the probability of a coincident failure.
• Is it possible that two devices protecting an area fail to operate.
• If these two devices fail, then, other actions have to be considered to prevent an
inability to detect a gas leak at that same instance.
• So, if it occurs, the unprotected area has to be watched by the personnel working on
the platform.

21. Theoretical Reliability Calculations (1)
• Dependent Devices
• Single Solenoid
- Failure rate of each device is 1%
- Reliability is 100% - 1% = 99%
(or 1 – 0.01 = 0.99)
• Two solenoid in series
- Probability of devices in operation
is a subset of the main device.
- Reliability is 99% x 99% = 98.01%
(or 0.99 x 0.99 = 0.9801)
(same 1 percent failure)
S S
1% failure 1% failure
S
1% failure

22. GD
1% failure
Theoretical Reliability Calculations (2)
• Independent Devices
• Single Detector
- Failure rate of each device is 1%
- Reliability is 100% - 1% = 99%
(or 1 – 0.01 = 0.99)
• Two detectors in the area
- Probability of devices in operation is the probability of first detector operating and
the second detector operating subtract both detectors operating (remove coincident
failure).
- Reliability of single detector is 99%
- Reliability of both operating is 98.01% (subset device A in B, or B in A)
(same 1 percent failure)
- Reliability is 99% (first device), 99% (second device), 98.01% (both), 99.99%
(calculated redundancy)
1% failure
GD
1% failure
GD
99%
reliable
99.99%
reliable

23. Dependent and Independent Detectors
dependent independent

24. In Actual (1)
F1 F2 F3
T1 T2 T3 365 days
Start
Record Duration : 1 year (or 365 days)
T1, T2, T3, Tn : Operating Days
F1, F2, F3, Fn : Failure Days
Reliability is total operating days / 365 of individual device in operation

25. In Actual (2)
A & B : Devices, Machines or Equipment
Record Duration : 1 year (or 365 days)
T1, T2, T3, Tn : Operating Days
F1, F2, F3, Fn : Failure Days
CT1, CT2 & CTn : Coincident Operating Days
CF1, CF2, CFn : Coincident Failure Days
F1 F2 F3
T1 T2 T3 365 days
Start
F1 F2 F3
T1 T2 T3 365 days
Start
C
F
1
CT1 CT2 CTn 365 days
Start
A
B
Coincident A
& B
C
F
2
Reliability is total operating days / 365 of both device A & B in operation

26. Solution to Redundant Failure
• Portable gas detectors
(wireless) will be able to
resolve this problem.
• It is a temporary
measure on areas with
redundant failure.

27. PART 2 : Block Diagram (Philosophy), Signal
Types and Redundant Failure)
• End of Lesson 2
• Questions

28. OWN NOTES
• Fire and Gas Block Diagram
• BY INDIVIDUAL BLOCK (Source/Destination)
- OFFSHORE PLATFORM – SIGNALS
- FIELD DETECTORS
- ALARM STATUS (FROM PANELS)
- TO OTHER SYSTEM (PANEL OR FIELD DEVICE)
- TO INDICATOR (CONSOLE/GRAPHIC SCREEN)
- FROM CONSOLE (HUMAN MACHINE INTERFACE HMI)
• TYPICAL BLOCK DIAGRAM – OFFSHORE
(FOR REFERENCE ONLY)
(this slide is from previous internal lecture)
• I/O and Signal Types (and Its Application)
• Failure Rate and Mean Time Between Failure
• Suppliers Performance Factors
• Redundant Failure
• Theoretical Reliability Calculations
• In Actual
• Redundant Solution