Basics on Fire & Bilge Alarm Systems

1. BY Lt NS Wickramasinghe Bsc E & E Eng(Hons )

2. There are four principal methods for detecting fire
Heat,
Smoke,
Flame
Combustion detectors

3. There are two methods for detecting fire from the presence of
heat
Fixed temperature heat detectors - operate when the ambient
temperature increases sufficiently to predetermined level heat
detector will operate
A rate-of-rise heat detector - operates when the ambient
temperature increases over time equal to or greater than the
rate of change the detector was manufactured to operate

4. These technologies can be broken down into four main types.
Electromechanical - As the name suggests electromechanical heat detectors operate due to a
combination of mechanical
movement creating an electrical circuit.
Optomechanical - This type of heat detector is a modern variation of the electromechanical
line-type heat detector and could be classified as an optomechanical distributed heat.
Electropneumatic - heat detectors comprise a controlled vented chamber containing a
diaphragm that moves due to a pressure differential according to the rate of change of the
ambient temperature.
Electronic (Thermistor) - A thermistor is a type of resistor whose resistance changes
significantly according to temperature.

6. Ionization Detectors - Ionization detectors have an ionization chamber
and a source of ionizing radiation. The source of ionizing radiation is small
quantity of americium-241 which is a source of alpha particles (helium
nuclei). The ionization chamber consists of two plates separated by about a
centimeter. The battery applies a voltage to the plates, charging one plate
positive and the other plate negative.

7. Advantages of Ionization Smoke
Detectors

Detects invisible products of
combustion
 detect other aerosol
 Quick acting
Disadvantages
of Ionization Smoke
Detectors
 Detects the presence of smoke only, not toxicity
 Has a potential for high false alarm rate
 Typical locations or hazards for ionization detection
Typical locations or hazards for
ionization detection
 Clean rooms Computer rooms
 Mechanical air ducts Locations where sensitive
detection methods are needed

8. Photoelectric Detectors - 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.

9. Advantages of Photoelectric Smoke
Detectors

Sensitive to visual particles of smoke

Detects smothering low heat fires Disadvantages of Photoelectric Smok
Detectors

Provide early warning
 Early contamination by dust causing
reduced sensitivity
Typical locations or hazards for
 Detects presence of smoke, not
photoelectric detection
toxicity
 Must be cleaned on a regular basis
 Office areas
 Has a potential for high false alarm
 Clean rooms
rate





Raised floor spaces
Computer rooms
Telecommunications rooms
Electrical equipment rooms
Sleeping rooms

10. Flame detectors are used to detect the light radiation
component of a fire. Typical detectors of this type detect the
wavelength of either IR or UV or a combination of the two.
These detectors are extremely fast acting and are used in areas
where rapidly occurring fires or explosions could occur.

11. Advantages of Flame
Detection

Extremely fast acting
Disadvantages of Flame
Detection




Narrow field of vision
Expensive
Requires unobstructed field
of view
Difficult to maintain

12. These detectors respond to the various gases produced
during the combustion process.




Carbon monoxide
Carbon dioxide
Steam
Other elements
The Fire-Gas detector employs two types of technology to
predict the fire. One method uses a semiconductor
material that changes the metals conducting potential in a
fire situation. The other method uses a catalytic element
encased in an Aluminium bead.

13. Advantages of Fire-Gas Detection
 Detects products of combustion
 Sensitive enough to detect levels of gases
 produced between the occurrences of
detectable
levels and detectable heat levels
 Detects gases prior to reaching lethal levels
particulate
Disadvantages of Fire-Gas Detection
 Can be prone to false alarms
 Must be mounted at a low level, leaving it susceptible to damage
 Can be poisoned
 Not suitable for areas where CO and CO2 and produced as
part of
the functions within the area

Cannot be considered as a universal replacement
for
smoke
and/or thermal detectors

High cost

14. For environments where detection of smoke is most critical, an
air-sampling system provides the earliest possible detection.
An air sampling or aspirating type fire detection system is a
self-contained smoke detection package compromised of five
primary components

Air-sampling system

Aspiration system
Filter assembly
Detector
Control system




15. Bilge pumps are placed in the hold or lower levels of a ship to
remove accumulated water from the lowest portions of the
vessel. Ship or boat owners install bilge pumps at the lowest
possible level of the ship below the sea surface in an area
called the bilge. The bilge forms the joint where two sides of a
ship or boat connects.

16. Mount the pump - You must not place the pump in the bilge
unrestrained. If it falls over it will suck air and burn out.
Use smooth-bore hose - Corrugated hose reduces pump output by as
much as 30%, so always connect the pump to the discharge fitting with
hose that has a smooth interior surface.
Place the discharge above the waterline - If the discharge is
submerged when the pump runs, the ocean siphons back through the pump
into the bilge when the pump shuts off.
Connect to the battery- When you turn the power off to leave the boat
unattended, you don't want to turn off the bilge pump. Connect an
automatic bilge pump directly to the battery, not through the distribution
panel.