M15.20 Fire protection

Question 1

What type of sensor is used to detect duct leaks?

Answer 1

Bi metallic strips

Question 2

What are the two types of fire loop detectors?

Answer 2

Semi conductor
Pneumatic loop

Question 3

What is the pneumatic loop known as?

Answer 3

The systron and donner loop

Question 4

What are the manufactures of semi conductor loops?

Answer 4

Graviner
Fenwall
Kidde
Edison

Question 5

How does a semi conductor system work??

Answer 5

Each loop has a metal tube that contains a semiconductor material. This
material decreases its electrical resistance with increasing temperature. An
alarm is triggered when the resistance between the central wire and the tube
decreases below a predetermined threshold

Question 6

Negative of a bi metallic strip sensor?

Answer 6

This sensor can fail in either the open or closed position, either failing to detect a fire or giving a false alarm. This system cannot be tested to find defective sensors

Question 7

On a continuous loop sensor, how is a false alarm prevented?

Answer 7

By using an AND gate

Question 8

How is a semi conductor loop assebled?

Answer 8

Each semiconductor loop has a stainless steel tube, filled with a
semiconductor ceramic material with a wire in the centre.
The ceramic material functions like an endless number of resistors. These
resistors have an NTC characteristic, because of the semiconductor material

Question 9

What type of electrical connection does the Graviner, fenwal, graviner and edison loops use?

Answer 9

All resistors are connected in parallel on one side by the internal wire that is
connected to the control unit. On the other side they are connected by the
tube that is connected to the ground

Question 10

What type of electrical conection does the Kidde loop use?

Answer 10

One semiconductor loop type has two internal wires. The upper wire is also
connected to the control unit and the lower wire is connected internally to
ground. This means that there is no difference in the function

Question 11

What is the resistance for short loops?

Answer 11

10 mega ohm

Question 12

What is the resitance for long loops?

Answer 12

1 mega ohm

Question 13

What is the trigger value for semi conductor loops?

Answer 13

500 ohm

Question 14

How is an open loop situation prevented on a semi conductor loop?

Answer 14

To prevent the situation of a fire which cannot be detected due to an open
loop, the end of the loop is connected to the beginning and a closed loop is
formed

Question 15

How is the semi conductor loop tested?

Answer 15

So that this double loop failure is almost impossible, the closed loop condition
is tested during the operational test, for example, before each engine start.
Normally the loop is closed via the relaxed contact of the test relay, but during
the test the loop will open at the end and is connected to ground via a test
resistor. An open loop condition is always detected during a fire warning test

Question 16

On a wheel well fire system with semi conductor loop what can cause a false alarm?

Answer 16

A short circuit as the resistance will drop

Question 17

How are short circuit false alarms prevented on duel loop semi conductor systems?

Answer 17

By using the duel loop, if one loop detects fire, and the second does not for 15 seconds the warning is cancelled and the loop indicating ire will be shown as faulty

Question 18

What is the maximum bend of a semi conductor loop?

Answer 18

3.2 MM

Question 19

What is the minimum bend radius of a semi conductor loop?

Answer 19

25.4 MM

Question 20

What makes up a modern gas pressure loop?

Answer 20

Two pressure switches and a resistor

Question 21

What are the two purposes of the pressure switches in a gas loop?

Answer 21

One is a monitor switch, and is typically closed by the gas pressure, typically the pressure in the loop is two times normal atmospheric pressure.
The second is the alarm switch which closes at a higher pressure.

Question 22

What is the purpose of the resistor at in the gas loop?

Answer 22

The resistor is the responder, the control unit uses the resistor to know is the switch is open or closed.

Question 23

What hapens to the resistor is the fire switch is triggered?

Answer 23

The fire switch triggers and the resistor is bypassed causing the alarm to be triggered by the control unit

Question 24

What are the conditions orequied to trigger an alarm in a gas loop?

Answer 24

Either the whole loop has an average temp of 20 degrees, or a small section is heated to 400 degrees.

Question 25

What happens if a small section reaches 400 degrees on a gas loop?

Answer 25

A discrete element made of Titanium Hydride sets additional gas
free that increases the loop pressure

Question 26

How is aa damaged gas loop detected?

Answer 26

If the internal gas pressure reduces, the monitor switch will open, triggering a faulty loop warning

Question 27

What is contained in a fire bottle?

Answer 27

Liquid halon 1301 held under 600 psi nitrogen pressure

Question 28

How is a fire bottle measured?

Answer 28

Without the discharge head fitted

Question 29

How many discharge heads may be fitted to an induvidual fire bottle?

Answer 29

As many as the compartments the bottle must supply

Question 30

What prevents the frangible disk from blocking spray nozzles?

Answer 30

A filter

Question 31

What type of explsive is used in the discharge head?

Answer 31

400 mg of class c explosive

Question 32

How does the discharge head get activated?

Answer 32

Wire known as a squib heats up and ignites the powder

Question 33

How long is a discharge cartridge guaranteed for?

Answer 33

Its expiry date, the max service life is 6 years, the bottle must be replaced after 10 years

Question 34

How can bottle pressure be checked?

Answer 34

By pushing a switch on the bottle, this illuminates the appropriate indication.
or by turning an Allen key which opens the pressure switch.

Question 35

How are fire bottles protected against overpressure?

Answer 35

When the spray nozzle of the bottle is installed in the same compartment as
the heat source, for example in the cargo compartment or in some aircraft on
the engines, the frangible disc also has a pressure relief function.
The frangible disc breaks when the pressure inside the bottle increases to
about 1700 psi. This is about three times the normal pressure. The halon is
then discharged to the compartment via the spray nozzle.
The fire extinguisher bottle has an extra overpressure relief valve when the
bottle and the spray nozzle are in different compartments. This is always true
for the APU system. In this case the relief valve is a thermal fuse that melts
when the temperature exceeds a safe value.
An overboard pipe guides the halon to a hole in the fuselage. The hole is
normally covered by a red disc. When the thermal fuse melts the halon is
released overboard, pushing out the red disc.
When the bottle discharges via the thermal fuse, the amber bottle discharge
light on the fire control panel in the cockpit comes on and the red disc is
missing on the fuselage

Question 36

How else might a used bottle be indicated?

Answer 36

Some aircraft feature a yellow disk that is pushed out by a piston when the bottle is discharged