Fire and Smoke

Question 1

Which smoke detector has radioactive components?

Answer 1

Ionization detector

Question 2

What are ionization detectors used for?

Answer 2

Invisible smoke (< 0.3um) such as during incipient phase or fast moving flame fires

Question 3

What are photoelectric light scattering detectors used for?

Answer 3

Best for larger smoke particles ( > 0.3 to 10um) such as in a smoldering phase or slowly developing fires

Question 4

What are laser smoke particle detectors used for?

Answer 4

Good for 0.001 to 10 um particles. Due to compact size can be used in ASD systems

Question 5

What are cloud chamber detectors used for?

Answer 5

Best for incipient phase as its good for sensing arcing wires or overheating of insulation

Question 6

What type of detection is not considered a life safety device?

Answer 6

Thermal Detector

Question 7

What causes false alarms in flame detectors?

Answer 7

Sources of UV/IR

Question 8

Describe the operation of a light obscuration smoke detector?

Answer 8

Smoke blocks the amount of light that the sensor receives and triggers an alarm

Question 9

Bimetallic strips are used in ________.

Answer 9

Thermal sensors

Question 10

Describe how an ionization detector works

Answer 10

Americium-241 in the sensor ionizes the air in the sensor which allows a small current to flow. If smoke enters the sensor the ions attach themselves to the smoke particles causing a decrease in current.

Question 11

What are the 4 phases of fire?

Answer 11

1) Incipient: thermal decomposition releases tiny combustion particles invisible to the eye

2) Smoke: visible smoke can be seen but no appreciable heat rise

3) Flames: visible flames are present due to combustion of gasses

4) Intense heat: flames are at their peak, oxygen is rapidly consumed, and superheated gasses are generated

Question 12

What type of detector can be used to monitor a zone?

Answer 12

Air Aspirating Smoke Detector

Question 13

What type of detector can be used to monitor an area?

Answer 13

Spot smoke detector

Question 14

Where should you avoid mounting a heat detector?

Answer 14

Air motion or significant drafts

Question 15

What are some considerations when installing a heat detector?

Answer 15

1) Make sure the area is enclosed
2) Should be installed in a location where a fire may be expected
3) Should be installed in an area with the most rapid heat rise

Question 16

What are the three types of heat detectors?

Answer 16

1) Fixed temperature detectors
2) Rate of rise temperature detectors
3) Rate anticipation detectors

Question 17

What are immediate changes to the environment by a fire called?

Answer 17

Fire signature

Question 18

What are the 3 functions of a fire and smoke detection system?

Answer 18

1) Detection
2) Annunciation
3) Protective measures

Question 19

Why are optical and ionization smoke detectors combined?

Answer 19

So they can detect a wider range of particles

Question 20

What type of smoke detection is suitable for detecting overheating wire insulation?

Answer 20

Cloud chamber smoke detector

Question 21

How can you test a smoke spot detector?

Answer 21

1) Single head testing: individual heads are accessed and calibrated with an aerosol
2) System testing: specific heads are injected with calibrated smoke

Question 22

If a smoke detector tests out of specification what procedure is followed?

Answer 22

1) Clean the detector
2) If still out of spec replace the detector

Question 23

How is optical flame detector sensitivity determined?

Answer 23

Sensitivity varies based on fuel and is tested against a reference flame size for a given fuel type.

Question 24

What are the three optical detector designs?

Answer 24

1) IR detectors
2) UV detectors
3) UV and IR detectors