Fire and Smoke Flashcards
Which smoke detector has radioactive components?
Ionization detector
What are ionization detectors used for?
Invisible smoke (< 0.3um) such as during incipient phase or fast moving flame fires
What are photoelectric light scattering detectors used for?
Best for larger smoke particles ( > 0.3 to 10um) such as in a smoldering phase or slowly developing fires
What are laser smoke particle detectors used for?
Good for 0.001 to 10 um particles. Due to compact size can be used in ASD systems
What are cloud chamber detectors used for?
Best for incipient phase as its good for sensing arcing wires or overheating of insulation
What type of detection is not considered a life safety device?
Thermal Detector
What causes false alarms in flame detectors?
Sources of UV/IR
Describe the operation of a light obscuration smoke detector?
Smoke blocks the amount of light that the sensor receives and triggers an alarm
Bimetallic strips are used in ________.
Thermal sensors
Describe how an ionization detector works
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.
What are the 4 phases of fire?
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
What type of detector can be used to monitor a zone?
Air Aspirating Smoke Detector
What type of detector can be used to monitor an area?
Spot smoke detector
Where should you avoid mounting a heat detector?
Air motion or significant drafts
What are some considerations when installing a heat detector?
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
What are the three types of heat detectors?
1) Fixed temperature detectors
2) Rate of rise temperature detectors
3) Rate anticipation detectors
What are immediate changes to the environment by a fire called?
Fire signature
What are the 3 functions of a fire and smoke detection system?
1) Detection
2) Annunciation
3) Protective measures
Why are optical and ionization smoke detectors combined?
So they can detect a wider range of particles
What type of smoke detection is suitable for detecting overheating wire insulation?
Cloud chamber smoke detector
How can you test a smoke spot detector?
1) Single head testing: individual heads are accessed and calibrated with an aerosol
2) System testing: specific heads are injected with calibrated smoke
If a smoke detector tests out of specification what procedure is followed?
1) Clean the detector
2) If still out of spec replace the detector
How is optical flame detector sensitivity determined?
Sensitivity varies based on fuel and is tested against a reference flame size for a given fuel type.
What are the three optical detector designs?
1) IR detectors
2) UV detectors
3) UV and IR detectors
