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Fire Protection Systems > Automatic alarm initiating devices > Flashcards

Automatic alarm initiating devices Flashcards

1
Q

Fixed temperature heat detectors

A
  • sounds alarm at a specific point, usually 135 deg or higher
  • relatively inexpensive compared to other types of systems
  • are the least prone to false alarms
  • reliable, but slowest to activate
  • not resettable
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2
Q

Fusible Elements

A
  • type of fixed temperature heat detector
  • holds a spring in a detector open until it melts and drops away spring to release and completes a circuit that sends an alarm signal.
  • fusible link must be replaced to restore the detector
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3
Q

Bimetallic

A
  • type of fixed temperature heat detector
  • 2 types of metal that have different heat expansion ratios in thin strips bonded together. one expands faster than the other when exposed to heat, causing strip to arch until it opens or closes a circuit sending the alarm signal
  • Most reset automatically
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4
Q

Continuous-Line

A
  • type of fixed temperature heat detector
  • operate by an increase in electrical resistance through a circuit (auto resetting) or a short in the circuit (fused portion must be replaced to restore)
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5
Q

Rate of Rise Heat Detector

A
  • respond in substantially lower temperatures that fixed-temp detectors
  • typically activate when temp increases 12 - 15 deg per minute
  • automatically reset
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6
Q

Pneumatic rate-of-rise line heat detector

A
  • large areas of a building
  • when air in metal tube expands from heat, a diaphragm responds and signals alarm.
  • limited to 1000 ft long
  • arranged in rows no more than 30 ft apart
  • 15 ft from walls
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7
Q

Pneumatic rate-of-rise spot detector

A
  • when air expands from heat, diaphragm responds signaling alarm
  • self contained, monitors specific location
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8
Q

Rate compensation heat detector

A
  • for use in areas subject to regular temp changes slower than that of fire condition
  • bowed struts contained in sleeve have slower expansion rate than sleeve. temp rises too fast, sleeve expands, causing bowed struts to signal alarm. a lower rise in temp will allow both the sleeve and struts to expand and not signal alarm
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9
Q

Electronic spot-type heat detector

A
  • can be calibrated to operate as rate-of-rise detectors and function at a fixed temp
  • designed to bleed or dissipate small amounts of current reducing chances of small temp change activating alarm
  • greater change in temp=larger amounts of current flowing and activation of alarm
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10
Q

about ___ of fire deaths are attributed to smoke inhalation and not to burns

A

65%

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11
Q

the preferred devices for occupancies such as residences, health care facilities, and institutional care facilities. Why?

A

Smoke detectors because they sense the presence of products of combustion much more quickly than heat-detection devices.

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12
Q

photoelectric smoke detectors

A
  • works on all types of fires
  • responds more quickly to smoldering fires than ionization smoke detectors
  • Best suited for living rooms and bedrooms because of large pieces of furniture that can burn slowly and create more smoke than flames
  • self restoring
  • function one of two ways: projected beam and refractory
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13
Q

Projected beam style smoke detectors (obscuration)

A
  • photoelectric smoke detector that uses a beam of light focused across area being monitored onto receiving device. When smoke obscures or obstructs the light, the amount of current produced is lessened and signals alarm
  • particularly useful where a large area of storage is desired (churches, atriums, or warehouses)
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14
Q

Refractory application (light scattering smoke detector)

A

-light doesn’t strike photocell normally, but when smoke particles enter the light beam, light reflects off particles in random directions onto the photocell causing the alarm to signal

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15
Q

Ionization Detector

A
  • has sensing chamber consisting of 2 electrically charged plates(1+ and 1-) and a radioactive source (americium 241) for ionizing air between plates.
  • products of combustion, larger than ionized air, enter the chamber and collide and combine with air molecules causing a reduction in the number of ionized particles. this decreases the the current between the plates and signals alarm
  • Changes in humidity and atmospheric pressure can cause to malfunction and signal false alarm
  • works on all types of fires but more quickly to flaming fires than photoelectric
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16
Q

Duct

A
  • prevent smoke and products of combustion from being spread throughout the building.
  • upon activation, the system will shut down or transition into a smoke-control mode
  • not a substitute for other types of smoke detectors in open areas
17
Q

Air-sampling

A

-continuously monitor a small amount of air from the protected area.

18
Q

Cloud chamber

A
  • type of air-sampling detector
  • air pump draws air into high-humidity chamber where high-humidity is imparted to lower the pressure in the chamber. moisture condenses on smoke particles creating a cloud. when the clouds density exceeds certain amount, alarm is triggered
  • most common air-sampling detector
19
Q

Spot-type aspirating smoke detector

A
  • type of air-sampling detector
  • combines spot-type photoelectric smoke detector with filtered periodic air sampling
  • designed for use in dusty areas
20
Q

Video-based smoke detectors

A
  • detects changes in a digital video image from a camera or a series of cameras.
  • closed circuit tv to a computer that looks for changes.
  • only work in lighted areas
  • provide image to operator monitoring
  • advantageous in large open facilities where there may be a delay in smoke movement
21
Q

Flame detectors

A
  • AKA light detectors
  • 3 types- 1. UV detectors 2. IR detectors (requires flickering action) 3. Combination
  • among the fastest to respond to fires
  • must not be blocked
  • false activation by welding, sunlight, and other bright light sources
22
Q

Fire-Gas detector

A
  • found in refineries, chemical plants, electronic assembly areas
  • implements semiconductors or catalytic elements, which are not used as frequently in other types of detectors
  • monitors CO and CO2 for fire detection purposes
23
Q

Waterflow devices

A

-activates when water flows though the sprinkler system

24
Q

Supervisory devices

A
  • supervises automatic sprinkler systems and monitor condition of the system.
  • monitor fire protection control valves that supply the sprinkler and other protection systems
  • if main water shut off is closed, a supervisory alarm is displayed on FACU.

Fire Protection Systems (4 decks)

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