SMOKE DETECTION SYSTEMS

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SMOKE DETECTION SYSTEMS

• IDENTIFY PARTICLES OF COMBUSTION
• MOST COMMON TYPES ARE PHOTOELECTRIC AND IONIZATION

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PHOTOELECTRIC DETECTORS
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PHOTOELECTRIC DETECTORS

• PARTICLES OF COMBUSTION DISTORT A LIGHT BEAM
• DISTORTED LIGHT BEAM ACTIVATES SIGNAL

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PHOTOELECTRIC DETECTORS
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PHOTOELECTRIC DETECTORS
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IONIZATION DETECTORS

• USE A PIECE OF OF RADIOACTIVE MATERIAL (ALPHA
  RADIATION)
• The alpha particles generated by the americium
  ionize the oxygen and nitrogen atoms of the air
  in the chamber.
• To "ionize" means to "knock an electron off of."
• When you knock an electron off of an atom, you
  end up with a free electron (with a negative
  charge) and an atom missing one electron (with a
  positive charge).

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Ionization Detectors

• The electronics in the smoke detector sense the
  small amount of electrical current that these
  electrons and ions moving toward the plates
  represent.
• When smoke enters the ionization chamber, it
  disrupts this current -- the smoke particles
  attach to the ions and neutralize them.
• The smoke detector senses the drop in current
  between the plates and sets off the horn.

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IONIZATION DETECTORS
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IONIZATION DETECTORS
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HEAT DETECTORS

• FUSIBLE ELEMENT
• BIMETALLIC
• PNEUMATIC
• RATE OF RISE VERSUS FIXED TEMPERATURE

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Heat Detectors
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Rate of Rise Detector
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Thermistor Rate of Rise Detectors

• If the air temperature increases rapidly, the
  change of temperature results in a change in
  resistance between the thermistors.
• When the ratio of resistance exceeds a factory
  preset level, an alarm is initiated.

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Pneumatic Rate of Rise Detectors

• Detectors use a reliable pneumatic rate-of-rise
  element which responds to a rapid rise in
  temperature of approximately 15F per minute.
• When the air within the sealed chamberexpands
  faster than it can escape through a calibrated
  vent, the resultant increase in pressure
  depresses the diaphragm, causing the electrical
  contact to close the circuit thus initiating the
  alarmsignal.

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Fixed Temperature Heat Detectors

• The fixed temperature element uses a fusible
  alloy and an efficient heat collector.
• Detectors are normally open devices and are
  available in either 135F (57C) or 194F (90C)
  ratings.
• When activated, the external heat collector drops
  away to provide quick visual confirmation that
  the detector has operated.

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Fusible Element Heat Detectors

• A spot type of fixed-temperature detectors is
  used mainly in unattended spaces to detect
  smoldering fires that increase the temperature of
  a detector above its design value, usually 135F
  to 145F or 185 to 200F.
• The higher temperature devices are used in spaces
  that may reach higher temperatures under ordinary
  conditions, such as boiler rooms, attics, or
  cooking areas.

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Fusible Element Heat Detectors
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Fusible Element Detectors

• The device usually is actuated by the melting or
  fusing of an element made of a fusible metal
  alloy.
• Actuated devices usually can be detected by
  visual examination.
• In some devices, the smaller diameter part in the
  center drops away. In others, the dimple becomes
  a hole when the detector operates.
• These fixed-temperature devices are often
  designed for one-time operation, and the whole
  device or the element needs to be replaced.

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BIMETALLIC HEAT DETECTORS
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BIMETALLIC HEAT DETECTORS

• USES TWO PIECES OF SANDWICHED METALS THAT EXPAND
  AND CONTRACT AT DIFFERENT RATES WHEN HEATED
• WHEN EXPOSED TO HEAT, THE METAL BENDS TO COMPLETE
  AN ELECTRICAL BRIDGE AND ACTIVATES THE DETECTOR

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UV FLAME DETECTORS
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UV Flame Detectors

• Ultraviolet detectors respond to flaming fires
  emitting light in the ultraviolet portion of the
  spectrum.
• UV detectors can respond to a fire condition in
  less than 10 milliseconds.

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UV Flame Detector Uses

• The ultraviolet (UV) flame detector is extremely
  fast and is used in high-hazard applications,
  such as aircraft maintenance areas, munitions
  production, and other areas where flammable or
  explosive liquids or solids are handled or
  stored.
• These detectors should not be used around arc
  welding, as they will respond to the ultraviolet
  light given off by the welding process.

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IR Flame Detectors
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IR Detectors

• Infrared detectors respond to flaming fires
  emitting light in the infrared portion of the
  spectrum.
• IR detectors can respond to a fire condition in
  less than 50 milliseconds.
• These detectors are designed to alarm to
  hydrocarbon fires, while ignoring things like arc
  welding, nuclear radiation and x-rays.

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IR Detectors

• The IR flame detector is ineffective for
  smoldering or beginning fires.
• It is used where possible fires would develop
  quickly (fuels, such as combustible gases and
  liquids, or loose cotton fiber), and it is
  capable of protecting a large area if it is
  mounted high on a ceiling or wall (30 to 50
  feet).

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TESTING FLAME-ACTUATED DETECTORS

• Flame-actuated detectors should be inspected
  monthly for physical damage, accumulation of lens
  deposits, and paint.
• A spot of paint on a lens can prevent the
  detector from "seeing" a critical area in the
  protected space.

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Testing Flame Detectors

• Be sure that auxiliary functions of the flame
  detection system are deactivated
• Inform the fire department and persons who would
  hear the alarm.

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False Alarms and Failure to Detect

• False alarms or failure to detect during a test
  may be caused by environmental factors or the
  aiming of the detector.
• Check that detectors are not blocked and that
  lenses are shielded from direct rays of the sun
  and other sources of IR, such as welding
  equipment, in the case of UV detectors.

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Testing IR Detectors

• The dark spot or dome at the bottom center of
  each IR device is the lens.
• Detector lenses must be kept clean to ensure the
  earliest possible detection of a fire.
• A 250-watt IR heat lamp several feet from the
  detector can serve as a flame substitute in
  testing an IR flame detector.

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Cleaning UV Detectors

• Keep UV detector lenses totally clean.
• A gradual buildup of contaminants frequently
  found in high-hazard spaces (oil, gasoline,
  petrochemicals, salt, and dust) block UV
  radiation.
• A layer thin enough to be undetectable to the
  human eye can cause a UV detector to be
  completely blind.
• Clean lenses according to the manufacturer's
  instructions.

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Testing UV Detectors

• Test feature designed into some detectors allows
  for checking the device.
• A small UV source inside the detector housing is
  shielded from directly illuminating the sensor.
• A test switch deactivates alarm circuits and
  illuminates the test lamp.
• The test lamp rays pass through the front window
  to the sensor.
• Detector response to the test indicates that the
  window is clean and that the sensor and
  electronic circuits are operational.

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ALARM SYSTEMS

• TYPES
• CENTRAL STATION
• LOCAL SYSTEM
• PROPRIETARY SYSTEM
• VOICE SYSTEMS
• INSPECT AND TEST AT LEAST ANNUALLY

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Fire Alarm Panels
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Fire Alarm Panels

• Zone Indicators
• Alarm Indicators
• Fire
• Trouble Alarm
• Loss of Signal/Connection
• Test and Alarm Resets

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Annunciator Panels

• Located near main entrance of buildings
• Identify zones for alarms

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Annunciator Panel
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Pull Stations
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Pull Stations

• Activate fire alarm in building
• Single action or dual action
• Most types these days have method for determining
  activation
• Break glass bar
• Require key to reset

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INSPECTION AND TESTING

• The employer shall assure that fire detectors and
  fire detection systems are tested and adjusted as
  often as needed to maintain proper reliability
  and operating condition.
• Local Fire Codes stipulate testing requirements

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OSHAs Employee Alarm Systems (1910.165)

• OSHA Standards apply emergency employee alarms
  installed to meet a particular OSHA standard.
• They also apply to discharge or supervisory
  alarms required on various fixed extinguishing
  systems or to supervisory alarms on fire
  suppression, alarm or detection systems if they
  are intended to be employee alarm systems.

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OSHAs Fire Detection Systems Standard (1910.164)

• Applies to all automatic fire detection systems
  installed to meet the requirements of a
  particular OSHA standard.
• Example 1910.38 Emergency Action Plans and Fire
  Prevention Plans

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NFPA 72 National Fire Alarm and Signaling Code

• Addresses design, installation, testing, and
  maintenance of alarm systems.
• Qualifications for installers, inspectors,
  monitoring personnel.