Smoke Detector

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Smoke Detector

• Bret Spencer
• ECE 5320 - Mechatronics

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ector.jpg
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Agenda

• History
• Types of smoke sensors
• Problems
• Applications
• Further research opportunities

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Why are they necessary?

• Death rate in homes are 45 lower when a working
  smoke detector is present
• Early and accurate detection of fires is crucial
  to minimize damage and loss of life

Image courtesy of Wikimedia Commons
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History

• First automatic electric fire alarm invented by
  Francis Robbins Upton in 1890
• Walter Jaegers failed poison gas detector
  functioned as a smoke detector in the late 1930s
• First commercial smoke detectors appeared in 1969

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Types of Smoke Sensors

• Optical
• Ionization
• Aspirating
• CO and CO2 Detectors

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Optical

• Uses LED and photodetector to detect presence of
  particulate matter
• Two types
• Scattered light
• Blocked light

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Scattered Light Method

• Under normal operation, the light passes the
  photodetector
• Smoke scatters the light
• Photodetector catches scattered light

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ctric20smoke20detector.jpg
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Blocked Light Method

• A tight beam of light shines from source to
  detector
• Smoke blocks path, triggering alarm
• This type can span large rooms

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ture1/index.html
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Pros

• Less Prone to false alarms
• Less sensitive to steam and cooking fumes
• Better at detecting smoke from smoldering fires

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Cons

• Slower to detect smoke than ionization method

LED
Photodetector
Image courtesy of Wikimedia Commons
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Ionization

• A radioactive source ionizes the air between two
  electrodes
• Changes in the current, due to particulate
  matter, trigger an alarm

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on20smoke20detector.jpg
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Pros

• Detects particles too small to be visible
• Cheaper than optical detector
• Better at detecting smoke from hot fires

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Cons

• Most prone to false alarms

Ionization Chamber
Image courtesy of Wikimedia Commons
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Aspirating

• Air is drawn from different sampling points
• Detector uses a solid-state laser and receiver to
  detect small particles

Diagram courtesy of Wikimedia Commons
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Pros

• Detects smoke very quickly
• High sensitivity
• Can detect multiple levels to smoke concentration
• Wide coverage area

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Cons

• Usually requires a large infrastructure
• High cost

Image courtesy of Wikimedia Commons
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CO CO2 Detection

• Trigger an alarm based on toxic levels of CO or
  CO2 concentration
• Not a common type of fire detection

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Video Smoke Detection

• Used in the Sydney Harbor Tunnel to successfully
  detect dangerous levels of smoke
• Uses standard CCTV cameras that are already
  present for traffic purposes
• Software detects evidence of smoke
• Multiple cameras are cross-checked to minimize
  error

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Video Smoke Detection

• Very fast detection
• Image can be verified by operator
• Very accurate sensing

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dustryNews/D-tec_Sydney_test_250.jpg
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Smoke Obscuration Levels
Typical smoke detector obscuration ratings Typical smoke detector obscuration ratings
Type of Detector Obscuration Level
Ionization 2.6-5.0
Scattered Light Method 6.5-13.0
Blocked Light Method 3
Aspirating 0.005-20.5
Laser 0.06-6.41
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Problems

• Many residential smoke detectors do not function
  properly due to expired batteries
• Kitchen smoke
• can cause false
• alarms

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tector.jpg.jpg
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Applications

• Smoke detectors are cheap enough to be placed in
  every room in any building
• Central systems allow multiple sensors to sound
  multiple alarms

Image courtesy of Wikimedia Commons
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Further Research Opportunities

• Types of photodetectors and the effectiveness of
  detecting smoke of each
• Electric CO and CO2 detectors
• Size of particulate matter and its effect on
  ionization and optic methods of detection

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Dont let this happen to you!

• Install smoke detectors
• Test them regularly
• Replace expired batteries

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trash.jpg
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Sources

• http//www.smokealarmdetectors.com/how-smoke-detec
  tor-works.html
• http//www.familyhomesecurity.com/how-to-choose-a-
  smoke-detector-for-your-home/
• http//home.howstuffworks.com/home-improvement/hou
  sehold-safety/fire/smoke.htm
• http//www.sourcesecurity.com/news/articles/co-58-
  ga-co-2248-ga.2115.html