A smoke detector or smoke alarm is a device that detects smoke and issues an alarm to alert nearby people that there is a potential fire. A household smoke detector will typically be mounted in a disk shaped plastic enclosure about 150mm in diameter and 25mm thick, but the shape can vary by manufacturer. This article does not cite any references or sources. ... For other uses, see Alarm (disambiguation). ... A forest fire Fire is a rapid oxidation process that releases energy in varying intensities in form of light (with wavelength not also in the visual part of the spectrum) and heat and often creates smoke. ...

Because smoke rises, most detectors are mounted on the ceiling or on a wall near the ceiling. To avoid the nuisance of false alarms, most smoke detectors are mounted away from kitchens. To increase the chances of waking sleeping occupants, most homes have at least one smoke detector near any bedrooms; ideally in a hallway as well as in the bedroom itself.

Smoke detectors are usually powered by one or more batteries but some can be connected directly to household wiring. Often smoke detectors that are directly connected to household wiring also have a battery as a power supply backup in case the household wiring goes out. It is usually necessary to replace the batteries once a year to ensure appropriate protection. Four double-A batteries In science and technology, a battery is a device that stores energy and makes it available in an electrical form. ...

Most smoke detectors work either by optical detection or by ionization, but some of them use both detection methods to increase sensitivity to smoke. Smoke detectors may operate alone, be interconnected to cause all detectors in an area to sound an alarm if one is triggered, or be integrated into a fire alarm or security system. Smoke detectors with flashing lights are available for the deaf or hearing impaired, although recent research suggests that their waking effectiveness is poor (see below). Ionization is the physical process of converting an atom or molecule into an ion by changing the difference between the number of protons and electrons. ... A Wheelock MT-24-LSM fire alarm horn and strobe. ... 1 example. ... The word deaf can have very different meanings depending on the background of the person speaking or the context in which the word is used. ... This article is about hearing impairment in the pathological sense. ...

A smoke detector cannot detect carbon monoxide to prevent carbon monoxide poisoning unless it has an integrated carbon monoxide detector. Carbon monoxide, with the chemical formula CO, is a colorless, odorless, and tasteless gas. ... Carbon monoxide poisoning occurs after the inhalation of carbon monoxide gas. ... Carbon Monoxide detector connected to a North American power outlet. ...

History

In 1902 George Andrew Darby, an electrical engineer of 211 Bloomsbury Street, Birmingham, England, patented the electrical Heat-Indicator and Fire Alarm. The device was a heat detector rather than a smoke detector and indicated an increase temperature in the apartment where it was fixed. The device operated by closing an electrical circuit to sound an alarm if the temperature rose above the safe limit. The contact was made by bridging a gap with a conductor, or allowing one plate to fall on another. The connection of the two plates was caused simply by a block of butter which melted as the temperature rose. This early device subsequently gave way to more modern fire and eventually smoke alarms. An engineers degree is an academic degree which is intermediate in rank between a masters degree and a doctorate; it is occasionally to be encountered in the United States in technical fields. ... Birmingham (pron. ... Motto (French) God and my right Anthem No official anthem specific to England — the United Kingdom anthem is God Save the Queen. ... Electro-pneumatic heat detector, rate of rise and fixed temperature operation. ... An electrical network or electrical circuit is an interconnection of analog electrical elements such as resistors, inductors, capacitors, diodes, switches and transistors. ... For other uses, see Alarm (disambiguation). ... In science and engineering, conductors are materials that contain movable charges of electricity. ...

In 1969, two Americans, Kenneth House and Randolph Smith patented the first battery powered smoke detector for home use.^[1] For other uses, see Patent (disambiguation). ...

Optical detector

Optical Smoke Detector
1: optical chamber
2: cover
3: case moulding
4: photodiode (detector)
5: infra-red LED

An optical detector is a light sensor. When used as a smoke detector it includes a light source (infra-red LED), a lens to collimate the light into a beam, and a photodiode or other photoelectric sensor at right-angles to the beam as a light detector. In the absence of smoke, the light passes in front of the detector in a straight line. When smoke enters the optical chamber into the path of the light beam, some light is scattered by the smoke particles, and some of the scattered light is detected by the sensor. An increased input of light into the sensor sets off the alarm. Description: Optical smoke detector 1: optical chamber 2: cover 3: case moulding 4: photo diode 5: infra red LED Authors: Apollo Fire Detectors Limited + User:Rainer Bielefeld Source: Brochure Engineering Product Guide from Apollo Fire Detectors Limited Licence: GFDL with friendly permisson of APOLLO by Mr. ... Description: Optical smoke detector 1: optical chamber 2: cover 3: case moulding 4: photo diode 5: infra red LED Authors: Apollo Fire Detectors Limited + User:Rainer Bielefeld Source: Brochure Engineering Product Guide from Apollo Fire Detectors Limited Licence: GFDL with friendly permisson of APOLLO by Mr. ... Photodiode closeup A photodiode A photodiode is a semiconductor diode that functions as a photodetector. ... Scattering is a general physical process whereby some forms of radiation, such as light, sound or moving particles, for example, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which it passes. ...

Another type of optical detector works by using a straight line infra-red beam from the sender to the receiver. When smoke enters the beam, some light is scattered which results in less light detected by the receiver. A decreased input of light into the receiver sets off the alarm.

Also seen in large rooms, such as a gymnasium or an auditorium, are projected beam detectors. A unit on the wall sends out a beam, which is either received by a receiver, or reflected back via a mirror. When the beam is less visible to the "eye" of the sensor, it sends an alarm signal to the Fire alarm control panel. A Siemens MXL fire alarm control panel (top) and graphic annunciator (bottom) for Potomac Hall, at James Madison University. ...

Optical smoke detectors are quick in detecting slow burning, smoky fires. They are less sensitive to false alarming from cooking and bathroom steam than are ionization smoke alarms.optical smoke detectors are a must for every house

Ionization detector

This type of detector is cheaper than the optical detector, however it is sometimes rejected for environmental reasons. It can detect particles of smoke that are too small to be visible. It includes a tiny mass of radioactive americium-241, which is a source of alpha radiation. The radiation passes through an ionization chamber, which is an air-filled space between two electrodes, and permits a small, constant current to flow between the electrodes. Any smoke that enters the chamber absorbs the alpha particles, which reduces the ionization and interrupts this flow of current, setting off the alarm. General Name, Symbol, Number americium, Am, 95 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery white Atomic mass (243) g/mol Electron configuration [Rn] 5f7 7s2 Electrons per shell 2, 8, 18, 32, 25, 8, 2 Physical properties Phase solid Density (near r. ... An alpha particle is deflected by a magnetic field Alpha particles or alpha rays are a form of particle radiation which are highly ionizing and have low penetration. ... An ionization chamber is a device used for two major purposes: detecting particles in air (as in a smoke detector), and for detection or measurement of ionizing radiation. ... An electrode is an electrical conductor used to make contact with a metallic part of a circuit (e. ... Electric current is the flow (movement) of electric charge. ...

Alarms and alerts

The second function of the detector is to alert persons at risk. Several methods are used and documented in industry specifications published by UL (see References section below).

Alerting methods include:

• Audible tones
  • usually around 3200 Hz due to component constraints
  • 85 dBA at 10 feet
• Visual strobe lights
  • 110 candela output
• Tactile stimulation
  • bed shaker
  • pillow shaker
  • no specifications and currently no UL approved devices

While current technology is very effective at detecting smoke and fire conditions, there have been concerns about the effectiveness of the alerting function in awakening sleeping individuals in certain high risk groups.

Initial research into the effectiveness of the various alerting methods is sparse. Recently (2005-2007), research sponsored by the NFPA has focused on understanding the cause of a higher number of deaths seen in high risk groups such as the elderly, those with hearing loss, and those who are intoxicated.

Research findings suggest that a low frequency (520 Hz) square wave output is significantly more effective in the high risk individuals at awakening. It is expected that products using the new alerting technology will be available in the future. Special concern has been raised regarding waking effectiveness by the deaf and hard of hearing community following research released in June of 2007. A press release from August of that year is in the external links section below.

Reliability

Residential ceiling-mounted smoke detector

In 2004, NIST issued a comprehensive report entitled Performance of Home Smoke Alarms - Analysis of the Response of Several Available Technologies in Residential Fire Settings. The report concludes, among other things, that "smoke alarms of either the ionization type or the photoelectric type consistently provided time for occupants to escape from most residential fires", and "consistent with prior findings, ionization type alarms provided somewhat better response to flaming fires than photoelectric alarms, and photoelectric alarms provided (often) considerably faster response to smoldering fires than ionization type alarms". This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... As a non-regulatory agency of the United States Department of Commerce’s Technology Administration, the National Institute of Standards (NIST) develops and promotes measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. ...

The National Fire Protection Agency has issued a fact sheet urging the replacement of home smoke alarms every 10 years.

Batteries

Most residential smoke detectors run on 9 volt alkaline batteries. If these batteries run out, the smoke detector will become inactive. Most smoke detectors should signal a low battery condition, but it is common for houses to have smoke detectors with dead batteries. As a result, public information campaigns have been created to remind people to change their smoke detector batteries regularly. In regions using daylight saving time, these campaigns usually suggest that people change their batteries when they change their clocks. Another option is to change batteries on a birthday. 9-Volt is a character from the action game Wario Ware. ... Alkaline batteries A Duracell AA alkaline battery 2 Duracell-Brand AAA Alkaline batteries Alkaline batteries are a type of power cell dependent upon the reaction between zinc and manganese dioxide (Zn/MnO2). ... Though DST is common in Europe and North America, most of the worlds people do not use it. ...

Some detectors are also being sold with a lithium battery that can run for about 7 to 10 years, though this might actually make it less likely for people to change batteries since their replacement is needed so infrequently. By that time, the whole detector should be replaced. Though relatively expensive, user-replaceable 9 volt lithium batteries (in the same configuration as the common alkaline ones) are also available. They should only be used in a fairly new detector. CR2032 lithium battery Lithium batteries are primary batteries that have lithium metal anodes. ...

Smoke detectors with missing batteries are also a concern. As a result, many detectors sold today are designed to provide a visual indication of a missing battery. One popular brand of smoke detector will not allow the user to close the battery door until a battery has been placed in the alarm; another contains a spring-loaded protrusion obstructing the attachment holes when the battery is missing, preventing reattachment to the wall or ceiling and making a missing battery situation immediately obvious. Some local governments do not permit the installation of smoke detectors with removable batteries.

In new construction, most building codes today require smoke detectors that are wired to the main electricity flow of buildings. Many of these units also include a battery backup to ensure operation during a power outage. A building code is a set of laws that specify how buildings should be constructed. ...

Rechargeable batteries should never be used in smoke detectors, since common NiMH and NiCd rechargeable batteries have a short life in between charges—in other words, they self-discharge relatively quickly. This is true even though they may provide much more power than alkaline batteries if used soon after charging (such as in a portable stereo). Also, a problem particularly prevalent in older technology rechargables is a rapid voltage drop at the end of their useful charge. This is concerning in devices like smoke detectors since the battery may transition from "charged" to "dead" so quickly that the low battery warning from the detector is either very brief, or may not occur at all. NIMH or NiMH may refer to: National Institute of Mental Health, a part of the United States National Institutes of Health. ... The nickel-cadmium battery (commonly abbreviated NiCd or NiCad) is a popular type of rechargeable battery for portable electronics and toys. ...

A quality alkaline battery should be installed and replaced every six months or so. The used battery will still probably have the majority of its charge, and can be reused in less critical applications such as a backup for a digital alarm clock. For those living in areas that observe daylight saving time, one handy way to remember this important maintenance event is to replace your smoke detector batteries the same day you adjust your clocks for the new season. Though DST is common in Europe and North America, most of the worlds people do not use it. ...

The alarm may chirp at intervals if the battery is low, though if there is more than one unit within earshot, it can be hard to locate.

Testing

Virtually all modern smoke alarm units come equipped with a "test" button. Alternatively, artificial smoke can be purchased, which has the advantage of also testing the detection mechanism itself. Many people simply wave a lit match underneath the detector to test it; this is dangerous, however, as it can set the smoke alarm and the rest of the house on fire. Another way is to blow cigarette smoke into the detector, but this is also dangerous. The health effects of tobacco smoking refer to direct tobacco smoking as well as the inhalation of environmental or secondhand tobacco smoke. ...

The National Fire Protection Association, through its fire protection program, urges homeowners to replace smoke detector batteries every six months when changing your clock for Daylight saving time, and to replace the entire smoke detector after ten years of use. The National Fire Protection Association (established 1896) is an independent, voluntary-membership, nonprofit (tax-exempt) organization. ... Though DST is common in Europe and North America, most of the worlds people do not use it. ...

Installation and placement

Place smoke detectors where they will do the most good.

In the United States, most state and local laws regarding the required number and placement of smoke detectors are based upon standards established in Article 72 of NFPA fire code. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... A state is a political association with effective dominion over a geographic area. ... This page is a candidate to be moved to Wiktionary. ... This article is about law in society. ... The National Fire Protection Association (established 1896) is an independent, voluntary-membership, nonprofit (tax-exempt) organization. ...

Laws governing the installation of smoke detectors vary depending on the locality. Homeowners with questions or concerns regarding smoke detector placement are encouraged to contact their local fire marshal or building inspector for assistance. However, there are some rules and guidelines that are relatively consistent throughout the country. In older existing homes, smoke detectors are generally required on every habitable level and within the vicinity of all bedrooms. Habitable levels include attics that are tall enough to allow access. In new construction, the minimum requirements are typically much greater. All smoke detectors must be hooked directly to the electrical wiring, be interconnected and have a battery backup. In addition, smoke detectors are required either inside or outside every bedroom, depending on local codes. Smoke detectors on the outside will detect fires more quickly, assuming the fire does not begin in the bedroom, but the sound of the alarm will be reduced and may not wake some people. Some areas also require smoke detectors in stairways, main hallways and garages. This article or section does not adequately cite its references or sources. ... A Building Inspector is a person who is employed by either a city or county and is usually certified in one or more disciplines, either as a Residential or Commercial Building Inspector a Plumbing, Electrical or Mechanical Inspector or other specialty to inspect structures at different stages of completion. ... Electrical wiring in general refers to insulated conductors used to carry electricity, and associated devices. ... Symbols representing a single Cell (top) and Battery (bottom), used in circuit diagrams. ... A bedroom is a room where people sleep. ... Spiral (double helix) stairway in the Vatican Museum Stairs, staircase, stairway, stairwell, and flight of stairs are all names for a construction designed to bridge a large vertical distance by dividing it into smaller vertical distances, called steps. ... Hall is a term often used to refer to several different types of room in a house or a building. ... This article or section does not cite its references or sources. ...

Detectors on the ceiling should be placed several inches away from any wall. If the ceiling is not flat, the detector should be placed at or near the highest point. If the highest point is a small recess, then the detector should be placed at the next highest level. Detectors placed on the wall should be several inches, but no more than a foot, from the top. Detectors should not be placed on a wall if the ceiling has a deep recess or if the ceiling slopes steeply or for a long distance. Detectors should be several horizontal feet away from a heating or cooling register, window, corner, the edge of a ceiling fan's sweep and doors to a kitchen or bathroom. They should be placed as far as possible away from combustion sources, like oil and gas-fired furnaces, space heaters, clothes dryers and water heaters, without compromising coverage or safety. Smoke detectors in a basement should be placed at the bottom of the stairs and an additional detector should be placed in or near sleeping areas in the basement. This intricate ceiling is part of the Capitol Theatre in Melbourne, Australia, designed by architect Walter Burley Griffin. ... // A ceiling fan is a device suspended from the ceiling of a room, which employs hub-mounted rotating paddles to circulate air in order to produce a cooling effect. ... A kitchen is a room used for food preparation and sometimes entertainment. ... A typical American bathroom A bathroom is a room that may have different functions depending on the cultural context. ... Heating oil, or burning oil, also known in the United States as No. ... Natural gas is a gaseous fossil fuel consisting primarily of methane but including significant quantities of ethane, butane, propane, carbon dioxide, nitrogen, helium and hydrogen sulfide. ... A furnace is a device for heating air or any other fluid. ... Space Heater is the title of the fifth album by The Reverend Horton Heat. ... An electric clothes dryer A clothes dryer or tumble dryer is a major household appliance that is used to remove the residual moisture from a load of clothing and other textiles, generally shortly after they are cleaned in a washing machine. ... A trio of propane hot water heaters. ...

It is recommended, and sometimes required, that smoke detectors not be placed in kitchens because the small amounts of smoke and particulates generated while cooking can set them off. Detectors designed for use near a kitchen may have a silence button to cancel accidental triggering. Particulates, alternatively referred to as particulate matter (PM), aerosols or fine particles, are tiny particles of solid or liquid suspended in a gas. ... Cooking is the act of preparing food. ...

Detectors should not be placed in a bathroom or near a bathroom door because moisture may cause false alarms or damage the detector. False alarms reduce the effectiveness of smoke detectors in preventing harm and property damage because people soon begin to assume that the alarm is false. Heat detectors, which sound an alarm when the temperature reaches a certain point and/or when it climbs more rapidly than a certain rate, can be used in kitchens, garages and areas with combustion sources that would otherwise generate nuisance alarms. A false alarm, also called a nuisance alarm, is the phony report of an emergency, causing unnecessary panic and/or bringing resources (such as fire engines) to a place where they are not needed. ... Electro-pneumatic heat detector, rate of rise and fixed temperature operation. ... Fig. ...

Canada and Australia requires a building to have a working smoke detector on every level.

References

1. ^ Hutchinson, Alex. The Top 50 Inventions of the Past 50 Years. Popular Mechanics, December 2005. Accessed on line on January 20, 2007. http://www.popularmechanics.com/technology/upgrade/2078467.html?page=3

• Journal of Applied Fire Science, Volume 6, Number 2, June 1997, article Risk Analysis of Residential Fire Detector Performance
• National Fire Protection Code, Article 72
• Underwriters Laboratories UL 217: Single and Multiple Station Smoke Alarms
• Underwriters Laboratories UL 1971: Signaling Devices for the Hearing Impaired

External links

Wikimedia Commons has media related to:

Smoke detector

• NFPA fact sheet on smoke detectors
• Smoke detectors and americium
• How stuff works - ionization-type smoke detectors
• Common smoke detector problems
• An excellent blog with current alerting and awakening research
• Alarm concern from the Hearing Loss Association of America
• Comparison of smoke detector specifications

v • d • e  Fire protection

General: Active fire protection — Fire alarm system Fire suppression: Fire extinguisher — Fire sand bucket — Fire sprinkler — Gaseous fire suppression Detection/alarm: Control panel — Heat detector — Pull station — Notification appliance — Smoke detector Practices: Fire drill — Fire drill regulations Image File history File links Commons-logo. ... Active fire protection is one of the three types of structural fire protection. ... A fire alarm system is an active fire protection system that controls all the fire alarms in a building. ... Fire extinguisher A fire extinguisher is a device used to put out a fire, often in an emergency situation. ... There are very few or no other articles that link to this one. ... Fire sprinklers are an active fire protection measure subject to stringent bounding. ... Gaseous fire suppression is a term to describe the use of inert and chemical agents or gasses to suppress a fire. ... A Siemens MXL fire alarm control panel (top) and graphic annunciator (bottom) for Potomac Hall, at James Madison University. ... Electro-pneumatic heat detector, rate of rise and fixed temperature operation. ... A Fire-Lite BG-10 manual pull station. ... A Wheelock MT-24-LSM electronic fire alarm horn and strobe. ... College students evacuate Potomac Hall, a dormitory at James Madison University, during a fire drill. ... The list of fire drill regulations contains information about regulations concerning fire drills in elementary, middle, and high schools unless otherwise stated. ...

Image File history File links Pixel. ... Image File history File links Download high-resolution version (713x983, 1371 KB) [edit] Summary Cropped and transparent photo of a Wheelock 7002T, photographed by Ben Schumin in Zane Showker Hall at James Madison University. ...