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A smoke detector is a device that senses smoke, typically as an indicator of
fire Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction products. At a certain point in the combustion reaction, called the ignition point, flames ...
. Smoke detectors are usually housed in plastic enclosures, typically shaped like a disk about in diameter and thick, but shape and size vary. Smoke can be detected either optically (
photoelectric The photoelectric effect is the emission of electrons when electromagnetic radiation, such as light, hits a material. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physics, and solid sta ...
) or by physical process (
ionization Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecul ...
). Detectors may use one or both sensing methods. Sensitive alarms can be used to detect and deter smoking in banned areas. Smoke detectors in large commercial and industrial buildings are usually connected to a central
fire alarm system A fire alarm system warns people when smoke, fire, carbon monoxide or other fire-related or general notification emergency, emergencies are detected. These alarms may be activated automatically from smoke detectors and heat detectors or may also ...
. Household smoke detectors, also known as ''smoke alarms'', generally issue an audible or visual
alarm An alarm device is a mechanism that gives an audible, visual or other kind of alarm signal to alert someone to a problem or condition that requires urgent attention. Alphabetical musical instruments Etymology The word ''alarm'' comes from t ...
from the detector itself or several detectors if there are multiple devices interlinked. Household smoke detectors range from individual battery-powered units to several interlinked units with battery backup. With interlinked units, if any unit detects smoke, alarms will trigger at all of the units. This happens even if household power has gone out. Commercial smoke detectors issue a signal to a
fire alarm control panel A fire alarm control panel (FACP), fire alarm control unit (FACU), fire indicator panel (FIP), or simply fire alarm panel is the controlling component of a fire alarm system. The panel receives information from devices designed to detect and re ...
as part of a fire alarm system. Usually, an individual commercial smoke detector unit does not issue an alarm; some, however, do have built-in sounders. The risk of dying in a residential fire is cut in half in houses with working smoke detectors. The US National Fire Protection Association reports 0.53 deaths per 100 fires in homes with working smoke detectors compared to 1.18 deaths without (2009–2013). However, some homes do not have any smoke alarms and some homes do not have any working batteries in their smoke alarms.


History

The first automatic electric fire alarm was patented in 1890 by Francis Robbins Upton, an associate of
Thomas Edison Thomas Alva Edison (February 11, 1847October 18, 1931) was an American inventor and businessman. He developed many devices in fields such as electric power generation, mass communication, sound recording, and motion pictures. These inventi ...
. In 1902, George Andrew Darby patented the first European electrical heat detector in
Birmingham Birmingham ( ) is a city and metropolitan borough in the metropolitan county of West Midlands in England. It is the second-largest city in the United Kingdom with a population of 1.145 million in the city proper, 2.92 million in the We ...
,
England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe ...
. In the late 1930s, Swiss physicist Walter Jaeger attempted to invent a sensor for poison gas. He expected the gas entering the sensor to bind to ionized air molecules and thereby alter an electric current in a circuit of the instrument. However, his device did not achieve its purpose as small concentrations of gas did not affect the sensor's conductivity. Frustrated, Jaeger lit a cigarette and was surprised to notice that a meter on the instrument had registered a drop in current. Unlike poison gas, the smoke particles from his cigarette were able to alter the circuit's current. Jaeger's experiment was one of the developments that paved the way for the modern smoke detector. In 1939, Swiss physicist Ernst Meili devised an ionization chamber device capable of detecting combustible gases in mines. He also invented a
cold cathode A cold cathode is a cathode that is not electrically heated by a filament.A negatively charged electrode emits electrons or is the positively charged terminal. For more, see field emission. A cathode may be considered "cold" if it emits more el ...
tube that could amplify the small signal generated by the detection mechanism so that it was strong enough to activate an alarm. In 1951, ionization smoke detectors were first sold in the United States. In the following years, they were used only in major commercial and industrial facilities due to their large size and high cost. In 1955, simple "fire detectors" for homes were developed, which detected high temperatures. In 1963, The
United States Atomic Energy Commission The United States Atomic Energy Commission (AEC) was an agency of the United States government established after World War II by U.S. Congress to foster and control the peacetime development of atomic science and technology. President ...
(USAEC) granted the first license to distribute smoke detectors that used radioactive material. In 1965, the first low-cost smoke detector for domestic use was developed by Duane D. Pearsall and Stanley Bennett Peterson. It was an individual, replaceable, battery-powered unit that could be easily installed. The "SmokeGard 700" was beehive-shaped, fire-resistant, and made of steel. The company began mass-producing these units in 1975. Studies in the 1960s determined that smoke detectors respond to fires much faster than heat detectors. The first single-station smoke detector was invented in 1970 and was brought out the next year. It was an ionization detector powered by a single 9-volt battery. It cost about and sold at a rate of a few hundred thousand units per year. Several developments in smoke detector technology occurred between 1971 and 1976, including the replacement of cold-cathode tubes with
solid-state electronics Solid-state electronics means semiconductor electronics: electronic equipment using semiconductor devices such as transistors, diodes and integrated circuits (ICs). The term is also used as an adjective for devices in which semiconductor electr ...
. This greatly reduced the detectors' cost and size, and made it possible to monitor battery life. The previous alarm horns which required special batteries were replaced with horns that were more energy-efficient and allowed the use of widely available batteries. These detectors could also function with smaller amounts of radioactive source material, and the sensing chamber and smoke detector enclosure were redesigned to make operation more effective. The rechargeable batteries were often replaced by a pair of
AA batteries AA, Aa, Double A, or Double-A may refer to: Arts, entertainment and media * '' America's Army'', a 2002 computer game published by the U.S. Army * '' Ancient Anguish'', a computer game in existence since 1992 * Aa!, a J-Pop musical group * D ...
along with a plastic shell encasing the detector. The photoelectric (optical) smoke detector was invented by Donald Steele and Robert Emmark from Electro Signal Lab and patented in 1972. In 1995, the 10-year-lithium-battery-powered smoke alarm was introduced.


Design

Smoke can be detected using a
photoelectric The photoelectric effect is the emission of electrons when electromagnetic radiation, such as light, hits a material. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physics, and solid sta ...
sensor or an
ionization Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecul ...
process. Fire without smoke can be detected by sensing carbon dioxide. Incomplete burning can be detected by sensing carbon monoxide.


Photoelectric

A photoelectric, or optical smoke detector, contains a source of
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
, visible, or
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
light — typically an
incandescent light bulb An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated until it glows. The filament is enclosed in a glass bulb with a vacuum or inert gas to protect the filament from oxi ...
or
light-emitting diode A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...
(LED) — a
lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements ...
, and a photoelectric receiver — typically a
photodiode A photodiode is a light-sensitive semiconductor diode. It produces current when it absorbs photons. The package of a photodiode allows light (or infrared or ultraviolet radiation, or X-rays) to reach the sensitive part of the device. The packag ...
. In spot-type detectors, all of these components are arranged inside a chamber where air, which may contain smoke from a nearby fire, flows. In large open areas such as atria and auditoriums, optical beam or projected-beam smoke detectors are used instead of a chamber within the unit: a wall-mounted unit emits a beam of infrared or ultraviolet light which is either received and processed by a separate device or reflected to the receiver by a reflector. In some types, particularly optical beam types, the light emitted by the light source passes through the air being tested, and reaches the photosensor. The received light intensity will be reduced due to
scattering Scattering is a term used in physics to describe a wide range of physical processes where moving particles or radiation of some form, such as light or sound, are forced to deviate from a straight trajectory by localized non-uniformities (including ...
from particulates of smoke, air-borne dust, or other substances; the circuitry detects the light intensity and generates the alarm if it is below a specified threshold, potentially due to smoke. In other types, typically chamber types, the light is not directed at the sensor, which is not illuminated in the absence of particles. If the air in the chamber contains particles (smoke or dust), the light is
scattered Scattered may refer to: Music * ''Scattered'' (album), a 2010 album by The Handsome Family * "Scattered" (The Kinks song), 1993 * "Scattered", a song by Ace Young * "Scattered", a song by Lauren Jauregui * "Scattered", a song by Green Day from ' ...
and some of it reaches the sensor, triggering the alarm. According to the
National Fire Protection Association The National Fire Protection Association (NFPA) is an international nonprofit organization devoted to eliminating death, injury, property and economic loss due to fire, electrical and related hazards. As of 2018, the NFPA claims to have 50,000 mem ...
(NFPA), "photoelectric smoke detection is generally more responsive to fires that begin with a long period of smoldering". Studies by Texas A&M and the NFPA cited by the City of Palo Alto, California state, "Photoelectric alarms react slower to rapidly growing fires than ionization alarms, but laboratory and field tests have shown that photoelectric smoke alarms provide adequate warning for all types of fires and have been shown to be far less likely to be deactivated by occupants." Although photoelectric alarms are highly effective at detecting smoldering fires and do provide adequate protection from flaming fires, fire safety experts and the NFPA recommend installing what are called combination alarms, which are alarms that either detect both heat and smoke or use both the ionization and photoelectric smoke sensing methods. Some combination alarms may also include a carbon monoxide detection capability. The type and sensitivity of light source and photoelectric sensor and type of smoke chamber differ between manufacturers.


Ionization

An ionization smoke detector uses a
radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferr ...
, typically
americium-241 Americium-241 (, Am-241) is an isotope of americium. Like all isotopes of americium, it is radioactive, with a half-life of . is the most common isotope of americium as well as the most prevalent isotope of americium in nuclear waste. It is com ...
, to ionize air; a difference due to smoke is detected and an alarm is generated. Ionization detectors are more sensitive to the flaming stage of fires than optical detectors, while optical detectors are more sensitive to fires in the early smouldering stage.Fleming, Jay
"Smoke Detector Technology Research"
, retrieved 2011-11-07
The smoke detector has two
ionization chamber The ionization chamber is the simplest type of gas-filled radiation detector, and is widely used for the detection and measurement of certain types of ionizing radiation, including X-rays, gamma rays, and beta particles. Conventionally, the term ...
s, one open to the air, and a reference chamber which does not allow the entry of particles. The radioactive source emits
alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be prod ...
s into both chambers, which ionizes some air
molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and b ...
s. There is a
potential difference Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
(voltage) between pairs of
electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials ...
s in the chambers; the
electrical charge Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...
on the ions allows an
electric current An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The movi ...
to flow. The currents in both chambers should be the same as they are equally affected by air pressure, temperature, and the ageing of the source. If any smoke particles enter the open chamber, some of the ions will attach to the particles and not be available to carry the current in that chamber. An electronic circuit detects that a current difference has developed between the open and sealed chambers, and sounds the alarm. The circuitry also monitors the battery used to supply or back up power, and sounds an intermittent warning when it nears exhaustion. A user-operated test button simulates an imbalance between the ionization chambers, and sounds the alarm if and only if power supply, electronics, and alarm device are functional. The current drawn by an ionization smoke detector is low enough for a small battery used as sole or backup power supply to be able to provide power for years without the need for external wiring. Ionization smoke detectors are usually cheaper to manufacture than optical detectors. Ionization detectors may be more prone than photoelectric detectors to false alarms triggered by non-hazardous events, and are much slower to respond to typical house fires.


Radiation

Americium-241 is an
alpha emitter Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be produce ...
with a
half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ...
of 432.6 years. Alpha particle radiation, as opposed to
beta Beta (, ; uppercase , lowercase , or cursive ; grc, βῆτα, bē̂ta or ell, βήτα, víta) is the second letter of the Greek alphabet. In the system of Greek numerals, it has a value of 2. In Modern Greek, it represents the voiced labiod ...
(electron) and gamma (electromagnetic) radiation, is used for two reasons: the alpha particles can ionize enough air to make a detectable current; and they have low penetrative power, meaning they will be stopped, safely, by the air or the plastic shell of the smoke detector. During the alpha decay, emits
gamma radiation A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically s ...
, but it is low-energy and therefore not considered a significant contributor to human exposure. The amount of elemental americium-241 in ionization smoke detectors is small enough to be exempt from the regulations applied to larger deployments. A smoke detector contains about of radioactive element americium-241 (), corresponding to about 0.3 µg of the isotope. This provides sufficient ion current to detect smoke, while producing a very low level of radiation outside the device. Some Russian-made smoke detectors, most notably the RID-6m and IDF-1m models, contain a small amount of Plutonium (18 MBq), rather than the typical source, in the form of reactor-grade mixed with Titanium Dioxide onto a cylindrical alumina surface. The amount of Americium-241 contained in ionizing smoke detectors doesn't represent a significant radiological hazard. If the americium is left in the ionization chamber of the alarm, the radiological risk is insignificant because the chamber acts as a shield to the alpha radiation. A person would have to open the sealed chamber and ingest or inhale the americium for the dose to be comparable to
natural background radiation Background radiation is a measure of the level of ionizing radiation present in the environment at a particular location which is not due to deliberate introduction of radiation sources. Background radiation originates from a variety of source ...
. The radiation risk of exposure to an ionizing smoke detector operating normally is much smaller than natural background radiation.


Disposal

Disposal regulations and recommendations for ionization smoke detectors vary from region to region. The government of New South Wales, Australia considers it safe to discard up to 10 ionization smoke detectors in a batch with domestic rubbish. The
EPA The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
considers ionizing smoke detectors safe to dispose with household trash. Alternatively, smoke detectors can be returned to the manufacturer.


Performance differences

Photoelectric detectors and ionization detectors differ in their performance depending on the type of smoke generated by a fire. A presentation by Siemens and the Canadian Fire Alarm Association reports that the ionization detector is the best at detecting incipient-stage fires with invisibly small particles, fast-flaming fires with smaller 0.01–0.4
micron The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Un ...
particles, and dark or black smoke, while more modern photoelectric detectors are best at detecting slow-smouldering fires with larger 0.4–10.0 micron particles, and light-coloured white/grey smoke. Photoelectric smoke detectors respond faster to fire that is in its early, smoldering stage. The smoke from the smoldering stage of a fire is typically made up of large combustion particles between 0.3 and 10.0 
µm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer ( American spelling), also commonly known as a micron, is a unit of length in the International System of Uni ...
. Ionization smoke detectors respond faster (typically 30–60 seconds) to the flaming stage of a fire. The smoke from the flaming stage of a fire is typically made up of microscopic combustion particles between 0.01 and 0.3 µm. Also, ionization detectors are weaker in high air flow environments. Some European countries, including France, and some US states and
municipalities A municipality is usually a single administrative division having corporate status and powers of self-government or jurisdiction as granted by national and regional laws to which it is subordinate. The term ''municipality'' may also mean the ...
have banned the use of domestic ionization smoke alarms because of concerns that they are not reliable enough as compared to other technologies. Where an ionizing smoke detector has been the only detector, fires in the early stages have not always been effectively detected. In June 2006, the Australian Fire & Emergency Service Authorities Council, the peak representative body for all Australian and New Zealand fire departments, published an official report, 'Position on Smoke Alarms in Residential Accommodation'. Clause 3.0 states, "Ionization smoke alarms may not operate in time to alert occupants to escape from a smoldering fire." In August 2008, the
International Association of Fire Fighters The International Association of Fire Fighters (IAFF) is a labor union representing paid full-time firefighters and emergency medical services personnel in the United States and Canada. The IAFF was formed in 1918 and is affiliated with the AFL� ...
(IAFF) passed a resolution recommending the use of photoelectric smoke alarms, saying that changing to photoelectric alarms "Will drastically reduce the loss of life among citizens and firefighters." In May 2011, the Fire Protection Association of Australia’s (FPAA) official position on smoke alarms stated, "The Fire Prevention Association of Australia considers that all residential buildings should be fitted with photoelectric smoke alarms..." In December 2011, the Volunteer Firefighter's Association of Australia published a World Fire Safety Foundation report, 'Ionization Smoke Alarms are DEADLY', citing research outlining substantial performance differences between ionization and photoelectric technology. In November 2013, the Ohio Fire Chiefs' Association (OFCA) published an official position paper supporting the use of photoelectric technology in Ohioan residences. The OFCA's position states, "In the interest of public safety and to protect the public from the deadly effects of smoke and fire, the Ohio Fire Chiefs' Association endorses the use of photoelectric smoke alarms in both new construction and when replacing old smoke alarms or purchasing new alarms." In June 2014, tests by the Northeastern Ohio Fire Prevention Association (NEOFPA) on residential smoke alarms were broadcast on ABC's
Good Morning America ''Good Morning America'' (often abbreviated as ''GMA'') is an American morning television program that is broadcast on ABC. It debuted on November 3, 1975, and first expanded to weekends with the debut of a Sunday edition on January 3, 1993. ...
’ program. The NEOFPA tests showed ionization smoke alarms were failing to activate in the early, smoldering stage of a fire. The combination ionization/photoelectric alarms failed to activate for an average of over 20 minutes after the stand-alone photoelectric smoke alarms. This vindicated the June 2006 official position of the Australasian Fire & Emergency Service Authorities Council (AFAC) and the October 2008 official position of the International Association of Fire Fighters (IAFF). Both the AFAC and the IAFF recommend photoelectric smoke alarms, but not combination ionization/photoelectric smoke alarms. According to fire tests conformant to
EN 54 The EN 54 Fire detection and fire alarm systems is a series of European standards that includes product standards and application guidelines for fire detection and fire alarm systems as well as voice alarm systems. The product standards defin ...
, the cloud from open fire can usually be detected before particulates. Due to the varying levels of detection capabilities between detector types, manufacturers have designed multi-criteria devices which cross-reference the separate signals to both rule out false alarms and improve response times to real fires. Obscuration is a unit of measurement that has become the standard way of specifying smoke detector sensitivity. Obscuration is the effect smoke has that reduces light intensity, expressed in percent absorption per unit length;Smoke Detector Sensitivity testing: Siemens and Canadian Fire Alarm Association
higher concentrations of smoke result in higher obscuration levels.


Carbon monoxide and carbon dioxide detection

Carbon monoxide sensor A carbon monoxide detector or CO detector is a device that detects the presence of the carbon monoxide (CO) gas to prevent carbon monoxide poisoning. In the late 1990s UL (safety organization), Underwriters Laboratories changed the definition ...
s detect potentially fatal concentrations of
carbon monoxide Carbon monoxide ( chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simpl ...
, which may build up due to faulty ventilation where there are combustion appliances such as gas heaters and cookers, although there is no uncontrolled fire outside the appliance. High levels of
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
() may indicate a fire, and can be detected by a
carbon dioxide sensor A carbon dioxide sensor or CO2 sensor is an instrument for the measurement of carbon dioxide gas. The most common principles for CO2 sensors are infrared gas sensors ( NDIR) and chemical gas sensors. Measuring carbon dioxide is important in monito ...
. Such sensors are often used to measure levels of which may be undesirable and harmful, but not indicative of a fire. This type of sensor can also be used to detect and warn of the much higher levels of generated by a fire. Some manufacturers say that detectors based on levels are the fastest fire indicators. Unlike ionization and optical detectors, they can also detect fires that do not generate smoke, such as those fueled by alcohol or gasoline. detectors are not susceptible to false alarms due to particles making them particularly suitable for use in dusty and dirty environments.


Residential

Smoke alarm systems used in a home or residential environment are typically smaller and less expensive than commercial units. The system may include one or more individual standalone units, or multiple units that are interconnected. They typically generate a loud acoustic warning signal as their only action. Several detectors (whether standalone or interconnected) are normally used in the rooms of a dwelling. There are inexpensive smoke alarms that may be interconnected so that any detector that triggers sounds all alarms. They are powered by mains electricity, with disposable or rechargeable battery backup. They may be interconnected by wires, or wirelessly. They are required in new installations in some jurisdictions. Several smoke detection methods are used and documented in industry specifications published by
Underwriters Laboratories The UL enterprise is a global safety science company headquartered in Northbrook, Illinois, composed of three organizations, UL Research Institutes, UL Standards & Engagement and UL Solutions. Established in 1894, the UL enterprise was founded as ...
. Alerting methods include: * Audible tones ** Usually around 3200 Hz due to component constraints (Audio advancements for persons with hearing impairments have been made) ** 85 dB A loudness at 10 feet * Spoken voice alert * Visual
strobe light A strobe light or stroboscopic lamp, commonly called a strobe, is a device used to produce regular flashes of light. It is one of a number of devices that can be used as a stroboscope. The word originated from the Ancient Greek ('), meaning ...
s ** 177
candela The candela ( or ; symbol: cd) is the unit of luminous intensity in the International System of Units (SI). It measures luminous power per unit solid angle emitted by a light source in a particular direction. Luminous intensity is analogous t ...
output *
Emergency light An emergency light is a battery-backed lighting device that switches on automatically when a building experiences a power outage. In the United States, emergency lights are standard in new commercial and high occupancy residential buildings, ...
for illumination * Tactile stimulation (e.g. bed or pillow shaker), although no standards existed as of 2008 for tactile stimulation alarm devices. Some models have a hush or temporary silence feature that allows silencing, typically by pressing a button on the housing, without removing the battery. This is especially useful in locations where false alarms can be relatively common (e.g. near a kitchen), or users might remove the battery permanently to avoid the annoyance of false alarms, preventing the alarm from detecting a fire should one break out. While current technology is very effective at detecting smoke and fire conditions, the deaf and hard of hearing community has raised concerns about the effectiveness of the alerting function in awakening sleeping individuals in certain high-risk groups. People part of groups like the elderly, those with hearing loss, and those who are intoxicated, may have a more difficult time utilizing sound-based detectors. Between 2005 and 2007 research sponsored by the United States
National Fire Protection Association The National Fire Protection Association (NFPA) is an international nonprofit organization devoted to eliminating death, injury, property and economic loss due to fire, electrical and related hazards. As of 2018, the NFPA claims to have 50,000 mem ...
(NFPA) focused on understanding the cause of the higher number of deaths in such high-risk groups. Initial research into the effectiveness of the various alerting methods is sparse. Research findings suggest that a low frequency (520 Hz) square wave output is significantly more effective at awakening high-risk individuals. Wireless smoke and carbon monoxide detectors linked to alert mechanisms such as vibrating pillow pads for the hearing impaired, strobes, and remote warning handsets are more effective at waking people with serious hearing loss than other alarms.


Batteries

Batteries are used either as sole or as backup power for residential smoke detectors. Mains-operated detectors have disposable or rechargeable batteries; others run only on 9-volt disposable batteries. When the battery is exhausted a battery-only smoke detector becomes inactive; most smoke detectors chirp repeatedly if the battery is low. It has been found that battery-powered smoke detectors in many houses have dead batteries. It has been estimated that in the UK over 30% of smoke alarms have dead or removed batteries. In response public information campaigns have been created to remind people to change smoke detector batteries regularly. In Australia, for example, a public information campaign suggests that smoke alarm batteries should be replaced on
April Fools' Day April Fools' Day or All Fools' Day is an annual custom on 1 April consisting of practical jokes and hoaxes. Jokesters often expose their actions by shouting "April Fools!" at the recipient. Mass media can be involved in these pranks, which may ...
every year. In regions using
daylight saving time Daylight saving time (DST), also referred to as daylight savings time or simply daylight time (United States, Canada, and Australia), and summer time (United Kingdom, European Union, and others), is the practice of advancing clocks (typicall ...
, campaigns may suggest that people change their batteries when they change their clocks or on a birthday. Some mains-powered detectors are fitted with a non-rechargeable
lithium battery Lithium battery may refer to: * Lithium metal battery, a non-rechargeable battery with lithium as an anode ** Rechargeable lithium metal battery, a rechargeable counterpart to the lithium metal battery * Lithium-ion battery, a rechargeable batte ...
for backup with a life of typically ten years. After this, it is recommended that the detector be replaced. User-replaceable disposable 9-volt lithium batteries, which last at least twice as long as alkaline batteries, are also available for smoke detectors. The US
National Fire Protection Association The National Fire Protection Association (NFPA) is an international nonprofit organization devoted to eliminating death, injury, property and economic loss due to fire, electrical and related hazards. As of 2018, the NFPA claims to have 50,000 mem ...
recommends that home-owners replace smoke detector batteries at least once per year, when it starts chirping (a signal that the battery is low). Batteries should also be when or if it fails a test, which the NFPA recommends to be carried out at least once per month by pressing the "test" button on the alarm.


Reliability

A 2004
NIST The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into physical sci ...
report concluded 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 (57 to 62 seconds faster response), and photoelectric alarms provided (often) considerably faster response to smoldering fires than ionization type alarms (47 to 53 minutes faster response)." Regular cleaning can prevent false alarms caused by the build-up of dust and insects, particularly on optical type alarms as they are more susceptible to these factors. A vacuum cleaner can be used to clean domestic smoke detectors to remove detrimental dust. Optical detectors are less susceptible to false alarms in locations such as near a kitchen producing cooking fumes. On the night of May 31, 2001, Bill Hackert and his daughter Christine of
Rotterdam Rotterdam ( , , , lit. ''The Dam on the River Rotte (river), Rotte'') is the second largest List of cities in the Netherlands by province, city and List of municipalities of the Netherlands, municipality in the Netherlands. It is in the Prov ...
,
New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...
died when their house caught fire and a
First Alert First Alert is the retail brand of American safety equipment manufacturer BRK Brands, Inc., established in 1976 and based in Aurora, Illinois, with a production plant in Juarez, Mexico. Products sold with the brand include carbon monoxide detecto ...
ionization smoke detector failed to sound. The cause of the fire was a frayed electrical cord behind a couch that smoldered for hours before engulfing the house with flames and smoke. The ionization smoke detector was found to be defectively designed, and in 2006 a jury in the United States District Court for the Northern District of New York decided that
First Alert First Alert is the retail brand of American safety equipment manufacturer BRK Brands, Inc., established in 1976 and based in Aurora, Illinois, with a production plant in Juarez, Mexico. Products sold with the brand include carbon monoxide detecto ...
and its then parent company, BRK Brands, was liable for millions of dollars in damages.


Installation and placement

In the United States most
state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * ''The State'' (newspaper), a daily newspaper in Columbia, South Carolina, United States * ''Our S ...
and local
laws Law is a set of rules that are created and are enforceable by social or governmental institutions to regulate behavior,Robertson, ''Crimes against humanity'', 90. with its precise definition a matter of longstanding debate. It has been vari ...
regarding the required number and placement of smoke detectors are based upon standards established in NFPA 72, National Fire Alarm and Signaling Code. Laws governing the installation of smoke detectors vary depending on the locality. However, some rules and guidelines for existing homes are relatively consistent throughout the developed world. For example, Canada and Australia require a building to have a working smoke detector on every level. The United States NFPA code cited in the previous paragraph requires smoke detectors on every habitable level and within the vicinity of all bedrooms. Habitable levels include attics that are tall enough to allow access. Many other countries have comparable requirements. In new construction, minimum requirements are typically more stringent. All smoke detectors must be hooked directly to the
electrical wiring Electrical wiring is an electrical installation of cabling and associated devices such as switches, distribution boards, sockets, and light fittings in a structure. Wiring is subject to safety standards for design and installation. Allowable ...
, be interconnected and have a
battery backup An uninterruptible power supply or uninterruptible power source (UPS) is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails. A UPS differs from an auxiliary or emergency power syste ...
. In addition, smoke detectors are required either inside or outside every
bedroom A bedroom or bedchamber is a room situated within a residential or accommodation unit characterised by its usage for sleeping and sexual activity. A typical western bedroom contains as bedroom furniture one or two beds (ranging from a crib f ...
, 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
stairway Stairs are a structure designed to bridge a large vertical distance between lower and higher levels by dividing it into smaller vertical distances. This is achieved as a diagonal series of horizontal platforms called steps which enable passage ...
s, main
hallway A hallway or corridor is an interior space in a building that is used to connect other rooms. Hallways are generally long and narrow. Hallways must be sufficiently wide to ensure buildings can be evacuated during a fire, and to allow people i ...
s and garages. A dozen or more detectors may be connected via wiring or wirelessly such that if one detects smoke, the alarms will sound on all the detectors in the network, improving the likelihood that occupants will be alerted even if smoke is detected far from their location. Wired interconnection are more practical in new construction than for existing buildings. In the UK the installation of smoke alarms in new builds must comply with British Standard BS5839 pt6. BS 5839: Pt.6: 2004 recommends that a new-build property consisting of no more than 3 floors (less than 200 square metres per floor) should be fitted with a Grade D, LD2 system. Building Regulations in England, Wales and Scotland recommend that BS 5839: Pt.6 should be followed, but as a minimum a Grade D, LD3 system should be installed. Building Regulations in Northern Ireland require a Grade D, LD2 system to be installed, with smoke alarms fitted in the escape routes and the main living room and a heat alarm in the kitchen; this standard also requires all detectors to have a mains supply and a battery back up.


Commercial

Commercial smoke detectors are either conventional or addressable, and are connected to
security alarm A security alarm is a system designed to detect intrusion, such as unauthorized entry, into a building or other areas such as a home or school. Security alarms used in residential, commercial, industrial, and military properties protect against ...
or
fire alarm system A fire alarm system warns people when smoke, fire, carbon monoxide or other fire-related or general notification emergency, emergencies are detected. These alarms may be activated automatically from smoke detectors and heat detectors or may also ...
s controlled by
fire alarm control panel A fire alarm control panel (FACP), fire alarm control unit (FACU), fire indicator panel (FIP), or simply fire alarm panel is the controlling component of a fire alarm system. The panel receives information from devices designed to detect and re ...
s (FACP). These are the most common type of detector, and are usually significantly more expensive than single-station battery-operated residential smoke alarms. They are used in most commercial and industrial facilities and other places such as ships and trains, but are also part of some security alarm systems in homes. These detectors don't need to have built in alarms, as alarm systems can be controlled by the connected FACP, which will set off relevant alarms, and can also implement complex functions such as a staged evacuation.


Conventional

The word "conventional" is slang used to distinguish the method used to communicate with the control unit in newer addressable systems. So-called "conventional detectors" are smoke detectors used in older interconnected systems and resemble electrical switches by their way of working. These detectors are connected in parallel to the signaling path so that the current flow is monitored to indicate a closure of the circuit path by any connected detector when smoke or other similar environmental stimuli sufficiently influences any detector. The resulting increase in current flow (or a dead short) is interpreted and processed by the control unit as a confirmation of the presence of smoke and a fire alarm signal is generated. In a conventional system, smoke detectors are typically wired together in each zone and a single fire alarm control panel usually monitors a number of zones which can be arranged to correspond to different areas of a building. In the event of a fire, the control panel is able to identify which zone or zones contain the detector or detectors in alarm. However, they cannot identify which individual detector or detectors are in a state of alarm.


Addressable

An addressable system gives each detector an individual number, or address. Addressable systems allow the exact location of an alarm to be plotted on the FACP, while allowing several detectors to be connected to the same zone. In certain systems, a graphical representation of the building is provided on the screen of the FACP which shows the locations of all of the detectors in the building, while in others the address and location of the detector or detectors in alarm are simply indicated. Addressable systems are usually more expensive than conventional non-addressable systems, and offer extra options, including a custom level of sensitivity (sometimes called Day/Night mode) which can determine the amount of smoke in a given area and contamination detection from the FACP that allows determination of a wide range of faults in detection capabilities of smoke detectors. Detectors become contaminated usually as a result of the build up of atmospheric particulates in the detectors being circulated by the heating and air-conditioning systems in buildings. Other causes include carpentry, sanding, painting, and smoke in the event of a fire. Panels can also be interconnected to monitor a very large number of detectors in multiple buildings. This is most commonly used in hospitals, universities, resorts and other large centres or institutions.


Standards


EN54 European standards

Fire detection products have the European Standard ''
EN 54 The EN 54 Fire detection and fire alarm systems is a series of European standards that includes product standards and application guidelines for fire detection and fire alarm systems as well as voice alarm systems. The product standards defin ...
Fire Detection and Fire Alarm Systems'' that is a mandatory standard for every product that is going to be delivered and installed in any country in the European Union (EU). ''EN 54 part 7'' is the standard for smoke detectors. European standard are developed to allow free movement of goods in the European Union countries. EN 54 is widely recognized around the world. The EN 54 certification of each device must be issued annually.


Coverage of smoke and temperature detectors with European standard EN54

* EN54-7: Smoke detector * EN54-5: Temperature detector * SA: Surface area * Smax (square meters): Maximum surface coverage * Rmax (m): Maximum radio Information that is in bold is the standard coverage of the detector. Smoke detector coverage is 60 square meters and temperature smoke detector coverage is 20 square meters. The height from the ground is an important issue for correct protection. An additional (harmonised) EN14604 also exists, which tends to be the standard usually cited at the domestic point of sale. This standard expands on the EN54 recommendations for domestic smoke alarms and specifies requirements, test methods, performance criteria, and manufacturer's instructions. It also includes additional requirements for smoke alarms, which are suitable for use in leisure accommodation vehicles. However, much of EN14604 is voluntary. A study published in 2014 assessed six areas of compliance & found 33% of devices claiming to meet this standard did not do so in one or more of the specifics. The study also found 19% of the products to have a problem with actual fire detection.


Australia and United States

In the United States, the first standard for home smoke alarms was established in 1967. In 1969, the AEC allowed homeowners to use smoke detectors without a license. The Life Safety Code (NFPA 101), passed by the
National Fire Protection Association The National Fire Protection Association (NFPA) is an international nonprofit organization devoted to eliminating death, injury, property and economic loss due to fire, electrical and related hazards. As of 2018, the NFPA claims to have 50,000 mem ...
in 1976, first required smoke alarms in homes. Smoke alarm sensitivity requirements in UL 217 were modified in 1985 to reduce susceptibility to nuisance alarms. In 1988 BOCA, ICBO, and SBCCI model building codes begin requiring smoke alarms to be interconnected and located in all sleeping rooms. In 1989 NFPA 74 first required smoke alarms to be interconnected in every new home construction, and in 1993 NFPA 72 first required that smoke alarms be installed in all bedrooms. The NFPA began requiring the replacement of smoke detectors after ten years in 1999. In 1999, Underwriters Laboratory (UL) changed smoke alarm labeling requirements so that all smoke alarms must have a manufactured date written in plain English. In June 2013, a World Fire Safety Foundation report titled, 'Can Australian and U.S. Smoke Alarm Standards be Trusted?' was published in the official magazine of the Australian Volunteer Firefighter Association. The report brings into question the validity of testing criteria used by American and Australian government agencies when undergoing scientific testing of ionization smoke alarms.


Legislation

In June 2010 the City of Albany, California, enacted a photoelectric only legislation after a unanimous decision by the Albany City Council; several other Californian and Ohioan cities enacted similar legislation shortly afterwards. In November 2011, the Northern Territory enacted Australia's first residential photoelectric legislation mandating the use of photoelectric smoke alarms in all new Northern Territory homes. From January 1, 2017, the Australian state of Queensland mandated all smoke alarms in new dwellings (or where a dwelling is substantially renovated) must be photoelectric, and not also contain an ionization sensor. They also were to be hardwired to the mains power supply with a secondary power source (i.e. battery) and be interconnected with every other smoke alarm in the dwelling. This is so all would be activated together. From that date, all replacement smoke alarms must be photoelectric; from January 1, 2022, all dwellings sold, leased, or where a lease is renewed must comply as for new dwellings; and from January 1, 2027, all dwellings must comply as for new dwellings. In June 2013, in an Australian Parliamentary speech, the question was asked, "Are ionization smoke alarms defective?" This was further to the Australian Government's scientific testing agency (the Commonwealth Scientific and Industrial Research Organisation -
CSIRO The Commonwealth Scientific and Industrial Research Organisation (CSIRO) is an Australian Government agency responsible for scientific research. CSIRO works with leading organisations around the world. From its headquarters in Canberra, CSIRO ...
) data revealing serious performance problems with ionization technology in the early, smoldering stage of a fire, a rise in litigation involving ionization smoke alarms, and increasing legislation mandating the installation of photoelectric smoke alarms. The speech cited in May 2013, World Fire Safety Foundation report published in the Australian Volunteer Firefighter Association's magazine titled, 'Can Australian and U.S. Smoke Alarm Standards be Trusted?' The speech concluded with a request for one of the world's largest ionization smoke alarm manufacturers and the CSIRO to disclose the level of visible smoke required to trigger the manufacturers' ionization smoke alarms under CSIRO scientific testing. The US state of California banned the sale of smoke detectors with replaceable batteries.


Notes


References


External links


Smoke alarm research from the national institute of Standards and Technology
{{DEFAULTSORT:Smoke Detector Active fire protection Americium American inventions Articles containing video clips Detectors Fire detection and alarm