Smoke detector

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smoke detector is a tool that feels smoke, usually as an indicator of fire. Commercial security devices emit signals to the fire alarm control panel as part of the fire alarm system, while the household smoke detector, also known as the smoke alarm , generally issues a local audible or visual alarm from the detector itself..

Smoke detectors are placed in plastic enclosures, usually shaped like discs about 150 mm (6 inches) in diameter and 25 millimeters (1 inch) thick, but the shape and size vary. Smoke can be detected either optically (photoelectric) or through physical processes (ionization); the detector can use either, or both, methods. Sensitive alarms can be used to detect, and thus prevent, smoking in prohibited areas. Smoke detectors in large commercial, industrial and residential buildings are usually supported by a central fire alarm system, powered by building strength with battery backup. Domestic smoke detectors range from each battery-powered unit, to several interlink-powered electric units with backup batteries; with these interconnected units, if any unit detects smoke, all of which trigger even if the household power has been extinguished.

The risk of death in home fires is reduced by half in homes with smoke alarms. The US National Fire Protection Association reported 0.53 deaths per 100 fires in homes with occupational smoke alarms compared with 1.18 deaths in homes without (2009-2013). Some homes do not have smoke alarms, some do not have a working battery; sometimes the alarm fails to detect fire.

Video Smoke detector

History

The first automated electric fire alarm was patented in 1890 by Francis Robbins Upton, a colleague of Thomas Edison. George Andrew Darby patented the first European electric heat detector in 1902 in Birmingham, England. In the late 1930s Swiss physicist Walter Jaeger tried to create sensors for toxic gases. He hopes that the gas entering the sensor will bind the ionized air molecules and thereby alter the electrical current in the circuit within the instrument. The device does not meet its purpose: the small gas concentration has no effect on the sensor conductivity. Frustrated, Jaeger lit a cigarette and was immediately surprised to realize that a meter in the instrument had recorded a decrease in current. The smoke particles from his cigarette have apparently done what can not be poisonous gas. Jaeger's experiment is one of the improvements that pave the way for modern smoke detectors. In 1939 the Swiss physicist Ernst Meili designed an ionization chamber capable of detecting flammable gases in the mine. He also invented cold cathode tubes that can amplify the small signal generated by a detection mechanism with enough power to activate the alarm.

The ionization smoke detector was first sold in the United States in 1951; they are only used in major commercial and industrial facilities in the next few years because of their large size and cost. In 1955 a simple house "fire detector" for home was developed, detecting high temperatures. The United States Atomic Energy Commission (USAEC) granted the first license to distribute smoke detectors using radioactive material in 1963. The first cheap smoke detector for domestic use was developed by Duane D. Pearsall in 1965, a replaceable battery-powered battery pack that could be fitted with easy. "SmokeGard 700" is a strong and honeycomb refractory steel unit. The company began mass-producing these units in 1975. Studies in the 1960s determined that smoke detectors reacted to fires much faster than heat detectors.

The first single station smoke detector was invented in 1970 and published the following year. It is an ionizing detector powered by a single 9 volt battery. It costs about US $ 125 and is sold at a rate of several hundred thousand per year. Some technological developments took place between 1971 and 1976, including the replacement of cold cathode tubes with solid-state electronics, which greatly reduced the size of the detector and made it possible to monitor battery life. Early alarm horns, which require special batteries, are replaced with more energy-efficient horns, allowing the use of generally available batteries. The detector can also function with a small amount of radioactive source material, and the smoke detector and enclosure space of the redesigned smoke detector for more effective operation. Rechargeable batteries are often replaced with a pair of AA batteries along with a plastic shell that wraps the detector. The 10-year smoke alarm-lithium-powered battery was introduced in 1995.

The photoelectric (optical) smoke detector was created by Donald Steele and Robert Emmark of the Electro Signal Lab and patented in 1972.

Maps Smoke detector

Design

Ionization

An ionization smoke detector uses radioisotopes, usually americium-241, to ionize the air; differences due to smoke detected and alarms generated. The ionization detector is more sensitive to the flame stage than the optical detector, whereas the optical detector is more sensitive to fire in the early stages of the embers.

The smoke detector has two ionization chambers, one opens into the air, and a reference room that does not allow particle entry. Radioactive sources emit alpha particles into both chambers, which ionize several air molecules. There is a potential difference (voltage) between the electrode pairs in the spaces; the electric charge on the ion allows the electric current to flow. The currents in both chambers must be equal because the same current is influenced by air pressure, temperature, and source aging. If the smoke particles enter the open space, some ions will stick to the particles and are not available to carry the current in the room. Electronic circuits detect that current differences have developed between open and closed spaces, and alarm sounds. This circuit also monitors the battery used to supply or back up power, and sounds intermittent warning when approaching fatigue. User-operated test buttons simulate an imbalance between the ionization chamber, and sound an alarm if and only if the power supply, electronics, and alarm device are working. The current collection of ionisation smoke detectors is low enough for a small battery used as a single supply or backup to provide power for months or years without the need for external cables.

Ionized smoke detectors are usually less expensive to fabricate than optical detectors. They may be more susceptible to false alarms triggered by harmless events than photoelectric detectors, and have been found much more slowly to respond to typical home fires.

Americium-241 is an alpha transmitter with a half-life of 432.6 years. Radiation of alpha particles, as opposed to beta (electron) and gamma (electromagnetic) radiation, is used for two additional reasons: alpha particles have high ionization, so that sufficient air particles will be ionized for their current existence, and they have low penetration power. , meaning they will be stopped, safe, by plastic from smoke or air detectors. About one percent of the radioactive energy emitted from ²⁴¹ Am is gamma radiation. The number of americium-241 elements is small enough to be released from regulations applied to larger sources. It includes about 37 kBq or 1 Ãƒ,Ã‚Î¼Ci radioactive element americium-241 (²⁴¹ Am), corresponding to about 0.3 Ãƒ,Ã‚Î¼g isotope. It provides sufficient ion currents to detect smoke, while producing very low levels of radiation outside the device.

The americium-241 in ionizing smoke detectors poses potential environmental hazards, although very small. Disposal regulations and recommendations for smoke detectors vary from region to region. The amount of radioactive material contained in the ionizing smoke detector is very small and thus does not represent a significant radiological hazard. If the americium remaining in the ionization chamber alarm radiological alarm is not significant because space acts as a shield for alpha radiation. A person should open up a closed space and swallow or inhale the americium so that the risk becomes significant. The risk of radiation exposure to ionic smoke detectors is much smaller than that of natural background radiation under normal operation.

Some European countries, such as France, and some US states and municipalities have banned the use of domestic ionic smoke alarms due to concerns that they are not reliable enough compared to other technologies. Where ionizing smoke detectors are the only detectors, fires in the early stages are not always detected effectively.

Photoelectric

A photoelectric , or an optical optical detector containing an infrared, visible, or ultraviolet light source (usually an incandescent light or a light-emitting diode), a lens , and photoelectric reciever (usually photodiode). In a type detector where all these components are arranged in a space where air, which may contain smoke from a nearby fire, flows. In large open areas such as atriums and auditoriums, optical rays or smoke detectors are projected to be used instead of space within the unit: wall-mounted units emit infrared or ultraviolet rays received and processed separately. device, or reflected back to the receiver by a reflector. In some types, especially the type of optical beam, the light emitted by the light source passes through the air being tested and reaches the photosensor. The intensity of light received will decrease due to scattering of dust particles, air-borne dust, or other substances; the circuit detects the intensity of the light and generates an alarm if it is below a specified threshold, potentially due to smoke. In other types, usually the type of space, the light is not directed at the sensor, which is not illuminated in the absence of particles. If the air in the room contains particles (smoke or dust), the light is scattered and partially reaches the sensor, triggering the alarm.

According to the National Fire Protection Association (NFPA), "photoelectric smoke detection is generally more responsive to fires beginning with a long period of smoldering". Study by Texas A & amp; M and NFPA cited by Palo Alto City of the state of California, "Photoelectric alarms react more slowly to rapidly growing fires than ionization alarms, but laboratories and field tests show that photoelectric smoke alarms provide adequate warning for all types of fires and have proven far less likely to be disabled by the occupants. "

Although photoelectric alarms are very effective at detecting blazing fires and providing adequate protection from burning fires, fire safety experts and the National Fire Protection Agency recommend installing so-called combination alarms, which are alarms that detect both heat and smoke, or use both processes ionization and photoelectric. Some combination alarms may include carbon monoxide detection capabilities.

The type and sensitivity of light sources and photoelectric sensors, and the types of smoke spaces differ between manufacturers.

Detection of carbon monoxide and carbon dioxide

The carbon monoxide sensor detects potentially fatal carbon monoxide gas concentrations, which can accumulate due to misplaced ventilation such as heating and gas cooking, although there is no uncontrolled fire outside the appliance.

High levels of carbon dioxide (CO ₂) can indicate fires, and can be detected by carbon dioxide sensors. Such sensors are often used to measure potentially unwanted CO ₂ levels but do not indicate a fire; this type of sensor can also be used to detect and warn of much higher levels generated by fire. One manufacturer says that detectors based on CO ₂ level are the fastest indicator of fire, and also, unlike ionization and optical detectors, detect non-smoke fires, such as those triggered by alcohol or gasoline. Fire detectors CO ₂ are not susceptible to false alarms due to particles, making them particularly suitable for use in dusty and dirty environments.

Performance differences

A presentation by Siemens and the Canadian Fire Alarm Association reported the ionization detector as the best in detecting new-stage fires with invisible small particles, fast-burning fire with smaller 0.01-0.4 micron particles, and black smoke or dark, while a more modern photoelectric detector best detects slow-burning fires with larger 0.4-10.0 micron particles, and bright white/light gray smoke.

The photoelectric smoke detector responds more quickly to the fire at an early stage, smoldering (before it bursts into a flame). Smoke from the burning fire stage is usually made of large combustion particles - between 0.3 and 10.0 Ã‚Î¼m. The ionization smoke detector responds more quickly (usually 30-60 seconds) in the flame stage. Smoke from the flame stage is usually made of microscopic burning particles - between 0.01 and 0.3 Ãƒ,Ã‚Î¼m. Also, the ionisation detector is weak in high airflow environments, and because of this, the photoelectric smoke detector is more reliable for detecting smoke in both fire-burning stages.

In June 2006, the Australasian Fire & amp; The Emergency Services Authority Council, the highest representative body for all Australian and New Zealand fire departments, published an official report, 'Position on Smoke Alarms in Residential Accommodation'. The 3.0 clause states, "The ionizing smoke alarm may not operate in time to warn the occupants early enough to escape from the burning fire."

In August 2008, the International Fire Association (IAFF, with more than 300,000 members in North America) passed a resolution recommending the use of photoelectric smoke alarms, saying that it turned into a photoelectric alarm, "Will drastically reduce the loss of life among residents and firefighters fire. "

In May 2011, the official position of the Australian Fire Protection Association (FPAA) on smoke alarms stated, "The Australian Fire Prevention Association considers that all residential buildings should be equipped with photoelectric smoke alarms..."

In December 2011, the Australian Volunteer Fire Association published the World Fire Safety Foundation report, 'Ionization Smoke Alarms is OFF', citing research that outlines the huge performance difference between ionization and photoelectric technology.

In November 2013, the Ohio Fire Brigade (OFCA) Association published an official position paper supporting the use of photoelectric technology in homes in Ohioan. The OFCA position states, "For the benefit of public safety and for protecting the public from the deadly effects of smoke and fire, the Ohio Fire Principles Association supports the use of Photoelectric Smoke Alarms... In both new construction and while replacing the old smoke alarms or buying new alarms, we recommend Photoelectric Smoke Alarm. "

In June 2014, tests by the North East Ohio Fire Prevention Association (NEOFPA) about residential smoke alarms were broadcast on ABC's 'Good Morning America' program. The NEOFPA test indicates the smoke ionisation alarm fails to activate at the burning startup stage. The ionization-photoelectric combination of the alarm failed to activate until an average of more than 20 minutes after the photoelectric smoke alarm stood alone. This justifies the official position of June 2006 from the Australasian Fire & amp; The Council of Emergency Services Authority (AFAC) and October 2008, the official position of the International Fire Brigade (IAFF). AFAC and IAFF recommend photoelectric smoke alarms, but not combinations of ionization/photoelectric smoke alarms.

According to a fire test corresponding to EN 54, CO ₂ clouds of open flame can usually be detected prior to particulates.

Due to the level of detection ability that varies between types of detectors, manufacturers have designed multi-criteria devices that cross-referenced separate signals to override false alarms and increase response time to real fires.

Obscuration is a measurement unit that has become the standard way to determine smoke detector sensitivity. Obscuration is the effect that smoke has on sensor visibility reduction, expressed in percent of ob- jurations per unit length; Higher smoke concentrations result in higher blending rates.