Smoke ionization

Sodium receipt system Smoke ionization detectors Flange joint defect 50... 

Smoke deteetion depending upon absorption of ionizing radiation by smoke partieles light seattering by smoke partieles light obseuration. 

Various types of detectors that recognize heat and/or smoke utilizing fused bimetallic strips, ionization chambers and the interruption of a light beam by smoke or other combustion products. It is important to select the most appropriate form of detector for the environment. Insurers give a modest discount from premiums if the alarm installation complies with the insurance rules. 

Most smoke alarms (Figure 19.1, p. 517) use a radioactive species, typically americium-241. A tiny amount of this isotope is placed in a small ionization chamber decay of Am-241 ionizes air molecules within the chamber. Under the influence of a potential applied by a battery, these ions move across the chamber, producing an electric current. If smoke particles get into... 

Radioisotopes have important commercial applications. For example, americium-241 is used in smoke detectors. Its role is to ionize any smoke particles, which then allow a current to flow and set off the alarm. Exposure to radiation is also used to sterilize food and inhibit the sprouting of potatoes. Radioisotopes that give off a lot of energy as heat are also used to provide power in remote locations, where refueling of generators is not possible. Unmanned spacecraft, such as Voyager 2, are powered by radiation from plutonium. 

Exposure to cigarette smoke Exposure to ozone Exposure to ionizing radiation... 

Ionization smoke detectors that contain americium are safe when installed. However, you should not allow your children to play with these detectors and they should be promptly returned to the manufacturer for disposal if they are damaged or no longer being used. 

Both the general population and workers may be exposed to 241 Am from the production, distribution, and use of ionization chamber smoke detectors. The NRC investigated exposure relating to this device. Their 1979 report concluded that the sum of doses to the population resulting from production, distribution, use, and disposal of 14 million smoke detectors containing 3 pCi (100 kBq) of 241Am each (over 3 times that presently used) that were distributed in 1978 would result in a collective total body dose of 1,100 person-rem (11 person-Sv)—much lower than that which could potentially result in one cancer death (NRC 1979). Exposure to 241Am could result from improper disposal of smoke detectors. The detector could be broken and then disposed of in a municipal landfill or incinerated. The 241 Am from the broken detector could be consumed by a child. 

Populations with potentially high exposure to 241Am from commercial devices such as ionization chamber smoke detectors might include production workers and firemen attending to fires in production facilities, warehouses where a large number of sources or devices are housed, or homes where a small number of the devices might be used. 

NRC. 1979. Environmental assessment of ionization chamber smoke detectors containing Am-241. U.S. Nuclear Regulatory Commission. Washington, DC. NRC-02-78-045. NUREG/CR-1156. http //www.nrc.gov/. December 13, 2000. 

Petersen GR, Gilbert ES, Buchanan JA, et al. 1990. A case-cohort study of lung cancer, ionizing radiation, and tobacco smoking among males at the Hanford site. Health Phys 58(1) 3-11. 

Ionization and condensation nuclei detectors alarm at the presence of invisible combustion products. Most industrial ionization smoke detectors are of the dual chamber type. One chamber is a sample chamber the other is a reference chamber. Combustion products enter an outer chamber of an ionization detector and disturb the balance between the ionization chambers and trigger a highly sensitive cold cathode tube that causes the alarm. The ionization of the air in the chambers is caused by a radioactive source. Smoke particles impede the ionization process and trigger the alarm. Condensation nuclei detectors operate on the cloud chamber principle, which allows invisible particles to be detected by optical techniques. They are most effective on Class A fires (ordinary combustibles) and Class C fires (electrical). 

Smoke detector Senses invisible and/or visible products of combustion. The two principal types of smoke detector are photoelectric and ionization detectors. The major differences between these devices are described below Photoelectric smoke detectors react to visible particles of smoke. These detectors are more sensitive to the cooler smoke with large smoke particles that is typical of smoldering fires. Ionization smoke detectors are sensitive to the presence of ions produced by the chemical reactions that take place with few smoke particles, such as those typically produced by fast-burning/flaming fi res. 

Nicotine is distilled from bnming tobacco and carried proximally on tar droplets (also called particnlate matter), which are inhaled. Absorption of nicotine across biological membranes depends on pH. Nicotine is a weak base with a p fa of 8.0. In its ionized state, snch as in acidic environments, nicotine does not rapidly cross membranes. The pH of smoke from fine-cured tobaccos, found in most cigarettes. 

Ionization smoke detectors contain a small radioactive source (Americium 241) which ionizes air in a small chamber. The ions flow to a charged plate giving a measurable current. Products of combustion in the chamber are not easily ionized and absorb the radiation and reduce the current. The low current trips the alarm circuit. The size and composition of the particles are crucial to successful detection so that some types of smoke or vapor are detected at very low (invisible) levels. 

Ionization smoke detectors can be used in general accommodation areas such as corridors and public restrooms, to monitor the escape routes. They may be used in some types of equipment spaces, depending on ventilation. 

In either case the material is passed into a chamber where an ionizing element, often 63Ni, a radioactive isotope that produces /3 particles (electrons), converts the molecules in the chamber to ions, the same technique used in many household smoke detectors. Newer designs sometimes use 241 Am, which decays in a particles and y rays. To avoid the regulatory inconvenience of radioactive material, several electronic ionizing techniques have also been proposed. 

One of its isotopes, Am-241, is a portable source for gamma radiography also a source of ionization for smoke detectors. In the glass industry, it is used as a radioactive glass thickness gage. Other isotopes do not have much commercial application. 

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