Smoke photoelectric

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. 

There are several types of smoke detectors. The photoelectric type detects smoke particles which interrupt a light beam resulting in the generation of an electrical signal. Photoelectric detectors are used where very slow evolving, smoky fires are expected. 

Once the fire starts to smolder and smoke is present, photoelectric sensors can be used to activate alarms. As the smoke density rises, less light passes from the source to the receiver, and an alarm is activated. 

S.W. Wilson, JRNBS 52, 195-99(1954) CA 48, 11061(1954)(A photoelectric colorimeter for measuring the chromaticities of pyrotechnic smokes) 20)Snell Snell 4(1954) [Colorimetric tests of various org compds including many expls and their primary materials, such as CarbazoIe(pp 314-15) Chloro-2,4-dinitrobenzene (p 17) 2,4-Dinittoanisole(p 19) Dinitrobenzene (p 16) Dinitrocresol(p 19) Dinitronaphthalene (p 19) Dinitrophenol(p 13) 2,4-Dinitroresorcinol (p 13) 2,4-Dinitrotoluene(p 18) Dinitroxylene ... 

Smoke Production. Smoke production can be a critical problem in fire-retardant formulations. The 25-ft tunnel test uses a photoelectric cell to measure the amount of smoke evolved. The smoke density is measured continuously and is assigned a value relative to the behavior of red oak. The effect of fire retardants on smoke production varies depending on the chemical. Figure 6 demonstrates this effect as measured in the 8-ft tunnel however, smoke values measured in various tunnel tests may not agree or correlate. 

ASTM E 84 Steiner Tunnel Test. This test, which uses very large samples (20 ft x 20 1/4 in.) is referenced in all model building codes for evaluating flame spread and smoke emission of foam plastic insulation. The test apparatus consists of a chamber or tunnel 25 ft. long and 17 3/4 X 17 5/8 in. in cross section, one end of which contains two gas burners. The test specimen is exposed to the gas flame for ten minutes, while the maximum extent of the flame spread and the temperature down the tunnel are observed through windows. Smoke evolution can also be measured by use of a photoelectric cell. The flame spread and smoke evolution are reported in an arbitrary scale for which asbestos and red oak have values of 0 and 100, respectively. More highly fire-retardant materials have ratings of 0-25 by this method. 

In this test, developed from the original Rohm and Haas XP-2 apparatus, measurements are made in terms of the loss of light transmission through a collected volume of smoke produced under controlled, standardized conditions. The flame and smoke can be observed during the test. Smoke density is measured by a photoelectric cell across a 12-inch light path. 

Uses a photoelectric cell to determine smoke obscuration. 

The test for luminometer number (ASTM D-1740) was developed because certain designs of jet engine have the potential for a shortened combustion chamber fife because of high liner temperatures caused by radiant heat from luminous flames.The test apparatus is a smoke point lamp modified to include a photoelectric cell for flame radiation measurement and a thermocouple to measure temperature rise across the flame. The fuel luminometer number (LN) is expressed on an arbitrary scale on which values of 0 to 100 are given to the reference fuels tetralin and iso-octane, respectively. 

The smoke developed during the test is determined by the reduction in output of a photoelectric cell. The value of smoke developed is derived by calculating the net area under the curve for the test material and comparing this area with net area under the curve for uncovered red oak flooring. 

Two separate (and not necessarily related) readouts of the test are (a) flame spread along the surface of the specimen as a distance traveled by the boundary of a zone of flame over time and (b) smoke developed as a change in optical density (as a progress curve of light absorption percent) between the light source and the photoelectric cell mounted in the vent pipe. These data are used to calculate the respective FSI and SDI as described in the ASTM test procedure. The indexes are calculated as relative values to those of select grade oak (FSI arbitrarily set as 100) and inorganic reinforced cement board (FSI set as 0) surfaces under the specified conditions. 

Smoke detectors (photoelectric) Detects smoldering fires Low cost Easily contaminated Indoor use... 

Smoke detectors are particularly useful in those situations where the fire is likely to generate a substantial amount of smoke before temperature changes are sufficient to actuate a heat detection system and before a fire eye will detect a flame. Smoke detectors use a photoelectric beam between a receiving element and light source. If smoke obscures the beam an alarm is sounded. There are... 

Photoelectric fire sensors that detect changes in infrared energy radiated by smoke or by the smoke particles obscuring the photoelectric beam. A relay closes to complete the alarm circuit when smoke interferes with the intensity of the photoelectric beam. 

Commercial smoke detectors may function using a photoelectric detector or an ionization chamber. An ionization detector consists of two plates across which a voltage (supplied by a battery) is applied (see diagram). One plate has a hole in it, and under the hole lies a small quantity (t q)ically 2 x 10 " g) of an a-particle emitter with... 

In the first step of the test procedure, the flammability of a red oak specimen is measured. With a correct adjustment of the experimental conditions (gas flame, air supply), the flame reaches the end-point of the wood specimen in 5.5 min. The thermocouple reading and the photoelectric cell output at the vent end are recorded every 15 s and the curves of the flame spread distance and the smoke density are plotted against time. In the second step, the same procedure is followed using an asbestos cement board then, in the third step, using the test specimen. 

For characterization of smoke formation, light absorbance measured by the photoelectric cell is plotted against time. The area under the curve for the specimen is divided by that for the red oak and then multiplied by 100 to obtain a numerical index for the performance of the material in comparison to that of the red oak, regarded arbitrarily as 100 (while the asbestos-cement board represents the zero point of this scale). 

Smoke Detectors In many fires there is smoke before there is any significant heat buildup. As a result, smoke detectors will usually detect fire before heat sensors. Smoke detectors operate on one of two principles ionization or photoelectricity. 

Figure 25.77 Photoelectric smoke detector. (Courtesy Chubb Fire Security Ltd)...

D 3917 DIMENSIONAL TOLERANCE OF PULTRUDED SHAPES D 3998 PENDULUM IMPACT OF EXTRUDATES D 4065 DYNAMIC MECHANICAL PROPERTIES OF PLASTICS D 4093 PHOTOELECTRIC BIREFRINGENCE D 4100 GRAVIMETRIC ANALYSIS OF SMOKE/PLASTICS D 4218 DETERMINATION OF CARBON BLACK CONTENT D 4272 IMPACT BY DART DROP... 

Smoke and heat detection is the most common approach in educational occupancies to detect fires. Smoke detectors utilize either photoelectric or ionization technology, both of which we will discuss. First, there are smoke detectors and smoke... 

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