Sheathed flames

A few burners are available that can produce a sheathed flame. Such flames usually are surrounded by an inert gas that prevents the flame from entraining air from its surroundings. Thus oxygen in the air does not enter the flame to react with the metals atoms that are present. 

Gravesend, 2002, pp.2. 30cms. 25/4/2002 CATAPYRRIC SX545 CM540U SILANE CROSSLINKABLE LOW-SMOKE LOW-TOXICITY HALOGEN-FREE FLAME-RETARDANT COMPOUND, FOR INSULATION OF LV CABLES AND SHEATHING OF ALL TYPES OF CABLES AEI Compounds Ltd. 

The value of G was shown to have a profound effect upon the flame location and distribution of temperature, fuel vapor, and oxygen. Four types of behaviors were found for large G numbers. External sheath combustion occurs for the largest value and as G is decreased, there is external group combustion, internal group combustion, and isolated droplet combustion. 

Powder sheathed with various protective layers. It is used mainly for mining and quarrying operations. The flame developed is transmitted along a preselected path to the pyrotechnic charge, where it can either initiate the chge directly or initiate one or several squibs that are used as chge igniters... 

The action of safety sheaths has been widely investigated and it seems probable that the finely dispersed material of the sheath functions as a flame trap in the firedamp mixt, and prevents propagation of any flame or ignition (Ref 34a, p 22)... 

These are not to be confused with Bickford fuse or safety fuse manufactured by the same company, which consists of a central thread surrounded by a core of black powder enclosed within a tube of woven threads, surrounded by various layers of textile, waterproof material, sheathing, etc. This is miner s fuse, and is everywhere known as Bickford fuse after the Englishman who invented the machine by which such fuse was first woven. The most common variety bums with a velocity of about 1 foot per minute. When the fire reaches its end, a spurt of flame about an inch long shoots out for igniting black powder or for firing a blasting cap. 

Flame-spread and smoke-density values, and the less often reported fuel-contributed semiquantitive results of the ASTM E84 test and the limited oxygen index (LOI) laboratory test, are more often used to compare fire performance of cellular plastics. All building codes require that cellular plastics be protected by inner or outer sheathings or be housed in systems all with a specified minimum total fire resistance. Absolute incombustibility cannot be attained in practice and often is not required. The system approach to protecting the more combustible materials affords adequate safety in the buildings by allowing the occupant sufficient time to evacuate before combustion of the protected cellular plastic. 

Experimental. The experimental set up consisted of a -pum-ped-dye laser (Molectron UV-14, DL-400), spatial filters to isolate the central part of the dye laser beam, a H2 02-Ar or N2 flame supported by a capillary burner with Ar or N2 sheath, and a fluorescence detection system at right angles (a JY-H-10 monochromator, a photomultiplier, and a PAR 162-164 boxcar averager). All measurements were taken 1 cm above the burner top the concentration of Ca, Sr, In, and Na was low ( 1 yg/ml). The fluorescence waveform was monitored with a 75 ps sampling head (PAR 163). The laser spectral bandwidth was also measured with a JY-HR-1000 monochromator (6AS < 0.1 ). 

Hietaniemi et al. [76] used a prerelease version of FDS4 to model lire spread on several materials in several different configurations and compared the calculated results with experimental data. This is one of the most comprehensive (in terms of the number of materials and the number of different configurations simulated) large-scale flame spread modeling studies conducted to date. The materials simulated include spruce timber (SBI, room/corner, and 6 m cavity), medium density fiber board (SBI and room/corner), PVC wall carpet on gypsum board (SBI, room/corner), upholstered furniture (furniture calorimeter and ISO room), and polyethylene-sheathed cables in 6 m cavity. 

If the flame background emission intensity is reduced considerably by use of an inert gas-sheathed (separated) flame, then an interference filter may be used rather than a monochromator, to give a non-dispersive atomic fluorescence spectrometer as illustrated in Figure 14.36-38 Noise levels are often further reduced by employing a solar blind photomultiplier as a detector of fluorescence emission at UV wavelengths. Such detectors do not respond to visible light. The excitation source is generally placed at 90° to the monochromator or detector. Surface-silvered or quartz mirrors and lenses are often used to increase the amount of fluorescence emission seen by the detector. 

SAFETY PROFILE Human poison by unspecified route. Human systemic effects by ingestion nerve or sheath structural changes, extra-ocular muscle changes, sweating, and other effects. Flammable in the form of dust when exposed to heat or flame. Violent reaction with F2. When heated to decomposition it emits toxic fumes of Tl. Used as a rodenticide and fungicide, and in lenses and prisms, in high-density liquids, See also THALLIUM COMPOUNDS and POWDERED METALS. 

Also presented in Table I are temperatures of the flame as measured by others ( 16, 17) and the saturation currents measured by Frier. With the assumption that no colhsions between positive ions and neutral gas molecues occur within the ionic sheaths surrounding the probe wires (vahd here because the mean free path of the species considered is larger than the thickness of the sheath), the relation between the saturation current and the ionic concentration is ... 

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