Smoke, gray

Limits on emissions are both subjective and objective. Subjective limits are based on the visual appearance or smell of an emission. Objective limits are based on physical or chemical measurement of the emission. The most common form of subjective limit is that which regulates the optical density of a stack plume, measured by comparison with a Ringelmann chart (Fig. 25-1). This form of chart has been in use for over 90 years and is widely accepted for grading the blackness of black or gray smoke emissions. Within the past four decades, it has been used as the basis for "equivalent opacity" regulations for grading the optical density of emissions of colors other than black or gray. 

Following is an example of an American NGu proplnt, as given in Spec MIL-P-668A (Feb 1955) NC (13-3 to 13.4% N) 18.0 to 22, NG 18—20, NGu 52.7—56.7, ethyl centralite 5.40—6.60 cryolite 0.20—0.40%. It should be noted that flashless colloided proplnts contg NGu produce a considerable amount 0/ particulate gray smoke (more than other proplnts used... 

A small sample of AN in an evacuated tube was heated gradually to desired temps, and samples of the gas produced by decompn were pumped out, measured and tested. Decompn proceeded very quietly at temps below 200°, and only a small amt of gas was formed even on heating for several hours. The reaction proceeded more vigorously at higher temps and became rather violent at ca 260°. Between 260 and 269° gray smoke was produced and, after a time, an explosion took olacr. This also Orftirred after hearing... 

K chlorate 4.0 to 12.0 Amm acid fluoride 2.0 tc 8.0 parts. This compn, when ignited by a flame, produced on burning a heavy copipus, lavender-gray smoke and sublimate b)When using mono- or tri-chloroacetic acid in previous mixt, instead of fluoride, the color of smoke produced was grayish-black to blackish c)Equal parts of chromic oxide,... 

For use in trench warfare, for the purpose of obscuring the situation from the sight of the enemy, a very satisfactory dense white or gray smoke is procured by burning a mixture of zinc dust and hexachloroethane. The mixture requires a strong starting fire. The smoke consists largely of finely divided zinc chlo-... 

Flashless colloided powder containing nitroguanidine produces a considerable amount of gray smoke made up of solid materials from the decomposition of the substance. The gases smell of ammonia. The powder produces more smoke than the other flashless powders which are used in this country. 

This assumption however is not true, for powder which contains nitroguanidine produces a gray smoke consisting of solid decomposition products and yields gases which smell of ammonia. 

Uses Was used in trench warfare for producing gray smokes. 

Uses To produce a dense white or gray smoke by burning it in combination with hexachlorethane. For a grayer smoke, naphthalene or anthracene is added to the mixture. 

British System — The three classes of British chemical shell were distinguished from each other and from all other types of shell by distinctive body colors, as follows gas shell were painted gray smoke shell, light green and incendiary shell, red. In addition, for gas shell, the kind of gas filling was indicated by a system of colored stripes encircling the body of the shell as follows ... 

Military Concealment Operations. Deliberately generated smokes are used in military situations for local visual concealment of troop operations, such as movement and placement of artillery and other fire capabilities. They may also be employed against opposing forces to cause impairment of coordinated and operational activities. Generally these are white/gray smokes. Additionally, some screens are used for infrared obscuration purposes. 

Polyphenylene sulfide will not burn when tested by any of the common standard tests used for plastics, such as ASTM D635 and UL-94. However, when exposed In a fire, It will continue to burn until the externally applied flame Is removed. It burns with a yellow-orange flame, producing gray smoke with traces of black. 

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