Ringelmann chart

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. 

The original Ringelmann chart was a reflectance chart the observer viewed light reflected from the chart. More recently, light transmittance charts have been developed for both black (1) and white (2) gradations of optical density which correlate with the Ringelmarm chart scale. It is now common practice in the United States to send air pollution inspectors to a "smoke school" where they are trained and certified as being able to read the density of black and white plumes with an accuracy that is acceptable for court testimony. 

Ringelmann chart A method for the visual comparison of smoke from a chimney. The estimation is made by the comparison of the shade of smoke against shade cards. 

Ringed Roof. A furnace roof consisting of arches of bricks unbonded with adjacent arches (cf. bonded roof). Ringelmann Chart. A chart divided into five (Nos. 0-4) shades of darkness introduced in the late 19th century by Professor Ringelmann, of Paris, as a means of designating the blackness of smoke emitted from industrial chimneys. The charts have been standardized (B.S. 2742) and are used in the ceramic industry in compliance with the Clean Air Act in which dark smoke is defined as equal to, or denser than, Shade 2 on the Ringelmann Chart. 

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