5.1 There are a variety of darkening agents that contribute to air and surface contamination in industrial, urban and rural environments. Biofilms (fungal and algal), soil minerals, plant fragments, rubber fragments, metal corrosion and soot are common darkening agents. Soot is formed as an unwanted by-product of combustion and consequently varies widely with the type of fuel and combustion conditions. Carbon black, on the other hand, is purposely produced under a controlled set of conditions. Therefore, it is important to be able to distinguish carbon black from soot, as well as other environmental contaminants.

1.1 This practice covers sampling and testing for distinguishing ASTM type carbon black, in the N100 to N900 series, from other environmental particulates.

1.2 This practice requires some degree of expertise on the part of the microscopist. For this reason, the microscopist must have adequate training and on-the-job experience in identifying the morphological parameters of carbon black and general knowledge of other particles that may be found in the environment. In support of this analysis, Donnet's book² is highly recommended to be used as a technical reference for recognizing and understanding the microstructure of carbon black.

1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.4 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.