Response: The HCS does not contain a definition for “complex mixtures.”  However, OSHA considers a mixture to be a “complex mixture” if it has a range of complex (i.e., multiple) ingredients that vary due to variations in its composition. Paragraph (g)(4) provides that [w]here complex mixtures have similar hazards and contents (i.e., the chemical ingredients are essentially the same, but the specific composition varies from mixture to mixture), the chemical manufacturer, importer or employer may prepare one safety data sheet to apply to all of these similar mixtures See 77 Fed. Reg. 17574, 17731 (Mar. 26, 2012).

In the preamble to the HCS 2012, OSHA explained that petroleum streams are an example of a type of complex mixture, and that it would be appropriate to use a concentration range, rather than an exact concentration, for the ingredients that vary stream to stream. Id. OSHA also noted that when a manufacturer has a line of products that are very similar and pose the same hazard, but can be varied slightly in composition to meet the needs of customers (e.g. toner color with varying amounts of pigment), the manufacturer may use concentration ranges for multiple, similar products. Id. Thus, a "generic" SDS may address a group of complex mixtures, such as crude oil, natural gas, or bricks, which have similar hazards and characteristics because their chemical ingredients are essentially the same even though the specific composition varies in each mixture.

Based on the extracted MSDS information provided in your letter, it is difficult to determine whether the mixture is a complex mixture. Generally, Lignonsulfonate would be considered a complex mixture because of having a wide range molecular mass depending on whether it is produced from soft or hard woods.

Therefore, if the manufacturer includes only Barium Carbonate or Barium Chloride in the mixture at one time and these chemicals pose different hazards, then it is not permissible to use a single SDS that lists both chemicals. If, however, only Barium Carbonate or Barium Chloride is in the mixture at one time and these chemicals have similar health hazards, a single SDS would be appropriate.