Separation Distances of Ammonium Nitrate and Blasting Agents from Explosives or Blasting Agents (2002R- 226P), Advance Notice of Proposed Rulemaking [open pdf - 150KB]
From the Summary: "The Department of Justice (Department) intends to amend the regulations of the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) to replace the regulations' reference to an outdated guidance document. Based upon a petition ATF received, the Department wishes to gather information and comments from the public and industry about possible replacements for this guidance document."
Federal Register: http://www.federalregister.gov/
Federal Register (September 16, 2010), v.75, no.179, p.56489-56491