In the ICAO Technical Instruction as well as with the IATA DGR, there is no mention about a specific segregation distance except for the separation distance between explosives which is minimum 2 meters per DGR 188.8.131.52.5. For all other segregation other than explosives, since there is a great volume of traffic involving the United States, a 3-meter segregation is recommended following the stipulations spelled out in the U.S. 49 CFR.
The 49CFR deals on this subject in two places in their manual. The first place is at the Air Section in 175.78 "Stowage Compatibility of Cargo" where it carries a Segregation Table similar to the DGR Table 9.3.A. In sub-paragraph (b) it mandates "acceptable segregation" between packages but do not indicate a distance in figures. In sub-paragraph (c) (4) (iv) it specifies 2 meters but only for between explosives.
US DOT and FAA directs airline carriers to apply the Vessel Section of the 49CFR to Subpart D - General Segregation Requirements 176.83 "Segregation", sub-paragraph (c) Segregation requirement for break bulk cargo (2) Definition of the segregation terms (ii) "Away from" which spells "Effectively segregated so that the incompatible materials cannot interact dangerously in the event of an accident that may be carried in the same compartment or hold or on deck provided a minimum horizontal separation of 3 meters (10 feet) projected vertically is obtained."
This is the reference which DOT and FAA advises airlines to follow for "acceptable segregation" for all modes of transportation whether ocean, air or land for segregation of incompatible material or substances.