sawdust454... George is correct. The presence of diesel fuel does not create a "classified" area. This of course assumes that there isn't a gasoline tank nearby the diesel tank.
If you want more information, you should research NFPA 30A-2003, Code for Motor Fuel Dispensing Facilities and Repair Garages. This is the standard that classifies motor vehicle fuel dispensing areas.
You can review a "read-only" copy of 30A on-line at: http://www.nfpa.org/itemDetail.asp?...lopment%20process/Free%20online%20access
Hope this helps.