I am assuming that the container is locked during silent hours, and the doors are left open during the working day surley that would be enough ventilation for refueling pupose.. or am I missing something.??

I shouldn't worry about it too much - the ignition/Flash Point is too high for diesel (greater than 55*C) for it to be considered flammable. The auto ignition temp is ??? 450*C??? So unless you have a mechanism for spraying the diesel (plus a strong ignition source) or spilling on to a very hot surface then the flammable risk is pretty limited. The bigger issue is spillage/environmental damage etc.

To echo previous comments, there is no real risk regarding the vapour. To quote the HSE website "While diesel is not a particularly dangerous substance from a health and safety point of view, it is an environmental hazard" http://www.hse.gov.uk/fi...osion/petroleum-faqs.htm As an aside, how did the theft occurr previosuly? All bowsers I've come across have the facility to be padlocked shut, and you can install a wheel clamp onto the bowser's wheel. Unless someone lifted the entire bowser onto a flatbed?!!