No outer or inner package containing explosives shall contain more than one kind of explosive or contain any other article or substance:
Provided that there may be packed in the same outer package-
(a) an inner package containing a propellant and an inner package containing a different kind of propellant or gunpowder; or
(b) an inner package containing an explosive in category 1, class 6, division 1 and any article or substance which is not of an inflammable or explosive nature or liable to cause fire or explosion.