The main chemistry prep room at my institution (and also at the ambulance station) is labelled with the standard green compressed gas sign. However, there is a small '2' included within the diamond. None of the chemistry technicians, tutors or ambulance staff seem to know what it is referring to and I can't find any reference of it on the internet. Would anyone here happen to know?
The related products of this online provider show that other hazards have different numbers but some also have two (e.g. flammable). Is there a standard that is being referred to here?