Such products have properties which cannot be included elsewhere in the UN Class system, or which have a number of disconnected dangers crossing two or more Class boundaries.
The classic example of this diversity is self-inflating life rafts, which include in the package-
A large compressed gas cylinder, usually carbon dioxide, to inflate the raft and its canopy when it hits the water.
Various explosive flares, coloured smoke candles, etc, for attracting the attention of rescuing air and sea craft.
Flammable solid materials for heating food and providing warmth.
Fabric repair kits, containing flammable liquids as the base for adhesive solutions.
The Class sign is unique in the UN system in that it gives no indication of the particular danger, which can only then be obtained from written information.
There are two UN numbers in Class 9 for environmentally hazardous materials. UN 3077 Environmentally Hazardous Substance Solid N.O.S and UN 3082 Environmentally Hazardous Substance Liquid N.O.S.