Fortum(Formerly Komunekemi) is a Danish company dealing with hazardous waste and waste with an environmental impact. Their website contains the latest information, in Danish. Their Customer Service Center is also helpful.
The following sorting key provides an overview of Fortum's nine waste groups. It illustrates how to prioritize, sort and package the waste correctly, according to its properties. In general, the different types of waste are kept separate.
|Contains strongly oxidizing agents (eg. organic peroxide) or waste reacting strongly with water (violent reactions, the development of flammable gases or acid)
|Contains mercury (eg. mercury batteries or COD-fluids)
|Contains aerosols, gas cylinders, empty packing, asbestos, medical, isocyanates, batteries without mercury or mixed waste in small containers
|Contains pesticides or empty packaging from pesticides
|Contains only inorganic substances (eg. hydrochloric acid, sulfuric acid, nitric acid, soda, cyanide baths, metal salts or fertilizer and fertilizer residues)
|Contains only petroleum products (eg. lubricating oil, heating oil or diesel), but no emulsified substances
|Substances containing sulfur, fluorine, chlorine, bromine or iodine (eg. trichloro, freon, carbon-sulfur, mercaptans or PCB)
|Liquid with a calorific value of at least 18 MJ / kg (eg. gasoline, turpentine, thinner, toluene, alcohols or acetone) and water content exceeding 50%
|Organic chemicals without halogen or sulfur (eg. water-based glue, varnish or paint) or mixed organic and inorganic substances
Most chemical names sound similar in Danish and English, so many of the examples are readable even if you don't know Danish.
Hazardous waste is sorted according to the appropriate disposal method, not according to similarity. Therefore there is no guarantee that chemicals within the same waste group may be mixed together in any safety!
Particularly: group O, the organic peroxides, may not be mixed with oxidizing substances; and Class X wastes containing cyanide must be kept separate from acids.
The above is a translation of Fortum's(Formerly Komunekemi) rules as of May 2009. They may change - their website is the "real" one, but may only exist in Danish.