A substance becomes a hazardous substance if … … it is dangerous? In other words, a substance is a hazardous substance when it has been classified and has been labelled? This would at least be a straightforward definition. But as is so often the case, a more differentiated approach is required.
The substance lists
- In Annex VI of the CLP Regulation of the harmonised entries, there are currently 4,264 entries. 
- The GESTIS substance database currently contains 8,700 substances. 
- 22,808 different substances are currently registered with ECHA, with a total of 99,213 dossiers. 
All these substance lists have one thing in common: they do not contain any mixtures!
The use of a substance is of importance
In practice, a somewhat different approach has proven to be successful. Everyone will agree that a tiger is dangerous. But if you can never meet a tiger, e.g. if you never travel to Asia, the danger is real, but the risk is practically zero. In operations, a similar procedure should be followed. If a dangerous substance is not present in your company, it does not pose a risk. For this reason, only those hazardous substances which are used in operations are included in a hazardous substance index. These are usually substances which are labelled with a hazard symbol (or at least have a H statement). The use of the term “substance” is often imprecise, because it can mean a “pure substance” as well as a mixture.
Substances and mixtures
In the hazardous substances index of a company, a distinction is not generally made between pure substances and mixtures. A pure substance can often be identified because a CAS number or EC number is also listed. Mixtures generally have a designation which indicates the property of the mixture. Mixtures must of course also be classified, as already specified in the CLP Regulation for mixtures .
Implementation in GeSi³
GeSi³ contains a “Substances” module. The substances which are listed there are pure substances. In GeSi³, the substances of the “Substances” module are used as ingredients of mixtures. In occupational health and safety, it is useful to know the ingredients of your hazardous substance (mixtures), as it allows you to automatically monitor the limit values of these ingredients. Creators of safety data sheets require the ingredients to define their formulation. This means: a substance in the “Substances” module is far from being a hazardous substance. Neither does it make any sense to “collect” as many substances as possible in the “Substances” module. The GeSi³ philosophy is to only include those substances in the “Substances” module which are also used in a hazardous substance or formulation. Therefore, if pure substances are used in day-to-day operations, they should initially be recorded in the “Hazardous substances administration” module. There, they can be conveniently assigned to different workplaces (with consumption rates) and/or storage locations (with stored quantities) or be assessed in the risk assessment for hazardous substances e.g. with the “Easy-to-use workplace control scheme” (EMKG).
- In practice, substances are hazardous substances if they
- are classified as hazardous and
- are used in operations
- This applies equally to pure substances and mixtures
- Hazardous substances are entered in GeSi³ in the hazardous substances administration
- The “Substances” module is intended for pure substances which are used as ingredients in mixtures.
 Annex VI of the CLP Regulation (Table of harmonised entries)  Contents of the GESTIS substance database  ECHA – European Chemicals Agency: List of registered substances  Regulation (EC) No 1272/2008 of the European Parliament and of the Council of 16 December 2008 on classification, labelling and packaging of substances and mixtures, consolidated version