During many work activities, workers can potentially be exposed to hazardous substances and mixtures in the workplace. For this reason, every organization must have an up-to-date list of all chemicals used or produced with their associated hazards.
The hazard of a substance, due to its physical and toxicological properties, together with the degree of occupational exposure to this substance determines the potential health risk of that substance or mixture.
The chemical risk management system is a structured tool that helps to establish the priorities of risks and classifies controls based on the known or suspected toxic properties of a substance.

Risk assessment

The chemical risk assessment must contain the following information:

• analysis of the work process and classification of tasks;
• identification of hazardous chemical agents;
• hazardous properties of the identified chemical agents;
• health and safety information communicated by the manufacturer or supplier
  through the relevant safety data sheet or, alternatively, information obtained from scientific literature;
• the level, type and duration of exposure;
• the circumstances in which work is carried out in the presence of such agents, including their
  quantity;
• occupational exposure limit values ​​or biological limit values;
• the effects of preventive and protective measures adopted or to be adopted;
• any health surveillance actions already undertaken;
• the indication, for each substance (or family of substances), of the quantity and the
  mode and frequency of exposure that allow, also through the use of
  models and/or algorithms, to define the level of risk

Limit values

To identify the hazard of a substance, toxicity data are required. Only for a limited number of substances is a complete set of toxicity data available that allows a full risk assessment and the derivation of an occupational exposure limit (OEL). These limits have names and values ​​that may vary from country to country or depending on the organisation that sets these limits. Some chemical manufacturers may also issue a recommended exposure limit based on the data they may have in relation to the specific chemical.

These values ​​are usually indicated as an 8-hour TWA (time-weighted average). For substances with severe acute effects, in addition to a TLV or another 8-hour value, 15-minute short-term exposure limit (STEL) values ​​or limit values ​​(values ​​that should never be exceeded) may also have been established. Measurements must be carried out according to UNI-EN standards, in particular UNI-EN 689/97

Evaluation through the use of models

In the absence of limit values ​​or to screen a large inventory of substances, models, or indexed models or algorithms for risk assessment can be used. These allow, through a final synthetic judgment, to insert the result of the assessments into risk bands.

In the case of small and medium-sized enterprises, which are characterized by a high variability in the work tasks of the employees and the related exposure times, as well as the methods of use of chemical agents, algorithms or models can represent a particularly useful tool in risk assessment. However, in case of doubt, it is advisable to confirm the model results with one or more exposure measurements.