Determining the operating range class in accordance with Seveso

For several different hazardous substances at one location, it is possible to determine the operating range class in accordance with Seveso – even if the hazardous substances and ingredients have different hazard categories. If your company falls into the lowest or highest class in accordance with Seveso, you will be faced with additional duties. For the calculation, there are special specifications in the Seveso III Directive or in Seveso on how different mixtures, ingredients and associated hazards can be added up. For an extension to our hazardous substances administration, I am currently working on the exact same calculations and here, I provide a summary how the stored quantities of different hazardous substances can be added up.

Summary of hazards in groups

The first generalisation in the determination is that the hazards are divided into groups. These groups are, for example, listed in Seveso, Annex I. The following groups exist:

• Health hazards H, No. 1.1
• Physical hazards P, No. 1.2
• Environmental hazards E, No. 1.3
• Other hazards O, No. 1.4, subdivided into O1, O2 and O3

There are also groups for named substances, such as carcinogenic substances and mixtures. Here, all named substances of the same group are determined together, similar to the groups in the hazard categories. However, the individual groups have hazardous substances with different threshold values. As a result, simply adding them up is not possible.

Adding to determine the operating range class in accordance with Seveso – but in proportion

This means there has to be some proportionality. For this purpose, a quotient total is created for each group. This means, the maximum stored quantity of a substance is divided by the relevant threshold value. The trick is: even if two hazardous substances have different thresholds, they can be added. Here is an example: The maximum stored quantity of substance 1 is 500 kg and the threshold is 1000 kg. The maximum stored quantity of substance 2 is 250 kg and the threshold is 500 kg.

Accordingly, the total looks like this:

Both hazardous substances have each reached half of their threshold. The total is 1, so the threshold is reached. The operating range class in accordance with Seveso has now been determined. The calculation is carried out separately for both thresholds (lower and upper operating range). Sources: Twelfth Ordinance on the Implementation of the Federal Pollution Control Act (Seveso – 12. BImSchV), Status 08/12/2017