Linking Seveso with the CLP health hazard categories

Which health classifications are relevant to Seveso?

Currently, the EU Directives on Dangerous Substances and Dangerous Preparations (DSD/DPD) have three categories for acute toxicity: Very Toxic (T+), Toxic (T) and Harmful (Xn).

For the purposes of the generic categories of danger in Seveso (in Annex 1 Part 2) only the Very Toxic and Toxic categories are relevant.  These have qualifying quantities of 5/20 tonnes (lower tier) and 50/200 tonnes (top tier).

A substance falls into one of these Seveso categories if its overall DSD/DPD classification is Very Toxic (T+) or Toxic (T).

What are the new health categories in the CLP Regulation?

The CLP health hazards class has four categories for acute toxicity: 1, 2, 3 and 4.  The toxicity criteria for categories 1, 2 and 3 overlaps those for T+ and T.  The difficulty is how to align the current T+ and T classifications with the three CLP Categories.

What are the main differences between the DSD/DPD classification system and the new CLP classification criteria?

Although there are similarities between both classification systems (e.g. in the use of cut-off values on LD₅₀ and LC₅₀), there are a number of differences that could affect the scope of Seveso.  The main differences are:

• a straight forward shift in some boundaries of dermal and oral routes, and
• an exact agreement for inhalation exposures to vapours that are not near the gaseous state i.e. T+ = CLP Category 1 and T = CLP Category 2, but
• differences for exposures to gases and vapours near the gaseous state because:
  • CLP makes a classification distinction between vapours and gases, and
  • the current DSD/DPD system measures acute inhalation toxicity in terms of the mass (mg/l) inhaled in a given volume, whereas the CLP measurement for gases is based on the number of molecules inhaled in a given volume (ppm/V).

These alignment differences are illustrated in the following simplified comparison (which omits the LD₅₀ and LC₅₀ scales):

What are the implications of the new GHS/CLP classifications?

The TWG is looking at the alignment possibilities and their potential implications.  For example:

• precautionary alignment options that link T+ with CLP Category 1 and T with CLP Categories 2 and 3 could bring substances currently outside the scope of Seveso and with no major accident hazard potential into the Seveso regime.  There may then be a need to 'filter out' some Category 3 substances
• conversely, aligning T+ with CLP Category 1 and T with CLP Category 2 may exclude some substances that are currently T+ or T.  Some sites currently considered to have major hazard potential could fall outside scope (although these are likely to be mainly substances that are currently classified as T with the least severe acute toxicity within the range)
  
  One way to avoid this 'gap' would be to identify the substances affected, consider whether they have any industrial or regulatory significance and, if so, add them to the list of Named Substances in Annex 1 Part 1 of Seveso.  From a UK perspective two substances so far have been identified as falling into this category: these are the lower molecular weight gases ammonia and sulphur dioxide.

Details of various alignment possibilities and their potential impact are contained in the 'Health Hazards' section of the report of the TWG.

• Report of the Technical Working Group Report on the Application of GHS substances classification criteria for the identification of Seveso establishments.