Calculation method for HP 3 (fifth indent)
As already indicated, a substance is assigned H260 or H261 if it is capable of releasing a highly flammable gas at a rate in excess of 1 litre of gas per kilogram of substance per hour when water is added. If a waste contains a substance assigned H260 or H261, it is possible to calculate the limiting concentration of the substance in the waste that would make it hazardous by HP 3 (fifth indent). The background of this calculation method is, that the amount of the reactive substance needed to generate one litre of the flammable gas is calculated, based on stoichiometry and by applying the volume of a mol of gas at standard pressure and temperature. The concentration limit of one litre is taken from test method A.12. Flammability (Contact with water) as described in Part A of the Annex to the Test Method Regulation. Below this concentration the waste will not be hazardous as a result of HP 3 (fifth indent). At or above the concentration the waste should be assumed to be HP 3, or tested. An example of how to do the calculation is taken from the UK Guidance and presented below in Box 3 (5). Threshold limits derived from the calculation for some H260 and H261 substances are given in Table 11.
Source: EUR-Lex (Cellar) · retrieved 2026-09-25 · Text as adopted (Official Journal); later amendments are not incorporated in this text.