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). Calculation method HP 3 (fifth indent) 1. Write a balanced equation for the reaction that produces the gas. The general form of this equation should be as follows: rR + wW → pP + gG where R is the H260/H261 substance, W is water, P is a product of the reaction, and G is the gas released; r, w, p and g are the stoichiometric ratios that balance the equation. 2. Attribute molecular weights and stoichiometric ratios to the substances in the equation. 3. Divide (r × molar weight of R) by (g × 22,4). This gives the mass of R that will evolve 1 litre of gas. 1 mol of gas occupies 22,4 litres at standard temperature and pressure. 4. Divide this amount (in grams) by 1 000 (to convert to kilograms) and multiply it by 100 to give a percentage by weight, and thus the limiting concentration for HP 3 (fifth indent) of substance R. Example calculation: A waste contains aluminium carbide. Aluminium carbide is a H260 substance which reacts with water to give methane gas. Al4C3 + 6H2O → 2Al2O3 + 3CH4 aluminium carbide water aluminium oxide methane 144 g 18 g 102 g 16 g 1 mol 6 mol 2 mol 3 mol r = 1 mol of Al4C3, R = 144 g; g = 3 mol CH4. Limiting concentration of aluminium carbide in waste = [144 / (3 × 22,4)] / 1 000 × 100, which is 0,21 % (approximately 0,2 %). Box 3: Calculation method HP 3 (fifth indent) Threshold limits derived from the calculation for some H260 and H261 substances are given in Table 11.

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Source: EUR-Lex (Cellar) · retrieved 2026-09-07