Calculation method
A detailed example on a possible calculation method for HP 12 is taken from the UK Guidance and presented in the following. A substance is assigned EUH029, EUH031 or EUH032 if it is capable of releasing an acute toxic gas (34) when water or acid is added. If a waste contains a substance assigned EUH029, EUH031 or EUH032, it is possible to calculate the limiting concentration of the substance in the waste that would make it hazardous by HP 12. An example of how to do the calculation is given below in Box 4 (35). Calculation method HP 12 1. Write a balanced equation for the reaction that produces the gas. The general form of the equation is: rR + wW = pP + gG where R is the EUH029, EUH031 or EUH032 substance, W is water or an acid, 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 12 of substance R. Example calculation: A waste contains aluminium nitride (AlN). Aluminium nitride is an EUH029 substance which reacts with water to give ammonia gas. AlN + 3H2O = Al(OH)3 + NH3 aluminium nitride water aluminium hydroxide ammonia r = 1 mol of AlN, R = 41 g; g = 1 mol NH3. Limiting concentration of aluminium nitride in waste is ((1 × 41) / (1 × 22,4) / 1 000) × 100, which is 0,18 % (approximately 0,2 %). Box 4: Calculation method for HP 12 Threshold limits derived from the calculations for some EUH029, EUH031 or EUH032 substances are given below in Table 21.
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Source: EUR-Lex (Cellar) · retrieved 2026-09-07