Waste hazard properties HP 4 ‘Irritant’ and HP 8 ‘Corrosive’ by pH, acid/base buffer capacity and acid/base concentration

European "Technical Recommendations" have proposed, in addition to the use of substance concentrations, the use of a pH (≤ 2 or ≥ 11.5) and an acid / base buffering capacity to classify waste into according to their hazardous properties HP 4 'Irritant' and HP 8 'Corrosive'. Buffer capacity refers to a 2018 UK classification guide referring to the 'corrosive' level of a method proposed in 1988 for substances and preparations but not retained in EU regulations. The different methods of classifying products and wastes in terms of corrosivity or irritation are compared. The waste method using pH and buffering capacity is expressed as an acid / base concentration and compared to the product method (CLP). The “corrosive” level of 1988 corresponds to an average acid / base concentration ≥ 14.4Ͽie 14 times less severe than CLP (acid / base concentration ≥ 1Ͽ These methods were applied to five alkaline wastes (pH ≥ 11.5). Minimum pH waste is not classified by both methods, and three higher pH wastes are classified by both methods. Intermediate waste is classified by CLP but not by the proposed waste method. In order not to innovate and create a new divergence between products and waste, it seems preferable to use the product regulations for HP 4 and HP 8. Fortunately, the elimination of the danger HP 4 and HP 8 from acidic or alkaline waste can be obtained by neutralization (possibly by other wastes), including for alkaline wastes by (natural) carbonation by atmospheric CO2.