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Description of key information

Flammability (HEBMP-H): not highly flammable

Key value for chemical safety assessment

non flammable

Additional information

The substances are only commercially available as aqueous solutions. They are involatile and (are demonstrated to) undergo thermal decomposition. Therefore, they are not expected to be highly flammable. The requirement to test the substance for pyrophoricity and flammability in contact with water was waived in accordance with Section 1 of REACH Annex IX, because there is no indication on the basis of structure and experience in use and handling that the substance is pyrophoric (flammable in contact with air) or flammable in contact with water.

HEBMP-xNa has been determined not to be highly flammable as it failed to ignite in the preliminary screening test using method A.10 flammability of solids (Atwal 2012). The acids are not expected to exhibit higher flammable properties that the corresponding salt.

In solution, HEBMP-H (CAS 5995-42-6) undergoes a reversible internal condensation reaction to form a pH-dependent equilibrium mixture with the cyclised structure 4-(Phosphonomethyl)-2-hydroxy-2-oxo-1,4,2-oxaza-phosphorinane (CAS 32422-02-9, c-HEBMP) and water. The precise proportion of the two forms is dependent on pH, temperature and time, and under acidic or neutral conditions, the proportion of c-HEBMP in the multi-constituent substance may reach proportions as high as ≥50% w/w. Spectroscopic evidence from 31P-NMR analysis suggests that in the pH range ca. 1 – 7 a high proportion (50-75% w/w) is present as the cyclised form. The two forms exist in equilibrium therefore it is extremely difficult to separate and purify both forms. The properties of the whole substance, in which both forms are present at representative levels, are used in the chemical safety assessment.

Justification for classification or non-classification

The substance is not classified for flammability as no ignition was observed during the study conducted in accordance to EU Method A.10.