There are exceptions in BS 6262-4 where mirrors do not need to have an impact safety classification. Mirror glazing should be safety glass unless the pane is fully backed by a solid material, for example a wall, timber cupboard or wardrobe door, and is securely fixed to it so that there is a space of not more than 25 mm between the mirror and the backing.
[Reference: BS 6262-4: Glazing for buildings - Part 4: Code of practice for safety related to human impact]
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