The European Standard does not allow for safety spectacles to be tested and certified for grade B impact resistance.
Impact resistance is tested by firing 6mm steel ball bearings at varying speeds appropriate to the type and marking.
Grade B impact is tested at 120m/s (270mph) which is only applicable to goggles and face shields, whereas safety spectacles have a maximum rating of F (45m/s).
Faceshields have a maximum rating of A (190m/s). S, for increased or minimum robustness, is the lowest-rated impact marking and generally only applies to mesh protectors.