The Modification of Helmets for Caving: The Viper lights require that you drill three holes in your helmet for mounting the battery. This is unlikely to have an adverse effect on the overall strength or protection offered by the helmet shell but obviously this can't be guaranteed. Drilling holes into a helmet shell technically invalidates its certification as Personal Protective Equipment (PPE) and may have an adverse effect on the amount of protection provided by it so anyone who modifies or uses a modified helmet must be aware of, and fully accept, the potential incurred risks of the modification beforehand and during subsequent use.