Flashpoint refers to the lowest temperature of the oil (and other hydrocarbons) at which a vapour/air mixture is produced which can be ignited first-time.
Flashpoint depends on the molecular size or molecular weight and thus on viscosity.
Flashpoint is of no relevance in lubrication technology. There are no special safety-related requirements to meet at a flashpoint of over 100°C for VbF/TRbF (Verordnung über brennbare Flüssigkeiten/Technische Regeln für brennbare Flüssigkeiten [Ordinance on Flammable Liquids/Technical Rules on Flammable Liquids]), of over 61°C for GGVS (Gefahrgutverordnung [Ordinance on the Transport of Hazardous Goods]) and of over 55°C for GefStoffV (Gefahrstoffverordnung [Ordinance on Hazardous Substances]).
Exception: Underground mining. See also legal requirements.