Grade 4 safes are certified according to the European standard EN 1143-1 and provide resistance for a high risk profile — against an experienced and well-equipped professional intruder mastering modern techniques and powerful tools. They are widely used for the secure storage of jewellery, watches, cash and valuable documents in environments where a targeted, methodical attack is a real possibility. Grade 4 is also the first grade for which a minimum of two certified locks is mandatory according to EN 1300 class B.
During certification, specialised test laboratories attempt to force the safe open using a variety of attack methods — mechanical tools (such as hand tools and crowbars), power tools (such as hammer drills and angle grinders) and thermal tools (cutting torches, thermal lance) — under strictly controlled conditions by independent bodies such as ECB·S.
Under EN 1143-1, burglary resistance is expressed in Resistance Units (RU). For a Grade 4 safe, the resistance level is 120 RU for partial access and 180 RU for full access. Partial access refers to the creation of a limited opening through which a hand can be inserted, while full access implies complete access to the contents, for example by opening the door or creating a larger opening.