The Safety Integrity Level (SIL) is a classification for safety requirements. For certain certifications of complete machines, such a classification must be carried out. A classification for individual components that cannot fulfill any function on their own is usually not meaningful or possible. The levels are regulated in the international standard IEC 61508/IEC61511 and IDN EN ISO 13849-1 and 13849-2. Equivalently, a classification can be made according to the Performance Level (PL) of category a-e. The PL levels can each be transferred to SIL and vice versa. This is done using the following overview.
| Performance Level (PL) | Safety Integrity Level (SIL) |
| a | no correspondence |
| b | 1 |
| c | 1 |
| d | 2 |
| e | 3 |
The core of this classification is a risk assessment of the respective process, machine or product. Every possible error is considered for each individual sub-function, as well as the severity of the error and the probability of occurrence. The subject is usually the health of the employee or the user, damage to the environment or damage to property.
To perform a risk analysis, each risk of injury or damage is considered and classified on its own. The aim is to minimize the severity of the damage and the probability of occurrence. Common means to reduce the risk are, for example, electronic controls, programming, light barriers, but also simple means such as emergency stop switches, two-hand operation, protective grids and PPE (personal protective equipment).