There is no generally recognized definition of this term. The following definition is presented for consideration, therefore, as a basis for distinguishing the safety seal from the emergency seal and the shut-down seal: All three sealing systems are installed downstream from a primary seal. Each performs a different duty, however, and each takes over the sealing function at a different time. The safety seal takes over the sealing function with the shaft rotating. Its main duty is to take over the sealing function automatically after or shortly before the main seal fails, and to perform the sealing function until the working machine is brought to a proper standstill and the standby machine is switched on in its place.

A safety seal can also be used to seal, collect and selectively discharge leakage from the main seal (gas safety seal). The emergency seal, on the other hand, takes over the sealing function with the shaft at standstill or coasting. Its duty is to limit damage by taking over the sealing function automatically or by manual activation after the main seal fails. The shut-down seal takes over the sealing function with the shaft at standstill. Its duty is to take over the sealing function when the shaft is stopped intentionally; it does this automatically (e.g. when "glandless" pumps with hydrodynamic balancing are stopped) or after activating a jig from the outside (e. g. to change an agitator seal when the agitator vessel is full).