NBN EN 12953-6:2011

This part of this European Standard specifies the minimum requirements for safety related equipment for shell boilers as defined in EN 12953-1, to ensure the boiler operates within the allowable limits (pressure, temperature, etc.) and if the limits are exceeded the energy supply shall be interrupted and locked out without manual (human) intervention at the boiler.
NOTE 1 The maximum time of operation without manual (human) intervention should be defined for each boiler system.
NOTE 2 Annex C (informative) gives recommendations of operation and testing of the boiler system with a maximum time of operation without manual (human) intervention of 72 hours.