This document specifies the minimum requirements for safety related equipment for shell boilers (generator and/or assemblies) as specified in EN 12953-1:2012, to ensure the boiler operates within the allowable limits (pressure, temperature, etc.) and if the limits are exceeded the energy supply is automatically interrupted and locked out, irrespective of the degree of intervention. NOTE 1 For this document, the term “boiler” is applicable for generator and/or assemblies. NOTE 2 The maximum time of operation without manual (human) intervention can be specified for each boiler system. NOTE 3 Annex C gives recommendations of operation and testing of the boiler system with a maximum time of operation without manual (human) intervention of 24 h and 72 h.