1.1 This GSO Material Specification defines the minimum mandatory requirements for fail-safe, fault-tolerant, programmable controller based Emergency Shutdown (ESD) systems. 1.2 This GSO Material Specification is applicable for any redundant programmable controller based ESD system, i.e., dual-modular-redundant (DMR) 1-out-of-2D, triple-modular-redundant (TMR), 2-out-of-3 systems. 1.3 This GSO Material Specification together with a project ESD system Functional Specification Document (FSD), Specification Sheet(s) ISS 8020-623-ENG Sheets 1 and 2, and associated logic diagrams prescribes the minimum mandatory design, fabrication and testing requirements for the project. 1.4 Where a project Functional Specification Document (FSD) calls for more than one ESD system, this GSO Material Specification shall apply to each ESD system individually.