This standard establishes time response design criteria for safety-related operator actions to be used in the design of light water reactor (LWR) nuclear power plants. The criteria are used to determine the minimum response time intervals for safety-related operator actions that are taken to mitigate design basis events (DBEs) which result in an automatic reactor trip. This standard specifies time requirements that are to be met to receive credit in the safety analysis for operator actions that initiate or control safety-related functions. Specifically@ the criteria provide bases: (1) For establishing certain requirements for determining whether a particular action to initiate or control a safety-related system might be accomplished by operator action or must be accomplished by an automatic action. (2) For determining when design modifications can obviate the need for automatic actions that would otherwise be required. (3) For general guidance for hardware@ such as instrumentation@ controls@ indicators@ and annunciators necessary to support safety-related operator actions. Purpose. This standard provides an objective approach to ensure plant and systems designs allow time intervals for operators to perform safety-related actions that fall within the nominal range of empirically valid response times. The criteria give the designer a basis for determining or verifying the acceptability of time intervals provided by the design for operator actions required to accomplish safety-related functions for DBEs in nuclear power plants. An intent of this standard is to avoid excessive operator burden. The criteria in this standard identify time intervals and other restrictions that provide an adequate safety margin for safety-related system design and safety analyses of the DBEs. The criteria are not intended to serve as a basis for determining actual operator action times in procedures or training@ nor do they set requirements for operator staffing or qualification. The time intervals specified in these criteria are minimum values which shall be provided in the plant design to permit credit for safety-related operator actions.1 1 The bases for the time tests in the standard are contained in the Appendix. The rationale behind these criteria and examples to clarify specific sections are also provided.