Structures, systems, and components which are not designated as safety-class SSCs but whose preventive or mitigative function is a major contributor to defense in depth and/or worker safety as determined from safety analyses. [10 CFR 830] As a general rule of thumb, safety-significant SSC designations based on worker safety are limited to those systems, structures, or components whose failure is estimated to result in a prompt worker fatality or serious injuries or significant radiological or chemical exposures to workers. The term, serious injuries, as used in this definition, refers to medical treatment for immediately life-threatening or permanently disabling injuries (e.g., loss of eye, loss of limb). The general rule of thumb cited above is neither an evaluation guideline nor a quantitative criterion. It represents a lower threshold of concern for which safety significant SSC designation may be warranted. Estimates of worker consequences for the purpose of safety-significant SSC designation are not intended to require detailed DOE-HDBK-1188-2006 91 analytical modeling. Considerations should be based on engineering judgment of possible effects and the potential added value of safety-significant SSC designation. Note: Safety-significant SSC as used in this Standard distinguishes a specific category of SSCs other than safety-class SSCs. It should not be confused with the generic modifier "safety significant" used in DOE orders. See: Safety Class Structures, Systems, and Components; Safety-Class Structures, Systems, and Components; and Safety Structures, Systems, and Components