International Standardization Agreements. NATO Allied Ordnance Publication (AOP) -20 is the subject of an International Standardization Agreement. NATO Standardization Agreement (STANAG) 4157@ Safety@ Arming and Functioning System (SAF System) Testing Requirements is the covering document for AOP-20 and AOP-4157. AOP- 20 was originally derived from US Mi l i tary Standard 331. Where appl icable@ information relating to NATO usage of the test procedures included in this document is presented in Section 7 of the specific test. Application. This standard generally applies to all Safe@ Arming and Functioning Systems (SAF Systems)@ including Fuzes@ Fuzing Systems@ Ignition Systems@ as well as components of weapon systems serving a Fuzing or Ignition function@ such as torpedo exploders@ underwater mine-firing mechanisms@ and solid propellant rocket and guided missile motor ignition. Within this document the terms SAF System and ??Fuze?? or ??Fuzing System?? may be used interchangeably. They are intended to be inclusive of all the items listed above. The applicability of each test is determined by AOP- 4157. Test identification. The detailed requirements are documented as individual tests and contained as appendices to this standard. All current test requirements are described in the first five sections of the test. Superseded test requirements with applicable dates are located in Section 6 of the test and identified as alternate tests for older SAF Systems. Method of Revision New tests may be introduced for review by any NATO nation@ and included after common consensus. All tests are revised on an individual basis and issued as change notices when required. Revised tests are identified by a decimal number after the test number. Revised test parameters affecting test results apply to SAF Systems developed subsequent to the change notice. All current test requirements are described in the first five sections of the test. Superseded test requirements with applicable dates are located in Section 6 of the test and identified as alternate tests for older SAF Systems/Fuzing Systems. Method of reference Specific tests or test sequences may be invoked by the developing or procuring agency within a formal engineering development test plan or procurement specification. Additionally@ many tests permit variations which should be selected at the time the test is invoked. Variations may include test configuration@ materials@ methods@ sample size or pass/fail criteria. Decimal number revisions shall not be referenced