scope:

This standard describes tests used by the Department of Defense (DoD) to determine the safety, reliability and performance characteristics of weapon initiation systems, ignition safety devices, fuzes and their components at any stage in their life cycle.

Safety and Suitability for Service Assessment of Fuzing Systems. The central objective of Safety and Suitability for Service (S3) of Fuzing Systems is to confirm and document that the fuzing system is safe and performs as intended in all expected service environments. In the U.S., each service has a Board that reviews the compliance of fuzing and ignition safety devices with the requirements of MIL-STD-1316, MIL-STD-1901, MIL-STD-1911, and the result of tests conducted in accordance with the procedures described in MIL-STD-331. Guidance on qualification testing and quantities can be found in Joint Ordnance Test Procedure (JOTP)-052 available on https://assist.dla.mil/online/start/index.cfm

NATO. A similar process has been agreed by NATO's AC/326 SGA, with the design safety requirements standards being STANAG 4187, STANAG 4368, STANAG 4497 and the Safety, Arming and Functioning System test procedures document being Allied Ordnance Publication 20 (AOP-20). In addition, SGA has agreed on STANAG 4157, Edition 2, Safety, Arming and Functioning Systems: Test Requirements for Assessment of Safety and Suitability for Service, which is based on the principles of AOP-15, Safety and Suitability for Service of Munitions and Explosives. Both NATO and the DoD Fuze Engineering Standardization Working Group (FESWG) have agreed that, given their similar objectives, MIL-STD-331 and AOP-20 will in the future be published as one document. Background information on the objectives and requirements of STANAG 4157 is provided below to allow MIL-STD-331 users to understand and apply the principles of S3 assessment in their use of this publication.

STANAG 4157. The primary intent of STANAG 4157 is to require NATO nations to conduct S3 assessments of all new fuzing systems, and maintain on-file for provision (upon justified request) to other nations a Fuzing System S3 Assessment file containing all design reviews, test results, and the overall national assessment. Annex A of STANAG 4157 lists the National S3 Assessment Authorities for NATO nations which have agreed to the provisions. This includes the separate agencies for the U.S. Air Force, Army and Navy.

STANAG 4157 requires that nations conduct tests in accordance with test procedures described in AOP-20, in accordance with an agreed methodology described as follows:

a. Annex B lists the tests that have been agreed by NATO for conduct of a standardized S3 assessment of a fuzing/safety, arming and functioning system. It is important to note that these are not necessarily all of the tests that will be required for national qualification of a fuzing system, as specifying qualification requirements is a national responsibility. Also, nations may waive one or more of the tests if they can justify why conduct of the test is not required.

STANAG 4157, includes general provisions for selecting test quantities and pass/fail criteria, as well as tailoring test procedures:

a. Tailoring of Environmental Test Procedures: The standardized tests described in AOP-20 may be tailored in accordance with the following general principles:

(1) the environment to be simulated should be at least as severe as the expected service environment for the fuze;

(2) given their generally greater sensitivity to the service environment, fuzes warrant testing in more severe environments than the munitions in which they are installed;

(3) the rationale used in tailoring the standard environmental tests should be documented and retained as part of the S3 assessment file; the rationale could include avoiding duplication of tests conducted to meet national fuze standards. b. Electromagnetic Environment Testing: Testing of fuzes in service electromagnetic (EM) environments is conducted with two primary objectives:

(1) confirming that the fuze electronics will remain suitable for service after exposure to worst-case environments; and

(2) confirming that fuze safety is not degraded for fuzes employing electric detonators, or fuzes employing electronic circuits controlling all or part of the safety-and-arming system.

c. The safety and suitability test requirements for fuzes should be based on all scenarios examined in the Fuze Design Safety Hazard Assessment conducted in accordance with STANAG 4187 or MIL-STD-1316, and must include confirmation that:

(1) the energy passed through the initiating element of the fuze explosive train produced by a service EM environment will not exceed the factored no-fire safety threshold, as defined in STANAG 4187 (or MIL-DTL-23659); and

(2) the service EM environment will not degrade safety or suitability by damaging or upsetting the electronic circuitry controlling the safety-and arming and initiation systems, respectively.

d. Quantities: Quantities should be selected so as to provide statistically meaningful results and should reflect the quantities used in previous assessments of similar fuzes which subsequently entered into service. The overall objective should be to both meet national requirements and provide a convincing demonstration of fuze safety and suitability for service to other participating nations. The approval of the quantities of fuzes to be subjected to the mandatory and recommended tests is the responsibility of the National Safety Approving Authority (normally, the agencies listed in Table 1).

e. Pass/Fail Criteria: The general criterion for passing any of the mandatory and recommended tests is that an unsafe condition not be observed during the test or upon examination of the fuze after the test. Given the relatively small sample sizes generally employed, one observed unsafe condition generally constitutes a failure. Depending upon the fuze or system design requirement, a small decrease in fuze performance may be acceptable if safety is not affected; large degradations in fuze performance indicate that the fuze is not acceptable for service use. Pass/fail criteria are provided in the test procedures, where appropriate.

Application. This standard generally applies to all fuzes, ignition safety devices, as well as components of weapon systems serving a fuze function, such as torpedo exploders and underwater mine firing mechanisms. Within this document the term "Fuze" or "Fuzing System" is used inclusively and extends to ignition safety devices as well as other initiation systems.

Test identification. The detailed requirements are documented as individual tests and contained as appendices to this standard. Each test is identified by an alpha-numeric sequence which begins with a letter indicating the test group. This is followed by a sequentially-assigned number.

Method of revision. 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 fuzes 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 fuzes.

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 are not to be referenced.