1、Lessons Learned Entry: 0008Lesson Info:a71 Lesson Number: 0008a71 Lesson Date: 1991-06-10a71 Submitting Organization: JSCa71 Submitted by: J. ChappeeSubject: Hazard Criticality in the Design and Manufacture of and the Selection of Materials for use in High Pressure Gaseous Flow Systems (Oxygen) Desc
2、ription of Driving Event: A flash fire occurred during a performance record test of the shuttle Extravehicular Mobility Unit (EMU). This fire occurred when a shutoff valve was opened, supplying 6,500 psi oxygen to the EMU. Ignition occurred and a very high temperature oxygen- rich aluminum fire ensu
3、ed. The shutoff valve melted in the fire, relieving the system pressure and causing the metallic fire to extinguish. Residual fires were extinguished using carbon dioxide extinguishers. A finding of the mishap investigation board was that the most probable ignition site was within the regulator modu
4、le in a flow restrictor. This flow restrictor consists of two drilled passages, which intersect in a “V“ shape. Manufacturing practices allow some overdrill at the intersection of these two passages, which may have formed a stagnant volume at the base of the “V“. This stagnant volume allows compress
5、ion heating (adiabatic compression detonation) and/or shock heating, which ruptured and ignited a thin section of aluminum and spread to the other metallic components of the module in the oxygen enriched atmosphere. Other possible ignition mechanisms included (in priority order):A. Compression and/o
6、r shock heating of contaminant(s) entrapped in the stagnant volume of the flow restrictor (all five other regulators disassembled and inspected showed some particulate debris within the system).B. Mechanical heating of or by particulate contamination impinging on a surface.C. Compression and/or shoc
7、k heating of one of the silastic o-rings in the shutoff assembly.Testing at White Sands Test Facility was unable to duplicate these events in over 2200 attempts or confirm any of these ignition mechanisms.Lesson(s) Learned: Provided by IHSNot for ResaleNo reproduction or networking permitted without
8、 license from IHS-,-,-1. Failure to minimize flow passage configurations which can trap debris or create stagnation points in high pressure oxygen systems may lead to compression or shock heating effects causing fire, injury, and equipment damage.2. Failure to consider resistance to ignition and a t
9、endency to propagate a fire in the selection of materials for use in high pressure oxygen may lead to fire, injury, and equipment loss.Recommendation(s): 1. The mishap investigation board recommendations included: high pressure oxygen components should be designed to minimize flow configurations whi
10、ch may trap debris or create stagnation points, and minimize the generation of internal contamination.2. The mishap investigation board recommendations also included: evaluation of existing high pressure oxygen systems and replacement of existing metallic and non-metallic materials (silicone for sil
11、astic 675 in o-rings and monel for aluminum in regulators).Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): a71 Space Operationsa71 Exploration SystemsAdditional Key Phrase(s): a71 Extra-Vehicular Activitya71 Parts Materials & Processesa71 Pres
12、sure Vesselsa71 Test & VerificationAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 1993-09-09a71 Approval Name: Ron Montaguea71 Approval Organization: JSC/NS3a71 Approval Phone Number: 281-483-8576Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
