ISO 22538-3:2007

Overview

ISO 22538-3:2007 - Space systems - Oxygen safety - Part 3: Selection of non-metallic materials for oxygen systems and components - defines a structured process for selecting non‑metallic (polymeric and other soft) materials used in oxygen systems for ground support equipment, launch vehicles and spacecraft. The standard focuses on minimizing ignition and propagation risk in gaseous oxygen (GOX), liquid oxygen (LOX) and oxygen‑enriched environments by combining material testing, design considerations and materials control.

Key topics and technical requirements

• Scope and applicability: Applies to ground support equipment, launch vehicles and spacecraft; covers direct oxygen service and oxygen‑enriched atmospheres (>25% O2).
• Design considerations: Emphasizes that safe oxygen systems rely on both appropriate material selection and good component/geometry design (e.g., slow pressurization to reduce adiabatic compression heating).
• Ignition mechanisms: Discusses likely causes of ignition in non‑metals - adiabatic compression, mechanical impact, particulate impact, burning contaminants, extrusion of polymer surfaces - and the role of environmental factors (temperature, pressure, flow).
• Material testing and control:
  • Advises accelerated ageing and application‑specific testing where experience is limited (notably above 20 MPa).
  • Recommends batch/lot testing where manufacturing variability exists; testing decisions rest with the responsible design organization.
  • Lists material acceptability criteria including: few reactions on mechanical impact, high auto‑ignition temperature (AIT), low heat of combustion, high oxygen index, low flame temperature, high threshold temperature, and low burn rate.
• Materials certification: Materials must be certified by suppliers and, where practical, independently verified.
• Limits of testing: Notes no single universal test determines absolute ignition limits; multiple tests and hazard analyses are required.

Practical applications

• Use ISO 22538-3:2007 to:
  • Select seals, valve seats, hoses, gaskets and other non‑metallic components for LOX/GOX systems.
  • Define test plans and acceptance criteria for polymer batches destined for oxygen service.
  • Inform design reviews, hazard analyses and maintenance/cleaning procedures to reduce fire risk in oxygen environments.
• It is especially relevant when designing systems exposed to cryogenic temperatures or high pressures (typical experience base 1–20 MPa).

Who should use this standard

• Aerospace system designers and engineers (spacecraft, launch vehicles, ground support)
• Materials engineers and qualification/test labs handling oxygen‑service materials
• Procurement, quality assurance and safety engineers responsible for material certification and hazard analysis

Related standards

• ISO 4589 (Plastics - oxygen index testing)
• ISO 11114‑3 (Autogenous ignition test in oxygen)
• ASTM G86 (Ignition sensitivity to mechanical impact in liquid/pressurized oxygen)
• DIN 53508 (Accelerated ageing of rubber)

Keywords: ISO 22538-3:2007, oxygen safety, non‑metallic materials, space systems, LOX, GOX, polymers, material selection, ignition testing, oxygen‑enriched.