ISO 2685:1998

Overview

ISO 2685:1998 - "Aircraft - Environmental test procedure for airborne equipment - Resistance to fire in designated fire zones" defines fire-resistance test methods for components, equipment and structures installed in aircraft designated fire zones. It specifies the standard flame characteristics, burner types (gas and liquid), calibration and test procedures to verify two grades of fire resistance: fire resistant (5 minutes) and fireproof (15 minutes). The standard applies only to items inside designated fire zones and does not cover general flammability or combustion-chamber flames.

Key topics and technical requirements

• Standard flame characteristics: nominal temperature 1 100 °C ± 80 °C and heat flux density of 116 ± 10 kW/m² (measured at the standard apparatus).
• Resistance grades:
  • Fire resistant: withstand standard flame for 5 minutes.
  • Fireproof: withstand standard flame for 15 minutes.
• Burners and flame sources:
  • Examples and construction details for gas burners and liquid-fuel burners are given (Annex A).
  • Burner-to-specimen nominal axial distances established by calibration (approx. 75 mm for gas, 100 mm for liquid, as calibrated).
• Burner selection rule: ensure the flame covers critical parts; satisfy A ≤ 2B (A = major specimen cross-section area, B = burner nozzle flame area).
• Calibration and measurement:
  • Burners must be calibrated per Annex B using temperature (thermocouples) and heat flux (continuous-flow calorimeter) methods.
  • Calibration checks are required at intervals acceptable to the approving authority but no longer than 6 months.
• Test setup: specimens mounted to simulate aircraft installation; specific mounting and conditions are defined in equipment specifications.

Practical applications and users

ISO 2685 is used to demonstrate fire performance of equipment located in aircraft fire zones - typical users include:

• Aircraft designers and systems engineers specifying fire-zone equipment requirements.
• Avionics and equipment manufacturers preparing components for aircraft installation.
• Accredited test laboratories performing aircraft fire testing, burner calibration and heat-flux measurements.
• Certification and approving authorities assessing compliance with airworthiness fire-resistance requirements.
• Maintenance and modification organizations verifying retrofit or repair compliance for zone-critical items.

Related standards and guidance

• Annexes A–B (normative) provide burner designs and calibration procedures; Annexes C–G (informative) offer example test conditions for fluid systems, cables, structures and conversion factors.
• ISO 2685 is intended to work alongside regulatory and certification requirements set by aircraft approving authorities and other aviation safety standards covering fire safety and environmental testing.

Keywords: ISO 2685, aircraft fire test, resistance to fire, designated fire zones, standard flame, fire-resistant, fireproof, burner calibration, heat flux, avionics environmental testing.