Risk assessment and mitigation for the hazards of electromagnetic radiation to fuel during high intensity radiated field testing of aircraft

High Intensity Radiated Field (HIRF) testing of, in, and around, aircraft, and aircraft subsystems, that contain fuel (or other potentially explosive atmosphere creating substances) pose particular hazards for Radio Frequency (RF) Induced ignition - Hazards of Electromagnetic Radiation to Fuel (HERF). The primary threat is considered to be from ignition by RF induced sparking/arcing, as this requires far less energy than direct heating effects. Accepted international guidance that is used is contained in “CENELEC CLC/TR 50427: Assessment of Inadvertent Ignition of Flammable Atmospheres by Radio-Frequency Radiation” to identify risks posed by the testing. Where hazardous levels of RF energy are identified as being used within a HIRF test, various mitigations can be used to reduce the overall risk, such as: Air frame/fuel-system review and/or inspection to reduce the probability of any dormant or undetected make/break arcing mechanisms within the flammable atmosphere/ullage; read-across of Electrostatic Discharge (ESD)/Lightning Strike design protection measures that would make the risk non-credible; specifying a minimum fuel load so arcing mechanisms are not in ullage space; use of alternate fuels to change the fuel/air mixture in the ullage to being too rich or too lean; injection of inert atmospheres into the ullage to prevent ignition; identification of alternate assessment strategies and/or potential restriction on HIRF test levels, to identify safe and cost effective assessment solutions for aircraft HIRF clearance activities.