Experimental results of the distribution of halon-free cargo fire suppression agents in a cargo hold demonstrator

Today’s cargo bay uses Halon 1301 gas for fire suppression. While effective, this fluid is broadly banned due to its high global warming potential (GWP) of 5700 and its high ozone depletion potential. Hence, alternative agents for cargo fire protection are being sought. In this framework, tests were conducted in the Fraunhofer Flight Test Facility with the goal of evaluating the uniformity of spread of various fire suppression agents, specifically a blend of a Hydrofluoroolefine (HFO) and CO2. The facility’s cargo area, with a volume of 38 m3, features a low-pressure vessel integrating a previously operated aircraft segment. In a series of tests, the alternative extinguishing agent was supplied into the cargo hold demonstrator and concentrations were measured in different locations to understand the uniformity of distribution and the system behaviour under a realistic flight envelope. Test results show several interesting outcomes. In the empty cargo hold with air movement due to leakage, initial bottle filling weight and extinguishing agent initial concentration are consistent.
When no flow movement is applied to the cargo hold, a separation between upper and lower cargo hold concentrations is found. The heavy extinguishing agent necessitates a buoyancy correction of the measured pressure differential by air density and elevation.