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Analysis

Summary

The intensity, size and rapid onset of the fire after the balloon landed suggested that a rapid, uncontrolled leak of LPG had occurred. The most likely source of the LPG leak was the fractured liquid offtake valve. It is also likely that the fracture occurred during the landing. The yellow flames reported by witnesses and the sooting of the ruptured cylinder suggest that the fire was fuel-rich, consistent with a high-volume gas or liquid fuel supply.

The position of the pilot light valves indicated that the pilot lights were on during the landing. Each of the radios or the battery could have provided an ignition source, but it is most likely that the pilot lights ignited the leaking LPG. Had the pilot lights been turned off prior to the landing, in accordance with the flight manual and standard ballooning practice, it is unlikely the leaking gas would have ignited.

The condition of the ruptured fuel cylinder indicated that it had failed as a result of flame impingement and subsequent softening of the aluminium shell. The explosion of the cylinder was therefore a consequence of the fire, rather than contributing to its development.

The length of the broken fitting provided significant leverage that would have required only a relatively small force to be applied before the fitting broke. There was also limited protection for the fitting because it extended significantly beyond the fuel cylinder guard ring. While the Rego 8101P5/7141M combination liquid offtake valve may have been appropriate for some applications, it was not appropriate for aviation. A firm or tipover landing could have resulted in the fitting being bumped or otherwise subjected to stress by occupants or equipment moving around.

The occupants of the balloon generally sustained burns to exposed areas of skin. Had they been wearing natural fibre clothing that more effectively covered these exposed areas, the extent of their burns would almost certainly have been reduced.

The investigation revealed that fuel cylinder fittings similar to the fitting that failed are relatively common in the ballooning industry in Australia. This suggests that the ballooning industry as a whole is not sufficiently aware of the safety implications of fittings extending significantly beyond the fuel cylinder guard ring.

The selection of suitable fittings for fuel cylinders in balloons requires the expertise of both the gas supply industry and the aviation industry. Both industries have specific requirements related to fuel cylinder fitting selection and configuration that may not be completely understood by the other.

 
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