What happened
On June 22, 1960, a Van den Bernden free balloon, registration HB-BIP, completed a flight from Interlaken to the Valais region. After crossing the Alps at an altitude of approximately 5,250 meters, the pilot attempted to land in the valley near Brig. Due to local wind conditions, the landing took place at an elevation of roughly 1,250 meters in a forested area above Birgisch, where the basket became caught in the treetops.
Following the landing, the pilot and local residents attempted to move the undeflated balloon to a more suitable clearing near a cable car station to facilitate deflation and packing. During this ground transport, the balloon envelope repeatedly brushed against treetops. As the crew moved the balloon toward a nearby meadow, a strong upward gust of wind pushed the envelope and netting against a grain field and potentially the ground, causing the basket to tip over. At approximately 15:22, a fire erupted, consuming the envelope, netting, and basket. No injuries were reported.
The investigation
The investigation examined the circumstances of the fire, including the movement of the balloon through the forest and its contact with the grain field. Investigators reviewed reports from the pilot and a witness who assisted in the transport. The investigation focused on potential ignition sources, noting that there were no nearby power lines and no smoking was reported. The presence of a hydrogen-air mixture within the envelope was a significant factor in the rapid spread of the fire.
Findings
- The primary cause of the fire was likely an electrostatic discharge.
- The movement of the balloon envelope through the treetops and its contact with the grain field likely generated a static charge.
- A spark resulting from the discharge between the charged envelope and the ground ignited the flammable hydrogen-air mixture.
- The balloon was filled with 700 m3 of hydrogen at the time of the incident.