Explosion of a Model "Hot Air" Balloon
The balloon had a 3.5m external diameter envelope made of anti-tear fabric (same techniques used in full sized balloons of the same company). The inner balloon was a meteorological balloon made of latex. When starting filling the inner balloon with hydrogen (final full balloon relative pressure of 0.03 bar) a leak was noticed, due to a small rupture in the skin of the latex balloon.The filling process was stopped but by this time some hydrogen had become trapped between the inner latex balloon and the outer fabric envelope. According to the HSE report (see reference), the cause of the explosion was almost certainly a static discharge igniting the flammable hydrogen/ air mixture. It is believed that as the whole balloon was brought down to the ground, and onto a plastic sheet that had been put there to protect the balloon, a static discharge ignited the easily ignitable gas mix. The metal cage attached to the underside of the balloon had an earth line, but this had not made contact with the plastic sheet and would not have prevented such an incident.
Event Date
May 27, 1999
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
Immediate cause was the leaking of hydrogen from a tearing of the inner balloon shell and its ignition due to static electricity.The root cause was an adequate risk assessment, implying absence of a correct leak-check procedure before filling with hydrogen.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
hot air balloon
Storage/Process Medium
Storage/Process Quantity
100
Location Type
Location description
Unknown
Operational Condition
Pre-event Summary
The event occurred when filling with hydrogen.
Currency
Lessons Learned
Lessons Learned
The risk assessment which appears to have been " suitable and sufficient " in the original circumstances has now been amended to ensure filling is only done in a well ventilated area, that cotton material is used on the ground rather than the plastic sheet and that the latex balloon is thoroughly checked before use for any tear or splits in the latex.
Event Nature
Emergency Action
Onsite fire brigade alerted
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
Event description provided by HSE, original source confidential