I would have thought that balloon contact with a HT line would initiate immediate circuit de-activation
In that case, every time a bird alighted on a HT distribution line, the power to hundreds of consumers would be constantly tripped-out.
touching a high-voltage conductor is, not of itself, dangerous. The nasty bit occurs if you , at the same time, get too near a neutral/return point.
bridging HT to a low potential(IIRC, Neutral is maintained ~5V above" earth") is not to be recommended if you seek to reach mature years.
In my spotty youth, Iheard several anecdotes from a college lecturer in Evening Class...his daytime job was with CEGB (Central Electricity Generating Board ) He told us that the maintenance crews would traverse the live lines crossing the Thames in London.....A sort of gondola would be hooked (from a well-insulated platform) onto the wire....the men would mount and pull themselves hand-over hand to the next pylon on the opposite side of the river.
Perhaps balloon- fabric is sufficiently conductive to carry a trip-current if wrapped across several wires at varying potentials.....Hang-gliders, with their metal frames, would cause a somewhat spectacular bang in the same situation.
Westlakes is the professional, perhaps he can expand on the subject.