In sci.space.history Jochem Huhmann wrote:
OK, the debris is not exactly likely to move into the direction of
the exhaust, but having *some* pieces bouncing back could've been
enough...

Unless there was something for them to bounce-off of they'd have to
have been carried around by some sort of vortex leaving the tunnel.
Ostensibly, the outlet of the tunnel is supposed to be far enough away
from the launch vehicle to preclude exhaust gasses from getting back
to the stack. Does that then imply that larger "particulates" would
be unlikely to get back that far?

rick jones
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