From: Rock Climbing by Craig Luebben
"Static ropes work fine for rappelling and top roping, but never lead on a static rope."
From: The Mountaineering Handbook by Craig Connally
"Static ropes ..... are designed for caving, rescue, rappelling, canyoneering, hauling, expeditionary fixed lines, top roping, gym climbing ..."
Static lines are much more durable. Less rope stretch is part of the reason
why. Gym ropes can be semi static and split the difference in elongation. Personally I
own a 10 mill lead line, and a 9 mill rap and glacier line. At one point in my
life I wore out an 11 mill line one year top roping. If I had it to do over again, I
would have saved my lead line by buying an extra static for the top roping.
"thats odd as guides generally teach rappelling the usual way ... rappel down, usually with a prussik and possibly a firemans to start
i havent head of any accidents doing so under proper supervision
not saying its right or wrong ..."
All the places I have worked (about 6) for that did climbing with students used a separate and
independently anchored belay rope when rappelling. And the rappel rope was tied to the
anchor with a munter/mule hitch on a master biner. This way if the student got stuck (clothing in device etc.)
the rappel rope could be loosed and the student lowered enough onto the belay
while the device was cleared, or be lowered on the belay rope all the way down.
This can be particularly important on a summit with weather coming in. You don't
want a student stuck halfway blocking everyone's escape.