I just finished installing a torsion spring single garage door.. I purchased
it from a business that really wanted to do the install for me, but I lived
about 60 miles from their shop, so they just sold it to me with some
warnings about the dangers of setting up the torsion spring..

The manual that came with the door also gave additional cautions and advice
to have the professionals do it..

As a Life Long DIY, I did it myself, following the step by step
instructions. When I was finished, I was a nervious wreck. As the spring got
tighter, the more I became aware of the dangerous situation I had gotten
myself into. Towards the end of the process, it is necessary to lock the
spring and do some trial lefts on the door to see now much more torsion is
required.. As might be expected, I needed a few more turns.. This I did and
again it was scary, releasing the lock screws while holding that bar. This
time I took several turns, just to make sure I wouldn't have to release it
again..

As it turns out I never got hurt, however the spring has just a little bit
too much torsion, but I just force the door all the way down and hope the
spring will relax in time..

Even with this experience under my DIY Belt, I don't think I would want to
do it for a living..


--
My opinion and experience. FWIW

Steve