At 08:18 PM 6/4/2011, Rocket J Squirrel wrote:
>But I still don't see the problem. Maybe I'm simple.

No, you're trusting.

People get hurt when stored energy gets released in an uncontrolled
fashion.  What you're saying in effect is that you trust yourself -
with your life - that every time you work around this beast you will
not make a mistake and there will not be a material failure allowing
that release.  That's what we all do, it's what you have to do; and
there are inherent risks.  But you're loading the dice against yourself.

You're entirely right that the chance of a ramp slipping is low,
probably extremely low - at least if the concrete isn't too
smooth.  The stuff on garage floors tends not to grab well enough to
get the beast's weight up onto a metal ramp in the first place
without it being restrained.  So is the chance of a ramp cracking at
the bend and unfolding.  Or one of the ball joints suddenly letting
go so a wheel folds up.  And you're *certainly* right that as long as
you don't do any jacking things are much more secure.

But.  People do make mistakes and material does fail.  Chocks pop
out.  And you don't get do-overs with this one.  People under Monty
Python's 16-ton weight vanish, but people under cars die
horribly.  Leaving an unsecured - and anything held by its own
friction on a flat surface is unsecured - horizontal force vector
hanging over your head attached to a vehicle with wheels and 5,000 lb
of weight supported by springs and complicated suspension joints is
leaving a continuous multiplier waiting to suddenly complicate things
when some other unlikely event picks today to strike.  People used to
get killed by garage door springs, did you know?  They just sit there
looking innocent...until one day one breaks and then all hell breaks
loose.  Now we loop a length of cable through them to catch the
pieces or at least slow them down a lot.

It's your life.  But long before OSHA came along people decided that
working on vehicles on a hill was imprudent in ordinary human
terms.  If you're going to do it, is seems to me that eliminating
those risks that reasonably can be is a good idea.  YMMV so I'll be quiet now.

Yours,
David