I'm a service manager at a large dealership in Southern California. We use
twin post hoists, not 4 posters but the issues are the similar.
The Sears in Northridge used to leave all their cars all the way up in the
air so the cleaning crew could clean under them every night. From what I
heard when the quake hit in 1994 the cars on those racks went down
like dominoes. It is my understanding they lost 9 cars that night. Now I
don't know if these were all in ground hoists or above ground units.
About anchoring hoists, to bolt down a twin post hoist requires a 6" slab.
Most if not all residential garages have a 4" slab. The solution is to cut
out a section about 4 feet by 2' wider than the lift and pour a 6" slab in
that area. So if your hoist legs are 10 feet apart, the slab would be 4X12.
(had to do that with more than one hoist installation) But since these 4
post hoists are designed to work without bolting to the floor, you might be
able to get by with just the 4" slab. Consult the hoist maker for more
info.
In the event of a quake the size of Northridge or above, I would want a
hoist anchored to the floor. The movement in that quake, at my house, was
more vertical than it was horizontal. My water heater walked away from the
wall at the bottom (it was anchored at the top) and it wound up at a 30
degree angle. I would be afraid that a 4 post lift could walk and hit the
car underneath, or the legs might spread and possibly collapse. I don't
think that the top car falling is much of an issue for these type of hoists.
With a single or a twin post I would have that concern.
In closing let me pass along what I tell all of my techs to do in the event
of an earthquake.
RUN! get the hell out from under the cars, and get clear.
Hope this helps.
Rick
On Wed, Dec 16, 2009 at 8:19 PM, John Sims <ahbn6@verizon.net> wrote:
> Why not ask at one of your local repair shop what they do? Especially in
> the
> San Fernando Valley where I believe the last big one was???
>
> John Sims, BN6
> Aberdeen, NJ
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