04-03-1999, 11:55 AM #1rmooreFirehouse.com Guest
3-point vs. 4-point stabilization?
A Thread from Ron Moore
3-point or 4-point Stabilization?
Trevor posted a note in our tire deflation thread about using only three step chocks under a vehicle instead of the standard four. This intrigues me because I know a tripod is more stable than a square. Contrary to this, I've actually been experimenting with using 6 chocks, two behind the rear wheels, two at the C- or B-pillars and two at the A-pillar.
Trevor reported thatwith 3-point chocking, two chocks are placed on the "off" side of the vehicle where the least rescue work is conducted. Only one chock is placed on the "action" side of the wreck, under the B-pillar.
Does this work at crash scenes where the object we're stabilizing is bent, folded and mutilated? Or is that why it does work?
Can one chock on the work side actually make the vehicle more stable than two? It would be nice not to have to stumble over or work around an extra chock if it's really not necessary.
You mean after all this time, three is actually better than four?
04-06-1999, 02:21 PM #2FF341Firehouse.com Guest
Don't throw a three-point party just yet...
The triangle IS more stable than a square, but only in its upright position. (Like the tripod that Ron mentioned) The three point cribbing example is not actually utilizing the triangle's shape. It is simply extending the vehicle's undercarriage to the ground at three separate points. Not like a tripod, though, because the arms do not meet at a single point and are not tensioned like manhole tripods. To clarify - The triangle is strong standing up, not lying down.
To better visualize the car's stability under different conditions, picture the cribbing not as a very stable box crib, but rather as a single point of contact between the ground and the car. Like a high-lift jack, for example. Would you rather have only three jacks under the car, or four? Now, in practice niether configuration is all that stable using jacks. This is what makes the box crib so nice.
The rule of thumb I have always heard is the perfect crib job maximizes the contact between the car and the ground--how ever many crib spots that takes.
One last thought and then I'll shut up:
Think of the crib locations as wheels on an ATV. Three-wheel ATV's were outlawed because they weren't as stable as four-wheel ones, right?
04-07-1999, 04:33 PM #3unit3sfdFirehouse.com Guest
yes, we too have tried the three point method in several different areas not just the b pillar. sorry to say we were not to impressed.
we still like using the six point system. like ron was saying. a,b, in front of the rear wheel on four door or larger vehicles.
this seems to be the best over all cribbing position for the vehicle to be in any position on its wheels.
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