Well, here's one story I never thought I would be hearing. Review it and then let's hear what you thoughts are.
Here's the original story from a North Carolina career Fire Captain;
"I have a question for you. This is in regards to wood step cribbing chocks. Some instructors were sharing their opinion that inverting a step chock would cause catastrophic failure of the chock under load. I have personally never heard or seen that happening. Have you and if so, would you mind sharing?"
This is something that I find not realistically possible so I wrote back saying I do not believe it would happen; especially at a simple vehicle rescue stabilization incident.
What's your thoughts? How would you reply back to someone in your department who makes this type of statement?
In June, I'm going to invert a step chock beneath a load of just about 38 tons so we'll see what happens.
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05-14-2014, 04:05 PM #1
Inverted StepChock Prone to Failure?Ron Moore, Forum Moderator
05-14-2014, 05:06 PM #2
- Join Date
- Nov 2009
05-14-2014, 07:26 PM #3
My first exposure to an inverted step chock was exactly 10 years ago in an advanced vehicle rescue class...seemed unusual at the time, but those of us who took the class brought it back to our home department, and it has been a regularly used method of stabilization for us.
We've used it on every conceivable vehicle out there, and haven't had an issues or failures with it.Career Fire Captain
Volunteer Chief Officer
Never taking for granted that I'm privileged enough to have the greatest job in the world!
05-14-2014, 08:43 PM #4
- Join Date
- Nov 2002
The only concieveable problem I can see with an inverted chock is a vehicle sliding off of it if there are slick surfaces, or perhaps flipping on it's side if the vehicle were to rotate because it was not chocked or cribbed in other places. I can't see it structurally failing in normal use.
05-14-2014, 09:46 PM #5
- Join Date
- Nov 2013
Inverted StepChock Prone to Failure?
I have never heard of something like that happening, I'd be interested to hear the result of your test.
However, In any case an inverted step chock shouldn't be bearing too much weight as it is used to brace the vehicle to prevent movement.
In the vehicle on roof scenario the car is already tipped forward with the weight of the vehicle taken by the bonnet (hood) and A-pillar, the inverted step chock will only bear any force when weight is shifted in the vehicle (such as firefighters/paramedics gaining access from the rear and crawling on the roof). That force would be negligible compared to the strength of the chock. It is there to prevent movement backwards only.
Using the inverted step chock on an upright vehicle you are bracing the vehicle against other chocks or stabilisation equipment and not taking the weight of the vehicle. It is a different scenario to using cribbing or an "upright" step chock to hold the weight of the vehicle (flat tyre blocking etc.
Due to the angle that the inverted step chocks presents against the vehicle it would be inappropriate to use it for load bearing cribbing.
Personally, for a vehicle on its wheels I try to use the step chock upright in the first instance and brace it with a thin wedge as the increased surface contact with ground and vehicle reduces the risk of the chock slipping. However in many cases the height of the vehicle sill doesn't line up close enough with a step on the chock so quickly inverting it provides the next best option for fast and effective stabilisation.
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