Rescue Tripod "Footprint" Defined.
This may seem simple, but can you define it if a student or fellow team member asked you? The footprint of a rescue tripod is exactly what it implies.
Begin with something familiar: your footprint.
The footprint of a tripod is the area between the three legs.
The footprints you make in the sand are created by the compression of the sand by your body weight which is being transferred through your legs and down to your feet. Therefore the footprint represents an area of compression. The same definition applies to all artificial high directionals such as rescue tripods, bi-pods, and mono-pods. The footprint of these devices is defined by the surface area which supports the legs of the high directional.
But it's not just the area where the tripod's feet contact the supporting surface. The footprint of a high-directional is also the area between these points of contact. As long as the weight being supported by the rescue tripod is directly above the footprint (and stays there), the system will remain stable. If the resultant of the various forces (or vectors) points outside the footprint, the system will fall over. This is why we back-tie tripods if we anticipate a side pull of some sort. So the footprint of a tripod is a triangle. The bigger the triangle, the more lateral stability we can expect.
How about an “A” frame (bi-pod)? Now the area of support (or footprint) between the two legs is a single line that runs between them. Keeping the weight pointing down directly to this line is impossible unless we stabilize or back-tie the bi-pod to restrict its movement. The need to restrict movement is even greater with a mono-pod or 'gin pole,' since now the footprint is reduced to a single point. Proper use of high directionals requires assessing and managing the forces that we expect to point down to the footprint.
The ability to rig back-ties and accurately estimate the resultant of all the expected forces is vital for the safe and effective advance use of tripods, bi-pods, and mono-pods.
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This article was written by D2000 Safety’s Rescue Services Manager, Pat Rhodes, who along with D2000 Safety’s Lead Rescue Instructor Greg Arbizo will be teaching an Open-Enrollment Industrial Rescue Train the Trainer Class November 4-7, 2014 in Tempe, Az. You can find out more about this class by visiting our web site here: Industrial Rescue Train the Trainer.