The Split 4 to 1 M.A.
Often during a confined space rescue there is limited room. Hence the name – Confined Space Rescue!
In an industrial setting this is not only the case inside of the space but outside as well.
We tie our knots as small and as tight as possible, avoid using beckets on pulleys, and try not to use that swivel or extra carabineer. We use every trick we have learned to gain an inch here or foot there. Inevitably, there will be a scenario where we will have limited height and have to use a full length spinal packaging device, like a SKED stretcher.
Quickly, our options become limited in regards to rigging.
Two solutions that can be used are to rig for a low point edge transition with a pike (or pick) and pivot or rig a Split 4:1 Mechanical Advantage system, the focus of this discussion.
The split 4:1 mechanical advantage system (MA) is easily built and deployed. The rigger builds a 4:1 MA but uses 4 single sheaved pulleys instead of 2 double sheaved pulleys. To build this system the rigger:
terminates the rope with a knot (figure 8 is preferred) at the head of the tripod;
runs the rope through a pulley (Pulley #1) attached at the foot of the packaging device (any strap can be used, an Omni is used in the example below);
runs the rope through a pulley (Pulley #2) attached to the head of the tripod;
attaches a prussic on the load side of pulley #2 to capture the load when the rope is released,
runs the rope through a pulley (Pulley #3) attached to the master point of attachment at the top of the packaging device,
runs the rope through a pulley (Pulley #4) attached to the head of the tripod. A prussic can be attached on the load side of the pulley here also. This can be a help and hindrance. Yes, you will not drop the load when transferring from the 4:1 to the 2:1, however it must be minded when you lower the head or it has the ability to catch.
The rigger is then able to pull the standing end of the rope and operate the system. When the packaging device tops out (Pulley #3 attached to the master point of attachment, collapses to Pulley #4 attached to the tripod head) the rigger loads the prussic on the load side of Pulley #2 at the tripod head. A rescuer will need to steady the top of the packaging device as the rigger removes the line to the master point of attachment to the packaging device and the associated two pulleys out of the system, Pulley #3 and Pulley #4. This leaves the packaging device held by the prussic on the Pulley #2 and on a 2:1 MA (Pulley #1) at the foot of the packaging device. A rescuer will be needed to steady the load at the top. The packaging device can then be leaned back as it exits the space and the rigger pulls on the 2:1 MA, lifting the foot end of the packaging device. If you have added a prussic to the load side of the 4th pulley, you will may need to mind it as even when it is removed from the anchor it has a tendency to catch up on the line. Be careful not to hook the feet of the patient under the edge or lip of the access to the space. Once the package is out of the space, a rigger needs to mind the prussic in order to lower the package to the ground.
We have found that when employed correctly the split 4:1 can be utilized to remove a SKED stretcher from a standard manhole with as little as 4 feet of vertical room above the access.