Complex rescue lifts: 3 rules to get them right
Use these rules to safely analyze and perform complex and heavy lifts such as a school bus flipped on a car
You pull up on a school bus that has flipped on its side. Underneath the bus is a passenger vehicle with multiple victims trapped inside. It is immediately apparent that you are going to have to lift and stabilize the bus to get to the car.
Let’s pretend it is the magical land of rescue and you have an unlimited supply of awesome rescue struts, airbags, straps, chains and cribbing, and you can go to work. The first questions are, are you going to apply the equipment correctly, and are you thinking through all of the application formulas?
We are going to walk through some of the fundamentals of tackling this scenario. We will pay close attention to stabilization struts and what to understand to apply them correctly and safely.
Rule 1: Analyze the load
Every load, (in this case it is the bus), will typically present a natural lifting point and a natural pivot point. The pivot point is the part of the load that is already on the ground and provides the greatest degree of stability for pivoting.
The lifting point is typically the least stable part of the load and is not on the ground. If that is the case, focus anchoring and stabilization efforts on the pivot point and lifting efforts on the lifting points.
In this scenario, the wheels of the bus would be side loaded on the ground and the side of the bus would be elevated and resting on the car.
The initial survey would mean we want those wheels and tires to stay put and we want to prepare to lift the side of the bus. Basically, we are pushing the bus toward an upright position.
The secondary survey requires us to estimate balance points. The bus will most likely be much heavier toward the front where the engine is located.
If analyzing the bus as a lever and a lifting point as a fulcrum, then viewing the bus from front to back would dictate placing a lifting column closer to the front of the bus where the majority of the weight is to get an equalized lift.
This can be really challenging and is not an exact science in the field. So, there are two options.
First, we can place multiple lifting columns along the bus for a more distributed lift. This provides a great deal of forgiveness for a miscalculated balance point and it places less load on each lifting column. The downside is it requires more resources and more management.
The other option is to create multiple pivot points. This means intentionally moving the lifting column all the way toward the lightest part of the bus — the rear side.
In doing this, we expect the front of the bus to become a secondary pivot point and need to capture and stabilize that portion. This may require less lifting resources, but it can present a lot more challenges regarding load shifts and unpredictable or unexpected movement.
The only real advantage is that you are lifting with limited resources at the lightest part of the load. That means it is quick and efficient, potentially.
It is good to have both of these concepts in your tool box, because you may have limited access on a run or the load may present in an atypical way. The more equipped you are with knowledge, the more effective you will be at problem solving.
Rule 2: Know the weight
Check the bus identification placard or vehicle plate to learn how much it weighs. Other commercial vehicles will require additional assessment including shipping manifests and a driver interview to determine the additional weight of the materials being transported in the vehicle.
There are four types of school busses, Types A through D, and the most common ones weigh between 20,000 and 30,000 pounds. To turn this number into something usable, I apply a general rule of thumb.
Since I am only lifting a portion of the vehicle and not plucking it into the air like a crane, I can estimate that I will only be working with half of the load.
This is a rough calculation and I want to err on the side of caution. If the bus identification states that it is a 36,000-pound vehicle, I am going to round up to 40,000 pounds for safety and quick calculations.
To calculate the lifting weight, apply a half margin to end up with a projected lifting weight of 20,000 pounds. This drives all of the next decisions I will make regarding quantity, type and orientation of lifting and stabilization equipment.
Rule 3: Apply equipment correctly
Know the load capacities of the struts and airbags as well as for the connecting material for anchoring (ratchet straps and chains).
Struts vary radically in design and strength. Use the lifting load coefficient (20,000 pounds in the bus-on-car example) as a benchmark.
Struts have a load-capacity range directly related to their strength. As struts get longer they get weaker. Struts for these types of lifts should have engineering load charts that show their capacity throughout their range of throw or stroke.
If I am going to place these struts along the side of the roof line of the bus, I can see how long they are and determine what their load capacity is. Next, I need to determine how many of them I need for simple weight.
If each strut has a capacity of 5,000 pounds, then I will need four struts to support a 20,000-pound lifting load. The importance of advanced struts with higher lifting capacities is obvious. If each strut had a 20,000-pound capacity, then based on strength alone I would only need one strut.
The second consideration for struts is stability of the load. I may only need one strut for strength, but to effectively stabilize the load while lifting, I will most likely need several more points of contact for balance and weight distribution.
If the struts can lift, by an add-on turn crank, a mechanical collar or a hydraulic piston, determine their lifting capacity. This is often a different number than the strut’s static stabilizing capacity.
The last assessment for the struts is the anchoring requirements. This is based on the orientation angle of the strut to the load, the relationship between the baseplate of the strut and the ground and load itself.
The right angle
Let’s consider two basic angles on the struts — 45 and 60 degrees. From an engineering standpoint, a strut placed at a 45-degree angle to the load, whatever the load being applied vertically to the strut, should be multiplied times a coefficient of 1.5 to determine lateral load on the anchoring element.
Theoretically, with a 20,000-pound lifting load, the lateral load applied to the ratchet strap, chain or earth nails anchoring the baseplates would be carrying 35,000 pounds.
This is one of the most dangerously overlooked elements in these scenarios. If you are using 3,300-pound ratchet straps, that takes an awful lot of ratchet straps to carry that much load.
If you find yourself in that predicament, immediately think about chains instead of ratchet straps. A life safety chain will clearly identify its load capacity and will offer much greater strength than ratchet straps.
Another option is to walk the struts to a 60-degree angle. At 60 degrees, the coefficient for lateral load versus vertical load is 1.0; this offers an equalized load configuration and reduces that 35,000-pound lateral load to 20,000 pounds.
This is very theoretical math. A million variables can alter the outcome of this theory, including glass on the ground under the base plate, the baseplate’s size and surface design, etc. The more friction the baseplate can develop with the ground, the less load transfers to the anchoring material.
The downside of the 60-degree application is the potential reduction of lateral stability. As struts become more vertical, they become less stable in these scenarios. You will always be seeking the best marriage between load management and stability.
The final consideration for struts is what to attach the anchor material to. The anchoring material must never be attached to the lifting point.
This means I must connect my baseplates to either the pivot point of the load or an independent anchor.
To illustrate this, if the struts were run alongside the bus and the heads were placed along the roof line, the incorrect attachment would be anything along the side of the bus, such as the side rails or window rails.
As this portion of the bus is lifted and moves away from the baseplates, the anchoring material will attempt to resist that movement, and something has to give. Some portion of the equipment will eventually catastrophically fail.
The correct attachment is pinning the baseplates with earth nails or attaching materials under the bus. Best options are the near-side frame rail or to a structural element very close to the wheels that are on the ground.
The closer you can anchor to the pivot point, the better. Always choose secure and structural anchors.
There are a lot of other details to process and consider, but this offers a good approach template for making safe and efficient decisions.
Get your gear out and think through applying it to worst-case scenarios. Know the ins and outs of the engineering behind your gear and its limitations.
Train hard and be safe.
This article, originally published Dec. 7, 2016, has been updated