TOPIC: High-Pressure Airbags
OBJECTIVE: Understand Fundamental Lifting Principles and Practices of High-Pressure Airbags
TASK: Given a heavy object, the rescue team shall lift and stabilize the object utilizing cribbing blocks, wood timbers, and high-pressure airbags
Single-Point, Multi-Point, Tilting and Parallel Lifts
Our series on lifting heavy loads continues with this look at high-pressure rescue airbag operations. Regardless of what brand of airbag system your department has, there are certain principles of operation that are universal. The assignment presented in this lesson will be for you and your rescue team to lift a heavy object using high-pressure airbags and stabilize utilizing cribbing.
When lifting a load with airbags, your two strategic options include designing a single-point or a multi-point lift. The choice is yours to make at the incident scene based on the incident and the conditions present. A single-point lift means that the airbag(s) are placed at only one point or location beneath the object. The force of the airbag(s) creates upward force at just this one point. The other strategy, the multi-point lift, is accomplished when the lifting effort is delivered at two or more points along the object. To accomplish a multi-point lift with your airbag system, tactically you would use two airbags, but would place them in two different locations beneath the heavy object. Each lifting point is specifically selected to allow the load to be lifted simultaneously by both airbags. By controlling air flow to each individual bag, you are able to accomplish a controlled and balanced lift.
In addition to deploying either a single-point or multi-point lift for your scenario, you can design your lift strategy to accomplish a tilting lift or a parallel lift. A tilting lift is designed to raise one portion or side of a heavy object more than the other. A tilting lift would be used when just one specific area of an object needs to be raised to free a victim, for example. An example would be a scenario where a homeowner is found pinned beneath his vehicle in the driveway of his residence. The bumper jack that was holding the car up failed and the car dropped onto the backyard mechanic. With a tilting-lift strategy, rescuers would stabilize both sides of the vehicle but would only lift just one side to remove the victim.
The opposite strategy of this is called a parallel lift. A parallel lift raises the object or portion of the object that is trapping your victim evenly off the ground without causing the lifted area to be unbalanced or unlevel. Using the same man-under-car scenario, a parallel-lift strategy would have airbags placed on both sides of the vehicle near the victim. Both sides of the car near the victim would be lifted at the same time.
Single-Bag or Stacked-Bag Lift
Once the strategic decision is made as to whether the lift will be a single-point or multi-point lift and whether a parallel lift or tilting lift is desired, tactically, each lifting point can be a single airbag or a stack of two or even three airbags. The SAVA brand airbag system, for example, is designed to function in a one-, two-or three-bag lifting stack. Other systems typically work with a maximum of only two stacked bags. If two bags of unequal size are to be used together in a stack, the larger bag should be the base or bottom bag. The smaller size airbag should be positioned as the top bag.
Stacking airbags is a tricky thing and is inherently dangerous. On July 10, 2003, a 50-year-old male South Dakota volunteer firefighter, working that evening as a fire equipment salesman, died after being struck by a stacked rescue airbag when the load shifted. The victim placed a stack of three airbags under the rear bumper of a 191,000-pound front-end loader. The lift was accomplished, but as the airbags were being deflated, they shifted and burst out from under the loader. The middle airbag struck the victim on the head and chest resulting in his death.
"Soft" Bag Protection
Airbags are all vulnerable to physical damage or destruction; their surfaces are essentially a rubber material. High heat such as from a catalytic converter can melt an airbag. Sharp, pointed objects such as bolts or brackets can puncture into and through the airbag. The top surface of an airbag that contacts the object to be lifted should be protected from such damage. The bottom of the bottom airbag should likewise be protected. The most appropriate protective covers for airbags are soft and pliable materials; not something rigid or stiff. Old truck mud flaps, sections of rubber conveyor belts, treads from snow machines, or specially designed protective pads called Extrication Guards work well for bag surface protection. Hard, brittle or slippery materials such as plastic cribbing blocks or plywood when placed between the load and the airbag introduce a high probability of slipping out under load; a dangerous potential. Make your bag protection the soft stuff!
A fundamental element of lifting heavy loads with rescue airbags is knowledge of the lifting capacity of the airbags you have in your inventory. Strictly on paper, the airbag rating is square inches of airbag surface multiplied by the pounds per square inch air pressure. A 30-inch-by-30-inch airbag would theoretically have 900 square inches. This number is inaccurate, though, because measuring the outside dimensions of the bag includes the edges which are not part of the usable working surface. Anyway, if you multiply 900 square inches by, let's say, 100 psi, the airbag would theoretically lift 90,000 pounds of weight (45 tons), but that doesn't happen in the real world.
The reality is that the rated capacity of your airbag is achieved only when the entire lower surface of the airbag is in contact with the base or ground and the entire upper surface of the airbag is in contact with the object being lifted. This is almost an impossible situation. We rarely lift something that covers or contacts the entire upper surface of the airbag. In addition, once we start to inflate the airbag, the bottom edges curl and we lose square inches of contact with our base so we never really achieve 100% upper and lower surface contact. We are more likely to be operating at 50% of theoretical capacity or less in actual incidents.
Field experience shows that real-world rescuers place the largest airbag that will fit into position and hope that its real-world lifting force will be sufficient to lift the object, whether that turns out to be 10% of its capacity, 25% of the rating, 50% or more. We need what it takes to get the job done and the bigger bags have a greater chance of giving us that necessary lift. The victims don't care; they just want out.
The lifting capacity of stacked bags is limited by the capacity of the weakest inflated bag of the stack. The 20-ton capacity bag on top of a 30-ton bag will be the weak link; allowing the stack to lift only what the smaller bag will support. If lifting power is important, then a multi-point lift might be preferred over a stacked bag, single-point lift.
Bags Only Lift; Cribbing Stabilizes
It is crucial that rescuers realize that when a heavy object is lifted by one or more airbags, the object is literally floating on air. Without proper cribbing, the lifted load can actually be more unstable now than it was before the airbag lift started. Remember, bags only lift. They do not stabilize! Cribbing or struts are what stabilize the lifted load. Equipment to stabilize the lifted load must be in place before and during the entire lifting process. "Lift an Inch...Crib an Inch" is a common recommendation for crews to adhere to. With box cribs, wedge blocks help take up the small distances until a two-inch by four-inch or four-inch by four-inch cribbing block will fit under the load.
Command by Color
Every air hose in an airbag system should be a different color. No two hoses should ever have the same color in your airbag system. Confusion and errors can occur if this is the case.
"Up on red...Down on blue" are commands that should be familiar for rescue teams who are experienced with rescue airbags. Do not use commands that mention the "top bag," the "big bag" or anything other than the color of the hose connected to the airbag. Also some control units have colored levers to control air flow to or from the airbags. Do not connect a supply hose to the control unit of your system that is the same color as an inflate or deflate lever on the controller. The operator could make a mistake and operate the wrong lever when a color is called for that is the same color as the control lever.
"Bottom-First" Inflation Sequence
The procedure for inflating rescue airbags is important to the success and degree of safety of the lift. When deploying a two-bag stack for example, the recommendation is that the bottom or base bag be inflated partially first. This bag settles into the ground or cribbing beneath it and forms the foundation of the lifting stack. The bottom bag should initially be inflated no more than necessary to allow it to settle; maybe 25% inflation or less for now.
With the base bag set, the top bag can then begin to be inflated. As this bag expands, it will contact the load. As contact is made, personnel must assure that both the top contact point of the top bag and the bottom contact point of the bottom bag are acceptable. If they are, then you can proceed. If something isn't right, then adjustments can still be made relatively quickly at this early point in the lift.
With the top and bottom contact points all set, rescuers can continue to alternate inflation of the bottom and top bags to accomplish the lift. Pay close attention to the "nesting" of the two bags where they contact each other. Inflating the bottom bag to only 50% is a good intermediate stopping point for that bag. Inflation of the top bag to near 75% can follow next. The harder and rounder surface of the top bag should bond well into the softer and flatter surface of the bottom bag. This is called "nesting" of the airbags and is a good thing.
As the lift proceeds and you alternate between inflation of the bags, you want to have the top bag inflated more fully than the bottom bag to preserve the softer and more stable base. As more height is required and both bags go over 80% of their inflation height, your stack is now like trying to balance two basketballs on top of each other. This is risky for both you and the victim. In lieu of working with this balancing act, hold the lift, crib, deflate the bags, raise the stacked bags up, and lift again. With airbags, hard and round might not always be good thing!
Anytime an airbag is used to lift a load, rescuers must monitor the potential for "rolling" of either the lifted load or the airbag, especially when bags are stacked.
If a load shift occurs or if the airbag starts to roll out from under the load, it is most likely to come out in a line parallel to the bag. In other words, the danger zone during any airbag lift is the area directly in line with the bag. The area should be kept clear. Unfortunately, many rescuers responsible for running the airbag controller position themselves right in this area to "get good view" of what is happening. Well, you have long hoses, so move out of the way!
A critical safety assignment to put in place during an airbag lift is to assign two "safety spotters" to view the lift. Most important though is the fact that the spotters must be looking at the lifted object and the airbags from two different angles. They have to be monitoring airbag or object movement from vantage points that are perpendicular to each other. By being at a 90-degree angle from each other, they are more likely to see any unwanted load shift or airbag rolling.
No High-Pressure "Blow-offs"
Shutdown procedures for your airbag system should be learned so that the system is disassembled without disconnecting a hose or connection under high-pressure. High-pressure disconnects are unsafe, present an unnecessary danger to personnel and are avoidable. Shut off the high-pressure air source first. Operate the deflate levers to assure that pressure is released throughout the entire system. Disconnect hoses or couplings only after all the residual air has been released. No high-pressure "blow-offs" is the safety rule.
TASK: Given a heavy object, the rescue team shall lift and stabilize the object utilizing cribbing blocks, wood timbers and high-pressure airbags.
RON MOORE, a FirehouseÂ® contributing editor, is a battalion chief and the training officer for the McKinney, TX, Fire Department. He also authors a monthly online article in the Firehouse.com "MembersZone" and serves as the Forum Moderator for the extrication section of the Firehouse.com website. Moore can be contacted directly at Rmoore@firehouse.com.