The headline on the Firehouse.com news site flashes, "South Dakota Equipment Sales Rep Killed During Air Bag Demonstration" on my computer. This certainly got my attention and I hope that it has gotten yours.
Firstly, I want to express my sincere condolences to the family, friends, co-workers and fellow firefighters of South Dakota Volunteer firefighter Nathan Hamro. Firefighter Hamro was with the Renner Fire Department.
According to Inez Ford, Firehouse.com's news writer, Nathan Hamro of Sioux Falls, was demonstrating newly purchased air bags for lifting heavy objects when the incident occurred on July 11, 2003. Using air-bags to lift a heavy front end loader, Hamro apparently stacked three air-bags to perform the lift. It appears from reports that the lifted weight shifted and that the bags flew out from underneath the loader striking Mr. Hamro in the upper body causing massive head injuries. The Occupational Safety and Health Administration are investigating the incident to determine the exact cause of this terrible training accident. Wherever blame lies, is not for me to say but will be determined by officials.
However, this recent tragic training accident has spurred me to re-visit the topic of proper selection and use of lifting air bags that I wrote about in the March/April 2001 issue.
Air Lifting Bags for Rescue
There are three general types of lifting bags sold and used for rescue or heavy recovery work; high pressure, medium pressure and low pressure systems.
Low-pressure bag systems are essentially high lift bags that operate at 7 1/4 psi maximum working pressure. These low-pressure cushions provide vertical lift over a large surface area and work especially well on thin skinned, light walled vehicles like aluminum truck trailers, tankers, buses or aircraft.
The construction of low-pressure bags utilizes seven-ply strong, reinforced fabric material for the top and bottom surfaces. The internal structure is designed with nylon strapping supports. The cushion itself is constructed of a simple canvas of Kevlar that's impregnated and bonded to neoprene.
The largest low-pressure lifting bags that Holmatro sells are 52 inches square and can lift 16 metric tons while being only 2 1/3" thick. Maximum lifting capacity is achieved only when the bag is fully inflated.
(A word of caution: These low-pressure air bags are more susceptible to physical damage than high-pressure bags.)
Medium-pressure bag systems are designed to operate at 15 psi and are not very common. Most tasks can be accomplished with 8 to 12 psi. These bags are designed to function at 15 psi, but register bursting pressures between 58 psi and 100 psi, depending on the size and style manufactured. Generally, medium- pressure bags have thicker sidewalls than low-pressure bags.
High-pressure bags systems are without a doubt the most common type of bags found on rigs today. High-pressure air-lifting bags generally operate with inflation pressures of between 90psi and 145psi and can be supplied air from S.C.B.A. bottles, 2216 or 4500 psi cylinders, truck or train air brake systems, cascade systems that may be mounted on a rig, or air compressors. And if you're really desperate for compressed air, an inflated truck tire could be put to use. With a high-pressure system, there is a direct relationship between lifting capacity and inflation height.
All high-pressure air bags carry ratings for both the maximum force in pounds that they can exert and the maximum height they can achieve when fully inflated. To calculate the theoretical lifting capacity of a high-pressure air bag, use the following formula.
(In our example, we will calculate maximum force and maximum lifting for an air bag which has the dimensions of 30 inches by 30 inches and an internal air pressure if 118psi.
L x W x Internal air pressure of bag 30 x 30 = 900 square inches of working area 900 square inches x 118 psi = 106,200 lbs, which works out to a rating of 53 tons of lifting capacity.
The maximum inflation height would be about 18 inches, which would reduce the lifting capacity to 27 or 28 tons. A high-pressure air bag maintains a theoretical 100-percent capacity only until the center is approximately 2 inches in height. Continued inflation diminishes this capacity. Higher inflation, therefore, means lower capacity. Maximum capacity yields one-half maximum capacity.
You may be scratching your head over that last statement, but here's why it's so. As the bag continues to expand, the contact surface area begins to diminish, thereby reducing the total lifting capacity to the point that at full inflation, the height of the bag generally has only 50 percent of its original working surface area still in contact with the surface below.
As a high-pressure bag is inflated they tend to take the shape of a football, making it necessary to maintain stabilization on both sides of the bags. If two stacked bags were fully inflated, it would be like trying to balance one football on top of another. Full inflation would increase the risk of the bags kicking out of place, which would pose a serious threat to the safety of the personnel working around them. (As may have been the case in this tragic training incident, since three bags were stacked. Only the people there and the investigators will know for sure).
In this photo, the car's passenger has been ejected during rollover and the car has landed on top of him. The team of rescuers has placed 2 high-pressure bags on top of a solid box crib to prevent the car from crashing back down on the patient. Cribbing has been placed beside the patient's head (out of the picture). As the bags are inflated, the car starts to lift, but the team discovers the center of the rear section of the roof is collapsing. The team must reposition the bags to a stronger area of support. But, because the necessary blocking was in place, the car will not come back down onto the patient when the pressure is released.
Something to keep in mind when doing a lift with any tools is that if the driver's side of the car is being lifted, the passenger side must be lowering and it might move farther down and impinge upon a patient who's in that location. To eliminate this problem, cribbing blocks must be set up on the side of the vehicle opposing the lift to prevent such downward movement.
This photo, taken at an extrication challenge, shows a team that's done a nice job of positioning cribbing around a vehicle to stabilize it and prevent any accidental vehicle movements. (Notice the "slick" air cascade cart the challenge judge is standing by.) The controller operator maintains an ample distance back from the work area. Two high-pressure bags are stacked. One is connected to a green air line and another has a yellow line, so the rescuer calling the lift operations can identify which bag to lift and which bag to hold.
When using a two-bag stacked configuration, (like that shown in the 2nd photo), the lifting capacities depend on required inflation heights. The usable height of both bags can be added together to estimate the total lifting height.
When stacking air bags, always place the largest air bag on the bottom and the smaller air bag on top. Never stack more than two air bags on top of one another and never place anything between the bags or between the top bag and the object you're lifting, such as a piece of plywood. Why? Because the bags could kick out and the plywood could become a projectile and could injure someone.
Stacking air bags (versus simultaneously lifting an object from two separate locations) does not allow you to add the lifting capacities of the bags together to get an estimate of their lifting capacity. This means that the smallest capacity bag that is inflated is the maximum that the stacked bags will lift. A 10-ton capacity bag placed on top of a 26-ton capacity bag will lift a maximum of 10 tons.
Lifting capacity can be increased using two high-pressure bags side-by-side and simultaneously inflating the bags. In the diagram shown, two bags have been placed side-by-side on top of support cribs to get the bags as close to the object as possible, in order to maintain maximum contact and lift. One bag is rated for 21 tons of lift and the other is rated for 26 tons. Singularly, the bags cannot lift the 30-ton object, but together, these bags combine their potential lifting power to a hefty 47 tons and will thus be able to lift the object. Keep in mind that cribbing helps to maximize lifting height as well as lifting force.
The controller unit has gauges mounted on it which monitor the incoming pressure and air-bag pressures. All air-bag controllers should have "dead man"- type switches to protect against accidental inflation or deflation and require constant interaction to allow the air to flow. Should the flow-control valve be released, the airflow stops immediately. Once the air bag reaches maximum inflation, the built in relief valve will release air at 118psi.
This photo shows high-pressure air bags in use. In this example of vehicle override (in which the rear car has pinned a person between the cars), high-pressure air bags are used to raise the top car off the person. Air bags are used on both sides of the vehicle to maintain a level lift. A chain is wrapped around the lower car and its suspension to maintain tension and not allow the lower car to lift up when the top car is raised. The air in the rear tires of the lower car is removed to lower the car as well. This shows another style of double-bottle air cascade system in use, feeding air to the air bags, an impact gun and an air chisel set.
Lifting Bag Maintenance
Regardless of the bag types and sizes, a routine operational check should be done to ensure the safety of everyone involved in their use. Inspect bags for cuts, cracking, nicks or material separation before adding inflation pressure.
It's really unnecessary to do daily inflation checks, which tend to weaken the equipment. Daily checks actually harm the bladder and wear down the system if a bag is filled to near capacity level everyday. Most manufacturers recommend a weekly test--inflating the bags to approximately 30 percent of its normal operating pressure. Once inflated, lock the bag off with the airline shut-off and then check for leaks, tears and separations in the bag materials. Leave bags inflated for five minutes and check for any noticeable pressure loss.
Any bubbles that show up in the outer skin of a high-pressure bag can indicate a leak in the interior bladder and outer protective skin. If you find bubbles in your inspection, immediately remove the unit from service and have it inspected by a factory-authorized technician. And make sure you inspect all the hoses and couplings for damage and cleanliness.
Because lifting bags are made of rubber, they have a limited shelf life. The manufacturer should be contacted for a recommendation of service time. It's advisable to have your air bags inspected annually by a factory-authorized technician and keep records of all testing performed.
Training is the most important aspect of being competent as a rescuer. Air-bag systems probably get used less than spreaders, cutter, rams, hand tools, etc. However, you really should be familiar enough with them so you can put air-bag systems to work without hesitation, even in adverse conditions - say, on a pitch-black road during bad weather.
And, as we always urge you to remember whenever you're performing rescue work, B.E. S.A.F.E.R. - Before Everything, Stop And First Evaluate and then Re-evaluate.