AIR BAG BASICS
GARY SIEGEL
On Tuesday, September 22, 1998, at approximately 2030 hours, the Rockland County (NY) Fire & Emergency Dispatch Center (44 Control) received a call reporting an automobile accident involving a single vehicle at Grandview Avenue in the town of Ramapo. Grandview Avenue has two single lanes of traffic traveling east/west. The driver apparently lost control of her vehicle and hit a telephone pole. The car flipped over on its side. The driver, the only occupant, had her left arm out of the window on the driver`s side, and it became entrapped under the automobile. The first firefighters to arrive on the scene–the Hillcrest Fire Department, Rockland County, New York–reported that the woman was in extreme pain.
Size-Up
On arrival, the incident commander (IC) immediately called for an ambulance and ordered that extrication operations begin. It was obvious that this automobile would have to be “lifted” to free the driver`s arm. The decision was made to use air bags.
Operations
A firefighter made sure that the vehicle was shut off. He reached into the vehicle, shut it off, and removed the keys from the ignition. While he was doing this, another firefighter disconnected the car battery by forcing the car hood open using a hand-powered port-a-power spreader tool. After gaining access to the battery, he cut the negative battery cable with a bolt cutter. At the same time, firefighters stabilized the automobile using wheel chocks to hold the rear tires so that the vehicle would not slide. Wood step chocks were then placed along the car`s frame to prevent the vehicle from moving laterally. Next, the rear window was taken out using a spring-loaded center punch, and the glass was cleaned up so an EMS responder could enter the vehicle and stabilize the driver/victim.
A set of rescue air bags was placed under the automobile roof near the B-post, the second post on the vehicle and one of the strongest pivot points. (Most automobiles have three posts: A, B, and C. The A-post is the first post by the windshield; the C-post is the post behind the rear door.)
On command, the rescue air bags were inflated slowly as other firefighters placed cribbing under the vehicle to ensure its stabilization. The automobile was raised approximately six inches, freeing the victim`s arm. Paramedics stabilized the arm, placed the victim on a long board, took vitals, and transported her to a local hospital for treatment. Air bags helped to expedite this incident and ensure the operation`s success. They have many uses, including the following:
to lift vehicles, trains, planes, and so on, from soft or hard ground;
to lift odd-shaped objects;
to lift cylindrical objects;
to bend steel-reinforced bars on windows or fences;
to free trapped victims of natural weather occurrences/collapse;
to open inoperable elevator doors; and
to pull steering columns on heavy-duty trucks.
How do air bags work? How can they be used most efficiently? What precautions are needed to safeguard firefighters` safety? These and other issues are addressed below.
AIR BAGS: AN OVERVIEW
Air bags work on a simple proven law of physics. For each pound per square inch (psi) of compressed air inflated into a bag, the force is multiplied over the bag`s entire surface area, creating lifting force. For example, for a bag 30- x 30-inch, the lifting force would be 106,200 pounds or 53 tons (30- x 30-inch = 900 square inches x 118 psi = 106,200 pounds) Rescue air bags are made of steel reinforced/neoprene rubber or Kevlar®. These materials are extremely strong. In fact, they are impervious to most chemicals, including gasoline, diesel fuel, antifreeze, and most other liquids associated with motor vehicles. If liquid should get on a bag, simply wash the bag with soap and water when you return to the fire station.
Prevent Damage
The following conditions can damage air bags.
High temperatures (above 220 degrees F). A bag touching a vehicle`s muffler or catalytic converter could easily be exposed to this high temperature. For example, a catalytic converter, which can reach temperatures of 1,000 degrees F or more, could burn a hole through a bag, rendering the bag inoperable.
A large, sharp object. A screw or pointed bolt could penetrate the material and puncture the bag. Therefore, when space permits, protect an air bag from damage with a wood pad of 12-inch plywood boards–three layers of laminated first-grade wood glued and screwed together; countersink the screws.
Pulling on the air nipple inlet. If the air nipple is pulled out, the bag would be rendered inoperable. Handle these bags carefully.
Sizes
Air bags come in various sizes, ranging from 6 x 6-inch to 36 x 36-inch, and are available in sets that include various sizes. The six-inch bag has a maximum lift of three inches with a maximum weight capacity of 1.5 tons; the 36-inch bag has a maximum weight capacity of approximately 70 tons. Tonnage capacities vary slightly from brand to brand. The air bags used in the above incident and for rescue in general are considered high pressure; they have a working pressure of 118 psi vs. 14.7 psi for low-pressure multicell air bags. It takes only one inch of space to insert a high-pressure air bag into position for lifting a load.
Operations
Following the guidelines below will help to increase safety for rescuers:
Make sure all valves are closed before turning on the air source. This will reduce the risk of uncontrolled lift.
Always have the bag connected before placing it under the load to minimize exposure to the load area and eliminate the possibility of the operator`s positioning the bag with the air inlet under the load.
Inflate the bag slowly to minimize the chance of the load`s shifting.
As the bag is inflated, place cribbing alongside the object being lifted to prevent the object from slipping. Lift an inch, crib an inch. Once the load is lifted to the desired height, block or shore the load.
Unless conditions warrant otherwise, it is good general practice to inflate the bag to only 75 percent of its stated lifting capacity. This avoids the pillowing effect and reduces the potential for the bag to slip or kick out.
When using two bags for height, place the larger one on the bottom. Always inflate the bottom bag first. Do not stack more than two bags.
Never place wood in between the bags; it could slip or kick out.
When using two bags, place air nipples on opposite sides. This avoids the possibility of one air nipple`s pushing out the other nipple while being inflated. Also, have both air nipples pointing out toward the controller.
When stacking the bags, do not add together the maximum tonnage of the two bags to get the total lifting capacity. The maximum tonnage of the smaller bag is the maximum that can be lifted.
Change the air cylinder when pressure drops to 100 psi. Have another cylinder ready when using larger bags.
Reduce rated bag tonnage capacity by 50 percent to calculate the maximum tonnage capacity when the lifting height exceeds one inch–i.e., a 30-ton bag with a maximum lift of 10 inches will lift 30 tons one inch or 15 tons approximately 7.5 inches.
Conduct a proper size-up before selecting the size of the bag to be used.
Always maximize the bag`s contact area.
If space permits, use plywood boards on the top and bottom of the bags for protection.
The average life span of rescue air bags is from 10 to 15 years, regardless of the degree of usage. Bags used in a heavily industrial area will not last as long as bags used in a rural area.
Always wear protective clothing–helmet, bunker pants, coat, gloves, eye shields, and so on.
Never work under a load supported only by air bags. Crib. Crib. Crib.
Only one person should give the firefighter at the controller the order to lift.
If at all possible, the firefighter at the controller should have a radio.
Inspect the bags weekly; conduct a complete operational test.
Cribbing
Since rescue air bags do not provide stabilization, box cribs must be added as the bags begin to inflate. Place box cribs under the object on a solid surface. Construct the cribs from first-grade 4- x 4-inch or 6- x 6-inch wood. Place the cribbing at a 90 degree angle to each piece.
You can use two cribs per layer or three cribs per layer, depending on the weight being stabilized. The two-crib-per-layer method using 4- x 4-inch wood can support 24,000 pounds; if 6- x 6-inch wood is used, it can support 60,000 pounds. Using the same 4- x 4-inch in a three-crib-per-layer crib, 48,000 pounds can be supported; 6- x 6-inch in a three-crib set can support 120,000 pounds. To estimate the weight being lifted on a heavy-duty truck, for example, calculate 20,000 pounds per axle.
It is a good idea to place a rope handle on each piece of cribbing. It makes it much easier to carry numerous pieces of cribbing. Also, two members can carry more than 10 pieces of cribbing using a six-foot hook (pike pole) by placing the rope handles through the pole. A suggestion is to paint the ends of the cribbing different colors to signify different sizes. The cribbing`s maximum height should not exceed twice the cribbing`s length–for example, if the cribbing is 24 inches, the maximum height should not exceed 48 inches.
Step Chocks
Step chocks should also be placed under any object for added stabilization. Step chocks can be made of recycled plastic or of 2- x 6-inch first-grade wood (see Figure 1).
Labeling
All rescue air bags have a label imprinted with the size of the bag, maximum lift capacity, and maximum weight capacity. Over time, these labels become hard to see, especially at night. A suggestion is to spray paint these numbers on the bags. A two-inch number stencil can be used (see photos on page 72). Another suggestion is to paint the same numbers on the side of the bags with a hand brush. These numbers can be seen as one inflates the bag. It is recommended that the bags be stored in a horizontal position to reduce stress on the material.
Hoses
Hoses come in two lengths, 16 feet and 32 feet, and in various colors. Each color hose should be used on each particular bag. For example, one bag could have a red hose, another a blue hose, and the compressed air source hose could be yellow. The reason for this is simple. The individual at the air bag controller might not see the operation since he might be as far away as 32 feet. When the order comes to inflate the bag, the control person might mistakenly inflate the wrong bag. It is possible that the control person would not know which bag is the top bag and which is the bottom bag. Calling for the control person to inflate the red hose bag eliminates the possibility of inflating the wrong bag.
Remote Shutoffs
Most manufacturers sell remote shutoffs. The shutoff device is placed on the air nipple of the lifting bag. As soon as the bag is inflated to the required height, the remote shutoff knob or knife-turned handle switch (depending on the manufacturer) can be turned off, thereby cutting off the flow of air to the bag. That bag will remain inflated. The air hose can now be disconnected and attached to the other bag.
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The correct positioning when using two air bags. Note the larger bag is on the bottom. Plywood wood pads are used on the top and bottom of the bags to protect them. The bags have remote shutoffs, the air nipples are on opposite sides, and two different color hoses are used. (Photos by author.)
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Two-per-layer cribbing method. The maximum lift capacity is 24,000 pounds for 4- x 4-inch wood and 60,000 pounds for 6- x 6-inch wood.
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The three-per-layer cribbing method. The maximum lift capacity is 48,000 pounds for 4- x 4-inch wood and 120,000 pounds for 6- x 6-inch wood.
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Figure 1. A step chock made of wood can be made easily with some simple tools (a saw and a screwdriver). The chock should be constructed with waterproof glue or construction adhesive; countersink the wood screws. A single eight-foot-long 2- x 6-inch board will yield one chock.
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The maximum weight and lift are indicated on labeling on the air bag`s surface
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and side
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Remote shutoff on air bag.
Special thanks to Firefighter/Instructor James Harris for his assistance in the preparation of this article.
References
New York State Accident Vehicle Extrication Training (AVET) Manual.
Fire Department of New York Fire Academy Staff Lesson Plan.
Mosby Carbusters “Big Trucks Guide” by Kidd & Czajkowski.
GARY SIEGEL recently retired from the Fire Department of New York after 24 years of service. For the past five years, he was an extrication instructor at the FDNY Academy. He presently is an instructor at Rockland County (NY) Fire Training Center at Pomona, a New York State fire instructor, and a NYS certified accident vehicle extrication training instructor.
