Air Bag Operations – Part 2: The Science of Lifting

Air bag lifting capacity is based on simple physics. The operating pressure of the bag, in pounds per square inch (PSI), is multiplied over the entire surface area of the bag to equal lifting force. This article aims to explain how to calculate the air...


Notice the significant difference of 20,938 pounds between the modified theoretical lift capacity (31,407 pounds) and the actual lift capacity (10,469 pounds) when only 25% of the bag is making contact. Members need to recognize the pillowing of the air bag and realize the considerable difference between the stamped-rated capacity on the bag and what the air bag is actually capable of lifting.

Stacked Bags vs. Side-by-Side Bags

Under normal operating conditions two air bags, one smaller than the other, will be stacked on top of one another (Photo 3). This is done to ensure there will be enough lift height to achieve the objective. When two bags are stacked, the maximum lift capacity is that of the smaller bag. The capacities of the air bags are not added together. Therefore, if a 10-ton bag is placed on top of a 20-ton bag, the maximum theoretical capacity of the system is 10 tons. Of course the actual lift capacity of the system depends on the surface area in contact with the object to be lifted.

The only time the capacities of the two bags are added together is when they are placed side-by-side and inflated simultaneously. The bags being placed side-by-side increase the surface area in contact with the object to be lifted. Much more on bag placement will be covered in future articles.

Conclusion

It is necessary that members understand the load capacities of the air bag system. It is critical to be aware of the difference between the theoretical and actual lifting capacities to ensure that system failure does not occur. Quickly determining which air bags to use is essential for ensuring a safe and effective rescue operation.

 

JONATHAN HALL is currently a firefighter with the Saint Paul, MN, Fire Department. He previously served as a training and safety officer for the Township Fire Department in Eau Claire, WI. He is a certified fire instructor for the Chippewa Valley Technical College in Eau Claire. Jonathan frequently teaches firefighter survival and rapid intervention team concepts in both Minnesota and Wisconsin.