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|TOPIC:||Service life of high-pressure lifting airbags|
|OBJECTIVE:||Understand the concept of useful service life for high-pressure lifting airbags|
|TASK:||Using the high-pressure lifting airbags currently in service within your department, evaluate their service condition and estimate their total life expectancy|
Many fire and rescue organizations have purchased and placed sets of high-pressure lifting airbags in service. The concept that is not widely realized about this particular rescue tool is that they have a built-in “life expectancy” based on their “born-on,” date, after which there is an increased chance of failure during use. It seems out of place, but the reality is if you own rescue airbags that are 20 years old or older, they should be thrown away right now. If you own bags that are even 10 years old, be careful; they need to be checked.
Regardless of which brand of lifting airbag system your department owns, the bags consist primarily of a rubber material covering internal steel or synthetic fibers that give the bags their strength. It is this rubber that ages and depending upon use, care and maintenance, largely determines the useful service life of an airbag. Although no manufacturer will guarantee how long an airbag will last, the number “10 years” comes up a lot. We don’t normally throw away a rescue tool on its 10th birthday, but we might have to consider that possibility.
Courtesy of Carrollton FD
This is the scene immediately after an airbag failed during a drill in Carrollton, TX. The bottom bag ruptured along the left side and split open.
If you think about automobile tires, depending on how a car owner uses a vehicle and cares for the tires, the car will get either good mileage or the tires will wear out prematurely. Regardless, after a certain length of time, even a well-maintained tire wears out.
It is a similar concept with rescue airbags. The way we use our airbags and the way we care for and maintain them influences how long the bags can be expected to perform reliably. Factors such as frequency and use of the bags affect service life. Poor storage conditions or locations that cause airbags to rub or scrape as the rescue vehicle is driven are detrimental to getting the full life span out of an airbag. A bag put away dirty, especially with greases, vehicle fluids and oil residue on it, is a bad thing. Bags constantly exposed to high heat and humidity will not last as long or perform as reliably as a well-cared-for system. Even with tender loving care and maybe minimal use other than during training, the shelf-life of a typical rescue airbag does not exceed 20 years; with manufacturers such as Vetter Airbags, based in Zuloich, Germany, stating that rubber airbags can have a life expectancy of as short as 10 years.
Lifting airbags first arrived in the United States in 1975. Vetter-brand bags purchased in the late 1970s and any brand of airbags placed in service in the 1980s could be at or beyond their useful service life. It is the higher possibility of failure of these older-generation airbags that has focused renewed attention on airbag life expectancy.
In Carrollton, TX, the fire department was conducting a simple company-level “skill drill” with its airbags. During the lift of an SUV, the bottom bag in a two-bag stack suddenly failed. The blowout ruptured through the outer rubber layer of the airbag, causing the collapse of the bag itself. The cribbing, properly placed for the lift, safely took the load.
In Massachusetts, students attending a basic vehicle rescue class were using cribbing and a high-pressure lifting airbag to lift one side of an older automobile. The 20-by-24-inch, 26-ton-rated airbag was manufactured in 1985. With two box cribs in place, one on either side of the lifting airbag, the lift began. The airbag catastrophically failed at a working pressure of approximately 80 psi reading on the line gauge. Analysis afterward showed that the airbag had ruptured from the inside out, resulting in a slit approximately 10 inches in length near an edge of the bag. Due to proper cribbing placement, when the vehicle suddenly dropped, it rested on the cribbing. In both the Texas and the Massachusetts incident there were no injuries. This is due to the fact that in both training exercises, proper lift and cribbing procedures were followed.
Vetter recommends that the bags should be hydrostatically tested at age five years, seven years, nine years and then every year after. A hydrostatic test means that the airbag is filled and pressurized with water. A department can consult with the manufacturer of its brand of airbag equipment for full details on the feasibility of having service-life tests conducted for the units. For a department wanting to conduct its own life-expectancy test on its airbags, each bag must be placed outdoors on a level surface. You must create a system whereby you can completely fill the airbag with water and pressurize it with water at a pressure of 1.3 times the maximum working pressure of the airbag for three to five minutes. For example, an airbag that operates normally at 118 psi air pressure must be pressurized with water to a pressure of 153 psi (118 multiplied by 1.3). If the bag holds its water, it passes. If it fails, the bag blows out and self-destructs.
While there is no guarantee how long an airbag will perform during its years of service, having the water-pressure test conducted on your airbags increases the chance for successful performance.
Be aware that it is possible – even though unlikely– that a high-pressure lifting airbag could burst during the water test. For this reason, this test should be conducted in the open air, not indoors, at a safe distance from people, objects and buildings. Also, the operator should wear personal protective equipment.
Ron Moore, a Firehouse® 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.