CAN YOUR AIR BAGS PASS THE TEST?
BY ROBERT HACKWORTH
The high-pressure air bag has become an important component of the U.S. emergency services` equipment arsenal and has helped save many lives, but the need for adequately maintaining and regularly testing this equipment only now is becoming apparent.
The service life expectancy of high-pressure air bags is from 10 to 12 years, depending on various factors that are completely under the control of the user. The chief component of all high-pressure air bags is elastic rubber, which, as a “living” material, is subject to aging processes. The actual speed of the processes depends on factors such as the frequency and uses of the product; storage conditions; exposure to light, heat, and humidity; and the influence of oxygen and energetic rays. Regular testing, therefore, is imperative to safeguard the safety of the user(s) and all who may be affected by the bag`s use and ability to perform as intended. Safety should always be the highest priority.
(Note: This article addresses only high-pressure bags. Low- and medium-pressure bags also should be subjected to testing. The tests are less complicated and stringent than those for high-pressure bags, which represent the greatest potential for harm should they fail while in service. Consult the manufacturer for the appropriate testing protocol for the low- and medium-pressure bags.)
THE “PRESSURE VESSELS REGULATION”
In the United States, there are no laws or standards governing any facet of high-pressure air bag technology. Engineering, quality, manufacturing, and testing are all left to the discretion of the various manufacturers. Since this is the case, our company uses the only standard in effect worldwide–German law. The Germans have developed a comprehensive testing standard that governs all facets of high-pressure air bag technology. Known as the “Pressure Vessels Regulation,” the regulation sets standards and schedule requirements for pressure vessels testing, which include first-time, acceptance, and ongoing tests.
CLEAR TESTS PRIOR TO FIRST OPERATION
The current running production is in-spected by the German TUV (a third-party testing) organization. Each air bag is examined for the first time after its production before leaving the manufacturing plant. High-pressure bags are approved and released for sale after a pressure and type approval test have been completed by an authorized works inspector. The pressure test is conducted with water at a pressure of 232 psi (16 bar) for steel-cord reinforced bags and 174 psi (12 bar) for Kevlar® reinforced bags.
High-pressure bags and accessories should be rechecked regularly and especially after each use (so that they are ready for their next use) to ensure that they are in perfect condition and that they have not been damaged in transport, storage, or handling.
TEST FOLLOWING EACH OPERATION
The law does not require that a visual and functional test be carried out after each operation, but such testing is recommended. The bag`s effectiveness can be affected by a variety of factors such as contact with chemical products, mechanical strain, and environmental influences. High-pressure bags and accessories also should be tested following each operation to ensure operator safety and the product`s service life. Testing can be done easily (see Visual Test and Functional Test in box on page 112); no testing instruments are required.
ANNUAL TEST
Regardless of how the high-pressure bag is used, it should be subjected to annual visual and functional testing, since storage conditions, which can vary widely among departments, can affect performance. The annual test need not be done if the bag was tested following each operation during the year.
TEST EVERY FIVE YEARS
High-pressure bags should be pressure-tested every five years unless damage previously had been discovered during the annual or “postoperations” visual and functional tests–in which case, the pressure test should be done immediately after identifying the damage.
The bag must be tested “free” (i.e., unconfined by a load or other bracing) with water at a pressure of 150 psi (10.4 bar)–i.e., 1.3 times the maximum working pressure of the air bag, for three to five minutes. The failure pressure of the bag can be altered by as much as 40 percent, depending on whether the test is done with the bag free or confined. The obvious reason for hydrostatic testing is safety. Water lessens the effects should the air bag burst during testing.
The purposes of the test are to determine if the bags are capable of resisting 1.3 times their maximum working pressure and identify any deformation that could endanger safety. While there is no guarantee how long a bag will perform, using the over-pressure test instead of inflating the bag at partial or full pressure increases the chance for successful performance. By testing at partial pressure only to identify leaks, an unsound pressure vessel would be discovered after the fact instead of before failure occurs. Any leak, no matter how minor, constitutes a compromised pressure vessel and therefore test failure.
SAFETY CONCERNS
Be aware that it is possible–even though unlikely–that the high-pressure air bag could burst during the functional test. For this reason, this test should be conducted in the open air, not indoors, and at a safe distance from persons, objects, and buildings. Also, the operator should wear personal protective equipment in the form of safety glasses, hearing protection, and gloves.
The over-pressure test is practically a burst/no burst test–that is, when an air bag fails this test, it usually bursts. Therefore, the technician performing this test also must wear personal protective equipment. When an air bag fails this test, it must be taken out of service and discarded.
By maintaining your high-pressure bags and subjecting them to the appropriate testing, your department can ensure that the bags will be safer to use and more cost-effective. It is recommended that you contact the manufacturer of your air bag equipment for its air bag testing procedures/recommendations. n
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Air bag damage or deformities that would be grounds for immediate removal from service include (top left) a cut that exposes the belting; (top right) severe surface abrasion, exposing the belts; (bottom left) surface delamination, probably caused by excessive heat; and (bottom right) side wall deformity, indicating a belt separation caused by age (the internal pressure in this bag is about 50 psi).
VISUAL AND FUNCTIONAL TESTS
Any time the safety or condition of high-pressure bags or its accessories is in doubt, immediately perform a visual and a functional test. These tests also must be conducted after making any repair and should be conducted after each use.
Following are checklists for the visual and functional tests. Follow exactly the sequence of the testing method. Should you encounter an item that is checked off as “no” or “not available,” resolve that issue immediately before continuing with the checklist. After completing a “successful” visual test, perform the functional test.
VISUAL TEST
I. Pressure Regulator Yes/ No/
Available Not Available
a. Inlet gasket q q
b. Threaded handwheel inlet:
freely working/undamaged? q q
c. Pressure gauges: free from
visible damage? q q
d. Pressure adjustment handle:
freely working/undamaged? q q
e. Shutoff valve: freely
working/undamaged? q q
f. Pressure reducer hose: free
from cracks, cuts, or other damage
(i.e., hardening, effects of chemicals)? q q
g. Quick-connect fittings: without
visible damage? q q
II. Inflation Hoses Yes/ No/ Available Not Available
a. Coupling, female: without q q
visible damage?
b. Nipple, male: without
visible damage? q q
c. Coupling and nipple fitting: tight? q q
d. Inflation hose: free from cracks, cuts,
or other damage (i.e., hardening,
effects from chemicals)? q q
III. Controller
(F = fitting construction; D = deadman control)
Yes/ No/
Available Not Available
a. Inlet coupling: undamaged,
freely working? q q
b. Shutoff ball valve (F) or joystick (D):
freely working without visible damage? q q
c. Pressure gauge(s): without visible
damage? q q
d. Pressure gauge with red line marks at
maximum pressure, 116 psi (8.0 bar)? q q
e. Safety relief valve (F): without visible
damage? q q
f. Provided with lead seals? q q
IV. High-Pressure Bags
Dirty high-pressure bags first should be cleaned with soap and lukewarm water, rinsed thoroughly, and dried.
Yes/ No/
Available Not Available
a. Lifting bag connection without
mechanical damage? q q
b. Lifting bag surfaces and lateral
edges: free from punctures, cuts,
cracks, and/or other damage? q q
The visual test is complete. If any doubt regarding safety arises during this stage of the visual testing process, stop the test here.
First repair damaged pressure reducers, inflation hoses, and controllers. Then, perform a new visual test. In case of damage to the high-pressure bags, contact the manufacturer. Do not continue with the functional test until all issues raised in the visual test have been resolved.
FUNCTIONAL TEST
Refer to the safety concerns for personal protection before continuing.
I. Pressure Reducer Yes/ No/
Available Not Available
a. Inlet pressure gauge:
pressure in air cylinder is
recognized by gauge? q q
b. Outlet pressure gauge:
reads adjusted pressure? q q
c. Pressure adjustment is adjustable
over the total range of the unit. q q
d. Safety relief valve of the reducer
keeps tight while maximum
pressure up to 175 psi (12.0 bar) is
being adjusted? q q
e. Shutoff valve of pressure reducer
outlet closes tightly? q q
f. At a final adjusted pressure of 60 psi
(4.0 bar), the pressure does not con-
tinue to increase within five minutes
(shutoff valve in closed position)? q q
Connect pressure reducer by means of the inflation hose with controller. For fitting style controllers, close ball valves. Open reducer`s shutoff valve. Adjust pressure reducer to the maximum inlet pressure of the controller. For 116 psi (8.0 bar) controllers, the maximum inlet pressure is 175 psi (12.0) bar.
g. Inflation hoses and entry
coupling tight? q q
II. Controllers
(F = fitting construction; D = deadman control)
Connect inflation hose to the controller. Fix test gauge to output coupling of the inflation hose. For fitting type controllers, close the safety relief valves by turning the top cap to the right.
Yes/ No/
Available Not Available
a. Do couplings operate smoothly? q q
b. After opening the ball valve (F)
or deadman joystick (D), the con-
troller`s gauge shows the same
pressure as the test gauge. q q
c. Are the couplings tight? q q
d. Safety relief valve(s) open at
125 psi (8.6 bar) maximum (to this
pressure, adjust the outlet pressure
of the pressure reducer). q q
e. After closing the inflation valve,
the safety relief valve closes again at
102 psi (7.0 bar) minimum? q q
HIGH-PRESSURE BAGS/AIR PRESSURE TEST
Test in open air only!
Connect lifting bag and controller with a 20- or 35-foot inflation hose and fill to 60 psi (4.1 bar).
Yes/ No/
Available Not Available
a. Bag free from uncommon
deformities? q q
b. Bag free from stitches, cuts,
cracks, and other damage? q q
c. Nipple bedding of the bag: firm,
tight, and leak-free? q q
If no damage is discovered, increase pressure to 116 psi (8.0 bar).
d. Bag free from uncommon deformities? q q
The functional test is complete. Deflate lifting bags and relieve pressure from system. If the functional testing process raises any safety doubts, remove the equipment from service and contact the manufacturer. Do not reinstate the system components into service until all issues raised in the functional test have been resolved. n
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The high-pressure air bag system contains numerous elements that require visual and functional testing. (Top) The major component system includes (counterclockwise from top left) air cylinder, pressure regulator, pressure reducer hose (grey), deadman controller, inflation hoses (green and yellow), and powerlift bags. (Bottom) The pressure regulator: 1. inlet pressure gauge, 2. outlet pressure gauge, 3. shutoff valve, 4. quick-connect fitting, 5. pressure adjustment, 6. threaded handwheel, and 7. inlet gasket. (Top) The deadman controller: 1. pressure gauges with red line, 2. discharge coupling, 3. inlet coupling, and 4. joystick valve. (Bottom) Fitting construction controller: 1. pressure gauges with red line, 2. safety relief valve, 3. discharge coupling, 4. shutoff ball valves, and 5. inlet coupling. (Photos by author.)
ROBERT HACKWORTH is president of Safety Corporation of America, the sole U.S. distributor for Vetter® air bags. He served 15 years in the volunteer emergency medical and fire services and is a Connecticut rescue instructor and a specialist instructor in hazardous materials in the Fire Protection Training Division at Texas A & M University.
