airbag explodingSeat airbags are designed to deploy upon side impact only. In an accident, sensor at the base of the “B” pillar detects the impact and sends a signal via the SRS control module to the seat airbag.

Airbags are usually internally tethered for guidance and reinforced to prevent them from ripping under the extreme pressures involved in their deployment. At the heart of every airbag is a hybrid gas generator. This is a canister filled with a high-pressure gas and a flammable substance.

When an electrical signal reaches the canister, it fires the charge, which, in turn, releases the high-pressure gas. Rapid release of the gas inflates the airbag. When the airbag is deployed, it breaks out of its holder and bursts through the seat seam. This allows the airbag to inflate fully. All this happens within 70/1000 of a second!

If a seat seam has been altered outside of the manufacturer’s specifications, the airbag could deploy too early, or too late, or, possibly in the wrong position, and it won’t be effective. This means that any work done on seat upholstery must be done by someone who not only understands how airbags work, but also has an in-depth knowledge of the car seat upholstery trade. At Alphaline Auto, we have more than 40 years of experience in car upholstery.


airbag sewing machine
Computerised production
airbag sewing machine

We have found, through extensive testing, that every vehicle model needs to have a different thread combination to ensure compatibility.

All our airbag seams are sewn using data from comparative tests that provide the tensile strength of the original factory seams. This information is used to select the correct thread combination. The data is recorded on a tag that is sewn into the airbag seam. Each seam has a unique serial number that can be traced, if necessary, to reveal all the information about the seam.


Comparative testing

As the major Australian car upholstery market leader, Alphaline Auto has built up an extensive collection of most models’ static test results, which allows us to replace airbag seams with the assurance that the seams with deploy as intended.

Every model we have worked on since May 2000 has had its original seat airbag seams tested, and a comparable test has been done on the new seam.

We also film the airbag deployment using an ultra-high speed ballistics camera (imported from the U.S.A.) with which we can confirm our comparative test results. The camera allows us to show the airbag deploying within the time frame stipulated for factory-tested seats. These results are available on disc. Contact us for more information.

airbag footage airbag footage airbag footage airbag footage
Airbag high speed footage

All our tests that the results of static comparative tests done on our seams measure up to those achieved in factory testing of original seams. The Land Transport Safety Authority (LTSA) has witnessed our test procedures and sent us a letter recognising our procedures.

As we strive to maintain our high standards of safety and quality, we continue to investigate and implement the latest overseas technology and equipment as soon as it becomes available.

Airbag seam testing machine

We process every vehicle model side impact airbag (SIAB) through our seam data analyser, under a recognised procedure.

airbag sewing machine
Airbag seam testing machine


The criteria for the certification of airbag seams include:Airbag certification

  • Original factory covers must be tested and a comparison made between the thread combinations of the original and the new seams.
  • The new seams have been stitched according to tested samples.
  • The seat covers have been fitted by a trained installer, using the same method as the original fitment.