Aircraft Flammability Testing
Fire retardant material regulations and testing are widely utilised today to ensure the safety of all passengers, crew members, and of the aircraft itself. For fire retardant materials to be certified for use in an aircraft, they need to be thoroughly tested to ensure that the materials don’t decrease the existing levels of safety. This is done through the use of the following flammability testing methods that we’ll cover in this article.
Testing can be used to simulate the effects of a real fire and to measure the ability of items to continue to function, to quickly self-extinguish, and ensure re-ignition cannot occur.
Certifying interior materials and components to established regulatory flammability requirements are critical to aviation safety. The development of testing standards, and vigilant compliance with those standards, has undoubtedly saved lives and reduced passenger and crew injuries in aircraft accidents.
However, the process of certification can be confusing to those trying to introduce new materials into aircraft cabin designs. If their compositions have not been previously tested, these can react in unexpected ways when exposed to flame.
Let’s go back to how it began
In the past, fire safety and associated testing were an afterthought in the aviation industry, with the focus being on passenger convenience. The first flammability regulations were adopted between 1940 and 1960 and applicable to aircraft with 50-150 seats. Fire testing was limited to vertical flame spread assessments and many in the fire testing industry lobbied for a more comprehensive approach to testing to prevent fatalities.
In 1983, Air Canada Flight 797, a DC-9 flying at 33,000ft on the route from Dallas to Toronto started showing the first signs of trouble were the wisps of smoke wafting out of the rear lavatory. The fire spread within the walls and throughout the passenger compartment and soon involved the more combustible items within the aircraft such as the plastics and seat cushions. Thick black smoke filled the cabin and the plane began an emergency descent. The conditions intensified when the plane landed and the exit doors were opened, allowing for a fresh supply of oxygen. Sadly, 23 of the 46 people on board died.
The Federal Aviation Administration (FAA) understandably mandated that aircraft lavatories be equipped with smoke detectors and automatic fire extinguishers. Additionally, the authorities instated new regulations relating to the fire performance of aircraft materials. Within five years, seat cushions were retrofitted with fire-blocking layers. Aircraft built after 1988 have more flame-resistant interior materials as additional tests became mandatory. These regulations applied to transport category aircraft, i.e., 20 seats or greater.
The Vertical Bunsen Burner test is used by the aerospace/aviation industry to determine the resistance of cabin and cargo compartment materials to a flame applied for either 12- or 60-seconds. It is most commonly used to show compliance with EASA/FAR25.853 (a) App. F, Part 1 (A) 1 (i & ii)
After the test samples have been in the conditioning cabinet for at least 24 hours or until moisture equilibrium has been reached, the Bunsen burner flame is then set at 38mm in length and the temperature has to be at least 843oC. One test sample at a time is aligned vertically and exposed to the flame at its lower edge for either 12 seconds or 60 seconds (dependent upon final application in aircraft) and then pulled away from the sample. If the sample continues to flame, this flame time is recorded along with any flaming drips that may occur. After the test is over, the burn length is measured.
The pass/fail criteria are based on the flame time, drip flame time, and burn length averaged across three test samples. Below is the breakdown of what maximum averages are allowed in order to pass a burn test.
12-second test max averages allowed – Burn Length is 8 inches – After Flame Time is 15 sec – Dripping Time is 5 sec.
60-second test max averages allowed – Burn Length is 6 inches – After Flame Time 15 sec – Dripping Time is 3 sec.
Test Sample Requirements
Test samples must meet the following requirements:
- The standard sample size is 3-inch x 12-inch.
- A minimum of 3 samples must be tested for non-directional & a minimum of 6 samples must be tested for a directional test, however, we recommend 4 samples for non-directional tests and 8 in total for the directional test; 4 from Warp and 4 from Weft.
- If the material could react differently depending on which direction it is cut, it must be tested in two directions. For example, woven materials (e.g., carpet, fabric, etc.) must be tested with 3 samples cut up the roll (Warp) and 3 samples cut across the roll (Weft).
- The sample thickness must be no thicker than the minimum thickness to be qualified for use in the airplane. (Except for thick foam parts which are tested in 13mm (1/2″) thickness.)
- Samples may be tested either as a section cut from a fabricated part as installed in the aircraft or constructed to simulate that part.
- Fabricated units, such as sandwich panels, may not be separated for testing.
- The shorter edge of the test sample where the flame is applied must not consist of a finished or protected edge, i.e., it must represent a cross-section of the material or part as installed in the aircraft.
Products Requiring This Test
Items in commuter or transport category aircraft and in transport category rotorcraft require the Vertical Bunsen Burner Test when they are located in a compartment occupied by the crew or passengers. While there are some exceptions, these items typically include:
ITEMS REQUIRING THE VERTICAL 12 SECOND BURN TEST
- Floor Coverings
- Seat Cushions
- Coated Fabrics
- Trays and Galley Furnishings
- Electrical Conduit
- Air Ducting and Joints
- Joint and Edge Covering
- Molded and Thermoformed Parts
- Trim Strips
- Cargo Panel Flooring
- Cargo Covers and Transparencies
ITEMS REQUIRING THE VERTICAL 60 SECOND BURN TEST
- Interior Ceiling and Wall Panels
- Galley Structure
- Large Cabinet Walls
- Structural Flooring
- Large Stowage Compartments
Please note Aerofloor cannot conduct tests on all the items listed above, so please contact us prior to sending samples for testing.
COMPOSITE BURN TESTING
It is difficult enough to pass a new standalone material, but the complications are multiplied when running composite testing because the chemical interaction of the various elements can change the results of the tests. Even materials that pass the tests as a standalone material may not pass when combined. This failure sometimes results from the way the chemical properties of each material interact when set aflame. At other times, especially if an adhesive is required to bond the materials, the adhesive changes the flammability properties of the standalone materials, leading to test failure.
The chemical properties of the adhesives which have the best performance in their primary function often mean they result in test failures. To create a firm bond, those adhesives often contain volatile chemicals, and that volatility of the adhesive causes the composite material to fail. To counter this failure, the other material layers must be even more flame-retardant. However, treating the other materials with alternative flame retardants in order to better absorb the flammability properties of the adhesive can detrimentally affect other properties of the composite, such as colour, durability, and texture. Fixing one problem sometimes can generate another, so we understand that it sometimes can be a long process to get the composite right in order to get it to pass the burn test. We do our best to detect and pinpoint what is causing the test to fail to help our customers make the required adjustments to get the material to the right standard.
Testing is conducted Monday – Thursday only. The test fee is £127.50 per test.
A typed Burn Test Report will be issued irrespective of the result. Results are normally available within two working days from receipt of your order and test specimens.
Results will be notified by email with the originals to follow by post.
Flame Proofing Services
An additional service we provide is, after production Flame Proofing on certain carpet compositions. The maximum continuous length we can accommodate is 10 linear meters with a width of up to 2 meters.
GET IN TOUCH
Please contact us to learn more about how our Burn Testing Facilities and Flame Proofing Services can help you.
E: email@example.com T: 01206 798707