Fire and flame
in the cause of onboard safety
Fire safety laboratory at Lufthansa Technik in Hamburg
From fabric seat covers in economy class and fine leather upholstery in business class to noble wood veneer, golden applications and a fluffy carpet in a private VIP jet; the choices of materials to be installed inside an aircraft cabin nowadays are extremely manifold. However, from the perspective of fire safety, not every material that prettifies the passengers' stay on board is also suitable for the use inside an aircraft cabin. For this reason, all materials destined for the installation on board have to pass stringent flammability tests before they receive their approval. Lufthansa Technik carries out many such checks in its own fire safety laboratory in Hamburg.
An integral part of the laboratory is the furnace. In here, behind thick, shatterproof glass, all materials to be tested are exposed to the flame of a Bunsen burner. The specimens used originate from the most varied materials of all kinds of cabin furniture. From a thin wood veneer on a honeycomb structure which is to be installed only one single time in a unique government aircraft on to seat covers made of fabric, artificial or real leather, carpets, painted surfaces, decorative foils or wallpapers to be installed hundredfold in commercial aircraft; no matter if one of a kind or mass product, all materials have to pass the flammability tests.
As one can imagine, Lufthansa Technik in most cases does not burn entire pieces of furniture to assess their flammability. The interior workshops for this purpose pre-produce small specimens, usually in small stripes measuring 300 by 75 millimetres. In producing the specimens, the technicians have to pay special attention to the direction in which certain pieces of fabric are installed. Depending on the various material properties of filling and chaining threads, the woven textiles can show significant differences in the spread of fire that have to be taken into account by the interior engineers. To ensure the comparability with previous and future tests, all flammability testing has to be carried out under the exactly same environmental conditions. Hence, all specimens are stored in a climate chamber with a temperature of 21 degrees Celsius (+/- 3 degrees) and a humidity of 50 percent (+/- 5 percent) for 24 hours prior to testing.
Special attention on material combinations
When the specimens have reached the standardized temperature and humidity, they are positioned in the furnace with their lower side hanging directly above the Bunsen burner. With the ignition of the latter a timer on the furnace starts to run: When exactly twelve seconds have passed, the burner goes out. The fire, however, keeps flaring from the specimen as the timer starts running anew towards a critical mark: 15 seconds is the maximum afterburning time a material is allowed to show after the burner has been extinguished. All materials that exceed this time are banned from the use in an aircraft following the regulations of the US Federal Aviation Administration (FAA) and the European Aviation Safety Agency (EASA).
However, solely from passing a single flammability test, the fire safety assessment of a single material can never be considered complete, for a good cause: In the cabins of modern aircraft many materials do not emerge separately but in a multitude of combinations. Single materials easily passing the flammability test can hence show completely different properties of fire safety in interaction with different materials. Two examples: With sound-insulating foam, a copper mesh against electrostatic charge and the fluffy carpet itself even an inconspicuous floor covering has to be considered as a material combination and hence requires special fire safety testing prior to its approval for the use in an aircraft cabin. Likewise, a combination of honeycomb structure with laminated wood veneer and finally applied clear lacquer can show a completely different flammability than its three single components.
For this reason, the aviation authorities also mandate flammability tests for all combinations of materials that are to be used in close proximity inside an aircraft. Unlike the single materials, the combinations are exposed to the Bunsen burner's flame for an entire minute. After the burner is extinguished, the same 15 seconds afterburning regulation valid for single materials applies to material combinations as well. Moreover, the test record sheet contains additional information to decide about the approval of a single material or a combination: A possible drop formation due to the fire and also the length of the scorch mark on the specimen. The latter is precisely measured and gives Lufthansa Technik's experts additional valuable information about the behaviour of the material or combination in case of fire. Only if all parameters are within the regulatory limits, the fire safety laboratory approves the materials for the use in an aircraft.
Heat release tests maintain safe escape routes in case of a fire
Smoke also plays a part in the fire safety assessment of interior materials. Their safe use can only be granted if burning them does not produce any toxic fumes. Such tests, however, are not carried out by Lufthansa Technik's laboratory, the same applies to the so called "oil burner test– in which entire seats are exposed to a large flame for five minutes. A comparison of the seat weight before and after the flaming provides the experts with valuable information about the flammability of the materials used.
But open fire is not the only challenge for all materials used in an aircraft cabin. Regarding all aircraft types with more than 20 passenger seats the authorities additionally call for a heat release test. This procedure measures the heat emission of large surfaces such as cabin floors, ceilings or partition walls in order to ensure that escape routes can be used as long as possible to evacuate the aircraft in case of a fire in, for example, the cargo compartments underneath. To carry out such tests Lufthansa Technik in 2010 inaugurated a special heat release chamber in Hamburg.
With its exclusive materials and never ending ideas for unique interior of "flying palaces– it is especially Lufthansa Technik's business unit "VIP & Executive Jet Solutions– that provides a steady workload for the experts in the fire safety laboratories. Since more than 35 years they are playing a crucial role in the approval of new materials for the aviation industry. On average they are testing around 2.000 different materials or combinations per year. Every material that passes their stringent tests can soon be found touring the world in an aircraft cabin - with safety assured.