Darchem Flare fire testing ISO 2685

Aircraft interiors fire performance FAA 14 CFR:Part 25

Airborne equipment environmental test procedure for airborne equipment: Resistance to Fire in Designated Zones ISO 2685:1998

CALL +44 (0)1740 632915

Darchem Flare of Stillington Stockton-on-Tees Cleveland TS21 1LB UK

An independent unit, Darchem Flare provides testing to external "blue chip" customers as well as to the other Darchem business units, giving them an unrivalled ability to offer world class products.

Industry issues…

Halon replacement.

Halons used in certain aircraft applications (engine nacelles and auxiliary power units (APUs), cargo compartments, cabin portable extinguishers and lavatory bins) are still permitted for use.

Even with the critical use exemption, the aviation industry started researching alternatives over ten years ago. Many alternatives have been evaluated since then but because of the stringent safety and engineering performance requirements, implementation of alternatives has been challenging. For most aircraft fire protection systems, there are no current alternatives for new or existing aircraft, and for existing aircraft, replacement and retrofit of existing systems is considered currently not feasible.

Nevertheless the European Commission proposes to remove the critical use exemptions eventually.

Research and development on viable alternatives that are not interim solutions is ongoing and promoted by governments, the European Commission and the UN.

Fire testing of fuselage burnthrough resistance

Fuselage bunthrough refers to the penetration of an external jet fuel fire into the interior of an aircraft during a postcrash fire. The time to burnthrough is critical because in a majority of survivable aircraft accidents accompanied by fire, ignition of the interior of the aircraft is caused by burning jet fuel. Therefore, the integrity of the aircraft and its ability to provide a barrier against fuel fire penetration is an important factor related to the survival of aircraft occupants.

Fuselage burnthrough resistance becomes particularly important when the fuselage remains intact following a crash, which occurs frequently in survivable accidents. The best example of an accident with large loss of life where fuselage bunthrough was determined to be critical to the outcome was the B737 accident in Manchester, England in 1985. In this accident, the investigators concluded that burnthrough occurred within 60 seconds and did not allow sufficient time for all occupants to escape (55 people died from the effects of the fire).

Fuselage burnthrough resistance may be simplistically viewed as the time interval for a fuel fire to penetrate three fuselage shell members: aluminum skin, thermal acoustical insulation, and sidewall consisting of cabin panels and cabin flooring. Flame penetration may occur in other areas as well, such as windows, air return grilles, and seams/joints. The burnthrough resistance of the aluminum skin is well known. It takes only about 20 to 60 seconds for the skin to melt, depending on its thickness. The thermal acoustical insulation is the next impediment to burnthrough following the melting of the aluminum skin. In past FAA outdoor fuel fire burn tests on surplus fuselages, it was determined that the fibreglass insulation provided an additional 1 to 2 minutes of protection, if it completely covered the fire area and remained in place. Thus, the method of securing the insulation to the fuselage structural members is important.

The sidewall panels/flooring offer the final barrier to fire penetration. Sandwich panels comprised of honeycomb cores and fibreglass facings are effective barriers; however, full-scale fire tests also show that the fire can penetrate into the cabin through the air return grilles, seams, joints or window reveals. Moreover, some airplanes utilize aluminum sidewall panels which offer minimal burnnthrough resistance. FAA researchers are focusing on the thermal acoustical insulation as the most potentially effective and practical means of achieving a burnthrough barrier.

Aircraft thermal acoustical insulation batting is typically comprised of lightweight fibreglass, encapsulated in a thin film moisture barrier, usually polyester or polyvinyl fluoride. Several materials have been tested which exhibit marked burnthrough resistance compared to the baseline thermal acoustical batting. The effective materials include a heat stabilized oxidized polyacrylonitrile fiber (OPF) as a replacement for the fibreglass, a lightweight ceramic fibre matt used in conjunction with the present fibreglass, and a polymide film as a replacement for the polyester or polyvinyl fluoride films.

There has been much additional testing for evaluation of additional potentially effective materials/concepts (e.g., polymmide foam, intumescent paint, etc.).

Commercial transport aircraft primarily utilize aluminum alloy structural members.

Onboard cabin water spray systems.

The idea of cabin water spray system (CWSS) as a means of increasing passenger evacuation and survival time following an accident has received considerable publicity and has been the subject of testing by the regulatory agencies in both the United States and Europe. The return to service costs for an aircraft that would experience an uncommanded operation of a CWSS without the presence of fire is an issue. A CWSS might delay evacuation.

Cargo compartment fire protection.

The FAA have been involved in aircraft cargo compartment full-scale fire testing, with particular reference to combustible fires, bulk-load fires, containerized fires, surface burning, flammable liquid fires, aerosol explosion, Halon 1301 replacement/alternative, minimum performance standards, and gaseous and nongaseous fire suppression systems.

Flight data recorder fire resistance.

Of course fdrs and cvrs have to be fire resistant as well as impact and pressure resistant, in order to do the job they were designed for.

Seat covers flammability testing.

Modern fire safety criteria are largely the consequences of the engine fire on that Boeing 737-200 taking off from Manchester airport in August 1985. The fire brigade arrived within 25seconds of the aircraft stopping, but one of the emergency doors jammed, some passengers became trapped in narrow aisles or between the seat rowsleading to the over-wing exit, and the cabin furnishings burned so rapidly and produced such noxious fumes that 54 people died in a matter of minutes. Most succumbed to toxic smoke and gas inhalation; only six succumbed to what the accident report terms ‘thermal assault’ before they could inhale the incapacitating or fatal levels of carbon monoxide and hydrogen cyanide exhibited by the others.

One of the accident report’s 31 recommendations was that “the applicable regulatory requirements for aircraft cabin materials certification should be amended at the earliest opportunity to include strict limitations of smoke and toxic/irritant gas emissions. The equipment available to test at the time was without correlation with the intensity or indeed the survivability of the fire. It’s very difficult in real terms to say that the amount of smoke that a piece of material produces will or will not hinder the cabin evacuation. Airbus decided to impose some arbitrary limitations on harmful chemicals. It’s arbitrary as to how toxic or non-toxic the smoke is,and indeed the density of the smoke.Toxicity and flammability testing requirements particularly affect trimming and finish ie the surfaces, backrests, tables and so on that the passenger sees. It limits materials selection, and it also makes it quite expensive.Manufacturers cannot use materials they would like from, say, the automotive industry.

Moulded polycarbonate

The prevalence of asphyxiation as a cause of death in aircraft accidents is to be stressed and the importance of different plastics used in cabin furnishings as sources of smoke and toxic gases.

Acrylic windows.

Research has evaluated an advanced aircraft window material that may be able to prevent fire penetration almost four times longer than current stretched acrylic windows.

The window consists of an inner sheet of polycarbonate plastic laminated to an outer epoxy sheet.

When exposed to fire testing, the window's outer epoxy layer chars. This impedes heat radiation and conduction because the char forms an opaque coating as well as thermal insulation.

Materials that burn away leaving little char, such as the common stretched acrylic windows, provide less protection than those that form a heavy char.

Aircraft fibreglass insulation.

flammability testing was performed by eight laboratories on thermal acoustical insulation blankets and films used as

insulation coverings. Test samples were subjected to vertical Bunsen burner testing and cotton swab testing. The test data

indicated that the cotton swab test produced consistent test results, whereas the vertical flammability test did not. This work was

requested by the aircraft industry as a result of actual incidents involving flame propagation on the thermal acoustical blankets. The cotton swab test had been developed by the aircraft manufacturers. These cotton swab tests were performed by placing ignited alcohol saturated cotton swabs on a test-sized blanket and measuring the longest burn length. Test results indicated that the cotton swab tests produced consistent test results. This was especially

apparent with one particular film covering which passed the vertical test according to 50% of the participating laboratories while this same film during the cotton swab tests was reported to have

been consumed by all but one laboratory which reported that 75% of the sample was destroyed.

Graphite fabrics.

Flammability, thermal, and selected mechanical properties of composites fabricated with epoxy and other thermally stable resin matrices are going to prove useful to the aircraft designer. Properties include limiting-oxygen index, smoke evolution, thermal degradation, total-heat release, heat-release rates, mass loss, flame spread, ignition resistance, thermogravimetric analysis and selected mechanical properties. Graphite composite panels are fabricated using four different resin matrices and two types of graphite reinforcement. The resin matrices include a blend of vinylpolystyrylpyridine and bismaleimide, a bismaleimide, a phenolic and a polystyrylpyridine. The graphite fibre used is in the form of either tape or fabric. The prop erties of these composites include low heat release rate.

Low ignitability, low heat release, fire containment and fire endurance testing are all industry issues.