Does CFRP burn? Explaining why CFRP is safe even if its strength decreases at 200 degrees Celsius.

The safety of CFRP (carbon fiber reinforced plastic), which is used as the main structural material of airplanes, has been the focus of much attention in the wake of the JAL plane crash in 2024, in which the fuselage of the plane caught fire. Some people are concerned that CFRP may be less heat-resistant than aluminum (melting point: 600°C) or steel (melting point: 1500°C) because its strength decreases at around 200°C.

In reality, however, CFRP has the property of slow combustion while maintaining its shape, and post-accident verification has led some to point out that the material may have taken advantage of this property.

This article describes the combustion characteristics and safety of CFRP based on temperature data and actual cases.

We will also discuss environmental issues in disposal and processing, so please read on if you are concerned about the safety of CFRP.

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Is CFRP a flammable material?

CFRP is composed of carbon fiber and resin, and because the resin used is flammable, it is a material that can burn under certain conditions.However, when CFRP burns, the resin burns, while the carbon fiber itself has very high heat resistance and remains flammable.

In this chapter, we will confirm whether CFRP is a flammable material in terms of melting point and safety.

Comparison by melting point

The following table summarizes at what temperatures CFRP and other metals are considered to lose strength.

CFRP	Around 200 degrees Celsius
duralumin	700 degrees
aluminum (Al)	600 degrees
iron	1500 degrees

The above table shows,Compared to other metals, the melting point of CFRP is much lower, so it seems to be more flammable.

However, the reason CFRP loses strength at around 200°C compared to other metals is not the carbon fiber itself, but the thermal decomposition temperature of the resin (such as epoxy resin).

The carbon fiber itself, which makes up CFRP, has extremely high heat resistance and maintains its performance even at temperatures of approximately 2000°C. On the other hand, the epoxy resin used as the matrix begins to decompose at around 200-300°C. As a result, the overall strength of CFRP decreases. On the other hand, the epoxy resin used as the matrix is thermosetting and begins to decompose at around 200-300℃, resulting in a decrease in the overall strength of the CFRP.

Although this characteristic makes it seem that CFRP is more flammable, a comparison of melting points alone cannot accurately evaluate its performance in actual operating environments.

Actual safety

Comparing CFRP by melting point, at first glance it may seem flammable, but referring to the "Haneda Airport ground collision" of a JAL aircraft,We find it difficult to say that CFRP is flammable.

When Japan Airlines Flight 516 (Airbus A350) caught fire at Haneda Airport on January 2, 2024, CFRP was used for the wings and fuselage.

The reason that all 379 passengers on board the JAL airplane were able to escape safely despite the fuselage catching fire may have to do with the characteristics of CFRP, which burns while retaining its shape.

In this case, CFRP appears to play a role in maintaining safety, since it is important for the aircraft to retain some shape in the event of a fire in order to escape.

Rather, the property of retaining its shape during combustion is an advantage in terms of ensuring evacuation time.

Why CFRP is a safe material

CFRP is used in a wide variety of fields due to its lightweight and high-strength properties. However, it is also a material with many other excellent properties in terms of safety.

Here are three reasons why CFRP is a safe material.

• Because they are less likely to collapse rapidly.
• Because there is little deterioration even after long-term use.
• Because it absorbs vibration easily.

Because they are less likely to collapse rapidly.

CFRP is a safe material in terms of its resistance to rapid collapse, which allows time for evacuation.

In fact, when an Airbus A350 made of CFRP caught fire, all 379 passengers were able to escape safely, possibly due to CFRP's resistance to burnout.

In this accident, passengers did not begin to evacuate until about 6 minutes after the fire, and it took about 12 minutes for the captain to finally leave the aircraft, but the fire did not spread to the cabin until later.

This example shows that the aircraft maintains its shape and does not collapse in the event of fire; the use of CFRP makes it easier to allow time for evacuation.

Because there is little deterioration even after long-term use.

CFRP is a material that is suitable for long-term use because it does not deteriorate easily even after long-term use.Factors that contribute to less deterioration include CFRP's resistance to weathering, corrosion, and fatigue.

Its excellent resistance to weather and corrosion makes it particularly resistant to moisture and chemicals, reducing deterioration caused by these factors.

It also has excellent fatigue resistance and is resistant to repetitive loading, thus maintaining structural strength over long periods of use.

Unlike metals, the resistance to sudden destruction, such as metal fatigue, is also an important factor in safety.

CFRP, which can maintain stable performance with high durability, is widely used in aircraft, automobiles, wind power generation blades, and other important structures that require safety.

Because it absorbs vibration easily.

CFRP's superior vibration absorption is another reason why it is a safe material.The ability to absorb vibration easily increases safety during impact and works to reduce structural damage.

Another feature of this product is its ability to mitigate impact to occupants when used in aircraft and automobiles.

Furthermore, CFRP's high vibration absorption properties reduce fatigue and extend the service life of machinery and equipment. These characteristics make it ideal for structures that are used under harsh conditions, such as machine parts and buildings that are expected to be used for long periods of time.

Some studies have shown that CFRP releases toxic substances when burned.

A research study by the German Defense University confirmed that when CFRP is subjected to high temperature flames, carcinogenic and toxic substances are emitted.

(Citation:https://cmcre.com/wp-content/uploads/2014/09/20140818carbonfib_2.pdf)

In addition to the German Defense Academy, the Fraunhofer Institute in Hanover has also announced that when CFRP is set ablaze, subatomic particles fly off, damaging respiratory mucous membranes and skin, with a very high probability of becoming a carcinogenic factor.

The results of these studies show that safety management during manufacturing and disposal is extremely important when using CFRP.

Disposal and treatment of CFRP

Due to its characteristics, CFRP is a difficult material to incinerate, and most of it is currently disposed of in landfills. Incineration requires a large amount of fuel, resulting in huge energy costs, and there is concern about the environmental impact.

It should also be noted that if CFRP waste is not properly disposed of, it can cause toxic emissions and environmental contamination.

Improving recycling technologies and establishing new disposal and treatment methods that reduce environmental impact will be important issues in the future.

Summary

This article has explained whether CFRP is a flammable material, from the perspective of its melting point and actual safety.

In terms of melting point, it may seem to be more flammable than other metals, but the example of the Airbus A350 that actually caught fire shows that it is highly durable and appears to be safe. Verification against the material will be conducted in the future, and various experts are paying attention.

However, CFRP should be handled with care, as some studies have shown that CFRP releases toxic substances when it burns.

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