Extrication tips: October 2016
By Randy Schmitz
Some questions are being asked in the fire-rescue community about the use of carbon-fiber material in new vehicle construction. Although carbon fiber has been in the aircraft industry for many years, it is now being used in many late-model vehicles coming off the assembly line. It’s important that rescuers understand how carbon fiber is made and its properties in order to safely and efficiently predict and deal with this material
Carbon fiber is a lightweight, strong alternative to common steel. It is used in everything from an airliner fuselages to racing-bike frames and protective cell-phone cases. Carbon fiber was invented in the United States in the late 1950s but it wasn’t until a new manufacturing process was developed at a British research center in early ’60s that carbon fiber’s strength and lightweight potential was truly realized.
Carbon fiber reinforced polymer, or CFRP, is a process of combining strands of acrylic yarn together and baking the material to 1,400 F, which activates the carbonation of the yarn, hence the term carbon fiber. Each carbon fiber has roughly 10 layers of fabric; it is placed in a heavy press, air is extracted, a chemical resin is injected under high pressure and heated again for a specific time; then the fiber is cooled and the part is formed. When the part is removed from the press, the edges are very jagged so they are trimmed and sanded. The outer layer is the product’s final color and finish, which is a dark grey or black; the parts can be painted any colour, but are often left in the original colour, which has a unique, professional high-tech look.
One of the main advantages of this material is the strength-to-weight ratio of carbon fiber after the above process is completed; the actual weight of the component is a fraction of that of the same part made of steel. This transmits into reduced weight of vehicle parts which, in turn, can result in an overall increase in fuel economy of 20 to 30 per cent; that saving really motivates the auto industry to include carbon fiber in production lines. As a result, there will be a big push in the next few years of carbon fiber and aluminum combinations mated with other lightweight materials in modern vehicles. Anywhere the manufacture can reduce weight results in better fuel economy.
Another area that has undergone change is inside the vehicle passenger compartment, where structural strength is not important but cosmetic appeal is desired. Carbon fiber, with its sleek, stylish, eye-catching look really complements the interior of even the entry-level vehicle and is well suited for door panels and handles, outer seat contours and dash parts. These components do not have to conform to structural standards and can be made slimmer, quicker and cheaper for this reason.
On the structural side of things, auto manufacturers have established methods to give carbon-fiber parts more strength in a specific direction, for example, increasing strength in a load-bearing direction, but not doing so in areas that bear less load. Developments are underway that allow for omni-directional carbon-fiber construction, which applies strength in all directions. This version of carbon-fiber association is mostly being used in the safety cell unibody chassis assembly. Another advantage as time has passed; carbon fiber reinforced polymer has proven to be very corrosion resistant; this is a very important characteristic in both the outer body panels of the vehicle and the structural makeup of the framework or safety cell.
Let’s look at one popular vehicle that uses versions of CFRP and aluminum that’s cutting edge technology. According to the engineers and stakeholders at the Beamer camp, “The new 2016 BMW fifth-generation 7 Series uses a passenger cell called a ‘Carbon Core’ to improve performance and fuel economy, which cuts the weight by 86.kilos (or 190 pounds.)”
While the BMW carbon core is not a complete carbon-fiber, reinforced plastic tub or a series of panels as is used in racecars or hybrid supercars, the BMW efficient lightweight technology combines carbon fiber with lightweight, high-strength steel, and aluminum body panels. There are some carbon-fiber brackets and stiffeners, such as the cross-member at the top of the windshield. CFRP is inside the steel roof pillars to keep the cabin intact in a rollover or severe side impact. More 7 Series body panels are now aluminum, including doors and the trunk lid. The brakes, wheels, and suspension have lightened by 15 per cent, BMW says; savings to the so-called un-sprung weight parts have a much greater effect on performance than taking the same weight out of the gearbox or seats. BMW liberally reinforces the already strong metal/aluminum passenger cell with CFRP in critical places. The 15 CFRP reinforcements include the header above the windshield, door sills, transmission tunnel, front-to-back and left-to-right roof reinforcement tubes and bows, the B-pillar between front and rear doors, the C-pillar, and rear parcel shelf.
Most of the discussion around CFRP from a rescuer’s perspective concerns actual tool use and the dust that is created when breaching or cutting into the material. Testing done by rescuers has shown that there can be a fair amount of CFRP dust when using tools such as a fine tooth reciprocating saw blade. Although each CFRP manufacturer uses different chemicals and resins to make its product, most of the material safety data sheets call to protect your airway with either a respirator or N95 particulate mask when working around CFRP airborne dust.
In discussions with the companies that make or work with CFRP, all workers have stated that when cutting, sanding or in any situation in which they are creating dust particles, they have either worn the proper PPE as mentioned above or if operating in a close environment, have done the work under a ventilation hood fan. It is my belief that rescuers should adopt these same protocols, err on the side of caution and wear N95 masks when working around the CFRP dust.
Another challenge worthy of mention is the fact that manufacturers may paint over the carbon-fiber components and thus give rescuers no indication whether the component it is steel, aluminum, or carbon fiber. The 2016 BMW7 series upper A-pillar is an example of this; the indicator in this case is the carbon-core stamp on the top of the B-pillar.
One method firefighters in the United Kingdom use to determine if a component is made of carbon-fiber material is to place a small, pocket-sized magnet on the suspected component; if the magnet doesn’t stick, the component is most likely carbon fiber or possibly aluminum, and therefore rescuers know to protect their airways accordingly with approved respiratory measures.
In terms of hydraulic rescue tools breaching CRFP material – the material is not a challenge to sever as it simply crushes the part, such as a B-pillar, with relative ease. When cutting or spreading, the material simply breaks apart into small fragments. Rescuers will have no problem cutting the material with hand tools such as reciprocating saws and air chisels; doing so would be similar to cutting fiberglass.
Most vehicle manufacturers are investigating, testing and using carbon fiber in some form or another. Ultimately, use of carbon fiber will help manufacturers meet stricter fuel-economy and crash-safety standards. The use of carbon fiber in a vehicle can significantly reduce the weight and size of the framework; this will allow engineers to design and create more passenger compartment space. Using more carbon fiber in the manufacturing process also reduces the volume of water and electricity used to build vehicle components and chassis. Advancements in carbon-fiber technology will trickle down to the mainstream, just as airbags, anti-lock brakes, and stability control have done. Staying abreast of the changes to vehicles will allow first responders to stay on the top of their game.
Randy Schmitz is a Calgary firefighter extensively involved in the extrication field. He is the education chair for the Transport Emergency Rescue Committee in Canada. firstname.lastname@example.org @firedog7