Introduction to How NASCAR Safety Works
A National Association for Stock Car Auto Racing (NASCAR) car is an amazing machine that pushes the physical limitations of automotive engineering. Crafting one of these cars is a meticulous task that takes dozens of designers, engineers and mechanics who put in hundreds of hours to perfect the car before it ever rolls onto a race track. On the track, the driver shows off his professional skills by directing this 3,400-pound (1,542-kg) machine around an oval track at speeds that would terrify most people.
For many, sitting at the helm of one of these custom-made dream machines is an appealing notion. With 750 horsepower under the hood, the cars have the ability to reach speeds of more than 200 mph (321 kph). But being behind the wheel of this car as it is spinning out of control on a high-banked super-speedway at 180 mph (289 kph), heading directly into aconcrete retaining wall -- this is the sober reality that professional drivers must face. Certainly, the tragic death of seven-time NASCAR champion Dale Earnhardt at the 2001 Daytona 500 race increased everyone's awareness of the dangers of professional car racing.
In an average street car equipped with air bags and seatbelts, occupants are protected during 35-mph crashes into a concrete barrier. But at 180 mph, both the car and the driver have more than 25 times more energy. All of this energy has to be absorbed in order to bring the car to a stop. This is an incredible challenge, but the cars usually handle it surprisingly well. In this edition of HowStuffWorks, you will learn how NASCAR drivers are able to walk away from so many crashes, and about the new safety devices being developed to prevent future race-related fatalities.
A NASCAR racing car is basically a skeleton of strong metal tubing covered with thin, metal sheeting. The cars are equipped with a variety of safety devices that have evolved over the years in response to accidents and crashes that have injured or killed drivers. Let's start with how the car protects the driver.
The Roll Cage
The key to surviving a crash is for the car to remove the energy from the driver's body as slowly as possible. Street cars have many safety devices designed with this in mind. The structure of a street car is designed to crush and thus absorb a lot of energy, giving the other safety devices, like seat belts and airbags, more time to slow the driver's body down.
A NASCAR race car uses some of the same techniques. There are three parts to the frame:
- Front clip
- Rear clip
- Middle section (including the roll cage)
The front and rear clip are built from thinner steel tubing so that they will crush when the car hits another car or a wall. The middle section is designed to be strong enough to maintain its integrity during a crash, thereby protecting the driver.
In addition to being collapsible, the front clip is designed to push the engine out of the bottom of the car -- rather than into the driver's compartment -- during an accident.
The seat has several important jobs:
- It must keep the driver inside the roll cage of his car.
- It must keep the driver from contacting anything hard during a crash.
- It must absorb some of the energy of the crash by bending.
In the past, several deaths occurred when drivers still in their seats were thrown from cars. To counter this, NASCAR rules now require that the seat be attached, at several points, directly to the tubular structure that forms the roll cage, which is sometimes the only part of the car left intact after a crash.
The shape of the seat is important, too. Most of the seats found in NASCAR race cars wrap around the driver's rib cage. This provides some support during a crash, spreading the load out over the entire rib cage instead of letting it concentrate in a smaller point. Some newer seats wrap around the driver's shoulders as well, which provides better support because the shoulders are more durable than the rib cage.
The net covering the driver's window is designed to keep debris out, and the driver's limbs in, during an accident.
The Restraint System
The safety belts and the seat transfer most of the driver's energy to the car during a crash. On a street car, the seatbelts are designed to stretch during a crash, which limits the force placed on the driver and gives him or her a little more time to slow down. On a NASCAR vehicle, however, the seat belts are much stronger -- they are designed to hold the driver tightly in his seat so that his body slows down with the car.
The restraint used on NASCAR race cars is a five-point harness. Two straps come down over the driver's shoulders, two straps wrap around his waist and one comes up between his legs. The straps are made from thick, padded nylon webbing. They are much stronger than the seatbelts in a street car.
Recently, several deaths have occurred as a result of severe head and neck trauma. Hoping to prevent those types of injuries, NASCAR will be requiring the use of an approved head-and-neck restraint. In October 2001, NASCAR officials mandated the use of head-and-neck-restraint systems for all drivers racing in the Winston Cup Series, Nascar Busch Series or Nascar Craftsman Truck Series.
The window openings on the cars are covered by a mesh made from nylon webbing. This webbing helps keep the driver's arms from flailing out of the car during a crash. The G-forces are so high during a crash -- between 50 and 100 times the force of gravity -- that it is impossible for the driver to control the position of his arms. This can be especially dangerous if the car rolls over and starts tumbling.
The net also has a quick release so that the driver can get it out of the way without much effort.
In 1994, NASCAR introduced roof flaps -- a safety device designed to keep cars from going airborne and tumbling over the track. Before this, when the cars spun out at high speeds (more than 195 mph / 324 kph), they would often fly into the air once they had rotated about 140 degrees. At this angle, the car takes on a shape that interacts with the wind very much like a wing.
When the car has spun around 140 degrees, its shape is very similar to that of a wing.
If the speed of the car is high enough, it will generate enough lift to pick up the car. To prevent this, NASCAR officials developed a set of flaps that are recessed into pockets on the roof of the car. Through wind-tunnel testing, NASCAR determined that the area of lowest pressure is at the back of the roof, near the rear window.
When the car reaches an angle at which it generates significant lift, the low pressure above the flaps sucks them open. The first flap to open is the one oriented at a 140-degree angle from the centerline of the car. Once this flap opens, it disrupts the airflow over the roof, killing all of the lift. An area of high pressure forms in front of the flap. This high-pressure air blows through a tube that connects to the pocket holding the second flap, causing the second flap to deploy. The second flap, which is oriented at 180 degrees, makes sure that the car continues to kill the lift as it rotates. After the car has spun around once, it has usually slowed to the point that it no longer produces lift.
The roof flaps keep the cars on the ground as they spin. This allows the skidding tires to scrub off some of the speed, hopefully allowing the driver to regain control. If not, at least the speed is reduced before the crash.
One part of a NASCAR car engine that was implemented for safety reasons is now being pointed at as the cause for many of the multi-car accidents during races. Restrictor plates are used at NASCAR's super-speedways, including Daytona and Talladega, to slow cars down.
The Windshield and Fuel Tank
The windshields on NASCAR race cars are made of Lexan, which is the same polycarbonate material used on fighter-plane canopies. This material is very strong, but also surprisingly soft. This softness is actually what gives it its strength. When an object hits the Lexan windshield, it doesn't shatter it. Instead, the object scratches, dents or imbeds itself in the windshield.
The windshields are usually constructed from three relatively flat pieces of Lexan. Each piece is supported by a framework built into the roll cage -- this gives the windshield the strength to resist large objects. The downside of a Lexan windshield is that it scratches very easily -- you could scratch one with your fingernail. A bare Lexan windshield would have to be replaced after every race because of scratches from sand and other grit on the track. But instead of replacing them, the NASCAR teams apply an adhesive film to the windshields that is harder than the Lexan and as clear as glass. After each race, the film can be peeled off and replaced, leaving the Lexan unscratched. Some teams apply several layers of this film and remove them one at a time during the race.
In the 1950s, NASCAR race cars used the fuel tanks from whatever street car they were based on. There were some schemes for wood reinforcements, but leaks and fires were common. Today's 22-gallon fuel tanks, also called fuel cells, have built-in safety features to limit the chance of them rupturing or exploding.
Fuel cells have a steel outer layer and a hard, plastic inner layer. The fuel cell is located in the rear of the car and is held in place by four braces that keep it from flying loose during an accident. It is filled with foam, which reduces the slosh of the fuel and any chance of explosion by reducing the amount of air in the cell. If the cell does ignite internally, the foam absorbs the explosion. The car also has check valves that will shut off fuel if the engine is separated from the car.
One part of a NASCAR car engine that was implemented for safety reasons is now being pointed at as the cause for many of the multi-car accidents during races.Restrictor plates are used at NASCAR's super-speedways, including Daytona and Talladega, to slow cars down. The New Hampshire International Speedway was recently added to that short list of restrictor-plate tracks following the deaths of Adam Petty and Kenny Irwin on that track within months of each other.
A restrictor plate is a square aluminum plate that has four holes drilled into it. Hole size is determined by NASCAR and varies between 0.875 inches and 1 inch (2.2 to 2.5 cm). Restrictor plates are placed between the carburetor and the intake manifold to reduce the flow of air and fuel into the engine's combustion chamber, thus reducing horsepower and speed.
Restrictor plates were implemented in 1988 following Bobby Allison's crash into a retaining fence at 210 mph (338 kph), which endangered hundreds of fans. Also in 1987, Bill Elliott set the track record by running a lap around the track at 213 mph (343 kph). Some believe that if restrictor plates weren't used, NASCAR cars could race on super-speedways at speeds in excess of 225 mph (362 kph) due to the improved aerodynamics of the cars over the past decade.
While NASCAR officials contend that restrictor plates are needed to prevent high-speed crashes like Allison's, many drivers complain that restrictor plates are the cause of multi-car accidents. Restrictor plates reduce speed by about 10 mph, leaving the field of more than 40 cars bunched tightly as they race around the track at 190 mph. If one of these cars crashes, it usually causes several other cars to crash along with it.
The Driver's Gear
NASCAR lacks many of the safety measures found in other racing series, including some type of safety committee, a medical or safety director or a consistent traveling safety team that attends every race. A heavy burden is placed on the NASCAR drivers themselves to make sure that they are as safe as possible when they step inside their cars.
Even under normal, street-driving conditions, there is a great chance that an accident will occur, and that numerous injuries will result. In stock-car racing, the chances for serious injury increase because the force at which these cars collide with other cars or walls is far greater. NASCAR race cars move faster and are heavier than conventional vehicles.
Before beginning a race, a NASCAR driver dons several pieces of protective equipment that could save his life if an accident were to occur. This gear covers the driver from head to toe and would even protect him if a fire were to break out in his car.
Perhaps the most recognizable piece of NASCAR racing gear is the driver's suit, which is emblazoned with patches of the team's sponsors. These suits are almost as recognizable as the drivers themselves. While most of us think of this suit as a walking billboard, it is actually quite important for the safety of the driver.
The suit is made out of either Proban or the same Nomex material that lines the inside of the driver's helmet. As mentioned before, Nomex is a fire-retardant material that protects the driver and crew if there is a flash fire in the pits or a fire resulting from a crash. Unlike other flame-retardant materials, the flame resistance of Nomex cannot be washed out or worn away.
The Nomex is woven into a material that is used to make the suit, gloves, socks and shoes worn by the driver. One of the most common injuries in NASCAR is the driver's feet being burned by the heat coming from the engine. These suits are given a rating to determine how long they will protect drivers from second-degree burns in a gasoline fire, which can burn at between 1,800 and 2,100 degrees Fahrenheit (982 to 1,148 degrees Celsius). Ratings are provided by the SFI Foundation, a non-profit organization that sets standards for various pieces of racing equipment. SFI ratings range between 3-2A/1 (three seconds of protection) to 3-2A/20 (40 seconds of protection).
The head is probably the most vulnerable part of the human body during an accident. While the driver's body is strapped in very tightly, the head can jerk around uncontrollably. Thehelmet is designed to dissipate impact energy over the entire helmet and prevent debris from puncturing it.
Every NASCAR driver is required to wear some type of helmet. Most wear a full-face helmet, which covers the entire head and wraps around the mouth and chin. Others wear an open-face helmet, which only covers the head. Drivers who wear the open-face helmet usually wear protective goggles. They claim that a full-face helmet restricts their peripheral vision.
According to helmet manufacturer Simpson Race Products, there are three parts to their racing helmets:
- Outer shell
- BeadALL liner
- Inner liner, padding and hardware
Once a shell design has been approved, a custom-made nickel model is created for that particular helmet. Construction of the outer shell begins with a thin layer of gelcoat. Then a special resin, consisting of several types of glass, carbon, Kevlar and other exotic fibers and weaves, is added to the shell. This all combines to make the hard, glossy outer shell.
Just underneath the outer shell is the BeadALL liner, which is a special foam layer in the crown of the helmet. The purpose of this liner is to absorb the energy that the outer shell has not absorbed. This layer is made of polystyrene or polypropylene.
The inner liner of most helmets is a form-fitting layer that is made of either nylon or Nomex. Nomex is a special fire-retardant material made by DuPont. It doesn't melt, drip, burn or support combustion. Helmets are also equipped with cheek pads, chin straps and visors. The visor is made of a tough Lexan plastic. Lexan, which is also used in NASCAR windshields, is commonly known for its use in bulletproof glass.
All helmets go through some sort of testing before they are considered safe enough for high-speed racing. Snell Memorial Foundation is an independent organization that sets voluntary standards for auto-racing helmets. To test the impact resistance of a racing helmet, Snell places the helmet onto a metal head form and drops it onto various types of anvils. If the peak acceleration impacting the metal head exceeds a magnitude of force equal to 300 Gs, or 300 times the force of gravity, it is rejected. This level of impact is hard to conceptualize -- a head-on impact at 30 mph (48 kph) into a concrete wall is measured at 80 Gs. Most impacts on a race track are between 50 and 100 Gs. A 100-G impact for a 160-pound (72-kg) man would feel like 16,000 pounds (7,257 kg) pressing on top of him.
Another piece of driver-safety equipment is called the HANS device. This one is still being debated. In the next section, you'll learn what a HANS device is and what the controversy is about.
The HANS Device
Four NASCAR drivers have been killed on the track since May 2000 -- Adam Petty, Kenny Irwin, Tony Roper and Dale Earnhardt Sr. All of these drivers were killed when their vehicles slammed head-on into a retaining wall, causing a fracture to the base of the skull. Some believe this type of injury is due to the driver's head being left unsecured in the car while his body is strapped securely to his seat.
The risk of severe injury, and possibly death, prompted six NASCAR drivers to try out a new device called the Head And Neck Support (HANS) system at the 2001 Daytona 500. This device was co-developed by Dr. Robert Hubbard, a professor of engineering at Michigan State University, and his brother-in-law, former IMSA car driver Jim Downing. The HANS device is designed to reduce the chance of injury caused by unrestrained movement of the head during crashes.
The HANS device is a semi-hard collar made of carbon fiber and Kevlar, and it is held onto the upper body by a harness worn by the driver. Two flexible tethers on the collar are attached to the helmet to prevent the head from snapping forward or to the side during a wreck. The device weighs approximately 1.5 pounds (0.68 kg).
Doctors have said that it is unclear if the HANS device could have saved Earnhardt, but it is believed that the device saved the life of a Championship Auto Racing Teams (CART) driver in January 2001. While practicing for an upcoming race, Bruno Junqueira spun out of control and slammed into a concrete wall at 200 mph (322 kph). Junqueira, who was wearing the HANS device, walked away from the crash without injury.
NASCAR officials have said that NASCAR race cars are different from CART cars, and they are unsure if the device would be as effective for NASCAR drivers. Drivers, including Earnhardt, have complained that the device is too bulky, would restrict movements and would make it difficult for drivers to exit the car in emergencies. Hubbard/Downing Inc. said it was producing only three to four of these helmets per day just weeks before the 2001 Daytona 500, but received nearly three-dozen orders within hours after Earnhardt's crash. Ford has offered to pay for a HANS device for any driver who wants to wear one.
In October 2001, NASCAR officials mandated the use of an approved head-and-neck-restraint system for all drivers racing in the Winston Cup Series, Nascar Busch Series or Nascar Craftsman Truck Series.
NASCAR races at about two-dozen tracks every year, and no two tracks are the same. There are ovals, tri-ovals, quad-ovals and road courses. There are short tracks, speedways and super speedways that range from 0.5 to 2.5 miles long.
Track safety is affected by the degree of the track's banking, the steepness built into the track. Tracks with a steep banking allow cars to go faster, especially around the corners, which is where a lot of the fatal accidents have occurred. If a track's banking were 90 degrees, then the track would be perpendicular to the ground. Obviously, no tracks are banked at a perpendicular angle.
There is no set standard for the degree of banking designed into a NASCAR track. Banking on NASCAR tracks range from 36 degrees in the corners to just a slight degree of banking in the straighter portions. Of course, road courses have no banking. Some believe that reducing the banking in the corners of oval tracks could prevent a lot of the fatal wrecks that we've seen recently.
Car racing is a dangerous sport -- possibly the most dangerous sport. In NASCAR, drivers are racing cars that weigh more than 3,000 pounds, speeding around a track at about 200 mph. Adding to the danger is the fact that cars usually race in tightly packed groups, and sometimes race three cars across on tracks that are only 50 feet (15 m) wide. Under such conditions, there are going to be accidents, and crashes. The purpose of the safety equipment is to minimize the harm caused when one of these cars veers out of control.
No track is the same, but most of them have one thing in common -- concrete retaining walls. The concrete walls are in place to contain a car that rides out of control. However, as we've seen, concrete walls don't absorb any energy, making any crash into one potentially deadly. Most NASCAR drivers who have died on the race track have died from crashing into the wall. One solution being proposed to make tracks safer is energy-absorbing walls, or "soft walls."
In the next section we’ll look at the different types of soft walls.
Types of Soft Walls
Soft walls are typically built of some kind of crushable material that can absorb the impact of a car at high speeds, dissipating the force of the crash throughout the material. Widespread implementation of soft walls on NASCAR tracks is probably still several years away. However, at least one track has already replaced small portions of concrete walls with soft walls. Here's a look at a few of the soft walls in use and in development:
- Cellofoam - This is an encapsulated polystyrene barrier -- a block of plastic foam encased in polyethelene. Lowes Motor Speedway, a NASCAR race track, has already installed small segments of Cellofoam on the inside retaining wall of turns two and four.
- Polyethylene Energy Dissipation System (PEDS) - The Indy Racing League (IRL) has been funding the PEDS system, which uses small polyethylene cylinders inserted inside larger ones. Designers of PEDS believe the system increases the wall's ability to withstand crashes of heavy race cars. Indianapolis Motor Speedwayhas already installed a PEDS on the fourth turn of its track.
- Impact Protection System (IPS) - Eurointernational has developed a soft wall made out of layered PVC material placed on a honeycomb structure. This inner piece of the wall is then wrapped in a rubber casing. The barrier walls come in segments that are 5 feet 9 inches (1.8 meters) long and weigh 475 pounds (215 kg). Holes are drilled in the concrete wall and cables are used to tie the segments to it. Click here for more information about the IPS.
- Compression barriers - Another soft-wall idea has been proposed by John Fitch, a Connecticut highway-safety expert. His idea is to place cushioning materials, such as tires, against the concrete wall, and then cover those cushions with a smooth surface that would give when impacted, and then pop back out to its previous shape once the impact is over.
According to NASCAR Chief Operating Officer Mike Helton, NASCAR has been researching soft-wall designs for three to four years, but hasn't found one suitable for its race tracks. Most of the designs they have tested have some prohibitive flaws. Some of the walls are made of material that breaks up, scattering across the track and delaying the race. Earnhardt, one of the biggest critics of new safety devices, once said that waiting for a splintered soft-wall to be cleaned up would be worth it if it saved someone's life.
Another criticism of soft walls is that a car can bounce off a soft wall and back into oncoming traffic, posing a danger to a greater number of drivers. Also, in NASCAR races, cars often scrape against the outside wall. Some believe that a soft-wall material would grab a car scraping the wall and cause it to suddenly stop. Another possibility is that a car crashing into a soft wall could get caught in the material, and that quick stop could concentrate the energy of the crash and cause even more damage.