Here is the follow up article on new car technology. This follows up where we left off from the last article and should give you some good information on vehicle safety systems.
Seat Belt Pretensioners
The first line of defense for any person involved in a motor vehicle collision is the seat belt. Studies done by the NHTSA estimate 9,500 lives are saved every year from safety belts. They go on to say that the risk of fatal injury is reduced by as much as 60 percent for those who wear lap belts and shoulder harnesses.
Seat belt pretensioners were introduced to aid in the protection offered by the safety belt. Many seat belts have slack in them as a result of bulky clothing or the spring loaded retractor failing to cinch the belt tight to the wearer. Seat belt pretensioners are designed to deploy with the airbag and remove the slack in the seat belt thereby reducing forward movement of the occupant. Manufacturers offer two different types of pretensioners. One model retracts the buckle while the other model backwinds the seat belt spool. The models that backwind the buckle have a pyrotechnic gas generator that activates and pulls a cable down thus tightening the seat belt.
Seat belt pretensioners that backwind the spool are generally located in the B-post. The pretensioner device is located near the spool. We must pay special attention to where the spool is located before we make any cuts on the B-post. As you can see by the photos below, the pretensioner can be located high on the B-post or low on the B-post. We must expose any area from now on before we attempt to make any cuts. We call this “Pry and Peek.” Keep a short flat head screw driver with you when you are doing extrication. Take a second to pry the plastic away from the area you plan to make a cut and look to see what is behind the plastic. You may encounter a sat belt pretensioner or an airbag canister. You DO NOT want to make a cut through either one of these devices.
Once you arrive on the scene it is difficult enough to tell if the auto has a seat belt pretensioner or not. If it does, you may not be able to tell if it has deployed or not. I tell my students to cut the seat belt early to avoid any problems associated with pretensioners.
The auto manufacturers are constantly trying to upgrade the safety of their vehicles, for example, in the new Dodge Durango they are using a new style seat belt with a Constant Force Retractor (CFR) and seat belt pretensioners in the front seat belts. This is designed to distribute the force of the seat belt according to the load that is exerted on it. CFR’s are engineered to gradually release the belt webbing in a controlled manner during a sever collision. The pretensioner will tighten the seat belt while the CFR balances the load on the upper body reducing the injuries from excessive seat belt forces.
Airbags were first introduced in the late 1960’s. In 1969 the Nixon administration proposed the development of some type of passive restraint system. In 1973 General Motors installed airbags in one thousand Chevrolets for fleet customers. In 1991 President Bush signed a law requiring auto manufacturers to begin phasing in airbags in the 1994 model year.
The NHTSA estimates between 1986 and March 1, 2000, airbags have saved as many as 5,300 lives during that period. As the percentages of autos on the road with airbags increase, so will the number of lives saved.
There are many different types of airbags on the market today. Here is a brief list of the different types of airbags you may encounter.
- Steering Wheel: SRS, SIR, Airbag
- Dash: SRS, SIR, Airbag
- Seats: SIPS, SRS/Airbag, Airbag
- Doors: SIPS, SRS/Airbag, Airbag
- Knee: SRS
- A-Post/Roof: HPS
- Side Impact Curtains: IC/Inflatable Curtain
- Head and Torso Airbag
- Head/Thorax Airbag
- Gentle Airbag: Airbag using computer technology will deploy with less force
- Intelligent Airbags
The way an airbag works is quite simple. Vehicles equipped with airbags have an electronic control module that contains a capacitor, a master sensor and other electronic equipment. The sensor senses a front end collision, a message is sent to a pyrotechnic gas generator that then inflates the airbag in a about 1/50th of a second. Early generation airbags would deploy at about 200 mph. Needless to say this caused a lot of problems when people were hit with this type of force.
There are many manufacturers placing “second” and even “third” generation airbags into their vehicles. Airbags used today in many vehicles are deployed at a rate consistent with the collision. If the rate of speed during the collision is low, the airbag deploys much slower. If the rate of speed during the collision is high, the airbag deploys much faster. This system protects the occupants from unnecessary injury by the airbag at slower speed collisions.
There are still other types of airbags that are called “Smart Airbags” or “Intelligent Airbags” These systems combine the sensor in the electronic control unit with sensors in the seat and the seat belt buckle. There are sensors in the seat that are weight sensitive and only deploy the airbag if someone is sitting there. The sensors in the seat belt buckle will deploy the airbag at different rates depending on whether the belt is buckled or not. There are other systems that utilize both weight and belt sensors as stated above, plus ultra sonic sensors to determine if someone is in the seat or not.
You may also see “Dual Threshold” airbags. These were first introduced in 1994 by BMW. The airbag will deploy the first stage in less severe accidents and during more severe accidents a second stage of the airbag will also deploy.
There are many different systems used in today’s vehicles. Airbag and canister placement may changes from year to year on the same model. Some can even change during the same model year. When you respond to a motor vehicle accident involving a vehicle with an airbag, the first thing you want to do is protect yourself and the passenger from accidental deployment, if the airbag has not already deployed. When working near airbags, I like using the 5–10–20 rule. Keep yourself and the victims 5 inches from any side impact airbag, 10 inches from any steering wheel airbag and 20 inches from any dash mounted airbag. These airbag systems have a capacitor which can store energy to an airbag for as long as 30 minutes. You must cut the battery cables early in the rescue to remove the energy to the capacitor. This will not guarantee the airbags will not deploy, treat all airbags as if they can and will deploy during the rescue. There are many devices available to place over the airbag to help minimize the deployment. These devices are placed over the steering column or dash to protect the victims and rescuers.
You must also pay attention to any side impact airbags that deploy from the seat and side curtains that deploy from the headliner. Side curtain airbags will deploy downward from the headliner and would certainly cause problems for a rescuer leaning into the auto. The photo below shows a side curtain airbag deployed.
During extrication operations there are several problems these airbags will present for us. First there are airbag sensors located in the doors and seats, traditional means of spreading the doors in these types of vehicles may accidentally set off these airbags. Care needs to be taken to avoid using you spreaders on these types of doors. The best way to remove this door is to cut the hinges, try to open the latch and roll the door off the pin or cut the pin. This will reduce the chance of putting pressure on the sensor and causing the airbag to deploy. In the photo below you can see the airbag module is placed very close to the latch side of the door.
We discussed an application earlier called “Pry and Peek” to look for seat belt pretensioners. The same practice holds true for airbag canisters, these canisters can be located in the A, B or C post and the roof rail. Many of them have stored pressures over 3000 psi. You wouldn’t want to cut into one of these because you were in a hurry and did not look where you were cutting. You have to have the mindset that no two cars are alike when it comes to the places manufacturers put airbag canisters. You must look before you spread or cut in every vehicle you encounter.
As you can see in this short article, there are many advances in the auto industry that can have an adverse effect on our day to day operation during a vehicle rescue. It is important that we learn about these advances and keep current on new technology as the auto industry introduces it. My goal for this article was to give you a little knowledge of what manufacturers are doing with vehicles today. There are many training courses available that are dedicated to new car technology and extrication techniques for new cars. This article should be a starting point for you to further your education on new car technology. Find a class that offers new car technology and vehicle extrication. Most of these classes are one and two day classes. If you have trouble finding a class, give me a call or email and I will try to help you locate a class. My phone number and email are available in the instructor bio at the end of this article.
For more information, go to www.footagerescue.com