Imagine being in a vehicle that sustains considerable damage as the result of being hit in the side during a collision. There is not a lot of space between the inside of the passenger compartment and the point of impact on the outside of the vehicle. That small amount of space does not allow much time for safety restraints to function successfully.
Now imagine that you walked away from such a collision with only minimal, if any, injuries. With improvements in today’s vehicle designs and construction materials, the chance of that happening is becoming more of a reality. Changes in government regulations have also driven improvements in side-impact protection.
Side impact protection
Protection from side-impact collisions is considered a serious issue by both the government and vehicle makers, and for a good reason. Side impacts put occupants in a very vulnerable position having only the door, rocker panel and pillar assemblies (versus 4 ft. of vehicle front-end assemblies) to protect passengers against collision forces.
The purpose of the first side impact protection standard, adopted in 1970 (FMVSS 214), was to increase door strength. This standard led to the development of door intrusion beams.
Additional standards were created and aimed at improving occupant side impact protection. These standards resulted in the integration of solid foam blocks, high-strength metals, side airbags and laminated side glass into the side of the vehicle.
Foam blocks
Installing foam blocks around the intrusion beams was one answer to adding side impact protection by some vehicle makers. These foam inserts provided protection during side impacts. They also filled spaces without adding weight.
These insert blocks are not like sprayable foam or sound-deadening pads, which are added for controlling noise, vibration and harshness. Foam blocks are specifically designed and positioned for enhancing side impact protection. In some cases, foam inserts in pillars and rocker panels may even add some rigidity to these panels.
If replaced, the foam blocks must be installed in the exact position as the original part, or the vehicle will not perform to the required safety specifications. Foam blocks used inside door assemblies have attachment clips to help ensure correct placement when being replaced.
Some Volvo vehicles are equipped with a Side Impact Protection System (SIPS) that includes parts made from a plastic honeycomb or foam block. Before beginning repairs to doors on a Volvo, remove the door interior trim panel and check for the presence of a SIPS block and remove it before applying heat to the door.
Quarter panel reinforcement bars
Some vehicles have quarter panel intrusion beams or reinforcement bars. Just like the door intrusion beams, the quarter panel reinforcement bars are made of ultra-high strength steel, and they are spot welded to the quarter panel at each end of the intrusion beam. Unlike door intrusion beams, quarter panel reinforcement bars are often available as a replacement part.
Reinforcements and crossbeams
Side impact protection standards lead to increased passenger protection by requiring the addition or modification of reinforcements used in the pillars, roof and floor. Structural changes were made to direct collision energy around the passenger compartment. The crossbeams and pillars help divert the collision energy forces upward to the roof rails, downward to the reinforced rocker panels, and outward to the floor cross members.
Steel alloyed with boron
Some vehicle makers use steel alloyed with boron in their vehicle designs. This material is used to provide additional strength for increased side impact protection. Steel alloyed with boron is so strong that it cannot be drilled through with conventional drill bits. In some cases, steel alloyed with boron may damage life saving extraction equipment, such as reciprocating saw blades, used by some fire or rescue personnel.
Steel alloyed with boron can be found in such places as door guard intrusion beams, inner B-pillars and roof rails. One specific example is the Volvo XC-90, which uses steel alloyed with boron for the inner B-pillars and the roof rails.
Due to its strength, Volvo does not recommend straightening steel alloyed with boron. This is because of the amount of heat used when it is being formed. When steel alloyed with boron is damaged in a collision, the work hardening that has occurred as a result of the damage causes it to become too brittle to be restored.” Work hardening is when a metal is strained beyond the yield point and the metal apparently becomes stronger and more difficult to deform. Attempts to straighten a part that is steel alloyed with boron will usually result in the part cracking. Using heat may allow the part to be straightened without cracking, but heat will destroy the strength of the part. Volvo recommends replacing damaged boron steel parts.
Side airbag protection
Many late model vehicles are now available with side airbags, which offer extra protection during side impact collisions. Types of side airbag systems include those that deploy from the seat backs (seat-mounted airbags), those that deploy from the door, typically just below the window sill (side-panel or door-mounted airbags), or those that deploy from the roof rail (side-curtain airbags).
A seat-back airbag is designed to limit the force that an occupant experiences when making contact with the side of a vehicle during a side impact collision. Depending on the physical dimensions of the airbag used, the occupant may have side impact protection from their hips up to their head. Depending on the vehicle maker and model year, seat-back airbags may be either electrically or mechanically operated.
Because there is less space to separate a vehicle occupant from the force of a side impact versus a frontal impact, side airbags and curtains must deploy faster than frontal airbags.
Side airbags are designed to provide occupant protection from side collision forces, but there are risks with side airbag deployment.
The principle risks from deploying side airbags are the related injuries to the head, neck, and/or thorax. These injuries typically result when an occupant is in the deployment path of a side airbag. This can occur when a person is resting against the vehicle door at the time of side airbag deployment.
Some vehicle makers, such as Honda, limit the risk of injury to an out-of-position occupant through a seat-back sensor that suppresses the side airbag system. One way this system works is when a sensor mat that is located on the seat-back cushion assembly detects that an occupant is not in the proper position of leaning back against the seat, the side airbag is deactivated. Suppression systems may deactivate the side airbags when occupants are too near the deployment area or when the occupants are particularly vulnerable to injury (e.g., small children).
A type of restraint system called occupant position detection system (OPDS) measures occupant height and seat position to determine if the passenger seat-back airbag should be disabled. This seat-back airbag has an indicator lamp on the instrument cluster that illuminates when an occupant is detected in an unsafe position or if their backs are not pressed firmly against the seat back.
Conditions that may turn off the seat-back airbag include a small child leaning with his or her head in the deployment path of the side airbag, or an adult who is slouched forward (his or her back not fully contacting the seat) and leaning into the deployment path of the seat-back airbag. Either of these situations may injure the occupants if the seat-back airbag is allowed to deploy.
A mechanical seat-mounted side airbag uses no electronics, such as computers or electronic crash sensors. As the side of the vehicle structure moves in toward the occupant, the inner movement of the vehicle side structure contacts the igniter causing a detonation. When detonation occurs, gas generators are ignited and the side airbag is inflated.
Inflating a side curtain airbag is done using a cylinder of compressed gas. The primary function of a side curtain airbag is to protect a vehicle occupant’s upper body by reducing the force they might experience when their head and body make contact with the side of a vehicle.
Some side curtain airbags deploy during a vehicle rollover, side impact or frontal impact. Depending on the area, collisions that are outside of the vehicle maker’s frontal impact zone may not be sufficient enough to deploy the side curtain airbags.
A unique type of curtain airbag is called the head protection system (HPS) by BMW. This type of curtain (tube) airbag is different because instead of being a rectangular (blanket-type) airbag attached to the roof rail and hidden by the headliner, it is a tubular airbag that connects to the A-pillar and attaches back near the C-pillar. This tubular airbag has a rubber inner liner that does not permit the quick release of the inflation gases and causes the airbag to remain inflated until the warm gases inside the tube cool and change state.
Side window glass
New types of intrusion-resistant laminated glass may be found in door glass. This glass is similar to laminated glass used in vehicle windshields. On impact, the outer layers of glass will crack, but the glass tends to remain adhered to the inner-plastic layer. This type of glass will not shatter into the vehicle and accident area.
Vehicle makers are constantly working on improvements that will enhance occupant safety and distribute collision energy forces throughout the vehicle structure. To learn more about these vehicle systems, how they work, and how to repair them, consider attending the following I-CAR classes: Restraints (RES01 & RES02), Moveable Glass (GLA01), Stationary Glass (GLA02), Volvo Collision Repair (VLV01-VLV06, Vehicle Identification, Estimating Systems, And Terminology (DAM01), and Structural Straightening Steel (SSS01).