A critically integral part of safety equipment is the driver restraint assembly, known simply as the seat belt. It is meant to keep the driver securely inside the vehicle’s roll cage (when applicable) where the least amount of injury will occur in a crash. A restraint assembly consists of several components which include but are not limited to:
– The shoulder harness is a belt assembly, one strap for each shoulder, intended to restrain movement of the upper torso and shoulder regions.
– The lap belt restrains movement of the pelvis.
– The anti-submarine strap prevents the pelvis from slipping forward from under the lap belt in the event of an accident.
– The buckle attaches the belts together. There are 3 types of buckles to choose from: latch/lever, turn/push, and cam lock.
Seat belts, especially in racing and motorsport applications, should be inspected and re-certified every 2 years due to degeneration over time and from exposure to the elements. Prolonged exposure of seat belt webbing and thread to sunlight can cause degradation of the fibers, which may lead to the loss of restraint integrity. The rate at which the breaking strength of the webbing decreases with outdoor exposure can result in up to 50% of its restraint strength in as little as one year. Old and weakened belts could easily snap under the loads imposed upon them in an accident. This is why replacement of the webbing every two years is essential to driver safety.
It is important to look for belts that are certified to meet performance specifications. Manufacturers whose products pass the standard laboratory tests participate in the SFI Foundation’s certification program. SFI is a non-profit organization established to issue and administer standards for all kinds of specialty/performance automotive & racing equipment. SFI standards primarily affect manufacturers of equipment as well as the rules for race sanctioning bodies. The consumer benefits from the program because it establishes recognized levels of performance and quality for a product, such as critical items like driver restraint assemblies. The standard that applies to safety belts is SFI Specification 16.1.
Specifications are created through a committee compromised of individuals from all facets of the industry who provide a comprehensive cross-section of knowledge. The effectiveness of a restraint assembly is also influenced by attachment techniques. The principal precaution for installing the mounting hardware to the vehicle is to minimize bending stress in the fitting by making sure the belts pull from a straight angle against the hardware. The attachment points must provide the optimum geometry to minimize movement of the belts. Lap belts perform best when they act at an angle between 45 and 55 degrees relative to the longitudinal axis of the vehicle. This angle permits the lap belt to react to the upward pull of the shoulder harness. A system installed with a shallow belt angle (less than 45 degrees) permits the shoulder harness to pull the lap belt up off the pelvic area and into the abdominal region with the likelihood of injury to internal organs. The end attachments of the shoulder harness must also be installed at appropriate angles. The ideal position for the shoulder harnesses are anywhere between 5 degrees and 30 degrees above the driver’s shoulder. Anything angle above 30 degrees or below 5 degrees is considered excessive. If the upper attachment point falls significantly below the driver’s shoulder (under 5 degrees), then a spinal compression injurt is likely to occur. In an accident situation, the shoulder belts pull down and back on the torso as they resist the forward motion of the driver. The resultant restraint force compresses the spinal column and will add to the stresses in the spine already caused by the force of the crash impact. If the upper attachment of the harnesses are too far above the shoulder (greater than 30 degrees), then two problems may occur. First, tension in the shoulder harness is increased and undue stress is applied to the harness and its structural attachments. Second, excessive angle will cause excessive motion. If the harness belts are too far above the shoulder, they will provide little resistance to forward motion of the driver’s upper torso. The result is impact with the steering wheel and the possibility of neck injury. The shoulder straps should also be 3-6″ apart behind the driver’s neck to prevent slippage off the shoulders.
The reliability of a restraint system is greatly affected by the way it is installed. It is imperative to follow the installation instructions provided by the seat belt manufacturer. The necessity of replacing or re-webbing seat belts every two years is quite important. As cars become more advanced and consequently go faster, everything possible must be done to make the racing experience safe as well as fun. Failure to do so can cause serious injury, or worse. Anything is possible and it is best to be prepared in order to prepare to be the best.