Setting the Record Straight: Seat Belt Overtightening
There are two issues related to a “tight fit” that often resurface in the CPS community:
Question #1: Can a seat belt be over tightened when installing a child restraint?
Typically, inspection stations and check up events find that loosely installed child restraints as one of the major misuses. However, we also have seen the issue of over tightening of the seat belt. Although the NHTSA curriculum states that child restraints should not move more than an inch in any direction when tested at the belt path, technicians often work with an overzealous caregiver or fellow technician. The overzealous caregiver or technician believes in the Zen experience that a child restraint must be “one with the car” in order to be safely installed. Our responses often include:
1. It isn’t necessary.
2. It isn’t any safer.
3. A caregiver would have difficulty in replicating that measure of tightness.
4. Always follow the manufacturer’s instructions.
These simple responses don’t always seem adequate for the overzealous caregiver or technician and often continue to over tighten the seat belt feeling that this is the best way to secure the child restraint safely. Recently, the Manufacturers Alliance for Child Passenger Safety, a group of child restraint manufacturers, was contacted about this issue.
This is their statement released on October 1, 2010 in reference to over tightening the seat belt:
Over-tightening a safety belt could damage a CR’s belt path and/or its lock-off*. CR’s should be installed according to the manufacturer’s instructions. Proper tightness should be confirmed by grasping the CR with one hand at or near the belt path and pulling on the CR. There should be no more than one inch of side-to-side or front-to-back movement at the belt path.
* Sunshine Kids does not endorse the statement above and it does not apply to any model Radian® car seat.
It is critical that technicians let go of the “one with the vehicle seat” mentality. Please work with any overzealous tech or parent to assure them that the manufacturers know best how to properly use their restraint.
Question #2: Can over tightening a seat belt affect built in occupant protection systems such as pretensioners?
We have also heard that over tightening the seatbelt may result in damaging the seat belt pretensioners that are an integral function of the built- in or automatic occupant protection system.
This is not the case and the Alliance offered this statement:
Manufacturers Alliance for Child Passenger Safety Statement for CPS Technicians/Instructors: Using Safety Belts with Pre-tensioners to install CRs:
Unless the CR manufacturer instructions state differently, using a safety belt with a pre-tensioner is allowed if allowed by the vehicle manufacturer.
2010 Members of the Manufacturers Alliance for Child Passenger Safety include: Britax, Chicco, Clek, Combi, Dorel Juvenile Group, Evenflo, Graco, Learning Curve (The First Years), Mia Moda, Orbit Baby, Recaro, Safe Traffic Systems, Sunshine Kids.
Vehicle manufacturers were contacted to get their perspective on over tightening CRSs with vehicle pretensioners.
Barbara Birkenshaw of Volkswagen Group of America, Inc.:
The vehicle seat belt can be loaded with more than 10 kN and it is not possible to tighten a CRS with more than 500N. So over-tightening may not be an issue.
Lisa-Townsend, Strategic Planning Specialist of Chrysler:
It would be difficult, if not impossible, for someone to damage the webbing or pretensioner of a seat belt when using it to install a child seat. The exception would be if something sharp was in contact with the webbing, it may be cut. Seat belts have to withstand pretty high forces during a crash that would be difficult for someone to achieve when tightening.
Julie Kleinert, Advanced Safety Development General Motors:
We have not had any issues with seat belt or belt pretensioner damage due to over-tightening of the seat belts in car seat installations.
M. Todd Moury, Engineering Group Manager - Advanced Product Development Active Safety Benchmarking / Validation of Delphi Electronics & Safety:
It is virtually impossible to over tighten a child seat into a vehicle without a mechanical aid of some sort. Most people who over tightened their seat belts utilized tightening devices . Others utilize the reclining seat mechanisms to apply the leverage necessary to over tighten the belt system. In this situation, they recline the seat and tighten the child seat in place then lever the seat back upright to further push the child seat against the belt system. Most often this situation happens in the reclining front seat locations which are not the best positions for the child.
Most reviewers/experts have concluded that the potential risks of damage to the seat belt and/or the child seat far outweigh the slight possibility that the child might be minimally better protected by a seat that has been excessively tightened into the vehicle. It simply is not necessary to excessively tighten a child seat into the vehicle.
However, the potential to damage the belt system can arise if the tightening device or the routing path of the child seat causes the belt webbing or other belt components to be damaged (frayed belts, cracked plastic, etc.). The over tightened seat belt can also damage the child seat (cracked plastic routing guides, cracked seat bases, etc.). It is also possible to tighten the seat belt so much that the seat belt buckle can become extremely difficult to disengage. This is caused by the excessively tightened belt driving increased forces on the friction surfaces within the buckle release mechanisms. In this situation, the parent may not be able to quickly remove the child seat / child from the vehicle if the need arises.
The CPS Express staff thank all the contributors to this article and offer this summary to technicians responding to the overzealous caregiver or technician who over tighten the restraint:
1. Always follow the manufacturer’s instructions.
2. It isn’t necessary.
3. It isn’t any safer.
4. A caregiver would have difficulty in replicating that measure of tightness.
5. It may damage the child restraint belt path and base as well as the lock-offs.
6. It may damage the seat belt buckle making it difficult to release to quickly remove the child seat and child from the vehicle in an emergency.
7. Always follow the manufacturer’s instructions.
It may also be reasonable to recognize that over tightening lower anchor attachments may result in similar ways. Stay tuned as our research unfolds!
)
