Interpretation ID: nht78-3.18
DATE: 02/16/78
FROM: AUTHOR UNAVAILABLE; J. J. Levin, Jr.; NHTSA
TO: Volvo of America
TITLE: FMVSS INTERPRETATION
TEXT: This responds to your letter of December 20, 1977, enclosing a previous letter requesting an interpretation of paragraph S4.3(j) of Safety Standard No. 209, Seat Belt Assemblies. I am sorry that your earlier letter was misplaced.
Volvo is correct in its interpretation that the requirements for emergency locking retractors in S4.3(j)(2) and (3) were promulgated for reasons of comfort and convenience, although this in turn is directed toward a safety objective. As you know, the more comfortable and convenient belts are, the more likely they will be worn by motorists. Further, the requirements in these paragraphs assure that the driver can make necessary movements in the occupant compartment safely.
Paragraph S4.3(j)(2) specifies that an emergency locking retractor
"shall not lock, if the retractor is sensitive to webbing withdrawal, before the webbing extends 2 inches when the retractor is subjected to an acceleration of 0.3g or less."
Volvo interprets this to require that the retractor not lock before the webbing extends 2 inches when the webbing is subjected to an acceleration of 0.3g. This is incorrect. The requirement specifically states that the retractor is to be accelerated. The agency does not agree that keeping the belt stationary and accelerating the retractor is equivalent to keeping the retractor stationary and accelerating the belt. This is due to the fact that inertial forces react upon the retractor during its acceleration that are not present when the webbing alone is accelerated. Therefore, results from the two methods of testing could differ significantly.
I hope this has been responsive to your inquiry, and if we can be of any further assistance please let us know.
Sincerely,
ATTACH.
December 20, 1977
Hugh Oates -- Office of Chief Council, National Highway Traffic Safety Administration
Dear Mr. Oates:
As per our telephone conversation, enclosed is one copy of Volvo's Request for Interpretation FMVSS #209 dated April 4, 1977.
We are looking forward to your response to this request for interpretation.
If additional information is required on this subject, don't hesitate to contact the undersigned.
Sincerely yours, William Shapiro PE -- Regulatory Analysis Engineer
ENC.
April 4, 1977
Frank Berndt -- National Highway Traffic Safety Administration
Re: Request for Interpretation FMVSS #209
Dear Mr. Berndt,
Volvo requests interpretation of certain provisions in Section 4.3(j) of FMVSS #209.
S4.3 (j) Emergency-locking retractor
An emergency-locking retractor of a Type 1 or Type 2 seatbelt assembly, when tested in accordance with the procedures specified in paragraph S5.2(j) -
(1) Shall lock before the webbing extends 1 inch when the retractor is subjected to an acceleration of 0.7g;
(2) Shall not lock, if the retractor is sensitive to webbing withdrawal, before the webbing extends 2 inches when the retractor is subjected to an acceleration of 0.3g or less;
(3) Shall not lock, if the retractor is sensitive to vehicle acceleration, when the retractor is rotated in any direction to any angle of 15 degrees or less from its orientation in the vehicle.
It is our interpretation that the requirements in Section 4.3(j)(1) were promulgated for safety reasons, while the requirements in Section 4.3(j)(2) & (3) were promulgated for comfort requirements for webbing acceleration sensitive retractors and vehicle acceleration sensitive retractors respectively.
Because we believe that the requirements in Section 4.3 (j)(2) were promulgated to prevent premature locking of the retractor when the webbing is being withdrawn, we interpret this to require that the retractor shall not lock before the webbing extends 2 inches when the webbing is subjected to an acceleration of 0.3 g or less. Is this interpretation correct? Also, we would like to point out that in our opinion testing the emergency-locking retractor system in the following two manners gives the same results.
1) Keeping the belt stationary and accelerating the retractor and
2) Keeping the retractor stationary and accelerating the belt.
If there are any questions pertaining to this issue, please feel free to contact me at your convenience.
In advance, thank you for your attention to this matter.
Sincerely, William Shapiro, P.E. -- Regulatory Analysis Engineer