Interpretation ID: nht73-1.48

DATE: 11/08/73

FROM: JOHN G. WOMACK FOR RICHARD B. DYSON

TO: American Safety Equipment Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This is in reply to your letter of October 5, 1973, concerning your proposed use of a tension reliever device in a seat belt retractor. As we understand the concept of the tension reliever, it allows a small amount of slack to be introduced into the webbing by a mechanism roughly similar to that of a window shade. If the webbing is pulled smoothly back and forth, the retractor exerts a normal retractive force. If, however, the retraction is halted at a certain point, as when the belt comes to rest against an occupant's shoulder, the reliever engages and the occupant is relieved of the active pull of the retractor until he moves forward by an inch or two and disengages the reliever.

Your initial question is whether a reliever-equipped retractor will be considered to meet the retraction force requirements of S4.3(j) (6) of Motor Vehicle Safety Standard No. 209. You state that it will meet the test so long as the procedures of S5.2(j) are strictly observed and no oscillations are introduced by the test apparatus. If the facts are as you state, it is our opinion that the retractor would meet. S4.3(j) (6).

Your other question, as clarified by telephone on November 1, 1973, is whether we have reservations about the concept of a tension reliever that would lead us to bar its use through amendment of Standard No. 209. Based on the information presently available, we have no such reservations.