Interpretation ID: 18561graco.a
Steve Gerhart, Product Compliance Engineer
Graco Children's Products Inc.
51 S. Pine St.
P.O. Box 100
Elverson, PA 19520
Dear Mr. Gerhart:
This responds to your letter to the National Highway Traffic Safety Administration (NHTSA) asking several questions about S5.4.3.2 of Federal Motor Vehicle Safety Standard No. 213, "Child Restraint Systems." I apologize for the delay in our reply.
Section S5.4.3.2 states, in pertinent part:
S5.4.3.2 Direct restraint. Except for a child restraint system whose mass is less than 4.4 kg, . . . each Type I and lap portion of a Type II vehicle belt that is used to attach the system to the vehicle shall, when [dynamically] tested in accordance with S6.1, impose no loads on the child that result from the mass of the system . . .
You ask about several final rules that amended S5.4.3.2, resulting in the text quoted above. Your questions relate to whether the agency has data showing a safety problem with child restraints having masses greater than 4.4 kg, and how NHTSA would test such a restraint to the requirement of S5.4.3.2.
The following background would be helpful in answering your questions.
Background
Prior to the amendment of S5.4.3.2, that section only applied to belts that were (a) part of a child restraint system; (b) designed to restrain a child using the system; and (c) designed to attach the system to the vehicle. These belts were prohibited from imposing any load on the child, resulting from the mass of the system, during the standard's dynamic test.
In a March 16, 1994 notice of proposed rulemaking (NPRM), NHTSA proposed to expand S5.4.3.2 to apply it also to each Type I (lap) and the lap portion of a Type II (lap/shoulder) vehicle belt that is used to attach the child restraint to the vehicle. These belts, which anchor the child restraint to the vehicle, function to absorb the forces of the crash into the frame of the vehicle. In the proposal, NHTSA tentatively concluded that, to protect the restrained child from the crash forces absorbed by these belts, the belts should be prohibited from transferring those crash forces to the child.
Several persons commenting on the proposal stated that the proposal would eliminate high-back belt-positioning booster seats from the marketplace. These boosters, which have backs supporting the head, neck and back of a child, are designed to restrain the child using a vehicle's Type II (lap/shoulder) belt. Some commenters stated that all belt-positioning boosters with seat backs will impose a load on the child through the lap belt portion (as well as the shoulder belt portion) of a Type II vehicle belt. The commenters were concerned that eliminating belt-positioning boosters was undesirable because there were no data showing a safety problem, and because the boosters were believed to perform well with Type II belts. Commenters also expressed concern that it was not practical to measure the load imposed on the test dummy. Some commenters suggested retaining the proposal but excluding any booster with a mass of less than 4 kilograms (kg) from the requirement. Four (4) kg was believed to be the maximum mass of belt-positioning boosters then on the market.
In a July 6, 1995 final rule, NHTSA responded to these commenters by stating that it did not intend to prohibit belt-positioning boosters with backs, nor did the agency believe there was a sufficient safety problem to warrant prohibiting current designs of such seats. Nonetheless, NHTSA further stated that it believed that limits on belt loading should be established to keep in check the potential for injury due to overloading a child occupant, such as from a "massive seat back" on a child restraint.
The agency adopted the approach suggested by some commenters of retaining the requirement, but excluding from it any restraint with a mass of less than 4 kg. The approach was consistent with requirements in Europe and with what the agency had believed to be the U.S. market at the time. NHTSA believed there was no data showing that a child restraint with a mass less than 4 kg imposes harmful loads on a child.
Gerry Baby Products petitioned for reconsideration of the amendment. Gerry said that NHTSA's belief that all the belt-positioning seats in the U.S. have a mass less than 4 kg was incorrect. Gerry stated that it sold seats with a mass of up to 4.4 kg, and had received no report of any problems or injuries associated with loads imposed on children by the booster seats.
In a June 18, 1996 response to the petition, NHTSA increased the 4 kg limit to 4.4 kg. NHTSA had been unaware that there were boosters with a mass greater than 4 kg (no commenter to the NPRM had indicated otherwise). The agency increased the limit based on Gerry's experience which had indicated that boosters with a mass up to 4.4 kg had not imposed unsafe loads on children.
The 1995 decision to limit the potential for overloading a child from elements such as a massive seat back on a belt-positioning seat departed from a July 21, 1994 rule that first established requirements for belt-positioning seats. In the 1994 rulemaking, the agency decided not to specify limits on seat back loading. The agency believed there was a lack of data indicating a safety problem and there was no procedure for measuring loads or for determining a threshold value for the loads imposed. In the 1995 rule, the agency explained that in 1994 it had not considered that a lap belt portion of a Type II belt system could transfer crash forces to a child from the back of a belt-positioning booster seat. The agency stated that after further consideration, in the context of S5.4.3.2, it had determined that a limit on the mass of the booster seat back was warranted to avoid potential injury to the child occupant.
With this background in mind, we turn to your questions, which we have restated below. Our answers follow each question.
Discussion
You first ask about NHTSA's 1995 decision to limit the mass of the seat back of belt-positioning seats after it had initially decided against doing so in 1994. You ask:
1. Was there any testing done after this [1994] rule was issued to confirm or deny [some commenters' beliefs that NHTSA ought to limit the weight of booster seats]? What was the outcome, or where could I find this information? Does NHTSA feel that higher booster seat weight would result in higher HIC's, G forces and excursions? Would this data be available also?
NHTSA did not conduct testing to confirm or deny the views that booster seats should be restricted in weight to limit overloading the child occupant. At the time of the rulemaking, and continuing to today, there are no test dummies that can reliably measure abdominal loading, nor is there an established injury criterion that correlates abdominal loads to the likelihood of injury. Also, there was, and is, no established test procedure in Standard 213 that measures seat back loads on the child dummy and that correlates those to injury. Yet, it was believed that seat back loads could, at some level, injure a child in a crash, when loads were excessive. In view of the confines at the time of the rulemaking on developing a test that would distinguish between excessive and acceptable loads on the child occupant, NHTSA adopted an alternative approach that limits loading by way of limiting the mass of the booster seat. The agency had insufficient data on which to determine whether we agreed or disagreed with the belief expressed by a commenter that increasing booster seat weights results in higher HIC's, G forces or excursions.
Your second question asks about the agency's 1995 decision to limit the potential for injury due to overloading the child from "a massive child seat back." You ask:
2. What does the agency see as massive? Is there any data or history on seats viewed as massive that injured a child due to back loading? If so, how much did the seat weigh? If there are no data, would there be an acceptable method to test the loads imposed on the back of the child, and how would threshold values be determined?
NHTSA has not identified a value above which injury could result from loading a child occupant and below which injury is not likely to occur. Yet, child restraints with a mass of less than 4.4 kg are viewed as not likely to injure, based on the field experience of Gerry Baby Products with its 4.4 kg booster seat.
We do not know of actual injuries caused by seat back loading. However, in 1996, the Federal Aviation Administration (FAA) and NHTSA conducted a rulemaking relating to excessive seat back loads in the aircraft environment (61 FR 28423, June 4, 1996)(copy enclosed). FAA sought to prohibit the use of backless boosters seats on aircraft because it believed the seats were incompatible with aircraft seats that have a "breakover" seat back. (A breakover feature allows the seat back to rotate forward easily when impacted by an occupant from behind.) FAA determined that a child dummy restrained in a backless booster seat experienced an increase in abdominal loading when an adult dummy in the seat rearward of the child impacted the seat back. The increase in loading was unacceptable to FAA, although it was recognized that there are no accepted criteria to assess the relationship between differences in measured levels of abdominal loadings and any resulting risk of abdominal injury, and the type and severity of such injury. FAA's methodology for the research program is discussed in NHTSA's 1996 final rule, a copy of which is enclosed for your information.
3. How is a restraint tested if it is over 4.4 kg? How are loads measured in S6.1 if the restraint is over 4.4 kg?
A restraint that is over 4.4 kg is evaluated to ascertain compliance with the requirements of S5.4.3.2 in accordance with NHTSA's laboratory test procedure for that section, which you ask about in your fourth question. The evaluation is based on a visual inspection. NHTSA believes that all belt-positioning booster seats with a back will load the child through the lap belt portion of a Type II belt. Thus, a belt-positioning seat, unless excepted because it is less than 4.4 kg, generally will not meet S5.4.3.2. In essence, that section functions to limit the mass of belt-positioning boosters with backs.
4. In the Laboratory Test Procedure for FMVSS 213, the section 5.4.3.2 for Direct Restraint Belts (page 104) lists 3 yes/no questions as pass/fail criteria, with 3 yes answers failing the restraint. The questions are: (1) Belt/dummy contact for restraint; (2) Rigid structure behind dummy; and (3) Belt/child restraint slip possible. What does the third criterion mean? How does the 4.4 kg requirement within FMVSS 213 relate to this testing procedure?
The three criteria indicate the factors which NHTSA evaluates to determine whether a child restraint meets S5.4.3.2. A restraint fails if all three criteria are answered "yes." If only two of the questions result in a "yes," then we determine there is no loading of the child dummy. Under (1), to determine whether S5.4.3.2 applies, the agency checks to see if the belt in question contacts the dummy. Under (2), the agency checks to see if there is rigid structure between the dummy and the back of the standard seat assembly because that structure could impose excessive loads on the child. Under (3), NHTSA checks to see if the child restraint can move ("slip") relative to the belt system. A child restraint that moves forward against a relatively stationary belt can load the child occupant.
I hope this information is helpful. Again, my apologies for the delay in responding. If you have further questions, please contact Deirdre Fujita of my staff at (202) 366-2992.
Sincerely,
Frank Seales, Jr.
Chief Counsel
Enclosure
ref:213
d.2/22/99