Interpretation ID: 24207.jeg

Jim Smith, Managing Engineer
Exponent
Failure Analysis Associates
1850 West Pinnacle Peak Road
Phoenix, AZ 85027

Dear Mr. Smith:

This responds to your letter concerning the calculation of chest g's for purposes of Standard No. 208, Occupant Crash Protection.

S6.3 of Standard No. 208 provides that, in specified tests, chest acceleration "shall not exceed 60 g's, except for intervals whose cumulative duration is not more than 3 milliseconds." You stated that your company's procedure totals up the maximum peaks and checks that the resultant acceleration does not exceed 60 g's, except for intervals whose cumulative duration is not more than 3 milliseconds. However, you have learned that NHTSA's Signal Analysis Software, consistent with SAE J1727, calculates chest g's with the 3 millisecond clip limit determined on a continuous basis. The practical effect of this latter approach is that chest g's will sometimes be lower (but never higher) than the former approach. You also noted that the "cumulative duration" language also appears in Standards No. 203 and No. 213.

Thank you for bringing this matter to our attention. We plan to initiate rulemaking shortly to address this issue.

Sincerely,
Jacqueline Glassman
Chief Counsel
ref:208
d.7/2/02