The purpose of this report is to present the methodology used to determine how sensitive helmets are to impact attenuation tests on the flat anvil in the range of impact velocities 5.8 m/s to 6.2 m/s. This report is the product of a larger study, and the results presented here are preliminary. Specifically, an experiment was conducted to measure the effect on the cumulative dwell time at accelerations greater than 200g for helmets tested on a flat anvil at the extreme ends of the tolerance interval.

When likely confounding effects such as conditioning of a helmet, headform size, model of helmet, drop sequence, and location of impact on the helmet are taken into account, the difference in the values of dwell200 measured at the extreme ends of the velocity tolerance interval is essentially zero at a level of significance of .05. The implication is that the criterion of failing a helmet based on dwell200 will remain valid should the velocity at the moment of impact lie within the interval (5.8 m/s , 6.2 m/s).