NOCSAE Severity index
Football Helmet Testing
The NOCSAE Severity Index (SI) is a calculation of impact severity that has a well-established basis in science.
“A” is the instantaneous resultant acceleration expressed as a multiple of g (acceleration of gravity), dt is the time increment in seconds, and the integration (∫) is carried out over the essential duration (T) of the acceleration pulse.
Importance of the Severity Index
Other standards organizations base their testing on a simple measure of peak acceleration force (g’s) to measure a helmet’s ability to reduce forces experienced by the head during an impact. This method, however, does not consider the change in speed over time of an impact. NOCSAE’s SI gives a fuller picture of the severity of an impact event by incorporating the duration of the impact into its calculation. This is important because, in general, as the duration of the impact increases the potential for injury also increases. Human brains can withstand very high accelerations if the duration is short. Helmets that perform in testing below 1200 SI have been shown to reduce skull fracture, TBI, and other significant head and brain injuries. SI provides an accurate way to assess head injury risk that can be replicated across laboratories and under different impact scenarios.
Definition
A measure of the severity of impact with respect to the instantaneous acceleration experienced by the headform as it is impacted. Acceptable SI levels measured during impact cannot exceed the limit specified in the relevant NOCSAE standard performance specification.
Related Information
See brief videos about test methods required in NOCSAE standards and read quick facts about our biofidelic headform.