The HIC can be used to assess safety related to vehicles, personal protective gear, and sport equipment.
Normally the variable is derived from the measurements of an accelerometer mounted at the center of mass of a crash test dummy’s head, when the dummy is exposed to crash forces.
[1][2] where t1 and t2 are the initial and final times (in seconds) chosen to maximize HIC, and acceleration a is measured in gs (standard gravity acceleration).
The time duration, t2 – t1, is limited to a maximum value of 36 ms,[1][2] usually 15 ms.[3] This means that the HIC includes the effects of head acceleration and the duration of the acceleration.
A value of 700 is the maximum allowed under the provisions of the U.S. advanced airbag regulation (NHTSA, 2000) and is the maximum score for an "acceptable" IIHS rating for a particular vehicle.
[5] A HIC-15 (meaning a measure of impact over 15 milliseconds) of 700 is estimated to represent a 5 percent risk of a severe injury (Mertz et al., 1997).
A "severe" injury is one with a score of 4+ on the Abbreviated Injury Scale (AIS) [6] Data for specific vehicles can be found on various automotive review websites.
Some sample data is as follows, for comparative purposes: [11] A comprehensive searchable database of vehicles and their HIC scores is available at safercar.gov.
[13] Studies have been conducted in skiing and other sports to test adequacy of helmets [14]