Head Injury Criterion (HIC)

Description

The Head Injury Criterion (HIC) measures the severity of translational head acceleration over the most severe interval of a specified maximum duration. WebSAT also reports the Skull Fracture Correlate (SFC) over the HIC interval and associated injury probabilities [1] [2].

When this feature is available

HIC becomes available when either the current curve selection or any loaded test contains a head-acceleration measurement set that meets the requirements. Only channels with a usable data status count.

The required measurement set contains either:

• One resultant head-acceleration channel with units G'S; or
• All three component channels at the same head location:
  • Axis: X - LOCAL, Units: G'S
  • Axis: Y - LOCAL, Units: G'S
  • Axis: Z - LOCAL, Units: G'S

The signal attachment may be HEAD CG or HEAD 9 ARRAY - CENTER. WebSAT checks each occupant or test subject independently, prefers the three component channels when both input paths are available, and prioritizes channels marked PRIMARY.

Settings

Setting	Default	Options
Filter Input Signal(s)	On	On or off
Filter CFC	1000	60, 180, 600, or 1000
HIC Window	15 ms	15 ms or 36 ms

How WebSAT processes the data

1. Load the resultant acceleration or calculate it from X, Y, and Z components.
2. Apply the selected filter when enabled and express acceleration in g and time in seconds.
3. Search all intervals no longer than the selected HIC window for the maximum value:

$HIC=(t_2-t_1)\left[\frac{1}{t_2-t_1}\int_{t_1}^{t_2}a(t)\,dt\right]^{2.5}$

4. Report the governing interval and calculate SFC from the average acceleration over that interval.
5. Evaluate the available AIS 2+ and AIS 3+ HIC risk functions and the SFC skull-fracture probability.

Reference values and injury risk

The ATD-specific HIC values below follow the published IARVs and the applicable FMVSS performance limits for adult and child dummies [3] [4] [5].

ATD	HIC15 IARV	HIC36 IARV
Q3s	570	—
CRABI 6-month	377	—
CRABI 12-month	390	1000
CRABI 18-month	440	—
Hybrid III 3-year-old	570	1000
Hybrid III 6-year-old	700	1000
Hybrid III 10-year-old	741	—
Hybrid III 5th female	700	—
Hybrid III 50th male	700	1000
Hybrid III 95th male	670	—
SID-IIs	779	1000
BioSID	700	—
ES-2re	—	1000

ATDs without a populated HIC15 or HIC36 value do not receive an ATD-specific HIC reference value. The risk probabilities can still be calculated from the HIC result because the risk relationships are not ATD-specific.

WebSAT reports AIS 2+ and AIS 3+ probabilities from the HIC risk relationships used by NHTSA [6]:

$P(AIS\,2+)=\Phi\left(\frac{\ln(HIC)-6.96362}{0.84687}\right)$

$P(AIS\,3+)=\Phi\left(\frac{\ln(HIC)-7.45231}{0.73998}\right)$

SFC probability uses the logistic relationship published by Vander Vorst et al. [2].

Results

HIC summary for the left- and right-front-seat occupants in test 10099.

Resultant head acceleration with the governing HIC interval highlighted.

HIC injury-risk curves with the calculated result marked.

Three-dimensional head-acceleration trajectory for the selected occupant.

The summary table reports the subject, HIC value, interval start and end, and skull-fracture risk. The result plots show the resultant acceleration with the governing HIC window, the HIC and SFC injury-risk relationships, and the three-dimensional head-acceleration trajectory.

References

[1] Hertz, E. “A Note on the Head Injury Criterion (HIC) as a Predictor of the Risk of Skull Fracture.” 37th Annual Proceedings of the Association for the Advancement of Automotive Medicine, 1993.

[2] Vander Vorst, M. et al. “Statistically and Biomechanically Based Criterion for Impact-Induced Skull Fracture.” Annual Proceedings of the Association for the Advancement of Automotive Medicine, 47, 2003, pp. 363–381.

[3] Mertz, H. J. “Anthropomorphic Test Devices.” In Accidental Injury: Biomechanics and Prevention. Springer, 1993, pp. 66–84.

[4] National Highway Traffic Safety Administration. “Federal Motor Vehicle Safety Standards; Occupant Crash Protection; Final Rule.” Federal Register, 65(208), 2000, pp. 67691–67703.

[5] National Highway Traffic Safety Administration. 49 CFR § 571.213b—Child Restraint Systems.

[6] National Highway Traffic Safety Administration. Evaluation of Belted and Unbelted Safety Requirements. DOT HS 812 232, 2015.