The following graph can be found within the technical ASTM 1292/3351 standards. The bottom of the graph shows the Head Injury Criteria (HIC) range from 0 to 3000. The left side shows the likelihood of injury as a percentage while the graph lines are color-coded to reflect the severity of injury as described in the legend on the right and as defined within the standard.
You will note that the 1000 HIC requirement set forth in the standard is the point at which a critical head injury begins to depart from zero, and the likelihood of a minor injury is about 95%.
