Head injury criterion

Key takeaways

Head injury criterion belongs to mathematics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Head injury criterion to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Head injury criterion from memory before moving on to harder problems.

Reference excerpt

The head injury criterion (HIC) is a measure of the likelihood of head injury arising from an impact. 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. It is defined as:

H I C = max t 1 , t 2 { ( t 2 − t 1 ) ⋅ [ 1 t 2 − t 1 ∫ t 1 t 2 a ( t ) d t ] 2.5 } {\displaystyle {\mathit {H}}{\mathit {I}}{\mathit {C}}=\max _{t_{1},t_{2}}{\bigg \{}(t_{2}-t_{1})\cdot {\bigg [}{\frac {1}{t_{2}-t_{1}}}\int _{t_{1}}^{t_{2}}a(t)dt{\bigg ]}^{2.5}{\bigg \}}} 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, usually 15 ms. This means that the HIC includes the effects of head acceleration and the duration of the acceleration. Large accelerations may be tolerated for very short times. At a HIC of 1000, there is an 18% probability of a severe head injury, a 55% probability of a serious injury and a 90% probability of a moderate head injury to the average adult.

Automobile safety HIC is used to determine the U.S. National Highway Traffic Safety Administration (NHTSA) star rating for automobile safety and to determine ratings given by the Insurance Institute for Highway Safety. According to the Insurance Institute for Highway Safety, head injury risk is evaluated mainly on the basis of head injury criterion. 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. 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) Data for specific vehicles can be found on various automotive review websites. Some sample data is as follows, for comparative purposes:

The 1998 Ford Windstar, marketed as one of the safest minivans of that year, tested out to a HIC=305 score for driver A small car, a 1998 Dodge Neon, tested at HIC=265. A common family sedan, a 1998 Toyota Camry, tested at HIC=288. A 2007 Camry at HIC=175.

A comprehensive searchable database of vehicles and their HIC scores is available at safercar.gov Archived 2010-05-22 at the Wayback Machine.

Athletics and recreation Sport physiologists and biomechanics experts use the HIC in the research of safety equipment and guidelines for competitive sport and recreation. In one study, concussions were found to occur at HIC=250 in most athletes. Studies have been conducted in skiing and other sports to test adequacy of helmets

Worked examples

Example 1 — a first encounter with Head injury criterion

Start with the simplest possible case. Write down what Head injury criterion claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In mathematics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Head injury criterion before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Head injury criterion ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Head injury criterion

In research: Head injury criterion appears in mathematics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Head injury criterion in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Head injury criterion is common in secondary-school and first-year university syllabi. It links to neighbouring topics Automotive safety, Brain injury, Mathematical modeling, so understanding it makes those chapters shorter.
In everyday life: Look for Head injury criterion outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Head injury criterion in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Head injury criterion means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Head injury criterion out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Head injury criterion in simple terms?

The head injury criterion (HIC) is a measure of the likelihood of head injury arising from an impact. The HIC can be used to assess safety related to vehicles, personal protective gear, and sport equipment.

Why does Head injury criterion matter?

Because it connects several mathematics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Head injury criterion?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Head injury criterion.