9.2 Impact Attenuation, Gmax & HIC

9.2 Impact Attenuation, Gmax & HIC

Domain 2B turns the F1292 label into numbers a CPSI can use. The laboratory method drops an instrumented metal headform onto a surfacing sample and records the acceleration/time pulse. Two scores come out of that pulse. G-max (also written Gmax) is the peak deceleration during the impact, expressed in units of gravity. The Head Injury Criterion (HIC) is a calculated integral of that acceleration pulse over the most severe time window. Long-standing ASTM F1292 teaching thresholds used throughout CPSI work are a maximum G-max of 200 and a maximum HIC of 1,000. Those numbers live in F1292. They are not a CPSC statute, and CPSC Handbook 325 (July 2025) does not publish a different pair. Do not invent a third unpublished limit, a "preferred" G-max of 150, or a sliding HIC scale. If a question stem asks for the F1292 fail thresholds, answer 200 and 1,000.

Either limit exceeded is a fail

A surface system fails F1292 when either score is exceeded. G-max above 200 is a fail even if HIC is under 1,000. HIC above 1,000 is a fail even if G-max is under 200. Both over the line is still one fail, not a special category. The exam loves the half-pass trap: a candidate who treats "G-max of 190 and HIC of 1,080" as acceptable because the peak G looked fine. It is not acceptable. The two criteria are independent gates. You need both gates closed.

Those thresholds exist to reduce the risk of a life-threatening head injury. They do not promise a bruise-free playground. CPSC §2.4 says a fall onto a shock-absorbing surface is less likely to cause a severe head injury than a fall onto a hard surface, and that some moderate injuries may occur no matter what material is used. Do not tell an owner that a passing F1292 report means children will not break wrists or collarbones. The test is a head-injury performance envelope, not a general-injury waiver.

Critical height is a laboratory rating

CPSC §1.8 defines critical height as the fall height below which a life-threatening head injury would not be expected to occur. Section 2.4 then explains how you get that number: laboratory testing using the methods in ASTM F1292 provides a critical-height rating of the surface. CPSC treats that height as an approximation of the fall height below which a life-threatening head injury would not be expected. Manufacturers and installers of playground protective surfacing should provide the critical-height rating of their materials. This rating should be greater than or equal to the fall height of the highest piece of equipment on the playground.

Fall height is a different term. CPSC defines it as the vertical distance between the highest designated play surface on a piece of equipment and the protective surfacing beneath it. Domain 2D and Domain 2E spend full sections on how to measure those two heights on slides, swings, climbers, and composites. Domain 2B only requires the relationship: the F1292 critical-height rating must meet or exceed the site's fall height. A 10-foot critical-height system under a 6-foot deck can be the right product. A 6-foot critical-height system under a 10-foot climber is the wrong product, even if the bag is IPEMA-labeled and the color matches the park brand.

F1951 is not F1292

ASTM F1951, Standard Specification for Determination of Accessibility of Surface Systems Under and Around Playground Equipment, measures how much work it takes for a wheelchair user to propel across the surface — firmness and stability, not head-injury attenuation. CPSC §2.4.2 tells owners of engineered wood fiber and rubber mulch to request both F1292 critical-height data and Americans with Disabilities Act / Architectural Barriers Act accessibility information based on F1951. That pairing is the teaching point. An F1951 laboratory report that says a surface is wheelchair-maneuverable does not say the surface passed G-max 200 and HIC 1,000 at the playground's fall height. A thick, soft loose-fill that attenuates beautifully can fail F1951 because wheels sink. A firm unitary tile that rolls easily can fail F1292 if it is too thin for the fall height. Accessibility law and impact-attenuation performance are both required conversations. One laboratory binder does not close the other.

The report must match the installed system

An International Play Equipment Manufacturers Association (IPEMA) certification mark or a manufacturer's F1292 report is evidence about a specified system at a specified thickness. It is useful only when all of the following are true:

• The report is for the same product system that was installed — the same unitary formulation, the same engineered wood fiber specification, the same loose-fill rubber, not a cousin product from the same catalog.
• The report's thickness matches the installed thickness. A 3.5-inch poured-in-place system does not inherit a 4.5-inch laboratory rating.
• The report's critical-height rating is greater than or equal to the fall height of the equipment it serves.
• The report is current enough to represent the product as sold. A faded 2009 printout for a discontinued formulation is not a 2026 compliance file.

IPEMA is a voluntary third-party product-certification program. It is not a field test and not a substitute for a site inspection. Domain 2C will say the same thing about a sticker on a bag of engineered wood fiber after the fiber has compacted and kicked out.

Heat, color, and what the drop test does not measure

CPSC §2.4.2.1 warns that some dark-colored unitary surfacing exposed to intense sun has caused blistering on bare feet. Check whether light-colored materials are available, or provide shade to reduce direct sun. Supervisors are told in §2.2.7 to check whether equipment and surfacing feel hot before children play and to make sure children wear footwear. Those are real injuries and real inspection notes. They are not G-max or HIC. A surface can pass F1292 in a laboratory and still burn feet at 2 p.m. in July. Write the heat finding as a maintenance and design issue, not as an impact-attenuation fail, unless you also have F3313 data that shows the hot or aged surface no longer meets 200 / 1,000.

Compressed into one inspection sentence: the surface system under this equipment has an F1292 critical-height rating that meets or exceeds this fall height; the laboratory G-max and HIC stay at or under 200 and 1,000; the report matches the installed thickness; F1951, if required for the accessible route, is a separate binder; and dark unitary in full sun is a blistering hazard even when the drop test passes.