What is a “G-Max Test?” A “Body” Impact Test
By partnering with leading testing facilities and universities around the world, Brock has been able to push the safety standards for the artificial turf industry forward. The current standard measurement for the “safety” of a playing surface is the Gmax test. According to the Penn State Center for Turfgrass Science, impact attenuation of a playing surface is measured by an accelerometer mounted inside the missiles, that indicates surface hardness and is reported as Gmax. The Gmax test essentially measures how fast the drop missle stops. The higher the g-max value, the poorer the shock-attenuation performance of the surface. Measuring impact-attenuation is a fundamental tool of athletic field safety testing. It is also useful in assessing the playability of a field. The Gmax test uses a 20 lb flat missile, so it best simulates a non-head surface impact, and does not measure head impact severity. To get an understanding of head impacts we recommend conducting a HIC test, which uses a spherical missile and better simulates a person’s head.
The GMax of a field is determined by dropping the missile 3 times in the same location and averaging the second two drops. It requires the missile to be dropped in a minimum of 10 locations around the field. No area on the field should be higher than 165 G’s (Synthetic Turf Council Guidelines). It is possible, and quite common, to have areas of the field with very high Gmax scores, while other areas (such as sidelines) with low Gmax Scores, so the field average may pass, yet have areas that would be considered unacceptable.
GMax is one benchmark at which to rate each field. Using GMax in combination with HIC and Vertical Deformation and obtaining scores equivalent to those of natural turf has led to dramatic improvements in playing surfaces in regards to players’ safety AND performance.
ASTM F355 A-Missile Measurements Tester
This test simulates impact attenuation of a playing surface.
Designing Artificial Turf Fields to Exceed G-Max Standards
ONE THING IS CERTAIN: SYNTHETIC TURF OVER ROCK GETS HARD OVER TIME. TOO HARD.
Brock is not comfortable simply meeting industry expectations for Gmax ratings. Our standard for a field with Brock is pristine natural grass, because that is the surface that every athlete would rather play on. The industry believes a Gmax of less than 165 G’s is acceptable, but natural grass Gmax ratings range between 70-115 G’s, so why would anyone accept 165?! But there are three main reasons fields get hard over time when installed directly over stone: Hours of use, climate, and maintenance (or lack thereof). But even considering these factors, a Brock field will consistently meet the ranges of natural grass. We’re so confident in our fields performing well in a Gmax test that we’ve developed the GMax Guarantee tied to our PowerBase line of products. And our Shock Pad Series will also deliver a GMax value in the range of great natural grass.
Beyond The G-Max Test: Testing for Head Injury Criterion & Deformation
There are three measurements used to characterize safety and performance of a surface
HIC is the internationally recognized test standard for head injuries. The test method has also now been accepted by ASTM as Test Method F355-16. It drops a 10 lb hemispherical impactor from increasing heights to determine Critical Fall Height. It’s the same test used in playgrounds, automotive crashes, wall padding, pole vault, and the WR Reg22 standard for artificial turf. The higher the Critical Fall Height, the more protective the surface is for head injuries.
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(FIRMNESS UNDER FOOT)
This test simulates the heel strike of an adult running athlete in stride. This is the softness or hardness under foot during play. A great natural grass field hits the “sweet spot” of being firm under foot while producing very low gmax and high Critical Fall Height. Which is why quality natural turf is the benchmark for quality artificial turf.
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When Artificial Turf Fields DO NOT Meet G-Max Test Standards
The safety of the playing surface only degrades over time. A typical five-year-old artificial turf field installed over a stone base will produce a Gmax of 160+. An impact of this magnitude results in a 93% chance of a minor head injury, a 62% chance of a moderate head injury, and a 22% chance of a major head injury.
A moderate head injury consists of a loss of consciousness, where a major head injury results in a skull fracture!
All are considered concussions.
IT’S TIME FOR A PARADIGM SHIFT
WHEN COMPARED TO OTHER LEVELS OF IMPACTS, ARTIFICIAL TURF OVER STONE IS OFF THE CHARTS.
Put into perspective, the impacts forces allowed on an artificial turf surface are somewhat ludicrous. Consider a boxer smashes you in the face, and that is 50 G’s. Two high school kids colliding generate 22 g’s. Yet when it comes to artificial turf and falling on it, we allow 165 G’s, over 3 times the force of getting punched by a boxer. Bringing the allowable GMax thresholds back to within reasonable limits is the current direction for most field designers and owners. And for good reason.