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G-Max Testing

Athletic and sports fields are facilities where there is an expectation for safety from the users of these fields. Proper design, installation, and maintenance are all necessary to reach that end.

Synthetic turf sports fields are designed with a pad and/or rubber infill to absorb the shock of someone's fall. Since personal injury can occur on fields that are too hard, this "shock absorbency" should be checked when the field is first installed, and then on a regular basis dependent on intensity of use. The shock absorbency of a field is easily tested by what is referred to as a G-max or shock absorbency test. This test involves using a specialized piece of equipment that includes a 20 lb hammer that is dropped from a height of 2 feet. An accelerometer is imbedded in the hammer that measures the rate that the hammer decelerates as it hits the surface. The faster this hammer comes to a stop, the harder the field. The deceleration is measured in units called gravities, thus the term G-max. The test simulates the impact of a head on the field surface.


The American Society for Testing and Materials (ASTM) has set standards for the testing and safety of synthetic fields. According to ASTM F1936, the G-max on a field should be no more than 200. Fields with values above this are considered unsafe and should be repaired or replaced. This standard is based on biomechanical test data that shows that the risk of life threatening head injuries increases substantially on surfaces with values above 200. The test does not does not address and may not relate to other injuries such as muscle, bone, or joint injuries.


The regularity of testing is often dictated by the original contract between the field owner and field installer. Some contracts require testing before the field is put into use, and then every one or two years for the length of the warranty. The information provided by this regimen ensures that the owner of the field is informed if the field meets ASTM standards for safety before the field is ever used and as the field ages and wears. Where there are no contractual obligations to test, it is certainly in the best interest of the owners to have this test performed on a yearly basis.




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