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GMax and HIC: Considerations for New Installations

With regard to new playground safety surfacing and synthetic turf fields, we are often asked: “What should the Gmax and HIC levels be at installation?”

While we don’t want to provide any recommendations, we will offer some points to consider:

  • ASTM F1292 requires a Gmax levels to be less than or equal to 200, and HIC levels to be less than or equal to 1000. This requirement is applicable at all times. So if at any time the Gmax or HIC level exceeds these requirements the surface is no longer considered safe.
  • All surfaces change over time. Binders in Poured-In-Place and Bonded-Rubber systems can harden over time. Rubber components in Poured-In-Place or Bonded-Rubber systems can also harder over time. Rubber tiles can harden over time, and engineered wood fiber breaks down over time. Loose fill material of all kinds migrates and forms depressions if not properly maintained.
  • New installations that are close to the maximum allowable levels can experience less change before they exceed the allowable limits set in ASTM and accepted by the CPSC.
  • The test methods and calculations associated with measuring Gmax and HIC have known error levels associated with them. For Gmax, the within lab error is about 10% near the 200 g level, and the between lab error is about 20% s near the 200 g level. For HIC, the within lab error is about 10%near the 1000 level, and the between lab error is about 25%.

So now that you have this information how could it be used? Well, some architects and communities believe that this information warrants specifying Gmax and HIC levels below the maximum allowed at the time of installation. As an example, some parks we have worked for required new installations to have Gmax levels of 150 or less (not 200), and HIC levels of 850 or less (not 1000). This does two things. First it helps to account for the known errors that occur during testing. Secondly it allows the surface to change (harden) over a longer time period before it exceeds the maximum allowable levels.

We advise communities and architects to set the allowable Gmax and HIC levels of their new surface below the maximum allowed levels of 200 and 1000. We feel this is sensible given that surfaces change over time and that there are known errors associated with measuring Gmax and HIC. Each community and their architect must determine must determine what they consider the appropriate level for a newly installed surface.

Note: At the time of writing this (Jan 2015), ASTM has been in the process of debating the merits of greatly reducing the allowed Gmax and HIC levels throughout much of 2014 and 2015. Proposals have been as large as lowering GMax to 125 and the HIC level  700.

For more information you can visit www.asetservices.com, where you’ll find information about all of the services they provide and the author, Paul Elliott http://asetservices.com/about-aset/.