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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?”

• 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 through the life of the surface, not just at installation.  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 harden 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%.

Guidelines for ensuring a safe surface is installed:

1 – Your specification must address validation testing after the installation is complete, regardless of the performance you require. We have seen several Poured In Place pads fail because they were poured 1/4″ to 1/2″ thinner than specified.

2 – Provide some buffer between your required performance at the time of installation and the maximum allowable performance during the life of the product. Gmax/HIC examples that we have seen include 160/700, and 175/850.

“The surface will be tested 14-45 days following the installation. This shall be considered part of the bid amount. The results of the test shall yield a Gmax less than 160/175/200, and a HIC less than 700/850/1000. “

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  what they consider the appropriate level for a newly installed surface.

Note: At the time of writing this (Jan 2017), 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.