How playground surface HIC and GMAX tests are done

A playground surface drop test or more specifically HIC (Head injury Criteria) or GMAX test is conducted to determine if the safety surface around the use zone of the equipment meets or exceeds the fall height of the actual equipment. Now that's a mouthful. In simple terms, this is the ultimate test that will tell us if the safety surface we installed around the play equipment will protect the children playing on the equipment from debilitating head injuries or death if they fall on it. The test uses a computerized head form that will register all kinds of data when dropped from a certain height. Note that the key measurements here have to do with head injuries, not long bone injuries. 

The Triax impact testing system.

It is undebatable now that falls from the play equipment to the surface lead to the most visits to the emergency room. About 70% of playground injuries are caused by falls. This is why it is important to pick the right type of safety surface, install it correctly and at the right depth, and also covering the right use zones of the playground equipment. Also important is to test these safety surfaces when they are first put into service, meaning when the playground is first opened to the public, as well as testing the surface frequently thereafter as they tend to deteriorate for multiple reasons.

The drop generates two readings that are similar in what they determine but slightly different in how they are interpreted: The GMAX reading, which is borrowed from well established tests in the auto industry is the maximum acceleration or shock generated by the impact of the head to the surface. That reading should not be more than 200 Gs. The HIC results on the other hand are slightly more complicated. It is a number that combines impact severity as well as the relationship between the magnitude and duration of the impact acceleration, a number not to exceed 1000.

These tests are quite involved and utilize complicated test equipment such as the Triax impact testing system. ASTM F-3313 is the field test specification that determines how these tests are to be conducted and compared the the findings of F1292, which is a lab test. Generally the drop test is conducted by a qualified technician, usually a certified playground inspector. The machine has to be calibrated by the manufacturer before the test can be done. The inspector follows these steps to conduct the test:

• The tech will conduct a pre test on a sample piece of rubber by dropping the balls three times  from a predetermined height and averaging the last two numbers to compare them to a predetermined calibration number. That number cannot exceed  5% from the nominal figure associated with the test rubber piece.
• The tech will record the temperature of the surface and the depth of the surface at each drop. 
• 3 adverse locations will be picked around each composite set where three drops will be conducted. The last two numbers will be averaged. 
• The height of the drop is determined either by the client as long as it is not less than the fall height or determined by the fall height of the equipment. Each type of play equipment has its designated fall height as per the manufacturer and ASTM 1487.
• After the first drop is made, the tech waits 1.5 minutes before they conduct the next drop. 
• If the surface is loose as it is the case in Engineered wood fiber or playground mulch, the tech will impact the space where the drop is to take place by dropping a 10" by 10" 15 pound weight 4 times.
• A detailed report will be generated for the client that has all the recorded drops, site information and pictures of every drop and other pertinent data. The name of testing agency, tech name and license number is also recorded.

It is important to keep TRIAX HIC and GMAX results as a benchmark document for future tests and in case an accident happens in your playground. 

Trassig offers Triax and ASTM compliant HIC and GMAX tests all over the world. If you want to schedule yours, give us a call at: 203-659-0456 or email us at info@trassig.com