Feature Article - February 2015
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Sports to the Max

Make the Most of Your Sports Fields

By Rick Dandes


Testing Field Hardness

A major trend in sports surface management is a movement toward becoming more aware of field hardness, explained Andy McNitt, director of Penn State's Center for Sports Surface Research. "Surface hardness is affected by many things. Certainly, wear is one of them. The more foot traffic you have on a native soil, especially on native soil fields, the more compact it gets. You will want to relieve that compaction."

What most affects the surface hardness of native soil is moisture content, said McNitt, who also serves as a technical advisor to the NFL groundskeeper association. "We know a native soil field is high in silt and clay and when it dries out it is very hard. When it's wet it is very soft. So, moisture management becomes critical and at a park and recreation level, sometimes that's very difficult to control."

One thing to do is set some kind of a use parameter or use discipline. Don't use the field if it's too wet, and don't use it if it's too dry. But how do you know if it's too wet or too dry? Something every park manager can do, "and I think it's smart to do from a liability standpoint, is go out and buy an impact tester," McNitt suggested. For example, a Clegg tester. "You can get them now calibrated to the NFL standard for about $4,000. In the past, when I've talked to park and recreation people and high school people they were like ostriches with their head in the sand. They said, well, if we don't test, we don't know, then we can't be liable. And I think that is a pretty shortsighted response that they don't want to know whether their fields are too hard or too soft. Primarily too hard."

Keeping Players Safe

The priority when maintaining sports fields at any level is to provide safe, playable fields for athletes. Turf safety is measured by what's called a G-max test, which measures the shock attenuation of a surface by dropping the impact tester's "missile" onto the turf and measuring the resistance and absorption rate. The resulting G-max value, Nardone explained, represents the ratio of deceleration upon impact to acceleration due to gravity. In other words, it measures how well the turf absorbs and slows the impact.

Right now the American Society for Testing and Materials (ASTM) and Synthetic Turf Council recommend keeping the G-max level below 200 (although there is talk of lowering it to 165). The NFL is testing requiring teams to maintain their fields below 165 as well. These lower numbers stem from growing research on concussions showing that any safety enhancements can help. So, the lower the turf's G-max value, the greater safety buffer the surface can help provide.

When well-maintained, typical natural grass turf systems inherently have a lower G-max value—usually in the range of 80 to 110. So, synthetic turf manufacturers are trying to create systems that get closer to those naturally lower levels, which involves designing a field with a padded turf. But, it is also important to remember that the variety of soil profiles in a field area, and the maintenance practices used (or not used) on the field, can make the safety level of natural grass fields harder to predict. While the NFL now tests its fields before every game—whether synthetic or natural—lower levels of competition don't have the resources to maintain that same kind of rigorous program to ensure the turf is at safe levels.

"Because of the publicity surrounding safety, and preventing concussions at every level of sport, there is increasing awareness that we need to monitor field quality," McNitt said. "So for the cost of a Clegg Impact Soil Tester and very little time, I think it would be very impressive if you're called into court because someone got injured on the field and you were able to produce documents that prove you test regularly, were way ahead of the curve and have use parameters."

Park maintenance staff should understand that a field has to be aerated if it gets too hard or irrigated, if that's available. "Just have some ongoing record," McNitt said.

Artificial turf is under the same scrutiny as grass—maybe even greater scrutiny now. "The thing about artificial turf is it needs to be maintained just as a natural grass field needs maintenance, but in a different way," McNitt said. "People are under a false assumption that synthetic fields get hard over time because of compaction, and that is really not true. Assuming that you are working with a quality vendor and they give you quality infill material, that infill material is going to be fairly uniformly sized and difficult to compact to any great degree."

What McNitt and his team of researchers learned is that fields get harder over time due to walk-off rubber. The infill crumb rubber gets in people's shoes or on clothing, and it slowly, almost imperceptibly, leaves the field. What you then need to do is buy a depth gauge, walk around and monitor the infill depth.

"In the NFL," McNitt noted, "they have to do it at a minimum of 40 locations before every game. The manufacturer will give you a target value and a range, and when the infill depth falls below that number, it is time to begin topdressing the crumb rubber. That is very easy to do. You need a topdresser and a broom, which you should have anyway, to drag behind it."

Put it down in small quantities and drag it back in. In the past what has happened is rather than do this routinely, people wait until it reaches the critical level, and there was too much crumb rubber lost and the fibers were too matted. Then, instead of a simple in-house correction, you'd have to hire a company to come in and renovate the field, add the crumb rubber and get the fibers to stand up straight.

McNitt suggests that it is much cheaper to go out once or twice a year and put on small amounts yourself. Monitor it with a gauge, put on small amounts of crumb rubber, broom it in and make sure you're buying the crumb rubber from the manufacturer you bought the product from so that the infill matches. That's important. If you do all this, you'll find it is more cost-effective than bringing in an outside company once every five years and spending tens of thousands of dollars to get the field back in shape.

With artificial turf, moisture content is not as important as long as the field isn't completely frozen with water in the infill. The worst-case scenario with a synthetic field, McNitt said, is you get some snow, snow partially melts and then it re-freezes. That is when those fields will get exceptionally hard. But, they don't hold much water, so usually freezing doesn't have a major effect on surface hardness. And, a properly designed drainage system can also help prevent problems.

"You don't have to guess if you have an impact tester," McNitt said. "You walk out, bounce it around, bounce it on the seams, bounce it on the inlays and make sure the field is in good shape, and I believe it really lowers your risk of injuries."

Another way to prevent injury is to install a safety pad underneath the infill. "More pads are going in than ever before—it's a trend," said Nardone. "Concussion prevention is a big part of the reason for the trend. Understand, though: Your infill depth is part of your safety system whether you have a pad or not. And depth of rubber."