By: Paul W Elliott, PhD, PE
Before discussing dead-spots, I want to briefly address field performance. If an architect, or owner, is concerned about the performance of individual installations, the specification must clearly state the performance levels that will be delivered and considered acceptable. Current North American specifications are vague and never state that the performance clearly applies to installed products. North American specifications currently leave owners with little to no ability to hold installers accountable for poorly performing installations. Installations throughout Europe are commonly tested to validate that field performance meets the specified levels, proving that it is not impossible to deliver performance and safety to the end user.
The term ‘dead-spot’ gets thrown around within the basketball community quite frequently. While, everyone uses the term the industry does little to define it. What does ‘dead-spot’ it mean? Does dead-spot mean the same thing to everyone? What should it mean? The reality is that the industry has never defined ‘dead-spot.’ The opinions presented here are my own, and are a reflection of more that 25 years as a designer and engineer active in the sport surface market.
Let me start with how we test a floor in the lab. The rebound property is assessed strictly using the height achieved during the rebound and comparing that to concrete. There is no consideration for sound, vibration or feel. It seems logical that since that is how the systems are evaluated in the lab, that the definition of a dead-spot in the field must use a similar measure. Defining dead-spots based on the rebound height achieved, nothing else. Further, lab tests are performed with a defined rebound height using a basketball that generally only has between 5 and 6 psi pressure. Well below the 7-9 psi recommendations on most balls. I know that is illogical but the standards are written and probably won’t change in my lifetime. Since this is how the products are designed and tested, it seems that the only course of action is to define dead-spots using the rebound height produced and the pressure specified in the standards.
During the process of dribbling a basketball a human receives multiple sensory inputs. They include sound, vibration, and yes the rebound height. It is my experience that when any of these properties changes, most people perceive it as a lower rebound height. And more than 20 years ago, I evaluated some data collected and found that the actual rebound height produced in the field had about a 50/50 chance of agreeing with the perception of the facility. However, the tone, or sound, had roughly a 60-70% chance of agreeing with the perception.
Taking this into consideration, I think a dead-spot would be defined as the following: an area where the rebound height is significantly different than other areas on the playing surface. Using this standard definition enables parties on both sides to understand the other. There are floor designs that just feel ‘dead’ but they are uniform and consistent. This is the nature of their design, and the floor can be more or less uniformly dead, without actually having dead-spots.
Now we have defined what a dead-spot is. What constitutes ‘significantly different’? Let’s once again turn to the standards that dictate floor performance and that are used in the lab for guidance. All of the current standards ASTM F2772, EN 14904, FIBA, MFMA allow floors to have rebound levels that deviate by as much as 3% from the average. That means that system designs can vary by as much as 6% (+3% and -3% from the average) in the lab and still pass these standards. Rebound levels in the field are to be tested using the same methods and standards used in the lab. Unless a manufacturer promises better uniformity, it seems illogical to apply a more strict limit in the field. With this in mind, it is my position that all points producing a rebound within 6% of the maximum value are not dead-spots.
This means that all points producing a rebound that is more than 6% away from the maximum value would be considered dead-spots. The advice I give is that rebound levels that are 7% to 9% less than the maximum are to be considered as marginally dead. Facilities need to weigh the effects of any repairs against the benefits that such repairs will produce. Rebound levels that are 10%, or more, below the maximum value are considered as severe dead-spots and warrant repairs. However a facility’s ability to leverage field testing to force repairs or compensation is limited by the strength of the performance sections of the project’s specification.
One point to keep in mind, is that the above assumes that the problem with a floor is a dead-spot. The opposite can be true, and hard-spot can produce abnormally high rebound levels and the correct course of action should be to repair those points rather than the points perceived as dead.
Lastly I’ll make a general comment on rebound levels. The difference between dead and non-dead areas is magnified as the inflation pressure is increased. Simply adding more pressure to the balls wills will cause the problem to be worse.
If you have concerns about the performance of your sports surface contact us. We will help you understand the benefits and limitations of field testing your facility. ([email protected])