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BACKGROUND 
       [0001]    1. Related Applications 
         [0002]    This application is a divisional of U.S. application Ser. No. 11/279,069, filed Apr. 7, 2006. 
         [0003]    2. Background of the Invention and Related Art 
         [0004]    Research has shown that, on average, more than 200,000 children are treated in U.S. hospital emergency rooms for playground-equipment-related injuries, many of which result from falls. To minimize the risks associated with playgrounds, a number of guidelines are established which require surfaces under the playgrounds to attenuate the impact of a fall. 
         [0005]    While the primary function of a surface is often safety, the Americans&#39; with Disabilities Act (“ADA”) also requires playgrounds be wheelchair accessible. Thus a surface must be soft enough to sufficiently attenuate the impact of a fall, while at the same time be firm, stable and slip resistant enough to comply with the ADA. Oftentimes, these two apparently conflicting requirements are reconciled by placing a solid access path to the playground structure. While such a path complies with ADA requirements, it also poses the risk that anyone falling onto the surface could result in serious injury or even death. 
         [0006]    A combination of guidelines promulgated from both government and independent bodies tackle the tricky issue of providing surfaces at play grounds that are soft enough to prevent most fall injuries but that are also firm and stable enough for wheelchair maneuvering. For example, the guidelines, based on American Society for Testing and Materials (ASTM) standards, state that wheelchair access, surfaces are required to be “firm, stable and slip resistant” as specified in Americans with Disabilities Act Accessibility Guidelines (ADAAG). Another example is the amount of force required to rotate the caster wheels of a wheel chair as set for in ASTM standard F-1951, which is based on a measurement of the physical effort to maneuver a wheelchair across a surface. Accessible surfaces within the use zone (the ground level area beneath and immediately adjacent to a play structure) are also required to be “impact attenuating” in compliance with ASTM F-1292 requirements for drop testing. 
         [0007]    Materials currently used as impact-absorbing surfaces under playgrounds include sand and gravel, shredded tires, poured rubber to name a few. Sand and gravel have been traditionally used because of their impact attenuation properties, wide availability and low cost. However, such a surface is not wheelchair accessible. In addition, sand and gravel tends to lump and harden when wet or frozen. In addition, the critical fall height for sand and gravel is merely nine feet, which is reduced to five feet when the sand or gravel is compressed. Furthermore, such a surface can cause abrasions when a playground patron falls, can cause a patron to trip when running, is tracked indoors and can cause scratches on floors, can be thrown, can be blown away with wind, as well as be an attraction for cats and other animals. Thus, sand and gravel are not ideal materials to use for playground purposes. 
         [0008]    Alternatively, shredded tires are used, however, these pose additional problems of becoming very hot when in direct sunlight, being flammable, and containing steel belts that were part of the original tire. Additionally, shredded tire installations, when properly installed to attenuate falls, do not meet the requirements for accessibility as defined in ASTM F-1959. 
         [0009]    Similarly, poured rubber is used because it is wheelchair accessible, however, it is expensive to purchase and install. In addition, as the rubber wears out under high traffic areas such as swings, the rubber cannot be replaced without significant additional expense. Furthermore, several obstacles arise during installation such as bonding the rubber to the cement base or ground and requiring completely level ground when the rubber is poured. Poured rubber is also prone to cracking and mechanical failure if exposed to ultraviolet light, extreme temperatures or water. There is evidence that, when exposed to environmental factors over time, a poured surface may deteriorate to the point where it will fail ASTM F-1292 testing. 
         [0010]    Matching the appropriate surface and application can also pose problems. For example, a pool and its surround deck are often made of cement which can get very slick when wet, and a fall thereon may cause a serious injury. Similarly an injury may result from a person diving into and hitting the bottom of a cement pool. Alternatively a cement surface can be so abrasive so as to cause blisters or cuts on swimmers&#39; feet. 
         [0011]    Given the known hazards and limitations of existing surfaces, an impact-attenuating surface, which is also firm, stable, and slip-resistant in accordance with the ADA, would be beneficial. 
       SUMMARY AND OBJECTS OF THE INVENTION 
       [0012]    Certain exemplary embodiments shown herein comprise an impact attenuating tarmac that may be used in conjunction with an impact attenuating base such as loose fill or poured rubber. Alternatively, the tarmac may be used in wet environments to improve surface traction, reduce blisters and scrapes on patrons&#39; feet and also to attenuate the impact of a patron falling. The tarmac further provides a firm, stable and slip resistant surface in accordance with the ADA. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0013]    In order that the manner in which the above recited and other features and advantages of the present invention are obtained, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. Understanding that the drawings depict only typical embodiments of the present invention and are not, therefore, to be considered as limiting the scope of the invention, the present invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
           [0014]    In order that the manner in which the above recited and other features and advantages of the present invention are obtained, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. Understanding that the drawings depict only typical embodiments of the present invention and are not, therefore, to be considered as limiting the scope of the invention, the present invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
           [0015]      FIG. 1  illustrates an exemplary play ground area for children according to some embodiments of the invention. 
           [0016]      FIG. 2  illustrates a partial side, cross-sectional view of an impact attenuation system of the play ground area of  FIG. 2 . 
           [0017]      FIG. 3  illustrates a partial, top perspective view of a mat that may form a tarmac of the impact attenuation system of  FIG. 2 . 
           [0018]      FIG. 4  illustrates a partial, bottom perspective view of two linked mats that may form the tarmac of the impact attenuation system  FIG. 2 . 
           [0019]      FIG. 5  illustrates a partial top view of two linked mats that may form the tarmac of the impact attenuation system  FIG. 2 . 
           [0020]      FIG. 6  illustrates a partial bottom view of two linked mats that may form the tarmac of the impact attenuation system  FIG. 2 . 
           [0021]      FIG. 7  illustrates an exemplary tarmac used under water according to some exemplary embodiments of the present invention. 
           [0022]      FIG. 8  illustrates an exemplary embodiment of an underwater mat. 
           [0023]      FIG. 9  illustrates an exemplary cut-away view of a mat having a plurality of tabs and slots fit together. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    It will be readily understood that the components of the present invention, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the system and method of the present invention is not intended to limit the scope of the invention, as claimed, but is merely representative of the presently preferred embodiments of the invention. 
         [0025]    This specification describes exemplary embodiments and applications of the invention. The invention, however, is not limited to these exemplary embodiments and applications or to the manner in which the exemplary embodiments and applications operate or are described herein. 
         [0026]    The Head Injury Criterion (“HIC”) is a measure of the severity of an impact and takes into account its duration as well as its intensity. The criterion is based on the results of research into the effects of impacts on the human head. HIC is defined by the following integral formula 
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         [0027]    Where “t” is defined as time and “a” is defined as deceleration at time t. 
         [0028]    G-max is the maximum deceleration experienced by the head (or headform) during an impact. It is a measure of the peak forces that a likely to be inflicted on the head as a result of the impact. It is measured in standard units of G, acceleration due to gravity −9.8 m/s/s. 
         [0029]    Critical fall height is the minimum free fall height resulting from all test drops of an instrumented head onto a surface for which an HIC less than 1000 or a G-max value less than  200  is obtained. Thus, for example, if the instrument is dropped from a fall height of X feet onto a non-impact attenuating surface the force of the impact may be HIC of 1500 and a G-max of 210. Such force may lead to injury in a person. In contrast if the same instrument were then dropped from the same fall height onto an impact attenuating surface the HIC might be 500 and the G-max might be 100, and accordingly the probability of an injury resulting is much less. 
         [0030]      FIG. 1  illustrates an exemplary play ground area  50  for children such as may typically be found in school yards, parks, etc. The play ground area  50  includes play ground equipment  56  (e.g., one or more swing sets, slides, climbing bars, etc.) and an impact attenuation system  12 . As will be seen, impact attenuation system  12  is designed to absorb energy from an impact and thus protect children from falls from playground equipment  56 , and impact attenuation system  12  may also be configured to have a sufficiently firm surface to allowed rolling equipment (e.g., a wheel chair, a baby stroller, etc.) to be pushed across the tarmac  15  of impact attenuation system  12 . The exemplary play ground area  50  shown in  FIG. 1  is surrounded on three sides by a lawn area  52  and on one side by an asphalt or concrete area  4 . A small ramp  6  is provided between asphalt area  4  and tarmac  15 . 
         [0031]      FIG. 2  shows a partial side, cross sectional view of an exemplary configuration of impact attenuating system (see  FIG. 1 ) according to some embodiments of the invention. As shown in  FIG. 2 , the impact attenuating system  12  includes fill material  14 , which is disposed on the ground  2  under play ground area  50 . Tarmac  15  is formed of a plurality of interlocking mats  5 , which cover fill material  14 . The fill material  14  may be loose or a solid-fill material such as those commonly used in the art for impact attenuation. Examples of such materials include wood chips, sand, gravel, shredded tires, poured rubber or other similar materials suitable for absorbing an impact from a child&#39;s fall. As shown in  FIG. 2 , each mat  5  includes a surface structure  10  and legs  20 , which may rest on an upper surface of fill material  14  or, as shown in  FIG. 2 , may extend at least partially into fill material  14 . Each mat  5  also includes a linking tab  24  that interlocks a mat  5  with an adjacent mat by sliding into slot  25  (see  FIG. 4 ). A plurality of mats  5  can thus be interlocked to form tarmac  15  in just about any desired shape and size. 
         [0032]      FIG. 2  also shows part of an asphalt area  4  and ramp  6 , which may be formed of a plurality of sloped mats that interlock with a linking tab  24  of a mat  5  as shown. Ramp  6  provides a sloped ramp structure from the asphalt area  4  to the tarmac  15 . 
         [0033]    Although fill material  14  shown in  FIG. 2  is loose, allowing legs  20  to sink into the fill material  14 , a landscape fabric (not shown) may be placed between fill material  14  and legs  20 , preventing legs  20  from sinking into fill material  14 . Such a landscape fabric (not shown) may additionally protect the fill material  14  from, for example, ultra violet light from the sun. 
         [0034]    Because the exemplary tarmac  15  shown in  FIG. 2  is modular, that is, formed of a plurality of interlocking mats  5 , individual mats  5  may be replaced as specific areas wear out. This may occur under swings or other high traffic areas or through damage and vandalism. Similarly as particular mats  5  of the tarmac  15  are adversely affected by weather or ultraviolet degradation from exposure to sunlight, or have a mechanical failure such mats  5  can be replaced. The upper surface of the tarmac  15  may comprise an undulating surface to improve traction, and to provide flex, which will attenuate an impact. The undulating upper surface of the tarmac  15  may optionally comprise a plurality of small flexible arches, the elasticity of the ach being determined by the materials from which the tarmac  15  is made. 
         [0035]    Mats  5  can be made from a number of different materials, including but not limited to, synthetic polymers such as PVC, as well as a variety of other polymers commonly known in the art. Furthermore, mats  5  can be formed in molds, using extrusion techniques, etc. An edging (e.g., comprising one or more ramps  6 ) can also be used to couple the tarmac  15  to another surface such as a cement or asphalt surface, or to reduce the amount of energy needed to get a wheelchair onto the tarmac  15  surface. The edge thus may be an extension from the tarmac  15  surface to another surface, or it may be tapered to provide a ramp from another surface up to the tarmac  15  surface (e.g., like ramp  6  shown in  FIG. 2 ). 
         [0036]    Extending from the bottom of each mat  5  are legs  20 . As mentioned above, the legs  20  may sit on top of the fill material  10 , or the fill material may work its way to fill the interstitial spaces between the legs  20 . Legs  20  may be a variety of different lengths. If the legs  20  have different lengths, each leg  20  will make contact with the fill material  14  at different times and thus increase energy impact dissipation and attenuation of an impact of a fall. Furthermore, the legs  20  further improve the impact-attenuation properties of the energy absorption system by concentrating force onto certain areas, and allowing the tarmac  15  surface to flex. The mats may also be used to reduce erosion in high traffic areas, or to promote growth of vegetation in high traffic areas. 
         [0037]    Mats  5  may be tethered to ground  2  to prevent the tarmac  15  from sliding off the fill material  14 . In addition, the tethers (not shown) may help anchor the fill material  10  in a stationary position. Any tethering structure suitable for anchoring mats  5  to ground  2  may be used. For example, rigid steel spikes may be driven through mats  5  and into ground  2 . As another example, mats  5  may be tied using string, wire or rope to spikes that are driven into ground  2  below tarmac  15 . 
         [0038]      FIGS. 3-6  illustrate an exemplary mat  5  or mats  5  that may be used to form the tarmac  15  covering over fill material  14 .  FIG. 3  illustrates a partial, top perspective view of a mat  5 ;  FIG. 4  illustrates a partial, bottom perspective view of two interlocked mats, each like the mat shown in  FIG. 3 ; and  FIGS. 5 and 6  show top and bottom views, respectively, of two interlocked mats  5  each like the mat  5  shown in  FIG. 3 . 
         [0039]    The exemplary mats  5  shown in  FIGS. 3-6  comprise a relatively thin surface structure  23  supported by a grid structure comprising an array of legs  20  that are connected one with another by rib structures  42 . As also shown, surface structure  23  includes a plurality of arches  35  each located generally between four legs  20  and four rib structures  42 . 
         [0040]    The exemplary embodiments teach at least three impact attenuation techniques which may be used either separately or in combination with each other. The mat  5  structure illustrated in  FIGS. 3-6  absorbs the impact of a child&#39;s fall in several ways. First, arches  35  are flexible and absorb or attenuate at least some of the force from a child&#39;s fall. Second, the rib-grid structure (formed by legs  20  and rib structures  42 ) allows the mat  5  to flex horizontally with respect to the top surface of the mat  5 . The rib-grid thus dissipates some of the force from the child&#39;s fall horizontally through mat  5 . Third, the mat  5  transfers some of the energy from the child&#39;s fall through legs  20  to fill material  14 , which as discussed above, itself is soft and readily absorbs at least part of the energy from the child&#39;s fall. 
         [0041]    As a result, when a child falls onto the tarmac  15 , three separate energy attenuating features aid in reducing the adverse effects of such a fall. First the impact causes the arches  35  to flex, absorbing energy. Second the entire tarmac  15  flexes horizontally dissipating some of the impact from the child&#39;s fall horizontally (e.g., generally level with ground  2 ). Third, the fill material  14  absorbs some of the force from the child&#39;s impact with the tarmac  15 . 
         [0042]    The amount of flex in the arches  35  depends on the radius of curvature in the arch, the height of the arch, as well as the material from which the mat  5  is made. The amount of flex provided by the grid structure depends on several factors, including the materials that form the legs  20  and rib structures  42 , and the size, spacing, and number of legs  20  and the size and thickness of the rib structures  42 . 
         [0043]    The arches  35  of mats  5  form an undulating pattern on the outer surface of the tarmac  15 , which may improve the tarmac  15 &#39;s traction by allowing increased surface contact between a patron&#39;s foot or shoe and the tarmac  15 . In addition, there are a number of pores  40  formed in a mat  5 , which allow water to drain through mats  5 . A seam  22  between two adjacent mats  5  also provides improved flex upon impact by spreading under a force, as well as the convenience of replacing the surface in a particular area for low cost and as needed. 
         [0044]    As best seen in  FIG. 6 , which shows the bottom side of two interlinked mats  5 , linking tabs  24  couple adjacent mats  5  by sliding into slot  25  (see  FIG. 9 ). Tab  24  is designed to provide a secure link and may also be designed to flex to absorb energy from an impact, such as a falling child. In addition to the linking tabs  24 , the mats  5  are secured using both an adhesive such as glue and a heat source where two adjacent mats  5  are configured to overlap. In such a case the mats  5  are bonded together using both an adhesive and a heat source to melt the contacting plastic and further improve the bond. For example, the linking tab  24  may be coupled to an adjacent mat, a heat gun may be used to melt and fuse the tab to the adjacent surfaces, and an adhesive such as a glue may then be used to bond the two adjacent mat surfaces. Of course the heat treatment can only be used on thermoplastics such as PVC. 
         [0045]    The combination of an impact attenuation fill material  14  and an impact attenuation tarmac  15  overlaying the fill material  14 , as shown in  FIG. 2 , has been found to provide greater impact attenuation than the sum of the impact attenuation of the fill material  14  by itself and the impact attenuation of the tarmac  15  by itself. That is, the impact attenuating system of  FIG. 2  absorbs more energy from an impact-and thus provides greater protection to a falling child-than the sum of the energy absorbed by the fill material  14  alone and the tarmac  15  alone. This unexpected, synergistic increase in the impact attenuation properties of the combination of tarmac  15  overlaying fill material  14  is believed to be due to the multiple ways in which the system absorbs energy from an impact. 
         [0046]    As discussed above, the impact attenuation system  12  of  FIG. 2  attenuates an impact in three ways. First, referring to the mat  5  depicted in  FIGS. 3-6 , the arches  35  deform generally vertically with respect to the top surface of surface structure  10  (which is generally in the direction of the impact force) and thereby attenuate energy from an impact. Second, as discussed above, the grid structure comprising the array of legs  20  and interconnecting rib structures  42  allows mats  5  to flex generally horizontally with respect to the top surface of surface structure  10  and thereby attenuate energy from an impact. Third, as also discussed above, energy from the impact is transferred through legs  20  to fill material  14 , which also attenuates energy from the impact. The energy from the impact is attenuated by the fill material  14  as individual pieces of fill material  14  move closer together and flex under the force of the impact. 
         [0047]    The performance of the exemplary system can meet the gmax&lt;200 and Head Impact Criterion&lt;1000 requirements from a critical fall height of 13 feet. 
         [0048]    In addition to absorbing energy from an impact (e.g., a falling child), the grid structure comprising the array of legs  20  and interconnecting rib structures provides mats  5  with a sufficiently firm surface to allow rolling equipment to be used on tarmac  15 . Generally speaking, the less a wheel sinks into a surface, the less effort and energy is required to roll the wheel across the surface and to turn the wheel on the surface. As one example, the grid structure formed by legs  20  and interconnecting rib structures  42  may be configured to provide tarmac  15  with a sufficiently firm surface for a baby stroller to be pushed on the tarmac  15  surface and the wheels turned on the tarmac  15  surface by a typical adult without requiring an uncomfortable effort from the adult. As another example, the grid structure formed by legs  20  and interconnecting rib structures  42  may be configured to provide tarmac  15  with a sufficiently firm surface to meet ADA standards for use of a wheel chair on the surface of tarmac  15 . 
         [0049]    Thus, as discussed above, the tarmac  15  shown in  FIG. 2  is able to meet both the impact attenuation requirements for protecting a child from a fall of the ASTM guidelines and the ADA requirements for wheelchair accessibility. That is, the combination of tarmac  15  and fill material  14 , as shown in  FIG. 2 , is sufficiently impact absorbing to protect a child from a fall while at the same time provide a sufficiently firm surface to allow the use of a wheel chair on the tarmac  15 . 
         [0050]    Referring now to  FIG. 7 , there is illustrated an exemplary embodiment of the present invention, wherein a tarmac  15  having legs  20  is used in a wet environment. Thus, the pores  40  allow water to leave the surface of the tarmac  15  and drain to the ground below. As discussed above, legs  20  may have a variety of different lengths and thus increase the impact attenuating properties of the tarmac  15 . 
         [0051]    The alternative exemplary embodiment of  FIG. 8  may also include using the tarmac  15  underwater, such as at the bottom of a pool. Oftentimes pools made of concrete are very rough and may cause blisters. To cure this problem, pool owners often need to acid wash their pools which is not only expensive, but also requires the pool to be fully drained and then refilled. The present invention allows the tarmac  15  to be placed in direct contact with the cement to provide a smoother surface for the bottom of the pool. In addition, the tarmac  15  increases the pool&#39;s safety by attenuating the impact of a diver hitting the bottom of a shallow end of the pool. Such protection is important because an impact with the concrete could result in a serious or fatal injury. 
         [0052]    Finally  FIG. 9  illustrates a exemplary embodiment of a cut-away view of the seam connecting two adjacent mats  5 . In this exemplary embodiment a plurality of tabs  24  from a first mat  5  are fit into a plurality of receiving slots  25  to secure the two mats. Additionally glue and/or a thermal bond may be formed between the mats so as to further strengthen the couple holding the mats  5  together. 
         [0053]    Although specific embodiments and applications of the invention have been described in this specification, there is no intention that the invention be limited these exemplary embodiments and applications or to the manner in which the exemplary embodiments and applications operate or are described herein.

Summary:
A system and method of providing a wheelchair accessible path through a variety of impact attenuating surfaces including loose fill materials. The combination of a tarmac and loose fill material provides an ASTM compliant impact attenuating surface for playgrounds and other activities. The modular tarmac 15 is also used in wet conditions to improve the traction and impact attenuation over traditional materials used in water parks, and also for reducing wear to park patrons&#39; feet.