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CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/553,351, filed on 31 Oct. 2011. The Provisional Patent Application is hereby incorporated by reference herein in its entirety and is made a part hereof, including but not limited to those portions which specifically appear hereinafter. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to drain constructions located in the bottom or along the sides of a pool or hot tub through which water flows under the action of gravity or a pump that acts to suck water out of the pool. 
     The dangers inherent in pools and hot tubs having circulating water systems are well known and documented. For example, suction or vacuum forces frequently occur near the water drains sufficient to hold a swimmer or user in life threatening situations. Entanglement or knotting of hair on or through a sump, suction line or a drain grate can also cause injuries and possibly drowning. 
     Limbs can be inserted into suction lines, such as PVC pipes, when the suction fittings or covers are removed or missing from a sump. Suction can draw the limbs into the pipes fitted to the sumps; here the limbs can be trapped by suction, friction, swelling of the limb, etc. 
     A homemade remedy for the limb entrapment hazard is to insert a couple of cross bolts in a simple pattern at the entrance to the pipe. Bathtub drains and slop sink drains adopt this concept. Some drain lines use manufactured perforated covers. These concepts generally introduce a hair entrapment hazard. They can also give rise to a mechanical finger entrapment hazard. Furthermore, they allow a hand to seal off a small pipe (2″ to 3″ diameter) and instantly develop close to the theoretical vacuum limit (14.7 psi). A three inch PVC pipe can develop nearly 100 lbs of holding force on a bather. 
     SUMMARY OF THE INVENTION 
     A general object of the invention is to provide an insert that can be inserted into a pipe of a pool water circulation system to prevent injuries that can be caused by limbs or hair getting trapped in the pipe. The general object of the invention can be attained, at least in part, through a plurality of fins extending inwards of the insert and protrusions extending from a top edge of the insert. 
     In a preferred embodiment, the insert includes a cylindrical body including an inner surface and an outer surface. The insert preferably further includes a plurality of fins mounted to the inner surface and extending inward of the cylindrical body. The fins are preferably sized to prevent limb insertion. The fins are also preferably shaped to shed hair thereby preventing trapping of a person by his or her hair. In one embodiment, the fins include an iso-friction curve that easily sheds hair strands. 
     In a preferred embodiment of this invention, the insert includes a plurality of protrusions that extend from the insert and outside of the pipe to provide a non-planar edge at an end of the pipe to prevent the formation of a vacuum seal with a body part. In an embodiment of this invention, the protrusion is formed as a part of the fin. In another embodiment of this invention, the protrusion is formed as a scalloped or castellated peripheral edge of the insert. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and features of this invention will be better understood from the following detailed description taken in conjunction with the drawings, wherein: 
         FIG. 1  is a perspective view of an anti-limb entrapment insert according to one embodiment of this invention. 
         FIG. 2  is a perspective view of the anti-limb entrapment insert of  FIG. 1  positioned within a pipe. 
         FIG. 3  is a cross-sectional view of the anti-limb entrapment insert of  FIG. 1 . 
         FIG. 4  is a perspective view of an anti-limb entrapment insert according to another embodiment of this invention. 
         FIG. 5  is perspective view of the anti-limb entrapment insert of  FIG. 4  positioned within a pipe. 
         FIG. 6  is a perspective view of an anti-limb entrapment insert according to another embodiment of this invention. 
         FIG. 7  is perspective view of the anti-limb entrapment insert of  FIG. 6  positioned within a pipe. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention provides an insert for a pipe of a pool circulation system. The insert prevents injuries that can be caused by hair or body parts getting trapped in the pipes. 
       FIG. 1  shows an anti-limb entrapment insert  10  according to an embodiment of this invention.  FIG. 2  shows the anti-limb entrapment insert  10  of  FIG. 1  positioned within a pipe  20 . Preferably, the anti-limb entrapment insert  10  is permanently adhered to the pipe  20  with an adhesive. Alternatively, the anti-limb entrapment insert  10  may be integrally formed with the pipe  20 . In a preferred embodiment, the insert  10  can be retrofit to existing pipes that are flush to mounting walls or sump walls. 
     The anti-limb entrapment insert  10  of this invention preferably includes a cylindrical body  12  and a plurality of fins  14  extending in from an inner surface  16  of the cylindrical body  12 . In this embodiment, the anti-limb entrapment insert  10  is manufactured from plexiglass, however, the anti-limb entrapment insert  10  need not be made from plexiglass and may be made from another material able to maintain sufficient strength to prevent limb insertion while exposed to chlorinated water including, but not limited to, PVC and metal materials. 
     The fins  14  are preferably designed and sized to prevent limb insertion into the pipe  20 . In the embodiment of  FIG. 1 , the anti-limb entrapment insert  10  includes four fins  14  that extend towards a center of the cylindrical body  12 . However, the anti-limb entrapment insert  10  may include any number of fins  14  and the fins  14  may extend inwards at an angle and away from the center of the cylindrical body  12 . 
     The fins  14  are preferably designed with a geometry that sheds hair preventing the entrapment of a swimmer by his or her hair. The fin geometry should also be designed to pass a “finger probe” test to prevent mechanical finger entrapment. The geometry may comprise, for example but not limited to, a smooth curve or a tapered surface.  FIG. 3  shows a cross-sectional view of the anti-limb entrapment insert  10  according to one embodiment of this invention. In this embodiment, an upper half of the fin  14  comprises a tapered surface and a lower half of the fin  14  comprises an iso-friction curve (μ=1) with a distance, R, at any point of the curve is defined by:
 
 R=R   o   e   (tan γ)(θ−θo)  
 
Where R o  equals an initial distance of the curve at an initial angle, θ o , θ equals the angle of R, α equals the angle of R to a tangent to the curve of the fin at R, and γ equals the compliment of the angle α. However, it should be understood that the anti-limb entrapment insert  10  of this invention may not comprise the curve shown in  FIG. 3  and may comprise any curve or other shape that does not allow hair to become entrapped or entangled in the pipe  20  of the pool circulation system.
 
     In the embodiment of  FIG. 1 , the fins  14  further include a protrusion  18  that extend from the cylindrical body  12 . When inserted in the pipe  20 , the protrusion  18  provides a non-planar surface at an opening of the pipe  20 . The protrusion  18  prevents the formation of a seal around the pipe  20  opening with a body part and thereby prevents the formation of a vacuum at the pipe  20  opening that could result in injury to a swimmer. In the embodiment of  FIG. 1 , the protrusion  18  also includes a catch  19  extending outside of the cylindrical body  12  to prevent the insert  10  from being inserted too far into the pipe  20 . In an alternative embodiment, the protrusion  18  may be formed as a part of the cylindrical body  12 . In another alternative embodiment, the anti-limb entrapment insert  10  may not include the protrusion  18 . 
       FIG. 4  shows another embodiment of the anti-limb entrapment insert  30  of this invention.  FIG. 5  shows the anti-limb entrapment insert  30  of  FIG. 4  positioned within the pipe  20 . The anti-limb entrapment insert  30  of this embodiment includes a cylindrical body  32  and a plurality of fins  34  extending in from an inner surface  36  of the cylindrical body  32 . In this embodiment, the cylindrical body  32  is formed with a non-planar top edge  38  in a castellation pattern. However, the non-planar top edge  38  may comprise any non-planar shape including, but not limited to, a scalloped edge, a triangle wave pattern and a saw tooth edge. The non-planar top edge  38  prevents the formation of a seal around the pipe  20  opening thereby preventing the formation of a vacuum that could result in an injury, such as drowning or disembowelment. In a preferred embodiment, the difficulty in sealing the pipe  20  opening is enhanced by a plurality of bosses  40  mounted to a portion of the non-planar edge  38 . In the embodiment of  FIG. 4 , each boss  40  is mounted to a merlon of the castellation pattern to increase the thickness and strength of the merlon. In an alternative embodiment, the bosses  40  may be integrally formed as a part of the cylindrical body  42 . The boss  40  also provides a catch  42  to prevent the insert  30  from being inserted too far into the pipe  20 . 
     In the embodiment of  FIGS. 4 &amp; 5 , the anti-limb entrapment insert  30  includes four fins  34  that extend towards a center of the cylindrical body  32  to prevent limb insertion. Alternatively, the anti-limb entrapment insert  30  may be designed with any number of fins  34  that prevent the insertion and entrapment of limbs and fingers. The fins  34  are preferably designed with a geometry that sheds hair preventing the entrapment of a swimmer by his or her hair. In this embodiment, each of the fins  34  comprises a tapered top half and a tapered bottom half. However, it should be understood that the fins  34  may not comprise the shape described above and may comprise a curve or another shape that does not allow hair to become entrapped or entangled in the pipe  20 . 
       FIG. 6  shows another embodiment of the anti-limb entrapment insert  50  of this invention.  FIG. 7  shows the anti-limb entrapment insert  50  of  FIG. 6  positioned within the pipe  20 . The anti-limb entrapment insert  50  of this embodiment includes a cylindrical body  52  and a plurality of fins  54  extending in from an inner surface  56  of the cylindrical body  52 . In this embodiment, the cylindrical body  52  includes a non-planar top edge  58  in a triangle wave pattern. However, the non-planar top edge  58  may comprise any non-planar shape including, but not limited to, a scalloped edge and a saw tooth edge. The non-planar top edge  58  prevents the formation of a seal around the pipe  20  opening thereby preventing the formation of a vacuum that could result in an injury. 
     In the embodiment of  FIGS. 6 &amp; 7 , the anti-limb entrapment insert  50  includes three fins  54  that extend towards a center of the cylindrical body  52  to prevent limb insertion and entrapment. However, the anti-limb entrapment insert  50  may be designed with any number of fins  54  that prevent the insertion and entrapment of limbs and fingers. In this embodiment, the fins  54  include a geometry that sheds hair preventing the entrapment of a swimmer by his or her hair. Each of the fins  54  comprises a straight horizontal top section that extends from the inner surface  56  near the non-planar edge and transitions to a smooth arc that extends further towards the center of the cylindrical body  52  before curving back towards the inner surface  56  of the cylindrical body  52 . However, it should be understood that the fins  54  need not comprise this geometry and may comprise any geometry does not allow hair to become entrapped or entangled in the pipe  20 . 
     In the embodiment of  FIGS. 6 &amp; 7 , the anti-limb entrapment insert  50  further include a plurality of tabs  60  extending from an outer surface of the cylindrical body  12 . The tabs  60  comprise a horizontal projection that prevents the insert  50  from being inserted too far into the pipe  20 . 
     In a preferred embodiment of this invention, the anti-limb entrapment insert  50  further includes a split  62 . In the embodiment of  FIG. 6 , the split  62  comprises a vertical opening in the cylindrical body  52 . The split  62  allows the insert  50  to be easily inserted into the pipe  20 . Additionally, the split  62  allows the insert  50  to accommodate various diameter pipes  20  with a single design. In the embodiment of  FIG. 6 , the split  62  comprises approximately 15% of the circumference of the cylindrical body  52  however, the split  62  may be designed to comprise a larger or smaller section of the cylindrical body  52 . 
     Thus, the present invention provides an insert that can be retrofit to a pipe of a pool water circulation system to prevent injuries that can be caused by limbs or hair getting trapped in the pipe. 
     While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.

Summary:
Missing covers on pipes of a pool circulation system can create a hair and limb entrapment hazard for swimmers. The present invention provides pipe insert with a cylindrical body having a plurality of fins that extend into the cylindrical body to prevent the entrapment of limbs in the pipes of the pool circulation system. The fins further comprise a geometry that easily sheds hair strands to prevent hair from getting trapped in the pipe.