Patent Publication Number: US-7896132-B2

Title: Multi-level fall protection system for high-rise construction

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 60/859,205 filed Nov. 15, 2006. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a multi-level fall protection system for a structure under construction and a method for providing such a system. More particularly, the invention relates to a multi-level fall protection system for a structure having multiple reinforced concrete decks, wherein flexible support lines are anchored to vertical support posts which extend between multiple decks, thereby providing fall prevention and/or fall arrest capabilities on multiple levels of the structure. 
     2. The Prior Art 
     Presently-used measures for preventing and/or arresting falls during high rise construction include wood planking loosely set in supports around the perimeter of a floor under construction, and harness systems worn by workers which are tethered to a support line consisting of a strap secured to an eye protruding out of the poured concrete. Other systems include horizontal netting supported by poles extending out from the construction site. These nets however are meant to stop and catch falling debris, not personnel. 
     The following references, the disclosures of which are incorporated herein by reference, relate to various fall protection systems. 
     U.S. Patent Application Publication No. 2001/0032435 to Austin describes a portable fall-arrest system temporarily attached to the reinforced concrete deck of a structure under construction. Threaded shafts are threaded into internally threaded inserts embedded in the concrete flooring or inserted through holes formed in the concrete flooring and secured with flanged nuts. Stanchions having a tubular posts and base plates are placed over the threaded shafts and a safety cable is strung between connector plates on two or more stanchions. 
     U.S. Pat. No. 6,691,826 to Dean describes a safety apparatus for construction workers working in elevated locations. The apparatus includes anchor members in the form of support posts which have flanged bases at their lower ends for clamping to an I-beam flange using a nut and bolt arrangement. Each support post has a radially extending lug on its upper end with an opening defined therein for receiving or securing a safety line. As shown in U.S. Pat. No. 7,048,090 to Dean et al., the support posts can have an I-shaped cross sectional configuration and can be clamped to a precast concrete structure, such as a concrete tilt panel. 
     U.S. Pat. No. 6,779,630 Choate shows a rebar stanchion horizontal lifeline fall arrest system wherein elongated tubular stanchions are slid over a section of rebar projecting from a reinforced concrete floor. The stanchions are supported with flexible guy members secured to additional projecting sections of rebar and a stanchion head slips over the top of the stanchion for supporting a cable lifeline. 
     U.S. Pat. No. 4,037,824 to Whitmer shows a safety post with a horizontal leg adapted to be detachably clamped to a structural beam and an integral vertical leg for retaining a safety cable. 
     U.S. Pat. No. 6,053,281 to Murray shows a safety rail system for installing around the perimeter of a rooftop work site. The system includes a plurality of vertical stanchions having links for receiving a safety cable tensioned with a winch. Each stanchion is supported in a sleeve portion of a hinged base plate and secured with a locking pin. The base plates are attached with appropriate fasteners to a vertical wall surface of the building and a second surface forming an edge with the vertical surface. 
     U.S. Pat. No. 6,763,910 to Cole shows a roof structure having safety stanchions mounted directly to a building roof for supporting a safety cable. The safety stanchions are secured to the roof structure at the intersections of the roof rafters and purlins. 
     U.S. Pat. No. 6,173,809 to Cole et al. shows a safety stanchion for supporting and anchoring a safety cable. The stanchion includes a tapered tubular post having an upper end for supporting a safety cable and a lower end attached to a support base that is mounted to a flanged structural beam. 
     U.S. Pat. No. 6,966,531 to Curtin shows a roof anchor for securing a safety line to the rafter of a timber roof frame. 
     Although a number of fall protection systems are known, a need exists for a multi-level fall protection system for a structure under construction which provides fall prevention and/or fall arrest on multiple levels of the structure, for example on multiple reinforced concrete decks or floors of a structure. Moreover, a need exists for a multi-level fall protection system which can be quickly and easily assembled, adapted to the particular structure as it is constructed, disassembled and re-used on additional structures. 
     SUMMARY OF THE INVENTION 
     An embodiment of the invention provides a multi-level fall protection system for a structure under construction, the structure having a plurality of reinforced concrete decks with a plurality of openings provided in the decks, the plurality of decks including a first deck and a second deck arranged above the first deck. The multi-level fall prevention system includes a plurality of bearing plates, each of the plurality of bearing plates arranged in an associated opening in the first deck and comprising a flange portion larger than the associated opening. 
     The system further includes a plurality of lateral support blocks, each of the plurality of lateral support blocks being arranged in an associated opening in the second deck. Each of a plurality of vertical support posts are detachably secured at a bottom portion to an associated bearing plate and extend upwardly through an associated opening in the second deck. The vertical support posts are supported laterally by an associated lateral support block. At least one flexible support line extends between and is coupled to a pair of the vertical support posts. 
     In a further aspect of the invention, the vertical support posts have a plurality of spaced apart openings therethrough for receiving a respective fastener. The fastener secures an end of the flexible support line to the vertical support post. 
     In a further aspect of the invention, at least one of the vertical support posts comprises a plurality of tubular sections coupled together. In another aspect, a tensioning mechanism is coupled to at least one of the flexible support lines. 
     In a further aspect of the invention, a plurality of flexible support lines extend between and are coupled to a plurality of pairs of vertical support posts. At least one of the flexible support lines may serve as a handrail for preventing a fall and at least one of the flexible support lines may serve as a lifeline for arresting a fall. The plurality of flexible support lines may form a plurality of handrails extending around a perimeter of a deck. The plurality of flexible support lines may form a plurality of lifelines extending along an interior portion of a deck. 
     In a further aspect, at least one of the bearing plates includes a connection member projecting upwardly from its flange portion, wherein the connection member is sized and shaped to receive the bottom portion of a vertical support post. The connection member may have a first opening therethrough, and the bottom portion of the vertical support post may have a second opening therethrough, wherein the bottom portion of the vertical support post is detachably secured to the connection member with a pin inserted through the first and second openings. 
     In a further aspect, at least one of the lateral support blocks includes a flange portion larger than the associated opening in the second deck and a substantially central opening for allowing a vertical support post to pass through the lateral support block. The lateral support block may comprises at least two lateral support block sections arranged in proximity to one another to form the substantially central opening. 
     An additional aspect of the invention provides a method for providing a multi-level fall protection system for a structure under construction, the structure having a plurality of reinforced concrete decks with a plurality of openings provided in the decks, the plurality of decks including a first deck and a second deck arranged above the first deck. The method includes the steps of arranging each of a plurality of bearing plates in an associated opening in the first deck, wherein the bearing plates comprise a flange portion larger than the associated opening in the first deck; arranging each of a plurality of vertical support posts so as to extend upwardly from the first deck through an associated opening in the second deck; detachably securing a bottom portion of the vertical support posts to an associated bearing plate; arranging each of a plurality of lateral support blocks in an associated opening in the second deck for laterally supporting an associated vertical support post; and coupling at least one flexible support line to each of a pair of the vertical support posts so as to extend between the pair of vertical support posts. 
     A multi-level fall protection system and method according to embodiments of the invention have the advantage of providing fall prevention and/or fall arrest on multiple levels of a structure under construction, for example on multiple reinforced concrete decks or floors of a structure. A multi-level fall protection system and method according to embodiments of the invention further provide the advantages of rapid and simple assembly, adaptation to a particular structure as it is constructed, disassembly and re-use. 
     A further advantage of a multi-level fall protection system and method according to embodiments of the invention is that both fall prevention, through the use of flexible support lines serving as handrails and fall arrest, through the use of flexible support lines serving as lifelines, may be provided. Moreover, the handrails and/or lifelines may be configured to extend around the perimeter of the structure and/or the interior of the structure, thereby providing the capability for both perimeter and/or interior fall prevention and/or arrest. 
     Another advantage of a multi-level fall protection system and method according to embodiments of the invention is that the components of the system may be provided in modular, standardized sizes and/or lengths which results in significant cost savings over known systems as components may be disassembled when no longer needed and re-used on another project. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It should be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the invention. 
       In the drawings, wherein similar reference characters denote similar elements throughout the several views: 
         FIG. 1   a  shows a side view and a frontal view of an upper vertical support post according to an embodiment of the invention; 
         FIG. 1   b  shows a side view and a frontal view of a lower vertical support post according to an embodiment of the invention; 
         FIG. 1   c  shows a side view and a frontal view of a splicing member for a vertical support post according to an embodiment of the invention; 
         FIG. 1   d  shows a side view of a vertical support post extending between multiple reinforced concrete decks according to an embodiment of the invention; 
         FIG. 2  shows cross section of a vertical support post comprising a plurality of tubular sections according to an embodiment of the invention; 
         FIG. 3  show some exemplary hardware for coupling a vertical support post to a bearing plate and for coupling a flexible support line to a vertical support post according to embodiments of the invention. 
         FIG. 4   a  shows a plan view of an opening in a reinforced concrete deck for a multi-level fall protection system according to an embodiment of the invention; 
         FIG. 4   b  shows a cross section along section AA of the opening shown in  FIG. 4   a;    
         FIG. 5   a  shows a plan view of a bearing plate according to an embodiment of the invention; 
         FIG. 5   b  shows a cross section along section BB of the bearing plate shown in  FIG. 5   a;    
         FIG. 6   a  shows a plan view of a two-part lateral support block according to an embodiment of the invention; 
         FIG. 6   b  shows a plan view of the two-part lateral support block shown in  FIG. 6   a  in an assembled condition; 
         FIG. 6   c  shows a cross section along section CC of the lateral support block shown in  FIG. 6   b;    
         FIG. 7  shows a portion of a multi-level fall protection system according to an embodiment of the invention, including flexible support lines and hardware for coupling the support lines to the vertical support posts; 
         FIG. 8  shows a multi-level fall protection system according to an embodiment of the invention with flexible support lines configured as handrails and being calibrated; 
         FIG. 9  shows the multi-level fall protection system shown in  FIG. 8  with the handrails at rest; 
         FIG. 10  shows the multi-level fall protection system shown in  FIG. 8  with a handrail being subject to a load; 
         FIG. 11  shows a multi-level fall protection system according to an embodiment of the invention with flexible support lines configured as handrails and visual barriers provided on the upper handrail of the top deck of a structure under construction; 
         FIG. 12  shows a multi-level fall protection system according to an embodiment of the invention with flexible support lines configured as handrails and lifelines, with the lifelines being calibrated; 
         FIG. 13  shows the multi-level fall protection system shown in  FIG. 12  with the lifelines at rest; 
         FIG. 14  shows the multi-level fall protection system shown in  FIG. 12  with a lifeline being subject to a load; 
         FIG. 15  shows a multi-level fall protection system according to an embodiment of the invention with flexible support lines configured as handrails and lifelines, with the lifelines being calibrated; 
         FIG. 16  shows the multi-level fall protection system shown in  FIG. 15  with the lifelines at rest; 
         FIG. 17  shows the multi-level fall protection system shown in  FIG. 15  with a lifeline of an interior span being subject to a load; 
         FIG. 18  shows a multi-level fall protection system according to an embodiment of the invention with a lifeline of an exterior span being subject to a load; 
         FIG. 19  shows a multi-level fall protection system according to an embodiment of the invention with flexible support lines configured as handrails and lifelines, with the lifelines positioned on the lower levels of the structure and being calibrated; 
         FIG. 20  shows the multi-level fall protection system shown in  FIG. 19  with the lifelines at rest; and 
         FIG. 21  shows the multi-level fall protection system shown in  FIG. 19  with the lifelines being subject to a load. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The invention relates to a multi-level fall protection system for a structure under construction and a method for providing such a system. The structure under construction may be for example a multi-story or high-rise structure including a plurality of reinforced concrete decks  10  ( FIG. 1   d ). The concrete decks or slabs  10  may include a first deck  11  and a second deck  12  arranged above first deck  11 . First deck  11  may be a base or stripping floor, and second  12  and subsequent decks may be intermediate or erection floors. A system according to the invention may also provide fall protection for an uppermost or new deck comprising wood studs and plywood sheets for laying the next concrete floor. The terms first and second deck as used herein are relative terms and refer to any two levels, slabs or floors of the structure which are arranged one above the other. 
     A plurality of openings  13  are provided in each of first deck  11  and second deck  12 . These openings may be formed by using an appropriately sized form or box, for example a wood box or “pack out” and casting the concrete around the form or box to provide an opening or void. Once the fall protection system is no longer needed and is removed, the openings may be filled with concrete or otherwise filled in or over. As shown in  FIGS. 4   a  and  4   b , the opening  13  in the deck have a substantially square tapered shape, with the opening being larger on a top surface of the deck and gradually tapering to a smaller opening on the lower surface of the deck. For example, an opening  13  may have a substantially square shape having sides of approximately twelve inches on the top surface of the deck and sides of approximately ten inches on the bottom surface of the deck. These sizes and dimensions are exemplary only, and openings  13  may be of any size and shape appropriate for arranging and supporting the various components of the multi-level fall protection system disclosed herein. 
     A plurality of bearing plates  20  are provided for supporting vertical support posts  40 . Each of bearing plates  20  is arranged in an associated opening  13  in the first deck  11 .  FIGS. 5   a  and  5   b  show an example of a bearing plate  20  according to an embodiment of the invention. As shown, bearing plate  20  may include a flange portion  21  which is larger in size than the associated opening  13  in the respective deck. In this way, flange portion  21  prevents bearing plate  20  from passing through opening  13 . Flange portion  21  may also include one or more handhold openings as shown in  FIG. 5   a  to facilitate lifting and carrying bearing plate  20  as it inserted and removed from openings  13 . 
     Bearing plate  20  and flange portion  21  may be formed from any suitable material providing sufficient support for the multi-level fall protection system, for example flange portion  21  may comprise a one quarter inch thick steel plate, having a substantially square shape with sides measuring approximately fifteen inches. These sizes and dimensions are exemplary only, and bearing plate  20  and flange  21  may be of any size and shape appropriate for arranging and supporting the various components of the multi-level fall protection system disclosed herein. 
     Bearing plate  20  may also include diagonal portions or plates which extend into opening  13  as shown in  FIG. 5   b . The diagonal plates may form a tapered structure substantially conforming to the tapered shape of opening  13 , thereby seating bearing plate  20  in associated opening  13 . 
     Bearing plate  20  may further comprise a connection member  22  projecting upwardly from flange portion  21 . Connection member  22  is sized and shaped to receive a bottom portion of a vertical support post  40  to be secured to the bearing plate  20 . For example, connection member  22  may include a length of round structural tube extending approximately six inches in height from flange  21 . A vertical support post  40  may comprise a round tube having an inner and outer diameter such that a bottom portion of vertical support post  40  may be inserted into connection member  22  or over connection member  22 , providing a secure fit. Connection member  22  and bottom portion of vertical support post  40  may of course comprise any other suitable shapes. 
     As shown in  FIGS. 5   a  and  5   b , connection member  22  may include a first opening  23  therethrough. The bottom portion of a vertical support post  40  may have a corresponding or second opening  41  therethrough, thereby allowing the bottom portion of the vertical support post  40  to be detachably secured to connection member  22  and bearing plate  20  with a pin  80  inserted through the first  23  and second  41  openings. Pin  80  may be any suitable fastener, such as, for example, a three quarter inch diameter stainless steel pin having detents or keepers at one end ( FIG. 3 ), a nut and bolt arrangement or the like. 
     Although, bearing plates  20  are shown configured to support vertical support posts  40  substantially perpendicular to decks  10 , bearing plates  20  may also be configured to support vertical support posts  40  at an angle. Moreover, bearing plates  20  may comprise a receiver cup projecting into opening  13  for receiving a bottom portion of a vertical support post. 
     Flange  21  may include outwardly extending tabs and a form may be used to produce an opening  13  in the cast concrete floor so that the opening is shaped to receive these tabs. In a further embodiment, square holes may be formed in the concrete floor and inserts may be used to form a round opening for accepting a round portion of the bearing plate  20 . 
     A plurality of lateral support blocks or lateral bracing blocks  30  are provided for supporting a vertical support post  40  in a lateral direction. Lateral support blocks  40  are arranged in an associated opening  13  provided in the second deck  12  or subsequent decks arranged over first deck  11 . 
     Lateral support blocks  30  may comprise appropriately sized sleeves or wedges removably inserted into opening  13  in an intermediate deck or floor for maintaining an associated vertical support post  40  in proper position and providing lateral support for the associated support post. Lateral support blocks  40  may be formed from any suitable material such as plastic, metal, rubber or wood, for example plywood or oak. 
     As shown in  FIG. 6   c , lateral support block  30  may include a flange portion  33  larger than the associated opening  13  in the second deck  12 . For example flange  33  may comprise a substantially square sheet of three quarter inch thick plywood with sides measuring approximately fifteen inches in length. Moreover lateral support block  30  has a substantially central opening  34  ( FIG. 6   b ) sized and shaped to allow a vertical support post  40  to pass through lateral support block  30 . For example, opening  34  may have a substantially square shape with sides measuring approximately four and nine sixteenth inches in length. The sides of lateral support block  30  may extend downwardly into associated opening  13  in deck  12  and may be formed to conform to a taper or shape of opening  13  such that lateral support block  30  is firmly and securely seated in opening  13 . For example, sides of lateral support block  30  may extend downwardly approximately three and one half inches from flange  33  into opening  13 . These sizes and dimensions are exemplary only, and lateral support block  30  may be of any size and shape appropriate for providing lateral support to an associated vertical support post. 
     As shown in  FIGS. 6   a  and  6   b , lateral support block  30  may be formed from two or more lateral support block sections  31 ,  32  which are arranged in proximity to one another to form the substantially central opening  34 . 
     The multi-level fall protection further includes a plurality of vertical support members or posts  40 . Each of the vertical support posts  40  is detachably secured at a bottom portion to an associated bearing plate  20 , extends upwardly through an associated opening  13  in the second deck  12  and is supported laterally by an associated lateral support block  30 . 
     Vertical support posts  40  may be fabricated from structural aluminum, steel or any material of suitable properties and strength and may have a round, square, rectangular or other shaped cross-section. Vertical support posts may be solid or tubular. Preferably, vertical support posts  40  are of a length and weight such that they may be lifted and positioned (“jumped”) from one floor to the next by hand (manpower). 
     Vertical support posts  40  may include have a plurality of spaced apart openings  41  therethrough for receiving a respective fastener  60  for securing a respective end of a flexible support line  50  to the vertical support post. Fastener  60  may comprise, for example, an eye bolt or an eye nut, or any fastener suitable for securing an end of a flexible support line  50  to post  40 . For example, as shown in  FIG. 3 , fastener  60  may include a length of three quarter inch diameter threadbar  61  and a pair of three quarter inch shouldered eye nuts threaded onto each end of the threadbar. 
     Vertical support posts  40  may further comprise a plurality of tubular sections  42 ,  43  coupled together. For example,  FIG. 1   a  shows a side view and a frontal view of an upper vertical support post according to an embodiment of the invention. The upper vertical support post may comprise a thirteen foot length of four inch nominal diameter schedule 80 aluminum pipe or tube having an outer diameter of approximately 4.5 inches and a wall thickness of approximately 0.337 inches. Spaced apart openings  41  may be provided on the post spaced at approximately six inches on center.  FIG. 1   b  shows a side view and a frontal view of a lower vertical support post according to an embodiment of the invention. The lower vertical support post may comprise a thirteen foot length of four inch nominal diameter schedule 40 aluminum pipe or tube having an outer diameter of approximately 4.5 inches and a wall thickness of approximately 0.237 inches. Spaced apart openings  41  may be provided on the lower post spaced at approximately six inches on center. 
       FIG. 1   c  shows a side view and a frontal view of a splicing member  44  used to join an upper and lower vertical support post Splicing member  44  may comprise a four and one half foot length of four and one half inch nominal diameter schedule 80 aluminum pipe or tube having an outer diameter of approximately 5.563 inches and a wall thickness of approximately 0.375 inches. Spaced apart openings  41  may be provided on the splicing member  44  spaced at approximately six inches on center. A portion of upper  42  and lower  43  vertical support posts may be inserted into the splicing member  44  and secured by inserting an appropriate fastener.  FIG. 2  shows cross section of a vertical support post  40  comprising a plurality of tubular sections  42 ,  43  and a splicing member  44  according to an embodiment of the invention. 
       FIG. 1   d  shows a side view of a vertical support post  40  extending between multiple reinforced concrete decks according to an embodiment of the invention. As shown, vertical support post  40  may comprise a number of sections spliced or otherwise joined together to stand three working levels in height. The vertical support post  40  is laterally supported at all three levels (by lateral support blocks  30  at the upper levels and bearing plate  20  at a first level) and vertically supported by a bearing plate  20  at a base only. 
     The vertical support posts  40  provide vertical and horizontal anchorages for horizontal lifelines and handrail systems provided at each level of the structure under construction. For example, the vertical support posts may be arranged approximately twenty feet apart on center along a perimeter and interior portions of the structure. At the uppermost working level, the vertical support posts act as interconnected cantilevered supports which provide varying degrees of flexibility dependent on the number of spans in line and the location of the posts along a particular run. At the lower levels, where bracing is provided by lateral support blocks or bearing plates, the anchorage deflection is much less pronounced. 
     At least one flexible support line  50  extends between and is coupled to a pair of the vertical support posts  40 . Flexible support line  50  may comprise a solid or stranded cable, nylon strapping, robe or any other flexible line of appropriate strength. Flexible support line  50  may include an eye at one or both ends to facilitate rigging the line to vertical support posts  40 . 
       FIG. 7  shows a portion of a multi-level fall protection system according to an embodiment of the invention, including flexible support lines  50  and hardware for coupling the support lines to the vertical support posts. As shown, the flexible support lines may comprises a handrail  51  for preventing a fall and or a lifeline  52  for arresting a fall. 
     Preferably, the multi-level fall protection system is arranged such that a plurality of handrails and/or lifelines extend around a perimeter of one or more decks of the structure. Additionally, one or more lifelines may extend along an interior portion of one or more of the decks. In this way, a multi-level fall protection system according to an embodiment of the invention can provide both handrails for fall prevention and lifelines for fall arrest. 
     With respect to the lifelines  52 , workers or other personnel on the structure typically wear safety harnesses which are tethered to the lifelines by a lanyard. Should a worker fall, the lifeline  52  which is coupled to the worker&#39;s harness via the lanyard, will arrest the worker&#39;s fall. In addition to preventing and arresting falls, a system according to the invention may be used to rescue a worker who has fallen and is suspended from a safety cable by attaching a boom mounted hoist to an anchoring member on a pole, lowering a line for the fallen person to hook to their harness, and lifting the person to safety. 
     As shown in  FIG. 7 , both the handrails  51  and lifelines  52  may be similarly rigged, however the handrail and lifeline support lines and rigging hardware will typically have different requirements and specifications. For example, a suitable handrail line may be one quarter inch diameter type  304  stainless steel stranded cable, 7×19 IWRC. A suitable lifeline may comprise three eighth inch diameter type  304  stainless steel stranded cable, 7×19 IWRC. Both the handrails and lifelines may be detachably coupled to the fasteners  60  disposed at the desired heights on the respective vertical support posts using an appropriate fastener  100 , such as a snap hook, carabiner or the like. An example of a suitable fastener  100  for coupling a flexible support line  50  to an eye bolt or eye nut mounted to vertical support post  40  is a 1.75 inch opening self locking snap hook. 
     A tensioning mechanism  70  may be coupled to the flexible support line  50  to impart an appropriate tension on the support line. Tensioning mechanism  70  may be, for example, a turnbuckle, such as a one half inch nominal diameter turnbuckle with six inches of take-up for a handrail  51  or a three quarter inch nominal diameter turnbuckle with six inches of take-up for a lifeline  52 . 
     The multi-level fall protection system according to the invention and all of its components should meet all applicable safety and/or regulatory standards. For example, with respect to the handrail system, the breaking strength of any individual component should exceed twice the maximum calculated load. The top handrail and mid handrail should have a minimum diameter of one quarter inch. The top rail should be capable of supporting a 200 pound load from any direction and should not sag below 39 inches upon maximum load. The mid handrail should be positioned approximately 18 inches below the top hand rail and should be capable of supporting a 150 pound load from any direction. 
     With respect to the lifeline system, the breaking strength of any individual component should exceed twice the maximum calculated load. Worker deceleration should be limited to a 900 pound load with personal shock absorber deployment limited to 42 inches. A worker should not come into contact with any obstacles during a fall and the worker&#39;s free fall distance should be limited to six feet. 
       FIG. 8  shows a multi-level fall protection system according to an embodiment of the invention with flexible support lines configured as handrails  51  and being calibrated. Handrails  51  should be calibrated on installation as follows. A 20 pound calibration weight is hung from a top handrail at a center span of the section or sections being calibrated. A 1.5 to 2.0 inch calibration cusp is allowable at all top rails. The lower hand rails have lesser requirements and should be set taught without exceeding the free hanging tension of the upper handrail. 
       FIG. 9  shows the multi-level fall protection system shown in  FIG. 8  with the handrails at rest. A maximum allowable sag for the top handrail at rest may be one quarter inch.  FIG. 10  shows the multi-level fall protection system shown in  FIG. 8  with a handrail being subject to a load. For example under a 200 pound, a top handrail initially at 45 inches above the deck should have a maximum deflection to 39 inches above the deck. 
       FIG. 11  shows a multi-level fall protection system according to an embodiment of the invention with flexible support lines configured as handrails  51  and visual barriers  55  provided on the upper handrail of the top deck of a structure under construction. Visual barriers  55  may comprise flags, ribbon or the like and improve visibility and awareness of the perimeter edge of the structure under construction. The visual barrier line may be provided, for example at the uppermost working level of the structure and may have no structural requirements. At this level, workers must be attached to a lifeline, as no functioning handrails may be provided. The visual barrier line may be transformed into a handrail as the next deck or floor is erected and the system is raised or jumped to the next floor. 
       FIG. 12  shows a multi-level fall protection system according to an embodiment of the invention with flexible support lines configured as handrails  51  and lifelines  52  with the lifelines  52  being calibrated. The horizontal lifelines  52  must be calibrated based on the location and configuration of the particular system. A ten pound calibration weight may be used and a three inch initial cup may be typical.  FIG. 13  shows the multi-level fall protection system shown in  FIG. 12  with the lifelines at rest. The lifelines  52  may sag by approximately one and one quarter inch at rest.  FIG. 14  shows the multi-level fall protection system shown in  FIG. 12  with a lifeline being subject to a load simulating a fall arrest, for example a 900 pound deployment load. 
       FIG. 15  shows a multi-level fall protection system according to an embodiment of the invention with flexible support lines configured as handrails  51  and lifelines  52 , with the lifelines  52  being calibrated.  FIG. 16  shows the multi-level fall protection system shown in  FIG. 15  with the lifelines  52  at rest. 
       FIG. 17  shows the multi-level fall protection system shown in  FIG. 15  with a lifeline  52  of an interior span being subject to a load and  FIG. 18  shows a multi-level fall protection system according to an embodiment of the invention with a lifeline of an exterior span being subject to a load. 
       FIG. 19  shows a multi-level fall protection system according to an embodiment of the invention with flexible support lines configured as handrails  51  and lifelines  52 , with the lifelines  52  positioned on the lower levels of the structure and being calibrated. For example, lifelines  52  may be calibrated with a ten pound load and deflect a maximum of approximately 18 inches.  FIG. 20  shows the multi-level fall protection system shown in  FIG. 19  with the lifelines  52  at rest. At rest, lifelines  52  may sag, for example, a maximum of approximately 16 inches.  FIG. 21  shows the multi-level fall protection system shown in  FIG. 19  with the lifelines being subject to a load simulating a fall arrest, for example a 900 pound deployment load. 
     Accordingly, while several embodiments of the present invention have been shown and described, it is obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.