Abstract:
An apparatus for determining the safety of a working environment comprising a panel assembly including first D-Ring indicia corresponding to D-Ring height, a first slider supported for movement relative to the panel assembly, the first slider including first anchor height indicia corresponding to anchor height and a Free Fall Distance (FFD) indexing arrow, a second slider supported for movement relative to the panel assembly, the second slider including FFD indicia corresponding to FFD first lanyard length indicia corresponding to lanyard length. The first slider is moved to a first slider FFD calculation position based on a determined anchor height. The second slider is moved to a second slider FFD calculation position based on a determined lanyard length and a determined D-Ring height. The FFD is determined based on a relative position of the FFD indexing arrow on the first slider and the FFD indicia on the second slider.

Description:
RELATED APPLICATION 
     This application claims benefit of U.S. Provisional Application Ser. No. 61/907,792 filed Nov. 22, 2013, which is incorporated by reference herein in its entirety. 
    
    
     TECHNICAL HELD 
     The present invention relates to fall protection equipment and devices. In particular, the invention relates to a device for establishing a Free Fall Distance (FFD) and Clearance Required (CR) for workers working at height by utilizing user input of measurements from a worker&#39;s personal protective equipment (PPE) (e.g., lanyard length) and certain work site conditions (e.g., anchor tie off height). 
     BACKGROUND 
     Workers that work at heights where there is a risk of injury from falling are required by law (Occupational Health and Safety Legislation) to calculate their Free Fall Distance (FFD) and Clearance Required (CR), and keep them within safe parameters. There is a long series of mathematical calculations necessary to determine the FFD and CR depending on the equipment the workers are using and their work site configuration. Workers in these situations often have limited education and mathematical skills, which make it challenging for them to accurately calculate the FFD and CR, as required by law. 
     There are website applications available online that will permit a worker to calculate FFD and CR. However, the equipment required to use these applications (e.g., computers, tablets or mobile telephones) is not intrinsically safe and is often unfeasible or prohibited from worksites. 
     Table 1 is a list of acronyms that are used in industry to determine FFD and CR.  FIG. 10  is an illustration which assists in the understanding of the terms in the following TABLE 1. 
     
       
         
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Acronym 
                 Description 
               
               
                   
               
             
             
               
                 L 
                 Length of lanyard, shock absorber &amp; connecting hardware 
               
               
                   
                 (initial overall length) 
               
               
                 B 
                 Distance from the feet to the harness D-Ring (Standing 
               
               
                   
                 worker) 
               
               
                 C 
                 Distance from the feet to the anchorage level (Standing 
               
               
                   
                 worker) 
               
               
                 SAE 
                 Shock Absorber Extension 
               
               
                 DS 
                 D-ring Slippage (typically 1 ft or 0.3 m) 
               
               
                 SM 
                 Safety Margin between bottom of feet and level below 
               
               
                   
                 (typically 2 ft (0.6 m) or 3 ft (0.9 m)) 
               
               
                 FFD 
                 Free Fall Distance = L + B − C 
               
               
                 TFD 
                 Total Fall Distance = FFD + DS + SAE 
               
               
                 CR 
                 Clearance Required 
               
               
                 CR A   
                 Clearance Required from the Anchor = TFD + SM + C 
               
               
                   
               
             
          
         
       
     
     Exposure to arrest forces that exceed safe limits can lead to injuries, such as: ruptured intestines, fractured liver, traumatic abdominal organ displacement into the chest cavity, and or fractures and tears to the extremities. Workers utilizing fall protection equipment must ensure that if they fall, the arrest forces imposed on their bodies during fall arrest are kept within safe limits. These arrest forces are determined in part by their FFD. As the free fall distance increases, so does the impact force on their bodies, anchor or anchorage, and all system components which could fail if forces are exceeded. 
     Free fall distance (FFD) is defined as the vertical distance from the onset of a fall to the point where the fall-arrest system begins to apply force to arrest the fall. To calculate the FFD, the length of lanyard, shock absorber and connecting hardware (L) is added to the distance from the worker&#39;s feet to the harness D-Ring (B), which is subtracted from the distance between the working level and anchor height (C). The formula may be stated as Free Fall Distance=Length of lanyard+D-Ring Height−Anchor Height and may be stated as follows:
 
FFD= L+B−C   (1)
 
     Total fall distance (TFD) is defined as the maximum distance fallen by the worker using a fall-arrest system between the onset of a fall and the instant when the worker first achieves zero vertical velocity. Total-fall distance is often determined as the displacement of the dorsal D-Ring on the full-body harness and is the sum of the free fall and the deceleration distance. It also includes any applicable swing-fall distance. It is essentially the vertical distance from the point at which a worker falls to the point where the fall stops (that is, after all fall arresting system components have extended). 
     To calculate the TFD, the Free Fall Distance (FFD) is added to the D-Ring Slippage (DS) and the extension of the shock absorber (SAE). The maximum shock absorber extension (as indicated on the unit) must be used when determining the total fall distance. The formula may be stated as Total Fall Distance=Free Fall Distance+D-Ring Slippage+Shock Absorber Extension and may be written as follows:
 
TFD=FFD+DS+SAE  (2)
 
     CSA Standard Z259.16-04 Design of Active Fall Protection Systems defines clearance as: “the distance from a specified reference point, such as the working platform or anchorage of a fall-arrest system, to the highest obstruction that a worker might encounter during a fall.” 
     Minimum fall clearance (CR) from the Anchor is the total fall distance (TFD) plus a safety margin (SM) of at least 0.6 m (2 ft) plus Anchor height. The formula may thus be written as follows:
 
CR A =TFD+SM+ C   (3)
 
     In summary, without the present invention, the worker must remember the following formulas (in bold) and complete calculations (like the example calculations shown below), which leave room for error and may lead to worker injury if miscalculated:
 
FFD= L+B−C   (1)
 
FFD=6+5−7
 
FFD=4
 
TFD=FFD+DS+SAE  (2)
 
TFD=4+1+4
 
TFD=9
 
CR A =TFD+SM+ C   (3)
 
CR A =9+2+7
 
CR A =18
 
     It would be beneficial if a system was developed which did not require a worker to remember the aforementioned formulas or perform calculations similar to those shown above, so as to reduce errors and worker injuries. 
     SUMMARY 
     The present invention is designed to address at least one of the aforementioned problems and/or meet at least one of the aforementioned needs. 
     A method and apparatus for determining Free Fall Distance (FFD) and Clearance Required (CR) is disclosed. The apparatus is in the form of a slide rule that includes first and second sliders that move within a front and back of the slide rule. The front of the first slider includes indicia corresponding to anchor height, while the front of the second slider includes indicia corresponding to lanyard length and FFD. By moving the sliders such that appropriate indicia are placed within corresponding windows on the front of the slide rule, the FFD may be determined without performing any mathematical calculations. 
     Similarly, the back of the first slider includes indicia corresponding to shock absorber extension values, while the back of the second slider includes indicia corresponding to lanyard length and CR. By moving the sliders such that appropriate indicia are placed within corresponding windows on the back of the slide rule, CR may be determined without performing any mathematical calculations. 
     The present invention may thus be embodied as a method for determining the safety of a working environment comprising the following steps. A panel assembly including first D-Ring indicia corresponding to D-Ring height is provided. A first slider for movement is arranged relative to the panel assembly. The first slider includes first anchor height indicia corresponding to anchor height and a Free Fall Distance (FFD) indexing arrow. A second slider is arranged for movement relative to the panel assembly. The second slider includes FFD indicia corresponding to FFD and first lanyard length indicia corresponding to lanyard length. The first slider is moved to a first slider FFD calculation position based on a determined anchor height. The second slider is moved to a second slider FFD calculation position based on a determined lanyard length and a determined D-Ring height. The FFD is determined based on a relative position of the FFD indexing arrow on the first slider and the FFD indicia on the second slider. 
     The present invention may also be embodied as an apparatus for determining the safety of a working environment comprising a panel assembly, a first slider, and a second slider. The panel assembly includes first D-Ring indicia corresponding to D-Ring height. The first slider is supported for movement relative to the panel assembly and includes first anchor height indicia corresponding to anchor height and a Free Fall Distance (FFD) indexing arrow. The second slider is supported for movement relative to the panel assembly and includes FFD indicia corresponding to FFD and first lanyard length indicia corresponding to lanyard length. The first slider is moved to a first slider FFD calculation position based on a determined anchor height. The second slider is moved to a second slider FFD calculation position based on a determined lanyard length and a determined D-Ring height. The FFD is determined based on a relative position of the FFD indexing arrow on the first slider and the FFD indicia on the second slider. 
     The present invention may also be embodied as apparatus for determining the safety of a working environment comprising a panel assembly, a first slider, and a second slider. The panel assembly includes numerical indicia corresponding to D-Ring height. The first slider supported for movement relative to the panel assembly and includes numerical indicia corresponding to shock absorber extension and a CR A  indexing arrow. The second slider is supported for movement relative to the panel assembly and includes numerical indicia corresponding to CR A  and numerical indicia corresponding to lanyard length. The first slider is moved to a first slide CR A  calculation position based on a determined shock absorber extension. The second slider is moved to a second slide CR A  calculation position relative to the panel assembly based on a determined lanyard length and a determined D-Ring height. The CR A  is determined based on a relative position of the CR A  indexing arrow on the first slider and the numerical indicia corresponding to CR A  on the second slider. 
     Other objects, features, embodiments and advantages of the invention will be apparent from the following specification taken in conjunction with the following drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a front view of an exemplary slide rule accordance with one embodiment of the present invention; 
         FIG. 2  is a rear view of the slide rule of  FIG. 1 ; 
         FIG. 3A  is an exploded view of the front of the slide rule of  FIG. 1 ; 
         FIG. 3B  is an exploded view of the back of the slide rule of  FIG. 1 ; 
         FIG. 4  is a schematic view of the front of the slide rule of  FIG. 1 , which shows a first slider that has been moved from its initial position and a second slider that is in its initial position; 
         FIG. 5  is a schematic cross-sectional view taken along line  5 - 5  of  FIG. 4 ; 
         FIG. 6A  is a plan view of the front panel of the device of  FIG. 1 ; 
         FIG. 6B  is a plan view of the front of the first and second sliders of  FIG. 1 ; 
         FIG. 7A  is a plan view of the back panel of the device of  FIG. 1 ; 
         FIG. 7B  is a plan view of the back of the first and second sliders of  FIG. 1 ; 
         FIG. 8  is a front view of the slide rule of  FIG. 1  showing the slide rule in use to determine Free Fall Distance; 
         FIG. 9  is a rear view of the slide rule of  FIG. 1  showing the slide rule in use to determine Clearance Required; and 
         FIG. 10  is a schematic view which diagrammatically depicts certain parameters used in determining Free Fall Distance and Clearance Required, along with defining certain terms. 
     
    
    
     DETAILED DESCRIPTION 
     While this invention is susceptible of embodiments in many different forms, there is shown in the drawings and will herein be described in detail, several embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspects of the invention to the embodiments illustrated. 
     With reference to  FIGS. 1 and 2 , a slide rule  10  for determining Free Fall Distance (FFD) and Clearance Required (CR) is shown. Specifically,  FIG. 1  illustrates a front view of the slide rule  10 , while  FIG. 2  is a rear view of the slide rule  10 . 
       FIGS. 3A and 3B  are exploded front and rear views, respectively, of the slide rule  10 . As shown in  FIGS. 3A and 3B , the slide rule  10  has five main components, namely, a first (front) panel  20 , a second (back) panel  30 , a third (center) panel  40 , a first (upper/top) slider  50  and a second (lower/bottom) slider  60 . 
     As shown in  FIG. 4 , which is a schematic front view of the slide rule  10 , the device  10  is constructed, such that the first and second sliders  50 ,  60  are moveable relative to the front, back and center panels  20 ,  30 ,  40 , all of which are fixed relative to one another.  FIG. 5 , which is a cross-sectional view taken along line  5 - 5  of  FIG. 4 , shows that adhesive  70  is used to attach the front panel  20  and the center panel  40  to each other. Similarly,  FIG. 5  shows that adhesive  70  is used to attach the rear panel  30  and the center panel  40  to each other. 
     With reference again to  FIGS. 3A and 3B , the center panel  40  is generally U-shaped and has a first (upper) leg  80 , a second (lower) leg  90 , a base  110  connecting the first and second legs  80 ,  90 , and a central member  120 . As will be understood with reference to  FIGS. 3A, 3B, 4 and 5 , adhesive  70  is applied between the front panel  20  and center panel  40  and between the rear panel  20  and the center panel  40 , so as to create first and second elongated slots  130 ,  140  (exaggerated in size in  FIG. 5 ), in which first and second sliders  50 ,  60 , respectively, move. Accordingly, in one embodiment, adhesive is applied in a configuration that essentially matches the shape of the central panel  40  (both front and back). 
     As shown in  FIGS. 3A and 3B , in order to retain the first slider  50  in first slot  130 , the first leg  80  of the center panel  40  includes an extension  150  that cooperates with a tab  160  of the first slider  50 . Similarly, in order to retain the second slider  60  in second slot  140 , the second leg  90  of the center panel  40  includes an extension  170  that cooperates with a tab  180  of the second slider  60 . Because the first and second sliders  50 ,  60  are designed to be retained within the first and second slots  130 ,  140 , in one embodiment, they are placed at an appropriate location during construction of the device, as they normally cannot be inserted into their respective slots after the front panel  20 , back panel  30  and central panel  40  have become fixed relative to one another. 
     In one embodiment, the front panel  20 , back panel  30 , center panel  40 , first slider  50  and second slider  60  are each made of plastic and are flexible. In one embodiment, the center panel  40  is white plastic with no printing thereon. In one embodiment, the first and second sliders  50 ,  60  are made of white plastic with indicia printed thereon (to be described in further detail in connection with  FIGS. 6B and 7B ). In one embodiment, the front and back panels  20 ,  30  are made of clear plastic with white coloring and indicia printed on portions thereof, such that certain areas (portions not colored with white) form windows (to be described in further detail in connection with  FIGS. 6A and 7A ). 
     Reference is now made to  FIG. 6A , which is a plan view of the front panel  20  of the slider  10  of  FIG. 1 . The front panel  20  includes indicia thereon, including title indicia  210 , operational indicia  220  (for free fall distance determination), diagrammatic indicia  230 , legend indicia  240 , units indicia  250 , anchor height window identifier  260 , lanyard length window identifier  270 , numerical indicia corresponding to D-Ring height  280 , D-Ring height indicia indicator  290  and index indicia  310  (vertical lines). The front panel also includes windows, including anchor height (top) window  320 , lanyard length (bottom) window  330  and main (middle) window  340 . The front panel  20  is generally rectangular with rounded corners and includes an arcuate notch  350  to permit a user to access ends of first and second sliders  50 ,  60  (see  FIG. 1 ). 
     In one embodiment, the index indicia are printed on the inside of the main window  340  (back of the front panel), as shown in  FIG. 3B . It should be noted that the horizontal lines in the main window  340  are not necessarily present, but are provided in  FIGS. 3A and 6A  to demonstrate the approximate lowermost position of the first slider  50  (in the case of the upper horizontal line) and the approximate uppermost position of the second slider  60  (in the case of the lower horizontal line). 
       FIG. 6B  is a plan view of the front of the first and second sliders  50 ,  60 . The front of the first slider  50  includes numerical indicia corresponding to anchor height  360 , along with an anchor height identifier  370 . In addition, the front of the first slider  50  includes an indexing arrow  380  (other shapes may be used) that cooperates with index indicia  310  of  FIG. 6A  (described and shown infra). As shown in  FIG. 6B , the indexing arrow  380  is aligned under the center of the numerical indicia corresponding to an anchor height  360  of 0. The numerical indicia corresponding to the anchor height  360  have a center-to-center spacing that corresponds to the spacing between adjacent index indicia  310  (see  FIG. 6A ). 
     As shown in  FIG. 6B , the front of the second slider  60  includes numerical indicia corresponding to free fall distance  410 , along with a free fall distance identifier  420 . The front of the second slider also includes numerical indicia corresponding to lanyard length  430 , along with a lanyard length identifier  440 . The numerical indicia corresponding to free fall distance  410  and the numerical indicia corresponding to lanyard length  430  have a center-to-center spacing that corresponds to the spacing between adjacent index indicia  310  (see  FIG. 6A ). Furthermore, to the extent that the numerical indicia corresponding to free fall distance  410  and the numerical indicia corresponding to lanyard length have equal numerical values, such values are vertically aligned with one another. In addition, the numerical indicia corresponding to the free fall distance  410  cooperates with the index indicia  310  and indexing arrow  380  (other shape may be used) to enable a user to determine a free fall distance (shown and described infra). 
     Reference is now made to  FIG. 7A , which is a plan view of the back panel  30  of the slider  10  of  FIG. 1 . The back panel  30  includes indicia thereon, including title indicia  510 , operational indicia  520  (for clearance required determination), D-Ring slippage indicia  530 , Safety Margin indicia  540 , cautionary indicia for Stretch Harness  550 , legend indicia  560  (for CR A  and SAE), units indicia  570 , numerical indicia corresponding to D-Ring height  580 , D-Ring height indicia indicator  590 , shock absorber extension window identifier  610 , lanyard length window identifier  620  and index indicia  630  (vertical lines). The back panel  30  also includes windows, including shock absorber extension (top) window  640 , lanyard length (bottom) window  650  and main (middle) window  660 . The back panel  30  is generally rectangular with rounded corners and includes an arcuate notch  670  to permit a user to access ends of first and second sliders  50 ,  60  (see  FIG. 2 ). 
     In one embodiment, the index indicia are printed on the inside of the main window  660  (back of the back panel), as shown in  FIG. 3A . It should be noted that the horizontal lines in the main window  660  are not necessarily present, but are provided in  FIGS. 3B and 7A  to demonstrate the approximate lowermost position of the first slider  50  (in the case of the upper horizontal line) and the approximate uppermost position of the second slider  60  (in the case of the lower horizontal line). 
       FIG. 7B  is a plan view of the back of the first and second sliders  50 ,  60 . The back of the first slider  50  includes numerical indicia corresponding to shock absorber extension values  680 . In one embodiment (shown in  FIG. 7B ), non-numerical indicia  690  (in this case, dots) are placed between numerical indicia corresponding to shock absorber extension values. Such non-numerical indicia indicate half of the numerical increment between adjacent numerical indicia (e.g., 1.5, 2.5, 3.5, etc.). In addition, the back of the first slider  50  includes an indexing arrow  710  that cooperates with index indicia  630  of  FIG. 7A  (described and shown infra). As shown in  FIG. 7B , the indexing arrow  710  is aligned under where the center of the numerical indicia corresponding to shock absorber extension values  680  of −2 would be. The numerical indicia corresponding to shock absorber extension values  680  have a center-to-center spacing that corresponds to the spacing between adjacent index indicia  630  (see  FIG. 7A ). 
     As shown in  FIG. 7B , the back of the second slider  60  includes numerical indicia corresponding to clearance required  720 , along with a clearance required identifier  730 . The back of the second slider  60  also includes numerical indicia corresponding to lanyard length  740 , along with a lanyard length identifier  750 . The numerical indicia corresponding to clearance required  720  and the numerical indicia corresponding to lanyard length  740  have a center-to-center spacing that corresponds to the spacing between adjacent index indicia  630  (see  FIG. 7A ). Furthermore, to the numerical indicia corresponding to clearance required  720  having a value of 13 is vertically aligned with the numerical indicia corresponding to lanyard length  740  having a value of 0. In addition, the numerical indicia corresponding to clearance required  720  cooperates with the index indicia  630  and indexing arrow  710  to enable a user to determine clearance required (shown and described infra). 
     With reference to  FIGS. 6A, 6B, 7A and 7B , in one embodiment, the color of the numerical indicia alternates (e.g., odd numbers red and even numbers black), so as to permit such indicia to be more easily read. In one embodiment, certain indicia are in a special color (e.g., red) to emphasize their importance. For example, references to CR A  may be in a special color on the front panel  20  and/or back panel  30  of the slide rule  10 . 
       FIG. 8  is a front view of the slide rule  10  being used to determine Free Fall Distance (FFD). The operational indicia  220  on the front of the slide rule  10  specify three steps. In this example, the worker is tying off at an anchor 8 feet above the working platform (C=8 feet), the D-Ring height at the worker&#39;s back measures 4 feet (B=4 feet), and the Lanyard Length is 8 feet (L=8 feet). 
     Accordingly, the first slider  50  is adjusted to place the numerical indicia corresponding to the anchor height  360  (here, C=8 feet) into the anchor height window  320 . Next, the second slider  60  is adjusted to place the numerical indicia corresponding to the lanyard length  430  (here, L=8 feet) in the lanyard length window  330  above the numerical indicia corresponding to the D-Ring height  280  (here, B=4 feet). 
     Once the first two steps have been completed, the third step is to merely view the FFD, which is displayed in the main window  340 . Specifically, the indexing arrow  380  points to index indicia  310  that is associated with the numerical indicia corresponding to FFD  410 . In this case, the FFD reading on the slide rule  10  equals 4 feet, which is within safe limits. 
       FIG. 9  is a rear view of the slide rule  10  being used to determine Clearance Required (CR). The operational indicia  520  on the back of the slide rule  10  specify three steps. In this example, the shock absorber extension (SAE) has a value of 4 feet (which is normally printed on the lanyard), the D-Ring height at the worker&#39;s back measures 4 feet (B=4 feet), and the Lanyard Length is 8 feet (L=8 feet). 
     Accordingly, the first slider  50  is adjusted to place the numerical indicia corresponding to the SAE  690  (here, SAE=4 feet) into the SAE window  640 . Next, the second slider  60  is adjusted to place the numerical indicia corresponding to the lanyard length  740  (here, L=8 feet) in the lanyard length window  650  above the numerical indicia corresponding to the D-Ring height  580  (here, B=4 feet). 
     Once the first two steps have been completed, the third step is to merely view the CR, which is displayed in the main window  660 . Specifically, the indexing arrow  710  points to index indicia  630  that is associated with the numerical indicia corresponding to CR  720 . In this case, the CR reading on the slide rule  10  equals 19 feet. Therefore, the worker must ensure that he/she has 19 feet of clearance from the anchor point to any obstruction below. 
     In one embodiment, as shown in  FIGS. 1 and 2 , an aperture  810  is provided for clipping to belt, attachment to lanyard, or connection to a key ring (or the like). The aperture is only shown in  FIGS. 1 and 2  for clarity. In one embodiment, the aperture may be formed using a punch after construction of the device. In one embodiment, each of the front panel  20 , back panel  30  and center panel  40  has corresponding first, second and third apertures therein (not shown), which are aligned during construction of the device, so as to form the aperture  810 . 
     It should be understood that the slide rule may be designed in many different ways with respect to number and types of sliders, along with scaling increments, but still serve the same function. In one embodiment, the slide rule may also be designed to measure clearance from the working platform or other reference points. In one embodiment, the scale units and values may be adjusted to meet different safety code requirements or special corporate needs. In one embodiment, the slide rule can be constructed to be pocket size and is not electrically powered, making it possible to be used in areas which require intrinsically safe equipment. 
     The device comprises a hand-held precision instrument with sliders from which calculation of FFD and CR is obtained based upon user input of lanyard or lifeline length (connecting component of personal fall protection system) in relation to the height of the D-Ring above the working platform, height of the tie off point (anchor) above the working platform, and the shock absorber extension (printed on the shock absorber). One or more of the values input by the user may be obtained by measurement or be listed on the user&#39;s personal protective equipment. 
     The device is lightweight and credit card sized and designed to be carried in a worker&#39;s wallet or pocket, hung on a lanyard, or affixed to a harness or other fall protection equipment. Workers use the sliders to indicate the length of their equipment and tie off height (anchor height) and the device provides them with the resulting FFD, which they are required by law to keep within specific parameters. The reverse side of the device also provides them with the minimum CR, which they are also required by law to calculate. 
     Several embodiments of the invention have been described. It should be understood that the concepts described in connection with one embodiment of the invention may be combined with the concepts described in connection with another embodiment (or other embodiments) of the invention. 
     The foregoing description of the preferred embodiment of the present invention has been presented for the purpose of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teachings. It is intended that the scope of the present invention not be limited by this detailed description, but by the claims and the equivalents to the claims appended hereto.