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TECHNICAL FIELD 
     This invention relates to mobile lifts and more particularly to wheeled lifts having an elevatable platform with a hoist for rescuing a human from an enclosure; as well as lowering a human into and removing a human from an enclosure. 
     BACKGROUND ART 
     Mobile lifts have been used to elevate materials and workmen for a variety of purposes. One such lift includes a chassis mounted on four wheels with one section of an extension ladder rigidly supported on the chassis at an obtuse angle. An extensible section of the ladder supports a horizontal work platform. A hand winch is used to elevate and lower the extensible section of the ladder with the supported work platform. The work platform extends beyond the chassis of the mobile lift to permit placement of material or personnel beyond the area in which the wheeled chassis is free to travel. The platform may include a vertical entryway to permit access to the top opening of a container when the platform rests on the container with the entryway aligned with the top opening. Although these previously designed mobile lifts are advantageously used in numerous applications, there remains a need for equipment to quickly aid in rescue of incapacitated personnel from enclosures, such as storage tanks. 
     DISCLOSURE OF THE INVENTION 
     The present invention is directed to providing a mobile human lift unit for rescuing personnel from enclosures. An overhead hoist is mounted on an elevatable platform having a vertical entryway. The overhead hoist includes a winch having a cable reeved on an overhead pulley with its free end attachable to a human lift harness or the like. The rescue equipment is mobile to permit it to be quickly positioned to effect a human rescue operation. The platform is vertically adjustable to correspond to the height of a variety enclosures. The overhead hoist may take the form of a tripod, an overhead track and dolly or an overhead crane. The use of an overhead crane which pivots about a vertical axis, facilitates lowering of a rescued person to the ground. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a first embodiment of the invention showing a mobile human lift unit having a tripod mounted on an elevatable platform; 
     FIG. 2 is a top view of the platform of FIG. 1 with some parts removed for illustration purposes; 
     FIG. 2A is a view taken on the line  2 A— 2 A in FIG. 2; 
     FIG. 3 is a side view of a second embodiment of the invention and 
     FIG. 4 is a perspective view of the platform of the second embodiment of the invention with the overhead crane lowering a rescued person to the ground. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The mobile human lift unit shown in FIG. 1 includes a wheeled support vehicle  11  having a chassis  12  supported at it front end by a pair of side-by-side support wheels  13 ,  14  rotatably mounted on a steering fork  16 . The steering fork  16  is pivotally connected to a forward projecting part of the chassis  12  and the top end of the steering fork  16  is pivotally connected to a tow bar  17 . The rear of the chassis  12  is supported by a pair of laterally spaced support wheels  18 ,  19  and outriggers with vertically adjustable feet are secured to the chassis  12  to level and stabilize the chassis when it is placed in a rescue position. 
     A horizontal platform  26  is supported by a support structure which includes a ladder  27  whose extensible or fly section  28  is rigidly secured to the platform and whose butt section  29  is rigidly secured to the chassis by braces  31 ,  32 ,  33 ,  34 . A hand operated winch  36  is provided to adjust the extension of the ladder, thus adjusting the elevation of the platform  26 . The ladder  27  not only adjustably supports the platform, but also provides access to the platform  26 . The ladder  27  extends upwardly at an obtuse angle from the front end of the chassis  12 , whereby the platform  26  extends horizontal beyond the chassis  12  a sufficient distance to permit the platform  26  to be placed directly above the top opening of a container, tank or enclosure of the type having a top opening. A guard rail  35  is provided on the platform  26  in conformance with safety standards. 
     Referring also to FIG. 2, the platform  26  has a floor  37  and a vertical opening or entryway  38  which is sufficiently large to permit vertical passage of a human. Three sockets or support members  41 ,  42 ,  43  are mounted on the platform  26  and are shaped and spaced about the entryway  38  to matingly receive the bottom ends of the legs  44 ,  46 ,  47  of a tripod  48 . FIG. 2A shows the leg  44  positioned in the support member  41 . 
     As shown in FIG. 1, a hand operated winch  51  is rigidly mounted on the leg  44  of the tripod  48  and includes a cable  52  which is reeved on a pulley  52  rotatably supported on an apex or pulley support member  54  to which the upper ends of the tripod legs  44 ,  46 ,  47  are attached. The free end of the cable  52  is provided with a hook  55 , or, preferably, a releasable connector suitable for attachment to a human lift harness. 
     The mobile human lift unit shown in FIGS. 3 and 4 includes a vehicle  61  with a chassis  62  rigidly supporting the butt section  63  of an extension ladder  64 . The extensible section  66  of the ladder  64  supports a work platform  67  having a vertical entryway  68  adapted for placement directly above a top opening of a tank shown by broken lines  69 . The vehicle  61  and ladder  64  are of the same general construction as the vehicle  11  and the ladder  27  shown in FIG.  1 . The platform  67  includes a floor frame  71  supporting a partial floor  72  and defining the vertical entryway  68 . The corners of the four sided floor frame  71  support four corner posts  73 ,  74 ,  76 ,  77  to which a safety railing  78  is secured. A first overhead support beam  81  is secured by welding to the upper ends of the posts  73 ,  77  and a second overhead support beam  82  is welded to the upper ends of the posts  74 ,  76 . An overhead crane  83  is provided on the platform  67  which includes a pivotable mast  84  pivotally connected at its top to the beam  82  and pivotally connected at its bottom to the floor frame  71 . A horizontally extending boom or track  86 , which may be a flanged beam such as an I-beam, has one end rigidly secured, as by welding to the mast  84  a free end extending beneath and beyond the beam  81 . 
     The overhead crane  83  includes a trolley  87  having a horizontal leg  88  supported on the track  86  by a pair of dollies  89 , connected to the horizontal leg  88  by a pair of tension links  90 ,  91 . The trolley  87  also includes a vertical let  92  to which a hand operated winch  93  is secured. The winch includes a cable  94  reeved on a pair of pulleys  96 ,  97  rotatably mounted on the horizontal leg  88  of the trolley  87 . The free end of the cable  94  includes a releasable connector  99  adapted for connection to a human lift harness  98 . The mast  84  of the overhead crane  83  is pivotally connected at its top and bottom to the beam  82  and the floor frame  71 , respectively, by pivot pins  101 ,  102  for swinging movement about a vertical axis  103 . In order to provide additional support for the free end of the track  86 , a dolly  106  is installed on the beam  81  and a dolly  107  is installed on the track  86 . The dollies  106 ,  107  are interconnected by a tension member in the form of a rod  108 . The free end of the track  86  extends horizontally beyond the floor frame  71  to permit a rescued person to be moved through a gate  111  in the safety railing  78 . 
     Practical Application 
     A workman may accidently be overcome by fumes in a container in which he is working or preforming an inspection. Many containers can be accessed only through a top opening and such containers render rescue operations difficult. In rescuing a person from a container with a top opening, time is almost always a critical consideration; particularly in those instances where the fumes are life threatening. The mobile human lift unit of this invention provides equipment which can quickly be placed in a position for a human rescue operation and includes vertical lift apparatus for removing the rescued person from the container. The lift unit is also useful in lowering a person assisting in the rescue effort into the container. As shown in FIGS. 3 and 4, the lift unit not only lifts a rescued person from the container, but also is operable to move the incapacitated person through the gate  111  in the railing  78 , to swing the crane  83  about its vertical axis  103  and to lower the rescued person to the ground at one lateral side of the support vehicle  61 . In addition to rescue operations, the lift unit is advantageously used to lower workers into, and remove workers from, an enclosure in which work needs to be performed. 
     Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.

Summary:
A mobile human life unit includes an elevatable platform supported by a ladder mounted on a wheeled vehicle. A first embodiment of the mobile human lift unit utilizes a winch with a winch cable reeved over a pulley carried by a support having at least three legs which are held in fixed positions on the platform. A second embodiment of the mobile human lift unit has an overhead crane with a track which swings about a vertical pivot axis and carries a trolley with a winch.