P/00/011 Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION INNOVATION PATENT Improved Fire Retreat Shelter The following statement is a full description of this invention, including the best method of performing it known to me: 1 Title: Improved Fire Retreat Shelter 5 Technical Field The present invention relates to shelters which provide refuge for individuals during a bush or wild fire. 0 Background Art Bush fires and wild fires are uncontrolled fire events which often result in the tragic loss of life. These fires either start naturally or are deliberately lit. With the drying of the climate in Australia and in other countries such as Greece and 5 Spain and the US state of California bush fires are becoming an ever increasing problem. Unfortunately during catastrophic bush fire conditions such as those that occurred in the state of Victoria in February of 2009 many people lost their lives when attempting to flee the fires. In a number of cases individuals had attempted to defend their property only to be overwhelmed by the fires which 0 were driven by extremely strong winds. Given the above there is growing recognition that for people residing in bush fire prone areas there is a need to provide a safe haven in which to shelter during the most critical phase of a fire as fire front moves over an area. 5 A number of different fire shelters have been proposed such as that in US patents No 6 327 821 and 7 128 207 which are above ground shelters that rely on heat resistant materials to protect occupants. These materials may be expensive or not readily available. Other shelters are partly or fully buried 0 underground but are complex in construction and expensive to build such as those disclosed in US patents No 6 385 919, 5 832 680 and 7 428 800. It is an object of the present invention to provide a fire shelter which ameliorates at least some of the disadvantages of those described above. 35 The above references to and descriptions of prior proposals or products are not intended to be, and are not to be construed as, statements or admissions of common general knowledge in the art. 40 Disclosure of the Invention In one aspect the present invention provides an improved shelter suitable for placement below ground in a pit of appropriate dimensions said shelter 2 comprising a substantially cuboid structure which provides a space suitable for sheltering occupants during a fire, said structure comprising at least: a) a supporting frame of suitable strength; b) top and side walls made of suitable sheet material securable to said frame, and; c) a detachable door allowing side 5 entry into said space from said pit, wherein, when in use, insulation of occupants from radiant heat of a fire is provided by earth surrounding the structure, the improvement comprising that the structure is constructed readily available material. 0 The terms "below ground" and "below ground level" refer to the shelter being beneath the ground. The term "pit" refers to a hole or excavation in the ground. The term "a pit of appropriate dimensions" refers to the pit being large enough to accommodate 5 the structure and to provide an access way adjacent to the shelter. Preferably the pit is located in a suitable environment away from dense vegetation or other combustible material. The term "substantially cuboid structure" means that the shelter is a cube-like 0 prism however not all six faces of the prism may be provided by the structure. For example the bottom face or floor of the structure may be provided by the base of the pit itself which may have a sump for drainage. In addition a number of cube-like structures may be placed end to end in modular fashion to form a shelter having the shape of a rectangular prism. Such a rectangular 5 prism is within the definition of substantially cuboid structure. The term "a space suitable for sheltering occupants during a fire" refers to an internal space created by the shelter which is capable of sheltering one or more occupants, for example humans including fire crew and pets or other animals, 0 during the worst or critical phase of a bush fire. This critical phase may typically last from 5 to 20 minutes. The term "a supporting frame" refers to a rigid structure capable of supporting the walls. Preferably the frame is constructed of 12 members and eight corners 35 which define the edges and vertices of the prism respectively. More preferable the frame is made of suitable lengths of metal tubing and its corners are connected by suitable precast moldings. The term "of suitable strength" means that the members are of sufficient gauge 40 to support the walls of the structure and resist to pressure from the surrounding earth placed a minimal distance below ground level. A minimal distance below ground refers to the distance necessary to achieve insulation from radiant heat of a passing fire storm. This will generally mean that the top 3 wall will be about 30 cm below the surface and topped with earth depending on soil type and other conditions. The term "top and side walls made of suitable sheet material" refer to the top 5 wall (that closest to the above ground surface) and walls making up the sides being of material which is substantially flat or planar in nature and includes sheeting material such as corrugated sheet material such as corrugated iron, Zincalume@ sheeting and sheeting with other profiles such as Trimdeck@ and the like. The material must be of suitable strength and construction to hold 0 back ingress of surrounding earth into the shelter. The term "securable to said frame" means that the sheet material is suitable for securing to the frame by fixing means such as bolts or screws. 5 The term "a detachable door" refers to a door that is not fixed by hinges or the like and can be completely detached from the rest of the structure. Preferably the door is a piece of sheet material that may be slidably received by a side wall adjacent an opening in the structure. Still more preferably the removable door can be used to cover the adjacent access way when the shelter is not in 0 use thus preventing the access way from being open to ingress of water, wild animals and the like. The term "allowing side entry into said space from said pit" refers to a door which is able to cover an opening or doorway in a side wall. 5 The term "insulation of occupants from radiant heat of a fire is provided by earth surrounding the structure" means that the shelter is suitable to be buried deep enough in the ground so that the surrounding ground which abuts the structure on 5 sides is sufficient to prevent unacceptably high levels of radiant 0 heat entering the space. The term "surrounding" does not mean that the earth touches all six sides of the structure. While, in use, five sides of the structure the earth the remaining side, the sixth side of the shelter does not abut the earth however the sixth side and adjacent access way are below ground level and thus not susceptible to the heat of the fire. Unacceptably high levels of 35 radiant heat include levels which lead to serious injury or death in humans. The term "the structure is constructed readily available material" refers to most of the material being easily accessible from non specialist suppliers such as hardware stores and the like. Preferably the materials are available at a 40 reasonable price. An advantage of the present invention is that protection from radiant heat of a fire is provided by the surrounding earth not the materials used in construction of the structure. The materials used allow a vacant space to be created below ground which is insulated from the extreme above ground 4 temperatures experienced in some bush fires. This allows for a comparatively inexpensive shelter to be made. In another aspect the invention relates to an improved method of providing 5 shelter from a bush fire said method comprising provision of a below ground shelter comprising a substantially cuboid structure comprising at least a) a supporting frame of suitable strength to support said shelter; b) top and side walls made of suitable sheet material securable to said frame, and; c) a removable door on a side wall allowing entry into said space; said structure 0 being located in a pit of suitable dimensions to accommodate the structure and an adjacent access way wherein the structure provides a space where occupants shelter during a fire, and wherein insulation of occupants from radiant heat of a fire is provided by earth surrounding the structure, the improvement comprising that the structure is constructed of readily available 5 material, wherein the occupants retreat to the shelter during a critical phase of a bush fire. In another aspect the invention provides a kit when used to construct a below ground fire shelter in a pit which shelter comprises a substantially cuboid 0 structure with a space suitable for sheltering occupants during a fire, said kit comprising elongate members suitable to construct a supporting frame; sheet material to construct top and side walls securable to said frame and sheet material to construct a removable door allowing side entry into said space from said pit, and optionally fixing means wherein said supporting frame and walls 5 are of suitable strength to support said shelter when placed a minimal distance below ground level and wherein when in use, insulation of occupants from radiant heat of a fire is provided by earth surrounding the structure rather than the structure itself. 0 Preferably the elongate members comprise precut metal tubing, more preferably galvanized tubing. Preferably the sheet material comprises corrugated sheeting, more preferably Zincalume@ sheeting. 35 Brief Description of the Drawings The following non-limiting description of the invention with reference to the drawings is provided. 40 Figure 1 is a perspective view of the the shelter of the present invention without the door. 5 Figure 2a is side view of the shelter of the present invention as viewed from the access way without the door. Figure 2b is a view of the detachable door of the shelter of the present 5 invention. Figure 3 is a top view of the shelter and access way of the present invention in the excavated pit. 0 Figure 4 is a sectional side view showing the shelter of the present invention in situ underground adjacent the access way and shows an access means in the form of a ladder. Modes of Carrying out the Invention 5 The improved shelter 10 of the present invention is a substantially cuboid structure with internal supporting frame 20, top wall 30, side walls 40, doorway 50 and detachable door 60. Preferred dimensions for the shelter are 2m x 2m x 2m although if a larger space is required a series of shelters 10 may be aligned 0 in a modular type arrangement. Supporting frame 20 is made of twelve elongate members 21 making up the basic structure of the cuboid. These members may be of any suitably strong material. Preferably galvanized steel tubing of sufficient strength to support the 5 shelter when it is buried underground is used. More preferably the material is 40 mm galvanized steel tubing. Additional strength may optionally be provided by top reinforcing bar 25 made of the same material. Elongate members 21 are joined at corners 22 by any convenient means such as Elgate@ 4 way adjustable corners manufactured by Eltrack International and Staff Pty Ltd. 0 Similarly bar 25 can be fitted via Elgate@ fixed angle 3 way Tee. Top wall 30 and side walls 40 are made of any suitable sheet material such as corrugated iron or Zincalume@ sheeting. The sheets may be partly overlapped to avoid cutting the sheet material and to add extra strength. In addition, an 35 extra layer of sheeting placed at right angles to the first layer may be used to provide additional strength to top wall 30. Top wall 30 and side walls 40 are fixed to frame 20 by any convenient means such as by self tapping screws or bolts. Further the overlapping sections of sheeting may be pop riveted together. 40 Detachable door 60 is made of sheet material and has two offset horizontal reinforcing bars 65 that at one end extend beyond the sheet material of the door for handling and at the other end have pad bolts 66. Holes 67 in frame 20 6 adjacent doorway 50 are to receive pad bolts 66. The advantage of detachable door 60 is that it may be used as a cover for access way 80 to prevent ingress of vegetation and dirt when the shelter is not being used. Bar 25 provide added strength should a vehicle pass over the top. 5 A gap in the sheeting is left in one side wall 40 to create doorway 50 which is closable by detachable door 60. The sheeting adjacent doorway 50 is not attached to frame 20. This allows detachable door 60 to be slidingly received between the unattached sheeting and frame 20. Once slid in to place 0 removable door 60 may be secured from the inside via pad bolts 66 and holes 67. In use shelter 10 is located in an excavated pit 70. The pit must be of suitable dimensions to accommodate shelter 10 and adjacent access way 80 and be of 5 sufficient depth so that top wall 30 is at least 30cm below ground when covered with earth. Access way 80 is provided with a suitable access means from ground level such as ladder 90. Alternatively access way 80 could take the form of a ramp sloping from ground level to the floor of the pit for wheel chair access or the like. 0 The site of pit 70 must be chosen with care such as away from vegetation and geographical features such as north facing ridges which tend to be subject to fire fronts in bush fire prone areas. In addition if an access way in the form of a ramp is made care should be taken in the positioning of a ramp to avoid likely 5 fire fronts. Shelter 10 may be constructed above ground and then placed in pit 70 or partly constructed above ground and fully assembled in pit 70. The advantage of using Elgate@ 4 way adjustable corners is that the sheet material and 0 elongate members can be used to make the walls with attached partial frame above ground and the entire shelter can be assembled in pit 70. In the embodiment illustrated shelter 10 does not have a floor attached to frame 20 although optionally a separate floor such as a concrete slab could be provided. Preferably the floor of pit 70 has a sump for drainage of moisture. Gravel on 35 top of a tarpaulin or other appropriate material is preferably used on the floor. Once shelter 10 is completed and placed in pit 70 back filling around three sides of the shelter and placement of earth on top wall 30 can take place. Optionally, prior to back filling top wall 30 and the three sides are covered in tarpaulins to protect them from moisture and slow deterioration. Further, 40 optionally, depending on soil and/or subsoil conditions the walls of access way 80 may be lined with sheet material to prevent ingress of dirt into the access way. 7 It can be seen from the above that the substantially cuboid structure of the shelter provides a space where occupants can retreat from the worst phase of a bush fire as the fire front passes over. The advantage of the present invention is that the materials used in construction are readily and reasonably cheaply 5 available. Because the shelter relies on the surrounding earth to protect its occupants from radiant heat there is no need for expensive heat resistant materials or complex modes of construction. Side access to the shelter below ground level avoids the need for expensive heat proof doors. It is estimated even with excavation costs included that the shelter of the present invention is 0 about 3 0% of the cost of the next least expensive shelter available on the Australian market. Example 1: Kit of Parts 5 The following is a list of parts for a kit to construct a shelter in accordance with the present invention: Fourteen pieces of 40 mm galvanized tubing cut into lengths of 4 x 2m, 8 x 1.8m for the frame and 4 x 0.9m, two for the door and two to be joined for the reinforcing roof bar (This may be conveniently provided by four 6.5 m lengths 0 cut to 1x2m, 2x1.8m and 1x0.9m) 8 x 40mm corner connectors 2 x 40mm Tee connectors for the top wall reinforcing bar 15 x 2m Zincalume@ sheets Approximately 100 galvanized self tapping roofing screws or bolts 5 Approximately 100 pop rivets. Optionally extra Zincalume@ sheeting to reinforce roof and access way, ladder or steps for access way, tarpaulins to separate sheeting from the earth or the earth under gravel and gravel or concrete for a floor may be included. In addition, extra galvanized self tapping screw or bolts and extra pop rivets may 0 be provided for extra strength. Throughout this specification and the claims that follow, unless the context requires otherwise the words "comprise", "comprises", "comprising" will be understood to mean the inclusion of the stated integer, step or group of 35 integers or steps but not the exclusion of any of other integer, step or group of integers or steps. 8