Nestable Polymer Pallet with Conflagration Control Features

Abstract

A nestable polymer pallet is provided with a peripheral structure and an inner deck. The peripheral structure includes an outer deck and hollow legs for nesting engagement with the legs of a similar pallet. The inner deck is surrounded by the outer deck and has a fire-venting structure with a contiguous area of at least 80 square centimeters that is at least 80 percent open area for vertical airflow. When nested in a stack with other similar pallets, the fire-venting structures align to form a chimney structure allowing vertical airflow through the stack of pallets. In some embodiments, at least two thirds of an area of downward-facing surfaces of the pallet presents at least a surface layer of fire resistant material. In other embodiments, the fire-venting structure extends along an edge of the inner deck adjacent to the outer deck.

Claims

1. A pallet comprising: (a) a peripheral structure comprising an outer deck and a plurality of legs extending downwards from said outer deck, at least outward-facing surfaces of said peripheral structure being formed from a polymer material that generates flaming drips on combustion, said legs being hollow legs configured for receiving the legs of a similar pallet to allow nesting; (b) an inner deck surrounded by and cooperating with said outer deck to provide a total deck area for supporting a load; and (c) at least one fire-venting structure formed in or adjacent to said inner deck, said at least one fire-venting structure having a contiguous area of at least 80 square centimeters that is at least 80 percent open area for vertical airflow, wherein at least two thirds of an area of downward-facing surfaces of the pallet present at least a surface layer of non-dripping fire resistant material.

2. The pallet of claim 1, wherein said at least one fire-venting structure extends along an edge of said inner deck adjacent to said outer deck.

3. The pallet of claim 1, wherein said peripheral structure is formed with a plurality of channels for receiving a corresponding plurality of mechanical stiffening elements that extend along a majority of a dimension of the pallet for stiffening the pallet, said stiffening elements being formed from inflammable material.

4. The pallet of claim 3, wherein each of said mechanical stiffening elements is formed from at least one material selected from the group consisting of: metal; fiberglass; Kevlar; carbon fiber; and a thermoset polymer matrix.

5. The pallet of claim 3, wherein each of said mechanical stiffening elements extends vertically across a majority of a height of said inner deck such that, when the pallet is nested in a stack with other similar pallets, said mechanical stiffening elements align to form a majority-closed vertical barrier to horizontal spread of a fire.

6. The pallet of claim 5, wherein one of said mechanical stiffening elements passes adjacent to said fire-venting structure.

7. The pallet of claim 6, wherein said at least one fire-venting structure extends along an edge of said inner deck adjacent to said outer deck.

8. The pallet of claim 1, wherein at least part of said inner deck is provided by a deck insert formed from metal or from a non-dripping fire resistant polymer.

9. The pallet of claim 1, wherein said inner deck is formed from polymer materials.

10. The pallet of claim 9, wherein said peripheral structure and said inner deck are integrally formed.

11. The pallet of claim 1, wherein said inner deck further comprises a central leg.

12. The pallet of claim 1, further comprising a fire break element formed from inflammable or fire resistant material and deployed adjacent to said fire-venting structure so as to inhibit spreading of fire from said fire-venting structure to at least one adjacent region of said inner deck.

13. A pallet comprising: (a) a peripheral structure comprising an outer deck and a plurality of legs extending downwards from said outer deck, said peripheral structure being integrally formed from polymer materials; (b) an inner deck surrounded by and cooperating with said outer deck to provide a total deck area for supporting a load; and (c) at least one fire-venting structure extending along an edge of said inner deck adjacent to said outer deck, said at least one fire-venting structure having a contiguous area of at least 80 square centimeters that is at least 80 percent open area for vertical airflow while a majority of said inner deck has a proportion of open area for vertical airflow less than 50 percent.

14. The pallet of claim 13, wherein the pallet is a nestable pallet and said legs are hollow legs configured for receiving the legs of a similar pallet when nested.

15. The pallet of claim 14, wherein at least part of said inner deck is provided by a deck insert formed from metal or from non-dripping fire resistant polymer.

16. The pallet of claim 14, wherein said inner deck is formed from polymer materials.

17. The pallet of claim 16, wherein said peripheral structure and said inner deck are integrally formed.

18. The pallet of claim 16, wherein said inner deck further comprises a central leg.

19. The pallet of claim 16, wherein said peripheral structure is formed with a plurality of channels for receiving a corresponding plurality of mechanical stiffening elements that extend along a majority of a dimension of the pallet for stiffening the pallet.

20. The pallet of claim 19, wherein said mechanical stiffening elements are formed from inflammable or fire resistant materials and pass adjacent to said at least one fire-venting structure, said mechanical stiffening elements extending vertically across a majority of a height of said inner deck such that, when the pallet is nested in a stack with other similar pallets, said mechanical stiffening elements align to form a majority-closed vertical barrier to horizontal spread of a fire.

21. The pallet of claim 14, wherein said at least one fire-venting structure is subdivided by ribs such that a deck surface within said at least one fire-venting structure does not have any unsupported gap greater than 5 centimeters in either a width direction of the pallet or a length direction of the pallet.

22. The pallet of claim 14, further comprising a fire break element formed from inflammable or fire resistant material and deployed adjacent to said fire-venting structure so as to inhibit spreading of fire from said fire-venting structure to at least one adjacent region of said inner deck.

23. The pallet of claim 22, wherein said fire break element is implemented as a downward-extending flange along an edge of the inner deck.

24. The pallet of claim 22, wherein said fire break element is implemented as a reinforcing element extending along a majority of a dimension of the pallet.

25. The pallet of claim 22, wherein said fire break element extends vertically across a majority of a height of said inner deck such that, when the pallet is nested in a stack with other similar pallets, said fire break elements align to form a majority-closed vertical barrier to horizontal spread of a fire.

26. A pallet comprising: (a) a peripheral structure comprising an outer deck and a plurality of legs extending downwards from said outer deck; and (b) an inner deck surrounded by and cooperating with said outer deck to provide a total deck area for supporting a load, wherein said peripheral structure and said inner deck are integrally formed from polymer materials, at least said outer deck being implemented as a rib-supported structure with a proportion of open area for vertical airflow less than 50 percent and with a minimum deck-layer thickness of 2 millimeters, and wherein at least a sub-area of said inner deck corresponding to at least 5 percent of the total deck area is implemented as a fire-venting structure having at least 80 percent area that is covered by a membrane layer of thickness less than 1 millimeter so as to be opened for vertical airflow on exposure to fire while said outer deck remains intact.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

[0032] FIG. 1A is an upper isometric view of a first embodiment of a pallet according to the present invention;

[0033] FIG. 1B is a lower isometric view of the pallet of FIG. 1A;

[0034] FIG. 1C is a top plan view of the pallet of FIG. 1A;

[0035] FIG. 1D is an enlargement of a region of FIG. 1C designated I showing a fire-venting channel;

[0036] FIG. 1E is an exploded upper isometric view showing an inner deck lifted away from a peripheral structure and revealing rectangular reinforcing rods;

[0037] FIG. 2A is a side view of a stack of 4 nested pallets of FIG. 1A;

[0038] FIG. 2B is a cross-sectional view through the stack of FIG. 2A taken along the line II-II and with dashed arrows showing the chimney flow through the stacked fire-venting channels;

[0039] FIG. 2C is an upper cut-away isometric view of the stack of FIG. 2A cut away along the line II-II of FIG. 2A additionally showing a firewall effect of the reinforcing elements passing adjacent to the fire-venting channels;

[0040] FIG. 3 is a photograph taken during a fire test performed on a stack of nested plastic pallets having fire-venting channels similar to those illustrated in the first embodiment, showing clearly the flames leaping vertically above the stack while the fire is localized in the horizontal direction;

[0041] FIG. 4A is a top view of a second embodiment of a pallet according to the present invention;

[0042] FIG. 4B is an end view of a stack of 4 nested pallets of FIG. 4A;

[0043] FIG. 4C is a cross-sectional view taken through the stack of FIG. 4B along the line III-III and with dashed arrows showing the chimney flow through additional stacked fire-venting channels adjacent to the shorter sides according to the second embodiment;

[0044] FIG. 5A is an upper isometric view of a third embodiment of a pallet according to the present invention;

[0045] FIG. 5B is a lower isometric view of the pallet of FIG. 5A;

[0046] FIG. 5C is a bottom view of the pallet of FIG. 5A with a pair of horizontal dashed lines and a pair of vertical dashed lines indicating the outer boundaries of the region defining a fire-venting channel;

[0047] FIG. 6A is an isometric top view of a fourth embodiment of a pallet according to the present invention;

[0048] FIG. 6B is a cross-sectional view of the pallet of FIG. 6A taken along the plane designated IV-IV;

[0049] FIG. 6C is an enlarged view of the region of FIG. 6B designated V showing a region of a deck of normal thickness and a region of a sub-millimeter membrane;

[0050] FIG. 7A is an upper isometric view of a fifth embodiment of a pallet according to the present invention;

[0051] FIG. 7B is a lower isometric view of the pallet of FIG. 7A;

[0052] FIG. 7C is a top plan view of the pallet of FIG. 7A with a pair of horizontal dashed lines and a pair of vertical dashed lines for each of the four fire-venting channels indicating the outer boundaries of the region defining each fire-venting channel;

[0053] FIG. 8A is an upper isometric view of a sixth embodiment of a pallet according to the present invention;

[0054] FIG. 8B is an exploded upper isometric view of the pallet of FIG. 8A showing an inner deck lifted away from a peripheral structure and revealing more clearly reinforcing rods;

[0055] FIG. 9A is a top view of a nested stack of four pallets of FIG. 8A;

[0056] FIG. 9B is a cut-away upper isometric view of the stack of FIG. 9A cut away along a plane designated VI-VI;

[0057] FIG. 10A is an upper isometric view of a seventh embodiment of a pallet according to the present invention;

[0058] FIG. 10B is a lower isometric view of the pallet of FIG. 10A;

[0059] FIG. 11A is a cut-away upper isometric view taken through a stack of the pallets of FIG. 10A;

[0060] FIG. 11B is an enlargement of a region of FIG. 11A designated VII;

[0061] FIGS. 12A-12C are lower isometric views of an inner deck insert for use in the pallet of FIG. 10A showing the inner deck as a continuous closed surface, as an open mesh or as an open-centered frame;

[0062] FIG. 13A is a top plan view of an eighth embodiment of a pallet according to the present invention;

[0063] FIG. 13B is a cut-away isometric view of a nested stack of four pallets of FIG. 13A cut along line VIII-VIII in FIG. 13A; and

[0064] FIG. 13C is an enlarged view of a region of FIG. 13B designated IX.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] The present invention is a nestable polymer pallet with conflagration control features. The principles and operation of pallets according to the present invention may be better understood with reference to the drawings and the accompanying description.

[0066] Referring to the drawings generally, and initially to FIGS. 1A-1E and 2A-2C thereof, a pallet 100 is illustrated comprising a peripheral structure 102 and an inner deck 112. The peripheral structure 102 comprises an outer deck 104 and a plurality of legs 108, 110 extending downwards from the outer deck 104. In the illustrated embodiment, the legs include four corner legs 108 and four mid-edge legs 110, but it will be understood that the number and location of the legs may vary in other embodiments, for example, often including an additional center leg beneath the middle of the pallet. Inner deck 112 is surrounded by outer deck 104. Together, peripheral structure 102 and inner deck 112 cooperate to provide a total deck area for supporting a load to be carried by pallet 100.

[0067] Pallet 100 is preferably a nestable pallet in which legs 108, 110 are hollow and configured for receiving the legs of a similar pallet when nested to form a compact stack of empty pallets, as illustrated in FIG. 2A.

[0068] According to a first aspect of certain particularly preferred embodiments of the present invention, pallet 100 is formed with at least one fire-venting structure 116 formed in or adjacent to inner deck 112. The fire-venting structure 116 has a contiguous area of at least 80 square centimeters that is at least 80 percent open area for vertical airflow. In the particularly preferred but non-limiting illustrated embodiment, the fire-venting structure 116 is formed as a set of vertically extending channels adjacent to the long edges of the inner deck 112. It will be understood that other locations are possible in other embodiments.

[0069] When pallets 100 are nested in a stack with other similar pallets, the fire-venting structures 116 in successive pallets of the stack align to form what is referred to herein as a chimney structure passing vertically through the nested stack of pallets. Conventional thinking would lead the designer of polymer pallets to try to reduce the quantity of plastic material in a stack in order to reduce the heat emitted during conflagration. In a counterintuitive manner, through close nesting of a stack of pallets with consequent high energy density, the chimney effect of fire-venting structures stacked in close relation one above the other is enhanced. This chimney structure defines a vertical airflow path along which fire and heat can rapidly develop and be vented vertically upwards in a localized manner. The enhanced localized burning has been found effective to rapidly actuate an overhead sprinkler system immediately above the source of the fire, thereby promptly and effectively quenching the fire. Thus, despite the high energy density of closely nested plastic pallets, the proximity between the pallets actually facilitates formation of a well-defined chimney structure which leads to earlier extinguishing of a fire.

[0070] According to a second aspect of certain particularly preferred embodiments of the present invention, which may be used to advantage in combination with the first aspect, at least two thirds of an area of downward-facing surfaces 114 of the pallet 100 present at least a surface layer of fire-resistant material that does not generate flaming drips when exposed to fire. The phrase downward-facing surfaces is used herein in the description and claims to refer to horizontal surfaces which face downwards, such as the underside of the pallet deck and the bottom surfaces of the legs, as well as other surfaces which are directly exposed to flames in a scenario of a fire burning beneath the pallet. This latter category of surfaces includes vertical reinforcing ribs, such as those shown in FIGS. 5B and 7B, where both sides of a rib may rapidly be exposed to the heat of a fire. This use of fire resistant material that does not generate flaming drips helps to slow progression of a fire occurring when full pallets are stacked one above the other, and enhances performance in a corresponding fire safety test in which the bottom pallet of a stack of pallets carrying cardboard boxes is ignited beneath the middle of the bottom pallet. The rate of burning (heat release) should be below a defined limit. The main challenge of polymer pallets in this scenario is that heat exposure to the underside of the middle and upper pallets causes melting and dripping of flaming polymer material down into the fire, and a consequent rapid flare-up of the fire. By making sure that at least the underside of most of the pallet is fire resistant material, and in particular, fire resistant material that does not generate flaming drips, this flare-up effect is avoided, and the rate of burning is reduced to the required levels. Preferably, at least 90% of the underside surfaces of the pallet are formed from fire resistant material, and most preferably, substantially the entirety of downward-facing surfaces and rib surfaces are formed from fire resistant material, whereas surfaces that are externally exposed to impacts (such as the outer perimeter and the legs) are made from more a ductile impact-resistant polymer composition, despite the fact that it forms flaming drips when ignited. The fire resistant material may provide only the lower exposed surfaces of the pallet or may form the entirety of the inner deck thickness, either as an insert formed from polymer or other materials, or may be integrally formed with the peripheral structure through two-component injection molding.

[0071] Regarding the combination of the first and second aspects of the present invention, although the presence of fire venting structures 116 might be considered at odds with the concept of using fire resistant materials for the underside of the pallet to limit the rate of spread of a fire, it has been found that it is the non-dripping properties of the underside of the pallet that are critical for limiting the rate of spread of the fire, and the presence of fire venting structures in a loaded-pallet scenario is not problematic.

[0072] In certain embodiments of the invention, fire-venting structure(s) 116 extend along an edge of the inner deck 112 adjacent to the outer deck 104 of the pallet 100. In certain scenarios of exposure to fire, positioning of the vents adjacent to the sides of the pallet is believed to be particularly advantageous, enabling the chimney effect to occur as early as possible in the conflagration.

[0073] At this point, the significance of various aspects of the present invention will be clearly understood. As mentioned in the Background section, there is an inherent conflict between the demands of good mechanical properties for nestable, reusable pallets and the demands of fire safety regulations. Ductile polymer materials without flame-retardant additives or with low proportions of such additives have excellent mechanical properties, making them ideal for withstanding the rigors of shipping and handling. However, these materials are also highly flammable and can contribute to rapid fire spread in a storage or transportation setting. Conversely, materials with sufficient flame-retardant additives to render them self-extinguishing and to prevent generation of flaming drips typically suffer from compromised mechanical properties, becoming brittle and prone to cracking or breaking on impact. The present invention provides a suite of features, useful alone or in combination, to circumvent these limitations by controlling conflagration dynamics in a range of different usage scenarios. The peripheral structure 102, including the legs 108, 110 and the outer deck 104, is preferably formed entirely or primarily from polymer materials with uncompromised strength and ductility. This choice of materials ensures that the pallet 100 can withstand the stresses and impacts encountered during its service life. However, to maintain overall fire performance within the required standards, the invention incorporates several features that control the behavior of a fire in different scenarios. For example, in a situation where a fire originates near the base of a stack of nested pallets, the fire-venting structures 116 facilitate a rapid vertical spread of the flames, minimizing the horizontal spread and preventing the fire from engulfing a large area. This controlled vertical spread also ensures quick activation of overhead sprinkler systems, leading to faster fire suppression. In another scenario, where a fire occurs within a stack of loaded pallets spaced apart by cardboard boxes or other loads, the fire-resistant material on the downward-facing surfaces 114 prevents melting and dripping of flaming polymer, reducing the risk of a rapid flare-up and maintaining the rate of burning below critical limits. By strategically combining these features, the present invention successfully balances the need for robust mechanical properties with the requirements of fire safety, providing a practical and effective solution for nestable polymer pallets.

[0074] At this point, it will be useful to define certain terminology as used in the description and claims.

[0075] Flammable: A flammable material is one that ignites easily and burns rapidly. In the context of this invention, a flammable material is a polymer material that does not self-extinguish once ignited, even if it contains some fire-retardant additives. This means that the material will continue to burn even after the source of ignition is removed.

[0076] Inflammable: In the context of this invention, an inflammable material is a material that does not burn when exposed to the temperatures typically occurring during the burning of plastics or cellulose-containing materials. This includes materials such as metals, fiberglass, Kevlar, carbon fiber, and thermoset polymer matrices.

[0077] Fire Resistant: A fire-resistant material is one that resists ignition and burning. In the context of this invention, a fire-resistant material is a material that self-extinguishes after being ignited. This means that the material will stop burning shortly after the source of ignition is removed. Fire-resistant polymers can be classified according to the UL 94 standard, which defines different categories of flammability based on the burning behavior of the material.

[0078] Non-Drip Fire Resistant: A non-drip fire-resistant material is a fire-resistant material that does not generate flaming drips when exposed to flames. This is important in preventing the spread of fire, as dripping material can carry flames to other parts of the pallet or to nearby objects.

[0079] UL 94 Standard: The UL 94 standard is a widely recognized standard released by the Underwriters Laboratories (USA) for the flammability of plastic materials. It defines several categories of flammability, including 5V, V-0, V-1, V-2 and HB. 5V and V-0 are the most stringent categories, indicating that the material self-extinguishes quickly and does not produce flaming drips. V-1 materials self-extinguish in more time but do not produce flaming drips, V-2materials also self-extinguish but may produce flaming drips, while HB materials support slow horizontal burning.

[0080] In the context of this invention, the fire-resistant materials used in the inner deck insert or on the downward-facing surfaces are preferably non-drip fire-resistant materials that meet at least the UL 94 V-0 or V-1 standard. These are contrasted to polymer material that generates flaming drips on combustion which is used to refer to materials meeting only standards V-2 or HB, or not meeting any of these standards. More ductile and fracture resistant structural polymer materials, preferred for structural parts of a polymer pallet that are typically exposed to impacts during use, and particularly the outer periphery of the pallet, are typically in this category of polymer materials that generate flaming drips on combustion.

[0081] The notion of at least 80 percent open area for vertical airflow should be understood to encompass openings that are either continuous or are subdivided by the presence of ribs or other structural elements of the pallet. The ribs can provide structural support while still allowing for sufficient airflow to facilitate the chimney effect. The area of the fire-venting structure is referred to as contiguous in the sense that a closed shape can be drawn around the fire-venting structure in the plane of the deck (a horizonal plane) within which the 80 percent open criterion is evaluated. This contiguous area may include various ribs or other deck elements which subdivide the vent area into multiple openings. In most of the examples shown herein, the area over which the fire-venting structure is defined is rectangular, but other shapes and areas with more complex geometries that provide the required overall properties may also be used.

[0082] In the first embodiment of pallet 100, as shown in FIGS. 1A-1E and 2A-2C, the peripheral structure 102 and the inner deck 112 are distinct components, which may be attached to each other by any suitable form of attachment. In many cases, however, the peripheral structure 102 and the inner deck 112 may be integrally formed. In certain particularly preferred but non-limiting embodiments, reinforcing rods may be incorporated into polymer pallets of the present invention in order to provide enhanced structural strength and rigidity. Thus, as best shown in the exploded view of FIG. 1E, reinforcing rods 118 are anchored in the peripheral structure 102 and support the inner deck 112. These reinforcing rods 118 are also visible from below in FIG. 1B and from the ends of the pallet in FIG. 2A. When the pallets 100 are nested in a stack, as illustrated in FIGS. 2A-2C, the fire-venting structures 116 align to form a chimney structure allowing vertical airflow through the stack of pallets. This chimney effect is indicated by the dashed arrows in FIG. 2B. Additionally, the reinforcing rods 118 are preferably made from inflammable materials and pass adjacent to the fire-venting channels 116 such that, when the pallets 100 are nested in a stack with other similar pallets, the reinforcing rods 118 of successive pallets align one above the other to form a vertical barrier, preferably majority-closed along a corresponding virtual vertical plane 120, inhibiting horizontal spread of a fire. This fire break effect is best illustrated in FIGS. 2B and 2C. A conceptually similar fire break effect may alternatively be provided by other components of the pallet formed from inflammable or fire resistant materials, as will be exemplified below with reference to FIGS. 11A-11B and 13A-13C.

[0083] The photograph of FIG. 3 was taken during a fire test performed on a stack of nested plastic pallets having fire-venting channels similar to those illustrated in the first embodiment. The photograph shows clearly the flames leaping vertically above the stack sufficient to actuate overhead sprinklers (not present in this outdoor test) while the fire is localized in the horizontal direction so that the vast majority of the stack is not ignited.

[0084] FIGS. 4A-4C illustrate a second embodiment of a pallet 200 according to the present invention. The second embodiment is generally similar to the first embodiment, but instead of 4 vents 116 only along the long edges, it has 8 vents 116, with two along each of the shorter edges of pallet 200. Once again, the vents 116 are here located between the peripheral frame 102 and the inner deck 112, and there are two along each edge since they are interrupted by the leg 110 in the middle of each side.

[0085] In both pallets 100 and 200, vents 116 are positioned close to the periphery of the pallet and are therefore close to the likely source of a fire adjacent to a stack of nested pallets. Current tests typically ignite a fire next to the long side of the pallet, which is also statistically a majority of the periphery of the pallet, but the use of vents 116 along all of the sides as in pallet 200 may accelerate the chimney effect particularly in a case that the fire source approaches the stack from one of the short edges.

[0086] In a third embodiment, illustrated in FIGS. 5A-5C, a pallet 300 is illustrated as a one-piece injection molded plastic structure and has an additional central (9th) leg 302 in the middle of the inner deck 112. Parenthetically, it should be noted that the option of a central leg is not limited to one-piece implementations, and can also be implemented as part of an insert or supported by a bridge formed as part of the peripheral frame. In the one-piece implementation of pallet 300, there is no clear visible subdivision between the peripheral structure 102 and the inner deck 112, and the delineation between them may be somewhat arbitrary, although the peripheral structure 102 can be defined as including all of the structure which lies between the peripheral legs 108, 110. The vents 116 are shown as 8 rectangular openings positioned in a 3*3 grid where the central leg 302 is the middle of the 3*3 grid and the other 8 rectangles are open. As can be best appreciated in FIG. 5C, which is a bottom view of the pallet of FIG. 5A, not all of the rectangles are the same size. There are two rectangular openings each the same size as the footprint of the leg 302 on opposite sides of the leg 302 forming a middle row and two rows of three rectangular openings, each about half the size of those squares, on each side of the middle row. A pair of horizontal dashed lines separated by a distance d1 and a pair of vertical dashed lines separated by a distance d2 indicate the outer boundaries of the region defining the fire-venting channel 116. The third embodiment, like many of the embodiments described herein, has channels beneath the deck 112 in which there are reinforcing rods 118 extending along the length of the pallet. This is not an essential feature, but is present in various preferred embodiments.

[0087] FIGS. 6A-6C illustrate a pallet 400 according to a fourth embodiment of the present invention. In the prior exemplary embodiments, as well as in further examples illustrated below, the fire-venting channels are shown as openings, thereby immediately allowing air flow to provide the desired chimney effect in case of a fire. In certain cases, however, the presence of a region that is open over at least 80% of its area may impact convenience of usage, particularly when handling relatively small objects which might become lodged in an opening. To address this, a thin layer or membrane of plastic may be provided to initially close all or part of the fire-venting channel(s). If this membrane is made sufficiently thin, it disintegrates rapidly on initial exposure to a fire, thereby opening up the fire-venting channels to function in the same manner as has already been described above.

[0088] Although this principle is applicable as a modification to any and all of the embodiments illustrated herein, pallet 400 is presented here as a variation of the third embodiment 300 modified to illustrate the concept of a membrane 402 covering the fire-venting channels 116. The membrane 402 enhances usability by preventing small objects from falling through the openings and by providing a continuous flat surface across the top of the pallet 400. In the event of a fire, the membrane 402 will burn or melt rapidly, thereby opening the fire-venting structure 116 and allowing for the chimney effect to occur.

[0089] The membrane 402 preferably has a thickness of less than 1 millimeter, while the surrounding deck portions have a thickness of at least 2 millimeters, and typically around 3 millimeters. This difference in thickness allows the membrane 402 to burn or melt more quickly than the surrounding deck portions, ensuring that the fire-venting structure 116 is opened rapidly in the event of a fire. The extent of the sub-area of the pallet deck covered by membrane 402 can be equivalent to the various options for fire-venting structure 116 described throughout this application, typically corresponding to at least 5 percent of the total deck area. The exact timing of when the membrane will disintegrate will depend on the particular details of the temperature and flame exposure, but a sub-millimeter layer of flammable thermoplastic material will always disintegrate significantly before the regular thickness elements such as the deck, reinforcing ribs and legs, thereby ensuring that the fire-venting structure becomes operational in a timely manner.

[0090] It is noted that the membrane 402 option is a tradeoff. The enhanced usability of avoiding large openings in the deck comes at the cost of some delay in progression of the chimney effect until the membranes 402 of successive decks in the stack are removed by the fire.

[0091] This concept is also applicable to the embodiments in which the fire-venting channels 116 are located adjacent to the peripheral structure 102.

[0092] FIGS. 7A-7C illustrate a pallet 500 according to a fifth embodiment of the present invention. Pallet 500 is generally similar to pallet 400 but shows a further alternative location for deployment of the fire-venting channels 116. In this case, there are four fire-venting channels 116 located near the four corners of the inner deck 112 just inwards from the corner legs 108 and peripheral structure 102. Each fire-venting channel 116 is shown here as a rectangular area subdivided by reinforcing ribs into a 2*3 rectangular grid, delimited in FIG. 7C by dashed lines indicating the dimensions d1d2 of each fire-venting channel. Parenthetically, it is noted that areas of the inner and outer deck which are not part of the fire-venting structures 116 also have multiple openings, as is common in the art, which may allow for drainage during cleaning etc., but in other areas, the openings typically are only a minority of the area, certainly when averaged over a significant proportion of the pallet surface.

[0093] Parenthetically, it will be noted that the layout of fire-venting channels in all of the embodiments is preferably symmetrical under 180 degree rotation of the pallet. This ensures that the fire-venting channels of nested pallets are always aligned with each other independent of the relative orientation of the stacked pallets.

[0094] FIGS. 8A-9B illustrate a pallet 600 according to a sixth embodiment of the present invention. Pallet 600 is an implementation in which substantially the entire inner deck 112 functions as a fire-venting structure 116. Pallet 600 has a peripheral structure 102 similar to the previous embodiments and an inner deck 112 formed entirely from an open lattice structure 602 of non-flammable material, typically metal. As shown in FIG. 8A, the inner deck 112 is implemented as a flat sheet of metal with a marginal region without holes for attachment to the peripheral structure 102. Most of the remaining area of inner deck 112 is formed with a grid of square holes leaving a structure of crisscross strips to provide the inner deck load bearing surface. As in other embodiments, four lengthways reinforcing rods 118 are preferably anchored in the peripheral structure 102 and help to support the inner deck 112.

[0095] FIGS. 10A-12C illustrate a pallet 700 according to a seventh embodiment of the present invention. Pallet 700 uses an inflammable insert 702 for the inner deck 112. The fire-venting channels 116 are located immediately outside the edges of inflammable insert 702 adjacent to the peripheral structure 102. This is achieved by making the inner deck insert 702 undersized compared to the peripheral structure 102, thereby leaving a gap between the peripheral structure 102 and the inner deck insert 702 which serves as the fire-venting channel 116.

[0096] The inner deck insert 702 is preferably formed with a downward-extending peripheral edge 704 which defines one side of the fire-venting channel 116 and provides a firebreak function when the pallets are stacked. In the non-limiting example illustrated here, inner deck insert 702 is secured to peripheral structure 102 by outward projecting tabs 706 which can be secured to the peripheral structure 102 by any suitable form of attachment, such as by bolting or overmolding. Additionally or alternatively, ribs 708 may extend inwardly from the peripheral structure 102 to provide support and/or aid attachment of the inner deck insert 702 to the peripheral structure 102.

[0097] The inner deck insert 702 may be implemented using a range of non-flammable or fire resistant materials, including a continuous closed surface (FIG. 12A), an open mesh (FIG. 12B), or an open-centered frame (FIG. 12C) suitable for supporting large items such as crates.

[0098] FIGS. 13A-13C illustrate a pallet 800 according to an eighth embodiment of the present invention. Pallet 800 is similar to pallet 700 but incorporates reinforcing rods which interlock in two orthogonal directions to provide enhanced support for the inner deck insert 702. Peripheral structure 102 is formed with channels for four rectangular cross-section reinforcing rods 802 (equivalent to reinforcing rods 118 of the earlier examples) extending along the length of the pallet and for four round reinforcing rods 804 extending across the width of the pallet. The round rods 804 extend through round openings in the rectangular rods 802, thereby interlocking and providing enhanced rigidity and strength. Inner deck insert 702 is formed with openings in its sides 704 to accommodate the reinforcing rods 118.

[0099] All of the above embodiments may be implemented for a range of applications and sizes of pallet. Particularly preferred examples include pallets of dimensions 80120 cm, 100120 cm, and standard North American pallets of dimensions 4048 inch.

[0100] It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the scope of the present invention as defined in the appended claims.