EP2389986B1

EP2389986B1 - Vapor barrier for flammable liquid storage tanks

Info

Publication number: EP2389986B1
Application number: EP10164411.0A
Authority: EP
Inventors: Joseph Riordan
Original assignee: Individual
Current assignee: RIORDAN, JOSEPH
Priority date: 2010-05-28
Filing date: 2010-05-28
Publication date: 2015-11-25
Anticipated expiration: 2030-05-28
Also published as: EP2389986A1

Description

1. FIELD OF THE INVENTION

The present invention relates to buoyant spheres. The invention includes buoyant spheres useful in forming floating barriers on a liquid surface, particularly amongst other things to spheres useful for forming a vapor barrier for a flammable liquid that provides a vapor-impeding barrier layer with fire-suppressing capabilities . The invention also includes buoyant spheres useful for forming a gas barrier on the surface of a liquid and buoyant spheres useful for recovering oil from the sea, as well as other subject matter.

2. DESCRIPTION OF THE RELATED ART

Flammable liquids, such as oil, gasoline and the like, must be stored in specialized storage tanks due to the flammable vapor that forms above the liquid surface. A common storage tank, often used in the petrochemical industry, is the "floating roof" tank. A typical floating roof tank is illustrated in Fig. 2. Tank 100 includes a hollow cylindrical housing 112 having an open upper end. The open upper end is sealed by a buoyant cover 114, having a circular contour matching the dimensions of the interior of housing 112. Cover 114 floats on the flammable liquid L contained within the housing 112, thus providing a seal between the surface of the liquid L and the outside environment, preventing the buildup of flammable vapor (and exposure thereof to external hazards, such as sparks).
Typically, the cover 114 is fabricated from metal and has a hollow chamber divided by walls into an array of pontoons in order to provide sufficient flotation to carry the weight of the cover plus additional weight, such as the weight of snow which might form on the cover 114. In older oil tank equipment, the cover was constructed of a metal plate with pontoons mounted beneath the cover plate, while modern tanks typically have the pontoons located above the metal cover plate. Repairs to the cover may require welding equipment, which can be used only after the tank has been taken out of service in order to ensure that the cover is clean and that there are no flammable vapors present. If any flammable vapors are present during repair work on the cover, such as the repair of a pontoon of the cover, a spark from the welding may ignite an explosive burning of the vapor.
Repairs may also be made without taking the tank out of service. For example, one of the pontoons may sustain a relatively small opening through which liquid can seep resulting in a loss of buoyancy. By means of an access port, a person may enter the pontoon and apply foamed urethane plastic as a liquid that later hardens to maintain buoyancy. Use of the plastic is not intended as a permanent repair because the plastic may become impregnated with the flammable liquid. Further, the plastic is disadvantageous because, at the conclusion of the service interval when reconditioning is mandatory, it is very difficult to remove the plastic so as to be able to clean the cover and make any permanent repairs. Obviously, welding cannot be employed for repair until all liquid and liquid soaked flotation, such as the foamed plastic, has been removed.
As an alternative procedure of repair, one might consider insertion in the pontoons of hollow, non-foamed plastic bodies to provide sufficient buoyancy so that it is not necessary to repair the leak in the pontoon. However, the use of a plastic hollow body, such as a hollow ball, has been avoided in the petrochemical industry because such a plastic body is electrically insulating and susceptible to developing a static electric charge. There is a danger that the flotation body may suddenly discharge via a spark, which can ignite an explosion.
Additionally, in the past, foam products have also been applied to the surfaces of flammable liquids, creating an effective vapor seal between the flammable liquid and the vapor space thereabove. However, the foam degrades within a short period of time, thus defeating the desired suppression qualities. Moreover, foam applied in the event of a flammable-liquids fire is the traditional form of fire fighting, with the intent of the foam being to cool the surface of the liquid and to also separate the flammable liquid from contact with oxygen, thus suppressing the fire. The difficulty with this traditional method of using foam is that the strong convective hot air currents caused by the fire tend to displace the foam, thus exposing the flammable liquid to the existing fire.
Further, marine vessels currently do not typically employ any physical barrier between a stored flammable liquid and the vapor space formed thereabove. Typically, such vessels employ inert gas generators that create an oxygen-deficient deficient gas that is maintained above the flammable liquid in order to preclude the flammable vapor from mixing with oxygen that might otherwise create a flammable atmosphere. Such systems, however, do not provide backup prevention in case the gas generator fails.
GB 2454723A describes an apparatus according to the preamble of claim 1. The apparatus comprises a plurality of flotation members, which are arranged to float on the surface of the liquid such that they form a carpet of at least one flotation member in depth over substantially the entire surface of the liquid. The flotation members are preferably spherical and may consist of 2mm diameter hollow nylon spheres. Alternatively the flotation members may be fabricated from anti-static materials.
US 6220469 describes a plastic ball which has anti-static properties and can be used in flotation of oil tank covers without danger of developing a static charge. The balls are constructed of non-foamed high density plastics resin, HDPE, mixed with an anti-static additive.
GB 1454492 describes fire protection means. The fire protection means, in the form of a plurality of balls each supporting a fire protection substance, is contained external to and contiguous with a container for a flammable substance. The fire protection substance may include a natural rubber exterior coating or a coating of intumescent paint. The balls may be used around air craft fuel tanks.
US 2797141 relates to a composition comprising small hollow hole-free particles adapted to float upon, and to be effective in substantially decreasing the evaporation loss of, volatile products. Specifically, it is taught that the evaporation loss can be decreased by floating a volatile product on a layer of a sealing liquid, a gelling agent and such particles. The particles have an average diameter of from 1-500 µm.
Thus, a vapor barrier for flammable liquid storage tanks solving or mitigating the aforementioned problems is desired.

SUMMARY OF THE INVENTION

The invention provides a sphere for use in forming a vapor barrier on a flammable liquid, the sphere having a diameter of between 1 /16 inch (1.6mm) and 4 inches (10.2 cm), characterized in that the sphere has the following characteristics:

a specific gravity of less than 0.5
an outer layer which is oleophobic and anti-static
a support for the outer layer which is heat resistant or intumescent.

Further aspects and embodiments of the invention are described in the remaining claims.
Also disclosed is a vapor barrier is formed from a plurality of buoyant spheres. Each buoyant sphere has an antistatic outer surface on a support. The support may be intumescent or heat resistant. The antistatic layer is preferably formed from an oleophobic material. Further, each spherical buoyant member has a specific gravity selectively chosen so that the spherical buoyant members float at a desired level within the flammable liquid with which it is intended to use the buoyant members.
The vapor barrier for flammable liquid provides a gas-impeding layer for covering the surface of a flammable liquid. The vapor barrier further provides fire-suppression capabilities, and it should be understood that the vapor barrier may be applied to storage tanks, tankers, vessels, barges or any other type of container for flammable liquids. The vapor barrier prevents or reduces the build-up of flammable vapors over the flammable liquid surface.
Since the vapor barrier has fire-suppression capabilities, the spheres may be used for fire-suppression purposes. The invention includes the use of such spheres to suppress a flammable liquid fire by contacting the liquid with such spheres.
The disclosure includes individual buoyant members as well as plurality thereof e.g. a population of at least 100 buoyant members, for example at least 1000 or at least 10,000 buoyant members. The buoyant members may be floating on a flammable liquid or in a container for storing a flammable liquid.
The flammable liquid is suitably an oil, e.g. a petrochemical oil.
The subject matter of the claims is hereby included in the description.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an environmental front view of a flammable liquid storage tank, the tank being broken away to show a vapor barrier for flammable liquid storage tanks according to the present invention deployed therein.
Fig. 2 is a perspective view of a flammable liquid storage tank according to the prior art, broken away to show a portion of the interior of the tank and contents thereof.
Fig. 3 is an environmental, partial side view of the vapor barrier for flammable liquid storage tanks according to the present invention.
Fig. 4 is a section view of a single buoyant member of the vapor barrier for flammable liquid storage tanks according to the present invention.
Fig. 5 is an environmental, diagrammatic front view of an alternative embodiment of a vapor barrier for flammable liquid storage tanks according to the present invention.

Similar reference characters denote corresponding features consistently throughout the attached drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.
Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including the accompanying claims and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one of, or any novel combination of, the features disclosed in this specification (including the accompanying claims and drawings), and to any novel one of, or any novel combination of, the steps of any method or process so disclosed.
In the following description, the terms "buoyant member" and "buoyant body" are synonymous with "buoyant sphere". A reference in this specification to a "multiplicity" of spheres refers to a population of spheres substantial in number, e.g. at least 100 spheres and often at least 1000 spheres, for example at least 10,000 spheres in some applications. The spheres often exist in such populations.
Referring to Fig. 1, an exemplary storage tank 10 has a vapor barrier for flammable liquid storage tanks deployed therein, the barrier being designated generally as 28. In addition to preventing or limiting the escape of vapor, the vapor barrier further provides fire suppression capabilities, and it should be understood that the vapor barrier may be applied to storage tankers, vessels, barges or any other type of container for flammable liquids. The liquid storage tank 10 is shown for exemplary purposes only and suitably includes elements conventionally found in storage tanks for flammable liquids, such as oil, gasoline and the like. The housing 12 may be formed from steel, for example, as is conventionally known, and, by way of example, is either supported above the ground surface, or is at least partly buried in the ground. The tank is provided with a cover 22 and with pipes 18 and 20 for admitting flammable liquid L into the open interior region of housing 12, and for the withdrawal thereof when required. It should be understood that the vapor barrier 28 may in principle be used with any type of flammable liquid L, such as liquid natural gas, petroleum oil, gasoline or the like.
The surface of the liquid L is provided with at least one layer of buoyant bodies or spheres forming the vapor barrier layer 28, as will be described in greater detail below. The cover 22 may be further provided with a vent 26 and/or with an admission valve 24 for admitting an inert gas to the space above the stored liquid L, as is conventionally known. Preferably, a port 16 is formed through the sidewall of the housing 12, allowing the selective insertion of the vapor barrier layer 28 (in the form of individual spherical members, as will be described below) within the housing 12 via a chute 14. It should be understood that the chute 14 is shown for exemplary purposes only. It should be further understood that the vapor barrier layer 28 may be introduced into housing 12 in any suitable manner, such as, for example, through existing tank openings. Port 16 and chute 14 are shown for exemplary purposes only.
As best shown in Fig. 3, the vapor barrier 28 is preferably formed as a buoyant layer through the stacking of multiple sizes of buoyant members 30, 32, 34. Each buoyant member 30, 32, 34 is spherical, the buoyant members 30 having the largest radii, the buoyant members 34 having the smallest radii, and the buoyant members 32 having radii therebetween. It should be understood that the relative dimensions illustrated in Fig. 3 are shown for exemplary purposes only, and that a wider variety of buoyant members having distinct radii may be utilized.
In an exemplary embodiment, exactly two different sizes of buoyant member are used.
There may therefore be a population of buoyant members comprising a plurality of sub-populations, each sub-population having a different diameter, the sub-populations having respective diameters of from 1/16 inch (1.6mm) to 4 inches (10.2cm), e.g. from 1/16 inch (1.6mm) to 2 inches (5cm). The diameter ratio of each sub-population to the next biggest sub-population is typically of from 1:2 to 1:5, e.g. 1:2 to 1:4 as in the case of 1:2.5 to 1:3.5. In one embodiment, the size ratio is about 1:3. Conveniently, the population comprises a sub-population having a diameter of about 1 /8 inch (3.2mm) and a sub-population having a diameter of about 3/8 inch (9.5mm).
A population of buoyant members may consist of two sub-populations, each having a size mentioned in the preceding paragraph, e.g. of from 1/16 inch (1.6cm) to 1 inch (2.5cm), e.g. of from 1/16 inch (1.6mm) to a half inch (1.3cm), and the sub-populations optionally having diameter ratios as mentioned in the preceding paragraph. For example one sub-population may have a diameter of about 1 /8 inch (3.2mm) and the other a diameter of about 3/8 inch (9.5mm).
For all embodiments of the invention, the buoyant members may comprise a first set of buoyant members (or first sub-population of buoyant members) which are of a size to fit in interstices between buoyant members belonging to a second set of buoyant members (or second sub-population of buoyant members).
The spherical contour of the buoyant members 30, 32, 34 allows for a packed arrangement, as shown in Fig. 3, the buoyant members naturally settling under the force of gravity into a gas-impermeable layer when inserted into the housing 12 to float on the surface of flammable liquid L. In respect of all embodiments of the invention, the buoyant members may in use sit in the liquid, i.e. float partially submerged, as this stabilizes them against moving responsive to gas movements above them. The buoyant members of the disclosure therefore preferably have a construction (alternatively stated, a composition) such that they float partially submerged in a "target" liquid for which they are intended; a suitable construction may be determined empirically. The specific gravity of the buoyant members 30, 32, 34 is preferably in the range of between 0.05 and 0.5 so that the buoyant members 30, 32, 34 will remain partially submerged within liquid L, as shown, when flammable liquid L is a common flammable material, such as petroleum oil (specific gravity about 0.6) or gasoline. In some embodiments the specific gravity is from 0.05 to 0.3, e.g. 0.05 to 0.2; particular embodiments have a specific gravity of from 0.1 to 0.3, e.g. 0.1 to 0.2. As already indicated, it should be understood that the specific gravity may be varied, depending upon the particular composition of the flammable liquid L. The specific gravity is suitably selected such that the buoyant members are partially submerged so that the buoyant members provide a lower cross-sectional area below the level of the liquid L in the event of thermal wind currents or convective thermal air currents generated within the tank 10 in the event of a fire.
As shown in Fig. 3, the differently sized buoyant members 30, 32, 34 forming the vapor barrier layer 28 form a suppressing blanket effect for the surface of liquid L, minimizing possible liquid-vapor contact within tank 10 (of Fig. 1). The smaller spherical bodies 32, 34 fill in gaps between the larger bodies 30, thus blocking potential evaporation paths from the surface of the liquid L. Additional layers create interstitial vapor pockets, trapping vapors therein and preventing the release thereof into the area above the vapor barrier 28.
Fig. 4 illustrates a product of the invention, namely a buoyant sphere having the following characteristics:

a specific gravity of less than 0.5
a diameter of between 1/16 inch (1.6mm) and 4 inches (10.2 cm)
an outer layer 36 which is oleophobic and anti-static
a support 38 for the outer layer which is heat resistant or intumescent.

The spheres of the disclosure may be made by applying to a porous plastics core a coating to form a support layer followed by application as desired of a layer to provide an oleophobic outer layer. If desired, the plastics core may be collapsed to provide the sphere with a substantially gas-filled core.
Each buoyant member (i.e. sphere for use with flammable liquid) may comprise or consist of three layers. A single buoyant member 30 is shown in Fig. 4, although it should be understood that buoyant members 32, 34 are in one embodiment formed from identical materials, although having differing radii. In some embodiments, a population of buoyant members comprises a class of buoyant members made of a first combination of materials and a class of members made of a second, different, combination of materials. A central layer or core 40 provides buoyancy and may be wholly or partially gas-filled e.g. contain a porous plastics material. The core 40 is surrounded by a support 38 for an outer layer 36. The support 38 is a spherical layer or shell and may comprise, or consist of, an intumescent layer 38. In the event of a fire within tank 10 of Fig. 1, the intumescent layer 3.8, which is heat reactive, expands, thus ensuring that buoyant members 30, 32, 34 form a vapor-impermeable barrier. Alternatively, the intumescent layer 38 may be replaced with heat-resistant material, which is at least temporarily capable of maintaining a substantial spherical shape when in the vicinity of a fire. Suitably, a heat-resistant layer is formed from a material that is non-reactive to the flammable liquid, e.g. non-reactive to petroleum products. Many heat resistant plastics will be known to the skilled reader.
Heat-reactive, expanding foam materials that are non-reactive with petroleum products and that can withstand relatively high temperatures are well known and may be used to form the intumescent layer. Any suitable heat-reactive intumescent material may be utilized. There will be mentioned here the following intumescent materials:

i) ammonium phosphate
ii) hydrated sodium silicate
iii) intercalated graphite.

i) Ammonium phosphate

Products of this type were originally based on monoammonium phosphate (often abbreviated to MAP) but in recent years ammonium polyphosphate (APP) has also been used. The material has an activation temperature of about 180°C. Intumescent materials based on MAP or APP are hygroscopic and may be protected by a suitable binder system or a surface coating applied during manufacture.

ii) Hydrated sodium silicate

This material is also hygroscopic and the most widely used commercial version is coated with an epoxy resin to protect against atmospheric water vapour. The activation temperature of sodium silicate intumescent is about 110 - 120°C and is the lowest of the commercially used materials described here.

iii) Intercalated graphite

Intercalated graphite differs from ordinary graphite in having water molecules sandwiched between the layers of carbon. On heating, the water is turned into steam causing the graphite to exfoliate, producing a light 'fluffy' material. The activation temperature is typically around 200°C. Graphite is not hygroscopic so it does not require protection from the atmosphere.
In use, the smaller buoyant members, as best illustrated in Fig. 3, fall into the spaces between the larger buoyant members, thus forming a nearly continuous barrier against escaping vapor. This continuous barrier acts as a floating roof for preventing escape of the flammable vapor. It will be appreciated therefore that a population of spheres advantageously comprises a first set of spheres whose member spheres are of a size to fit in interstices between members of a second set of spheres. In use, with liquid natural gas or a similar substance, which is a liquid at cryogenic temperatures, the vapor barrier 28 forms a thermal insulation layer, preventing the cryogenic liquid from boiling off too quickly.
Where the spheres are to be used with a flammable petrochemical, the outer layer 36 is formed from oleophobic and antistatic material. It will be appreciated that such an oleophobic layer is useful in combination with flammable liquids which at least predominantly consist of one or more hydrocarbon oils. The outer layer 36 may be formed from, for example, a high-density plastic resin mixed with an antistatic additive or agent. The oleophobic resin may be Teflon^® or a Teflon^® derivative product; recalling that Teflon^® is a trade mark of Du Pont (Du Pont is also a trade mark) for fluoropolymer resins, e.g. PTFEs, it will be understood that PTFEs and other fluoropolymer resins are suitable oleophobic resins. The antistatic agent is effective in converting the electrically insulating plastic into an electrically conductive material that does not develop a static electrical charge. Antistatic materials are well known. One example of such a material capable of being mixed with a high-density plastic resin is manufactured under the mark GLYCOSTAT, manufactured by Lonza^® of Fair Lawn, NJ. GLYCOSTAT comprises HMS, a high glycerol monostearate-containing blend of fatty esterified glycerin. HMS contains glycerol mono-, di-, and tri-stearate, and glycerol. HMS is therefore a suitable anti-static agent. It should be understood that the core 40, the intumescent or fire retardant layer 38, and the oleophobic and antistatic layer 36 may be formed from any suitable materials, preferably so that the overall structure has a specific gravity within the range of approximately 0.05 and 0.5.
The spherical buoyant members 30, 32, 34 have diameters within the range of approximately 1/16 of an inch (1.6mm) to four inches (10.2cm). It should be understood that members 30, 32, 34 are not all required to be of identical construction. For example, intumescent or flame retardant coating 38 is preferably applied at a relatively large thickness, and thus may be able to be applied solely to the largest members 30 in order to maintain buoyancy. Thus, the invention includes a plurality of buoyant members of the disclosure, of which a portion have a support layer and a portion do not have a support layer. In an embodiment, there is provided a plurality of buoyant members of which a portion (particularly, a sub-population having the largest diameter) have an intumescent support layer and a portion do not have an intumescent support layer but may optionally have an flame retardant support layer. In one example, the smaller members 32, 34 would only include the core 40 and the antistatic and oleophobic layer 36. Alternatively, the intumescent or flame retardant material may be used as an outer shell for the spherical members, rather than being solely formed as an intermediate layer. It should be understood that any combination of the above-described layers and materials may be used, depending upon the liquid and the container.
Fig. 5 illustrates an alternative embodiment of the vapor barrier in which the vapor barrier layer 28 is combined with a floating roof, for example a conventional floating roof 114 of Fig. 2. Conventional floating roofs are typically formed as circular pans having a planar floor and a raised peripheral rim defining an open interior region in the upper side thereof.
Such roofs may sink due to environmental conditions, such as earthquakes or other external stresses, causing the pan to tilt and thus fill with liquid L. Some floating roofs include a central drain, but this can become clogged by snow or ice, for example.
In Fig. 5, a floating roof 114 is positioned within the tank, as in Fig. 2, but with a bag 31 containing members 30, 32 and 34 positioned within the open interior region thereof. The bag 31 is formed from a readily dissolvable material so that if floating roof 114 sinks, the bag 31 will dissolve in liquid L and a vapor barrier layer 28 will cover the surface of liquid L as described above, thus adding an additional layer of protection. It should be understood that any suitable number of bags 31 containing members 30, 32, 34 may be positioned within the upper interior region of roof 114, and that the bags 31 may be formed of any suitable material that is readily dissolvable in the flammable liquid, e.g. in a petroleum-based liquid. Additionally, it should be understood that any suitable type of container may be utilized, and that bag 31 is shown for exemplary purposes only.
As noted above, the vapor barrier may be applied to any type of storage tank, storage vessel, etc. For example, the vapor barrier may be used with conventional rectangular tanks or irregularly shaped tanks, such as those typically found on crude oil tankers or barges. Such tankers and barges typically have no floating vapor seal due to the difficulties of maintaining a sealing surface during the turbulent and oscillatory motion of the flammable liquid while the vessel is in motion.
The vapor barrier acts to suppress the evaporation of the flammable liquid into the vapor space above the liquid surface, and further provides a thermally activated barrier in the event of a fire. The spheres provide an effective thermal barrier absent sufficient heat to activate the intumescent layer. In the presence of sufficient heat (e.g., a fire within the tank, above the liquid surface), the barrier would be formed by the reaction of the intumescent layers of the spheres. Further, as noted above, the spheres may be added to the tank following a detection of fire in order to suppress the fire, either in support of, or in lieu of, fire fighting foam or other substances.
As previously described, a layer of spheres floating on a liquid surface is capable of restricting gas flow between the liquid surface and a gas above it (in fact, above the layer of spheres). Such a layer of spheres is particularly effective when it comprises spheres of two or more sizes, so that smaller spheres can fit in spaces between larger ones, for example can partially occupy interstices between larger spheres. It may also be beneficial for the spheres to have a specific gravity such that they float partially submerged, to help them resist being moved by gas streams. Such restriction of gas flow is useful in the case of flammable oils and the spheres are advantageously used with flammable oils.

Claims

A sphere for use in forming a vapor barrier on a flammable liquid, the sphere having a diameter of between 1/16 inch (1.6mm) and 4 inches (10.2 cm), characterized in that the sphere has the following characteristics:
• a specific gravity of less than 0 5

• an outer layer (36) which is oleophobic and anti-static

• a support (38) for the outer layer which support is heat resistant or intumescent.
A product for use in forming a vapor barrier on a flammable liquid, the product comprising a multiplicity of spheres according to claim 1.
A sphere of claim 1 or a product of claim 2 wherein the support is intumescent.
A sphere of claim 1 or a product of claim 2 or claim 3 wherein the specific gravity is from 0.05 to 0.5, and optionally from 0.05 to 0.3.
A sphere of claim 1 or a product of claim 4 wherein the specific gravity is from 0.1 to 0.2.
A sphere of claim 1 or a product of any one of claims 2 to 5 wherein each sphere has a diameter of from 1/16 inch (1.6 mm) to 1 inch (2.5 cm).
A sphere of claim 1 or a product of any one of claims 2 to 6 wherein the support comprises a hollow sphere of heat resistant or intumescent material, the hollow (40) optionally containing a plastics material.
A product of any one of claims 2 to 7 wherein the multiplicity of spheres comprises two or more sets (30, 32, 34) of spheres, the spheres of each set having the same diameter as each other and the diameter of each set being different from the diameter of each other set, optionally wherein the number of sets is exactly two.
A product of claim 8 wherein the sets of spheres comprise a first set whose member spheres are of a size to fit in interstices between members of a second set.
A product of claim 8 or claim 9 wherein the diameter ratio of each set, except for the set of largest diameter, to the next biggest set is from 1:2 to 1:5.
A product of claim 10 wherein said diameter ratio is from 1:2 to 1:4.
A product of claim 10 wherein said diameter ratio is from 1:2.5 to 1:3.5, e.g. 1:3.
The use of a product of any one of claims 2 to 12 to form a vapour barrier on a flammable liquid (L) or to suppress a flammable liquid fire.
A combination of a flammable liquid (L) and a product of any of claims 2 to 12, wherein at least a portion of the spheres sit floating in the liquid at its surface and any remaining spheres comprise spheres supported by the floating spheres.
A container which is for a flammable liquid and which contains a product of any of claims 2 to 10.
The container of claim 15, wherein the container contains also the flammable liquid.