NZ256483A - Insulated box for storing temperature sensitive materials: walls insulated with liquid layer - Google Patents

Description

«r New Zealand No. 256483 International No.

TO BE ENTERED AFTER ACCEPTANCE AND PUBLICATION Priority dates: 02.10.1992; Complete Specification Filed: 04.10.1993 Classification: (6) B65D81/38; F25D3/06.08 Publication date: 19 December 1997 Journal No.: 1423 Title of Invention: Storing temperature sensitive products Name, address and nationality of applicant(s) as in international application form: AIR CONDITIONING INSTALLATIONS LIMITED, a New Zealand company of 37 Cambridge Terrace, Lower Hutt 6009, New Zealand m NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION New Zealand No. 256483 International No. PCT/NZ93/00090 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION Title of Invention: Storing temperature sensitive products Name, address and nationality of applicant(s) as in international application form: AIR CONDITIONING INSTALLATIONS LTD, a New Zealand company of 37 Cambridge Terrace, Lower Hutt 6009, New Zealand 256483 STORING TEMPERATURE SENSITIVE PRODOCTS TECHNICAL FIELD This invention relates to a method and apparatus for storing temperature sensitive products such as, for example, vaccines and certain other drugs having a low weight to volume ratio when prepared for storage. The method and the apparatus are directed to maintaining the stored products at the mean temperature of the surrounding environment.

BACKGROUND ART A particular focus of the invention is the storage of vaccines, however, the invention is not to be taken as limited solely to that focus. The system of distributing vaccines from the manufacturer to the actual vaccination site is known as the "cold chain".

Vaccines are particularly temperature sensitive, exposure to temperature outside a preset range will result in loss of potency. Vaccine potency cannot be regained once lost, thus once a vaccine has lost its potency it can no longer be used to protect people from disease.

In general, if vaccines are maintained within a preset temperature range they will remain potent for a long time. For example, measles vaccine kept at +5°C will maintain its potency for at least two years. However, the same measles vaccine exposed to +40°C will lost its potency in one day.

The cold chain consists of a series of transport links during which adequate refrigeration is required to maintain vaccine potency. Typically vaccines are transported via air from the manufacturer to a national vaccine store. From there vaccines are transported to regional distribution centres,such as regional hospitals and then onto SUBSTITUTE SHEET PCT/N Z93/00090 sub-regional points, such as rural hospitals, or directly to the General Practitioners surgery or vaccination site.

National vaccine stores and regional distribution centres tend to store vaccines in specially designed vaccine dedicated refrigerators.

However, at the sub-regional points and in General . Practitioner surgeries vaccines are usually stored in standard domestic refrigerators.

Numerous studies have shown that, for several reasons, domestic refrigerators are not suitable or safe for vaccine storage: * Temperature gradients exist within the refrigeration compartment, so that temperatures are too high for vaccines in the shelves of the door and in the vegetable drawer at the bottom of the refrigerator.

* The thermostat differential, which sets the operating range of the refrigerator, is too wide, particularly with refrigerators incorporating an auto-defrost function. This problem is exacerbated by incorrect setting of the refrigerator thermostat, as this is the mean temperature of the operating range.

* During power failures, which can occur relatively frequently in many developing countries, '^he holdover time is relatively short because of poor insulation.

* When the freezer compartment is placed under load, such as when warm items are placed in it, the temperature in the refrigeration compartment rises, CJMRCTITIITF SWFFT O 94/07769 PCT/NZ93/00090 often out of the safe range for vaccines.

Recent research in New Zealand has identified that 8% of freeze sensitive vaccines are damaged by freezing 5 and 34% of vaccines are exposed to warm conditions sufficient to shorten their shelf life. A significant proportion of the temperature damage occurs during storage at regional distribution centres, sub-regional points, and General Practitioners surgeries or the 10 vaccation site. Most of this damage is attributable to the use of domestic refrigerators as the storage device.

The replacement value of impotent vaccines resulting 15 in New Zealand alone, with its population of a mere 3.5 million, has been estimated at US$240,000. As a large percentage of these impotent vaccines are actually administered under the belief that they are still potent the flow on effect and resultant cost 20 to the healthcare system generally is likely to be immense.

The World Health Organisation has recognised that a major problem exists in this area, and has supported 25 and encouraged a significant amount of research and development work.

The main thrust of the research and development work has been to design a modification kit for domestic 30 refrigerators. Such kits include adding containers of water to both the refrigerator and freezer compartments, and putting extra insulation into the door area.

Modification kits of the kind identified above go some way towards curing vaccine storage problems, in that they tend to reduce the magnitude of temperature gradients within the refrigeration compartment, reduce SU3STITUTE SHEET PCT/N Z93/00090 4- the effect of loading of the freezer compartment and dramatically increase the holdover time in cases of a power failure.

However, the modification kits have the reverse effect on the problems caused by thermostat differential and thermostat misadjustment, making matters worse. In this connection, any increase in the holdover capability of the refrigerator as a whole also increases the 10 refrigerator cycle time.

One full cycle of the refrigerator involves fluctuation of the refrigeration compartment temperature from one limit to the other limit, then back to the first limit. 15 In each cycle there is a cool down period, during which the refrigeration unit operates, and a warm up period during which heat leaks into the refrigeration compartment causing its temperature to rise (that is, assuming the temperature outside the refrigerator is 20 greater than the upper thermostat differential temperature limit).

The change in temperature during the cool down period of the refrigerator cycLa is relatively rapid, and 25 is substantially a straight line reduction. However, the temperature in the warm up period of the cycle increases at a rate which decreases exponentially as the refrigeration compartment temperature approaches the maximum differential temperature of the thermostat.

Thus, a greater proportion of the whole refrigerator cycle is spent above the mean temperature, and a significant proportion of time is spent near the maximum differential temperature. Increasing the holdover 35 time, and thus the total refrigerator cycle, increases the time spent near the maximum differential temperature limit.

A further problem associated with the refrigerator SUBSTITUTE SHEET modification kits, or at least not overcome by such kits is that: i) where bulk volumes of vaccine are stored, every 5 time a single vial or bottle is required the entire bulk is affected by a blast of warm air. where few vaccines are stored and the refrigerator is used for other purposes, e.g. storage of milk, fruit, lunches etc refrigerator door openings are likely to be a common occurance and, again, the stored vaccines will be subjected to warm air each time.

It is an object of the present invention to provide a method and apparatus to at least partially overcome the above noted problems.

SUMMARY OF THE INVENTION In a first broad aspect of this invention there is provided a container for storing material sensitive to temperature deviation from a specific temperature, the container having a storage chamber fully enclosed 25 by walls adapted to passively maintain the temperature of the chamber within an acceptable range of fluctuation about a temperature corresponding to the mean temperature of the environment directly surrounding the container, which environment fluctuates in 30 temperature outside the acceptable range.

Advantageously the container is sized to fit within the refrigeration compartment of a domestic refrigerator.

Preferably the container fits within the refrigeration compartment of a domestic refrigerator with a gap of at least 10 millimetres between all surfaces of the ii) SUBSTITUTE SHEET WO 94/07769 PCT/NZ93/00090 contaiher and the walls of the refrigeration compartment.

Desirably the container comprises a box having a lid 5 openable to gain access to the chamber within.

Preferably the lid provides a substantially air tight seal against the abutting container portion.

Optionally the container is a substantially rectangular box, the upper wall of which comprises the lid. Alternatively, the container can have a substantially rectangular base, front and back wall, with the front wall being smaller than the back wall, resulting in 15 the top sloping from the rear down towards the front.

Conveniently the lid can be substantially transparent.

Desirably the lid incorporates a temperature indicating 20 device to indicate the temperature inside the chamber, which indicated temperature can be read from outside the container.

Preferably the container walls are of sandwich 25 construction.

Desirably the inner lamina is formed from a material having a high thermal storage capacity.

Advantageously one of the lamina is water.

Preferably the outer lamina is a thermally insulative material.

Conveniently all of the walls of the -container are of substantially the same construction.

Optionally the lid is of a different construction to SUBSTITUTE SMFFT O 94/07769 PCT/N Z93/00090 the remaining walls of the container.

Desirably the inner lamina is formed from plastics material, expediently acrylic plastics material.

Advantageously the chamber is formed into two or more compartments.

Desirably each compartment is separated by a wall of 10 similar construction to the other walls of the container.

Advantageously the lid is split to accord with the compartments, so that access to one compartment is 15 possible while the remainder are closed.

Conveniently the compartments can be drawers, with the lid being the drawer front.

In a second broad aspect of this invention there is provided a method for storing temperature sensitive materials in an environment of fluctuating temperature utilising the container of the first broad aspect above, the mean temperature of said environment being equal 25 to a desired storage temperature, but said environment fluctuating unacceptably about the mean temperature, the method comprising placing the temperature sensitive materials inside the chamber of the container.

Preferably the environment is the refrigeration compartment of a domestic refrigerator.

Desirably the temperature sensitive material is vaccine.

Conveniently the maximum temperature insi'de the chamber is 10°C.

Advantageously the acceptable range of temperature CfnCTlTllTP QHPCT WO 94/07769 PCT/NZ93/00090 fluctuation inside the chamber is ±4°C.

Desirably the acceptable range of fluctuation insider the chamber is ±1°C.

Preferably the acceptable range of fluctuation insider the chamber is ±0.5°C.

Desirably the mean temperature is 4°C.

The inventive aspect to the present invention is the realisation that much of the problems associated with the storage of temperature sensitive materials in domestic refrigerators are caused by the 15 thermostat - either in its adjustment or its differential. Unlike previous approaches the key function of the present invention is to substantially isolate the storage chamber for the temperature sensitive material from the effects generated by the 20 thermostat.

The invention relies on a process sometimes known as thermal inertia, by utilising two features that: i) all materials require some input or loss of heat energy if their temperature is to change. ii) heat can only flow in or out at a finite rate, depending on the current temperature difference 30 between the object and it's surroundings, and the degree of insulation between them. This insulation can never be zero, as there is always a surface resistance in addition to any thermal insulation fitted.

A key mathematical development in the science of dynamic heat flows was made by Fourier (1768 - 1830), and the general mathematical basis of the approximate analysis temperature temperature QllBQTITHTf SHEET WO 94/07769 PCT/NZ93/00090 described below uses "classical" methods of solution for linear differential equations from a similar era.

The analysis is approximate in the sense that it uses 5 "lumped parameter" representation of the elements in the container, and does not include allowance for the effects of corners and wall thickness. These effects can be included, but to do so would greatly complicate the analysis and the application of the established 10 formulae without making the analysis any more representative, as the consequence of the approximations is to cause only moderate and fairly consistent errors of magnitude in the indicated response, and not a qualitative misrepresentation of the response.

The analysis may begin by considering what happens during an arbitrarily small time interval (dt): Heat in = Heat stored + Heat out (1) (In this case, heat out is always zero) (To - Tc) .A = m.S.103.dT (2) R dT = A . (To - Tc) dt R.m.S.10J 1 . (To - Tc) § where § = R.m.S.103 and is known as the "time constant" A or ( d_ + _1_ ) = 1 . To (3) ( dt § ) § SUBSTITUTE SHEET WO 94/07769 PCT/NZ93/00090 where; To = surrounding ambient temperature °C Tc = responding container temperature °C dT = change in temperature of the surrounding ambient temperature over time interval dt °<J A = total surface area of container m m = mass of container walls kg S = specific heat capacity of container walls kJ/kg.°C R = thermal resistance between container a mass and surroundings m .°C/W = Rw + Rs (Rwall + Rsurface) Equation (3) is a linear differential equation of the response Tc to a variable environment To. This equation is widely known, and it is feasible to simply look up the solution instead of solving it step by step. The solution of Equation (3) to constant amplitude sinusoidal values To, is given as: - For: To = p.cos(wt) (4) Then: T = X.p.cos(wt - u) (5) where: p « amplitude of cyclic swing To °C w = angular frequency of To (= 2.pi.f where f is frequency cycles/s and pi = 3.1416) radian/s X = 1 (1 + (w§)*) (6) tan (p) = (w§) (7) where: X = amplitude of cyclic swing Tc amplitude of cyclic swing To The response in Equations (5) to (7) show that the Cl fJOTITI frr WO 94/07769 PCT/NZ93/00090 entire problem is represented in the single parameter (w§) and the response of the container can be fully described by that alone. This in turn means that the thermal nature of the container itself can be 5 represented by the time constant § alone. viz: § = R.m.S.103 A (8) Note that since m A.t.D, where D is bulk density: § « R.t.D.S.103 (9) Moving on from the situation of a container of uniform ^3 construction, a container having walls of a sandwich construction receives thermal storage capacity from each of the lamina. Refering to Equation (2), it is clear that the term (m.S.101) represents the total heat capacity, J/°C of the container. The total heat capacity can be formed by summing the heat capacity of the several lamina as: - (M.S.103) = Al.tl.Sl.Dl.103 + A2.t2.S2.D2.10 + A3.t3.S3.D3.10 + A4 (10) where: t = thickness of layer S = specific heat capacity of the layer D = bulk density of the layer (the suffix number denotes the lamina) Similarly, if a container were built with more than one form of construction, (e.g. lid or some walls different to others), this can be adequately described by applying Equations (8), (9) or (10) separately to each, and then summing the results weighted according to area.

J/kg.°C kg/m SMBSTfTUTF SHEET WO 94/07769 PCT/NZ93/00090 Th is can be seen in the development of Equations (2) and (3) and the term A/R can be substituted by the sum: A - Al + A2 + A3 + ... (11) R R1 R2 R3 Considering now the situation when the container is subjected to a thermal shock, the term "thermal shock" is used to signify a disturbance such as the insertion of, for example, a warm vial in the container. This process is itimply described as a process of conservation of heat energy: - During insertion: Heat in Vial + Heat in container = constant i.e.: m .S .T + m ,S .T = (m .S + m .S ) = T2 where: m — mass kg S = specific heat capacity kJ/kg.°C T = temperature °C and suffixes v = vial (before insertion) c = container (before insertion) 2 = condition after insertion viz, the container and vial temperature immediately after inserting vial, is: - T2 = (mv.Sv/.Ty -i- m& .Sg..Tc °C (12) mv . Sv + ic. Sc.

Subsequently, the temperature in the container will converge on the mean refrigeration compartment temperature at a rate controlled by the time constant.

It is directly evident in Equations (8) and (9) that the thermal inertia (m.S) and the insulation value (R) are, to some extent at least, interchangeable, SUBSTITUTE SHEET WO 94/07769 PCT/NZ93/00090 and any combination of the two having the same product will have the same time constant. Equations (5) to (7) confirm that they will also have the same response.

Thus, for example, an alternative design with half the wall thickness of thermal mass material and extra insulation to double the total value of R would be indistinguishable in capacity to smooth fluctuations.

Turning now to the question of insulation value, if the container has reflective surfaces the surface resistance Rs will be different to that were it non metallic or painted. Rs should be regarded as a variable value but typically will be: - Surface Rs Non-metallic or painted 0.12 Bright metal 0.30 In summary then, as shown in Equations (5) to (7) the response to cyclic or sinusoidal disturbances of a system of this type is given solely by the parameter (w§) = 2.pi.f.§ In a system of this type, any input disturbance can be treated as a mixture of superimposed sinusoidal disturbances of different frequencies. Thus Equations 3Q (5) to (7) offer a sufficient description of the response to any disturbance.

Design of the container to have a longer time constant reduces the magnitude of temperature fluctuations in 35 the container chamber. The reduction will be in approximate proportion to the increase in time constant. The time constant fully describes the response to refrigerator door openings.

It would make no difference to the smoothing performance CI IOC TtTt itc eucrr whether the time constant is dominated by the heat storage or the insulation components. Substitution of insulation for some of the mass allows the total weight to be reduced without change to the performance, 5 however, there is a trade off in total wall thickness (thermal mass + insulation) after a point.

To limit the response to thermal shock there is some advantage in Massing the design towards heat storage 10 rather than insulation.

One final and extremely important point to note involves the philosophical difference between a container of the present invention and a cold box.

Firstly, the purpose of a cold box, unlike the container of the present invention, is to maintain the temperature of products stored therein at a value different to that of the ambient temperature (be it constant or 20 fluctuating).

Secondly, most cold boxes of conventional design simply comprise a layer, albeit a relatively thick one, of insulative material. As will be apparent from the 25 above analysis, particularly equations (8), (9), (10) and (11), of itself the layer of insulative material has very little advantage, not having significant thermal mass. Cold boxes work because of the thermal mass of the products stored in them - they provide 30 the thermal storage capacity, or heat side, with the layer of insulation controlling the rate of heat diffusion into the thermal mass.

As noted above, a container according to the present 35 invention is intended merely to dampen -the effect of temperature fluctuations in the surrounding environment on the storage chamber within. Moreover, this result is intended to be achieved regardless of whether there cnnQTlTlJTF SHEET O 94/07769 is anything actually present in the storage chamber. This latter fact is very important, because vaccines and like products tend to have a low weight to volume ratio, and thus have very little in the way of thermal 5 mass of their own.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention will now be 10 described, by way of example only, with reference to the accompanying drawings, in which: FIGURE 1 illustrates a perspective view of a container according to the present invention; FIGDRE 2 illustrates a cross section through the container of figure 1 at XX1; FIGURE 3 illustrates a perspective view of an 20 alternative container according to the present invention; FIGURE 4 illustrates a cross section through the container of figure 3 at YY1; FIGURE 5 illustrates a perspective view of a further alternative container according to the present invention; FIGURE 6 illustrates a cross section through the 30 container of figure 5 at ZZ*; FIGURE 7 illustrates a side elevation of a domestic refrigerator used to store vaccines without modification; FIGURE 8 illustrates a side elevation of a domestic refrigerator fitted with a modification unit; PCT/N Z93/00090 FIGURE 9 illustrates a side elevation of a domestic refrigerator housing containers according to the present invention ; FIGURE 10 illustrates a graph showing fluctuation of the temperature inside the chamber of a container according to the present invention relative to temperature fluctuation inside the refrigeration compartment of a domestic refrigerator, and relative 10 to outside air temperature; FIGDRE 11 illustrates a graph showing more particularly the temperature fluctuations of the chamber detailed in the graph of figure 10; and, FIGDRE 12 illustrates a graph showing the ratio of container chamber and refrigeration compartment temperature fluctuations as a function of the cycle frequency and time constant.

Referring firstly to figures 1 and 2, as illustrated, there is provided a vaccine storage container, as generally indicated at 1, of generally rectangular box construction, having a receptacle portion 2 and 25 a lid 3 which, when combined, define a chamber 4.

As shown in figure 2, the walls of the container 1 are formed from a sandwich of different layers, having em inner liner of acrylic plastics material 5 surrounded 30 by an outer layer of polystyrene foam 6. The outer surface of the outer 6 may be coated with a layer of smooth plastics material 7 for reasons of durability and hygiene. Sectioning of the liner 5 and outer 6 to define the line between the lid 3 and receptacle 35 portion 2 is offset with respect to each other to ensure that a better seal is obtained.

The container 1 is generally suited to longer term SUBSTITUTE SHEET O 94/07769 PCT /N Z93/00090 storage of vaccines, rather than for temporary or regular holding of partially used vials or bottles.

To assist in identification of the vaccines stored 5 within the container 1 labels (not shown) may be applied to an end 8.

Turning now to figures 3 and 4, an alternative embodiment of the invention is illustrated comprising 10 a container, as generally indicated at 10, having a receptacle portion 11 and a lid 12.

The receptacle portion 11 has a rectangular base 13, front wall 14 and rear wall 15. The height of rear 15 wall 15 is greater than that of the front wall 14, thus the upper edges 16 of the side walls 17 slope down from the rear wall 15 towards the front wall 14.

The lid 12 closes against the upper edges 16 of the 20 side walls 17 and also against the upper edges 18,19 of the front wall 14 and rear wall 15, respectively. The front edge 20 of the lid 12 terminates in a lip 21 which provides a handle for opening of the lid 12. The rear edge 22 of the lid 12 also terminates in a 25 lip 23, which lip 23 acts as a hinge when the lid 12 is opened.

As shown more particularly in figure 4, all of the walls of the container 10 are formed as a sandwich 30 structure. The base, side, front and rear walls 13,16,14,15, respectively, are of substantially similar construction, having an outer lamina 24 of polystyrene foam, the outer surface of which may be coated with a tough plastics film 25 for desirability. In from 35 the polystyrene lamina 24 is a layer of plastics material 26, in from which is a space 27 and then an inner lamina of plastics plate m<\terial 28. In use the space 27 can be filled with water.

The lid 12 comprises a gap 29 defined between an inner O 94/07769 and an outer plate of transparent plastics material 30 and 31 respectively. In use the gap 29 is filled with water.

The water filling of the lid 12 renders it relatively heavy, and thus when closed ensures a reasonably good seal against the edges 16/18,19 of the walls 17,14,15.

The sloping lid 12 means that access to the interior of the container 10 is relatively easy, even with it in a refrigerator. Further, the transparent lid 12 in combination with this feature means that it is possible to examine the contents of the container 10 without the need to open it.

As an added feature, a temperature indicating device (not shown) may be attached to the inner surface of the inner lamina 30 of the lid 12.

Figures 5 and 6 illustrate a container 40 of substantially similar appearance, and construction to the embodiment of figures 3 and 4. The two major differences are that the receptacle portion 41 is provided with dividers 43 in its interior, which dividers 43 are formed from thick plastics material, and the lid 42 is divided into portions corresponding to the compartments of the receptacle portion 41 created by the dividers 43.

Figure 7 illustrates how vaccines 50 are usually stored in a domestic refrigerator 51. The vaccines are packed in storage cartons and stacked into the refrigeration compartment 52 of the refrigerator 51. However, as noted earlier, the zone 53 adjacent the door 54 is too warm to safely store vaccines. Similarly, the zone 55 adjacent the cooling coils 56 is too cold.

Figure 8 indicates modifications which can be made SUBSTITUTE SHEET 'O 94/07769 to improve the suitability of the refrigerator 51 for vaccine storage. In this connection, a stabilising load of frozen ice packs 57 can be added to the freezer compartment 58, water containers 59 can be added to 5 the refrigeration compartment 52, extra insulation 60 can be added to the door 54, and vaccines 50 can be stacked in drawers 61. As noted earlier, these measures do not fully overcome the problems with vaccine storage in domestic refrigerators. As will be apparent 10 from the drawing, figure 8, significant storage space is also lost.

Figure 9 illustrates a domestic refrigerator 51 stacked with two storage containers 1 and one storage container 15 10. The containers 1, 10 should be spaced slightly from the inner walls of the refrigeration compartment 52 to allow air to freely circulate. It will be noted that other than the containers 1, 10 no other modifications are required.

While the containers 1 may be removed once empty it is envisaged that the container 10 would be a semi-permanent feature in the refrigerator 51, simply being refilled as and when required.

It will be appreciated that the particular features of shape and configuration of the storage containers 1,10,40 may be adjusted as required, and different materials may be used in their construction.

In designing a storage container the first step would typically be to determine the maximum likely cycle time for the refrigerator and the refrigerator temperature swing, or thermostat differential, Tl.

Next the maximum desired container storage chamber fluctuation, T2, should be assessed.

The ratio T2/T1 = X in equation (6) , SUR.QTiTi iTt (m WO 94/07769 PCJ7NZ93/00090 While it is relatively straight forward to obtain w § from figure 12.

Knowing the cycle time of the refrigerator allows w the required time constant § to be derived to achieve the desired level of temperature fluctuation damping in the container storage chamber.

Prom equation (9) exploring by trying different 10 combinations of insulation resistance R and thickness t of material having thermal mass the wall construction of the container can be established. The outcome will generally be dictated by available space, cost, weight and practicability. Thermal shock prevention may also 15 be a relevant consideration.

A prototype of the invention was constructed having an appearance substantially according with that of the embodiment of figure 3. However, the walls were of a different construction, all comprising inner and outer layers of 4.5 mm thick acrylic plastic (PERSPEX spaced apart to form a 20 mm cavity therebetween. This cavity was filled with water following treatment with a fungicide.

From equation (9) the theoretical time contant for the prototype can be calculated: § - R.t.D.S.101 As each wall is made up of three layers the equation can be reformulated as: S = R.10 . (t^.D^.S^. + t2.D2.S2 + t^.D^.s ) SUBSTITUTE SHEET WO 94/07769 PCT/NZ93/00090 In this case t^ = tj, and = Sg therefore § - R.10* (2 t^.D^ Si + t2.D.2.S2) The thermal resistance of water and PERSPEX™ is negligible for thicknesses of this magnitude, therefore R will equal the surface resistance. The surface of PERSPEX™ is relatively shiny, therefore a value of R of 0.16 would appear to be an appropriate approximation. tl = 4.5 x 10-3M 2 fc2 - 2.0 x 10- M 3 D1 = 1400 kg/M y D2 = 1000 kg/M S1 = 1.51 Jkg°C S2 = 4.2 J/kg °C Therefore S = 16484 sees, or approximately 4.6 hrs.

The response of the prototype container under fluctuating refrigeration compartment temperatures is shown in figures 10 and 11.

In figure 10: OT = the outside air temperature °C RCT = the refrigeration compartment temperature °C CT = the container storage chamber temperature °C Note: i) the peaks in the RCT trace result from door opening events. ii) tests were carried out in a refrigerator model Fisher & Paykel KP120JWHWH 110 litre ■*5 Considering the time period marked T on figure 10, the refrigerator cycle time is approximately 5 hrs and the refrigeration compartment temperature fluctuates with an approximate applitude of 8°C.

SMRSTiTt'Tc CUCCT 2564 wo 94/07769 PCT/NZ93/00090 Using equation (6), or figure 12 it is possible to obtain a value for X of 0.17. Based on the / refrigeration compartment fluctuation of 8°C theory predicts that the container storage chamber temperature 5 should fluctuate by 1.4°C. As can be seen from figure 11 this follows closely what actually happened.

It will be appreciated from the above discussion that the container of the present invention provides significant advantages, not the least being its simplicity of use, requiring only that the container be placed in the refrigerator to reach a stable temperature, then being filled with vaccine. No modifications are required to the refrigerator construction.

Additional advantages of the present invention will become apparent to those skilled in the art after considering the principles in particular form as discussed and illustrated.

Accordingly, it will be appreciated that changes may be made to the above described embodiments without departing from the principles taught herein. For example, the container may be fitted with handles to facilitate transport of the container, or to enable it to be easily lifted into and out of the refrigerator. Further, it may, in some circumstances, be desirable to fit a container semi-permanently into a refrigerator, and suitable attachment means may be used in this regard.

Finally, it is to be understood that this invention is not limited to the particular embodiments described 35 or illustrated, but is intended to cover all alterations, additions or modifications which are within the scope of the appended claims.

SUBSTITUTE SHEET

Claims (6)

1. 256483 What I Claim is: 1 A container for storing temperature sensitive material, consisting of a base, sidewalls extending upwards from said base, a top, with one side of the container being open, wherein: the base and sidewalls comprise at least one outer layer, at least one intermediate layer, and an innermost layer whose inner surface forms the interior surface of the container; the innermost layer, and a first intermediate layer immediately adjacent to the innermost layer being formed of liquid impermeable material, a gap being formed between said innermost Iqyer and said first intermediate layer, said gap being closed at the ends o?said sidewjrils and base adjacent said open side so as to form an enclosed space within said sidewalls and base which is fillable with liquid; the open side being closed by a lid which forms an end wall of a drawer in which the contents of the container are stored, the drawer being slidable from a closed position within the container to an open position outside the container.
2. 2 A container according to claim 1, where the lid provides a substantially airtight seal against the container wall structure.
3. 3 A container according to claim 1 or claim 2, where the container is a substantially rectangular box, the one side wall of which comprises the lid.
4. 4 A container according to any one of claims 1, 2, or 3, where the lid incorporates a temperature indicating device, visible from outside the container, which indicates the temperature within the container.
5. 5 A container according to any preceding claim wherein one of said at least one outer layers is made of a thermally insulative material.
6. 6 The container according to claim 7 where the thermally insulating material is a closed cell type of material. j 7 A container according to any one of the preceding claims wherein the innermost layer and the first intermediate layer are formed from plastic material. 8 A container according to any one of the preceding claims wherein the space within the drawer is formed into two or more compartments. w 25 6 4 8 3. 9 A method of storing vaccines which comprises placing a container according to any one of claims 1 to 8 in a domestic refrigerator, and placing vaccines in the container or removing vaccines form the container, without removing the container from the refrigerator. 10 A container according to claim 1 substantially as herein described, with reference to the accompanying drawings. 11 A method of storing vaccines according to claim 9, substantially as herein described, with reference to the accompanying drawings. ene- or