WO1994011682A1

WO1994011682A1 - Self-heating pouch

Info

Publication number: WO1994011682A1
Application number: PCT/GB1993/002381
Authority: WO
Inventors: Surinder Pal Grewal
Original assignee: Surinder Pal Grewal
Priority date: 1992-11-19
Filing date: 1993-11-19
Publication date: 1994-05-26
Also published as: AU5530594A; GB9224279D0

Abstract

A self-heating sachet comprises a first flexible-walled sachet (3) of liquid, e.g. water, and a second flexible-walled sachet (1) of exothermic reaction agent (5), e.g. Calcium Oxide. The second sachet is provided with a vent (7) arranged to open automatically, after mixing of the water with the Calcium Oxide, to allow water vapour, produced by the exothermic reaction of the Calcium Oxide with the water, to exit from the second sachet (1). The sachet may be associated with a foodstuff or beverage container to heat the foodstuff or beverage.

Description

SELF-HEATING POUCH

• This invention relates to a self-heating pouch which

4 may, for example, be associated with a foodstuff or

» 5 beverage container to heat the foodstuff or beverage. The pouch may also be used to heat non-foodstuffs/beverages, for example to heat steam towels.

US-A-4067313 discloses a hot pack comprising a sealed, flexible, impermeable, water insoluble outer

10 enclosure having high resistance against puncture, rupture and abrasion. It also comprises a sealed, flexible, impermeable, water insoluble inner enclosure having low resistance against puncture and rupture. The inner enclosure is of smaller size than the outer enclosure and

15 is disposed therein. The outer enclosure contains a particulate composition which produces an exothermic reaction when mixed with water. Upon rupture of the inner enclosure to cause mixing between the composition and water, an exothermic reaction starts, a moldable gel forms

20 and the moldable mass gradually reaches a temperature not in excess of about 107*C and maintains this temperature for about 20 minutes. This hot pack retains the products of the exothermic reaction within the outer enclosure, limiting the vigour of the. exothermic reaction that may

25 take place if the risk of explosion of the outer enclosure is to be avoided. Due to the temperature and contents of the outer enclosure during the exothermic reaction, any explosion of the outer enclosure would be highly undesirable, as well as potentially dangerous.

30 According to one aspect of the present invention there is provided a self-heating pouch comprising a first ^■1 flexible-walled sachet of liguid and a second flexible- walled sachet containing an exothermic reaction agent, said second sachet being provided with vent means arranged to be

35 opened automatically, after mixing of the liguid with the exothermic reaction agent, to vent from said second sachet vapour produced by the exothermic reaction of the liguid with the exothermic reaction agent.

The flexible-walls of the sachets allow for the second sachet substantially to be evacuated of moisture- containing air which may otherwise cause degradation of the exothermic reaction agent. Furthermore, it allows the pouch to be pliable and to occupy the minimum amount of space. The automatically opening vent means is provided to allow greater freedom over the conditions of the exothermic reaction and to reduce the risk of explosion of the pouch. Advantageously, means are provided between the first sachet and the exothermic reaction agent in the second sachet to encourage the mixing of released liquid from the first sachet with the exothermic reaction agent. These means may comprise a sheet of water absorbent and permeable material, arranged to conduct the liquid evenly and rapidly across the exothermic reaction agent, to cause even heat generation and to lead to rapid conduction of the heat to the exterior surface of the pouch. According to a further aspect of the present invention there is provided a container associated with a self-heating pouch of the type mentioned above, which container may be, for example, a foodstuff or beverage container. According to a yet further aspect of the present invention there is provided a steam generator comprising a self-heating pouch of the above type, and a water- containing sachet arranged to be heated by the self-heating pouch. Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a sectional side view through a first embodiment of self-heating pouch, viewed along the line I-I of Fig. 2;

Fig. 2 is a sectional plan view along the line II-II of Fig. 1;

Fig. 3 is a detail side view of the vent means of the Fig. 1 embodiment of self-heating pouch (omitting details of the exothermic reaction agent and conduit means) ,. showing the vent in a closed condition;

Fig. 4 is a similar view to Fig. 3 but showing the vent in an open condition;

Fig. 5 is a sectional side view through a second embodiment of self-heating pouch; Fig. 6 is an enlarged plan view of a modified form of first flexible walled sachet for use with embodiments of self-heating pouch in accordance with the present invention;

Figs. 7 to 9 are plan views of embodiments of self heating pouch in accordance with the present invention showing different arrangements of vent means;

Fig. 10 is a side-elevational view of the self- heating pouch of Fig. 1, shown in combination with a foodstuff; and Fig. 11 is a side-elevational view of the self- heating pouch of Fig. 1 combined with a water-containing sachet to form an embodiment of steam-generator; and Fig. 12 is a plot of temperature against time, showing the pouch temperature and pouch base temperature achieved in a test of an embodiment of the self-heating pouch of Fig. 1.

The pouch illustrated in Figs. 1 and 2 comprises a first flexible-walled sachet 3. This sachet 3 contains a liquid to react with an exothermic reaction agent (as will be described below) . The pouch also comprises a second flexible-walled sachet 1.

This second sachet 1 comprises two sheets of flexible material welded together around their edge 2. The material may comprise a laminate of an outer layer of polyester film, a middle layer of aluminium foil and an inner layer of polyethylene, the layers being approximately 12μm in thickness and bonded together using a suitable heat- resistant glue, such as a polyurethane glue.

In the embodiment of Figs. 1 to 4 the first sachet 3 comprises two sheets of cellophane bonded together at their edges 4 by heat welding. One edge may be welded at a lower temperature than the other edges so that the weld at this edge will be the weakest and will fail when the first sachet 3 is squeezed.

The first sachet 3 may be formed inside another similar sachet (not shown) and the space therebetween filled with a grease, for example petroleum grease, to reduce the risk of premature water loss through the wall of the first sachet.

The second sachet 1 comprises an amount of exothermic reaction agent 5. This exothermic reaction agent is preferably calcium oxide, which will react exothermically with water and turn to calcium-hydroxide. Whilst water and calcium oxide are the preferred liquid and exothermic reaction agent respectively, other suitable reactants may be chosen, such as hydrogen peroxide and manganese dioxide. The mass ratio of water to calcium oxide is, preferably, of the order of 1:2.8.

In the embodiment of Figs. 1 to 4 the exothermic reaction agent 5 is provided in a plurality of separate sachets 6. The material of these sachets 6 is water absorbent and water permeable and may, for example, be muslin or cotton. This material acts as a wick for the liquid from the first sachet 3, to encourage the liquid to react with substantially all of the exothermic reaction agent 5. These sachets 6 may, advantageously, be secured to an internal wall of the second sachet 1 by double-sided adhesive tape and may only be loosely filled with the exothermic reaction agent to provide room for expansion of its contents upon mixing with the liquid from the first sachet 3.

The second sachet 1 is provided with a vent 7 for the venting of gas or vapour produced by the exothermic reaction of the liquid from the first sachet 3 with the exothermic reaction agent 5 in sachets 6. When these reactants are water and calcium oxide, the vapour produced will be steam. The vent 7 is preferably, as shown, positioned out of alignment with any of the sachets 6. Prior to commencement of the exothermic reaction agent the vent 7 is required to be sealed, for example to prevent moisture in the atmosphere hydrating the calcium oxide which is the preferred exothermic reaction agent 5. In the embodiment of Figs. 1 to , the vent 7 comprises an aperture 8 provided in a wall of the second sachet 1, this aperture 8 being closed by a portion of a strip 9 of water- impermeable plastics material. One end of the strip 9 is bonded to the wall of the second sachet 1 around the aperture 8 using a peelable glue 10, such as LECTRO-STIK (Trade Mark) . The other end of the strip 9 is bonded to a portion of the wall of the second sachet 1 generally opposite to the aperture 8, for example by a heat weld 11. Prior to instigation of the exothermic reaction, the material of the strip 9 acts as a plug to seal the aperture 8. However, when the exothermic reaction is instigated by rupturing the first sachet 3, to release the liquid contained therein to mix with the exothermic reaction agent 5, the exothermic reaction generates vapour and/or gas, as well as heat. The generation of this vapour and/or gas causes the volume of the interior of the second sachet 1 to increase. This ballooning of the first sachet causes the opposite walls of the sachet 1 to move apart, tightening the central portion of the strip 9 and then peeling the end of the strip 9 away from the wall of the first sachet 1 in the region of the aperture 7 . In this condition (Fig. 4), the build-up of pressure in the second sachet 1 is released and the vapour and/or gas generated by the exothermic reaction is able to escape from the interior of the second sachet. In the embodiment of Figs 1 to 4 the exothermic reaction material is contained in a plurality of sachets 6. This arrangement has the advantage that spaces may be left between the individual sachets 6 to form passageways 12 therebetween to encourage the flow of liquid away from the first sachet 3. Varying the size of these spaces and the amount of the material contained in the sachets 6 can be used to alter the vigour of the exothermic reaction. Alternatively, or additionally, conduit means may be provided. These conduit means may take the form of straws 17, which may advantageously be perforated along their length as shown.

In addition, the material of the sachets 6 helps to contain the solid products of the exothermic reaction. For example, in the preferred arrangement where water is reacted with calcium oxide, the material of the sachets 6 helps to prevent hot calcium hydroxide from exiting out of the vent 7.

In the embodiment of self-heating pouch illustrated in Fig. 5 a first flexible-walled sachet 103, sealed around its edges 104, is provided containing a liquid to react with the exothermic reaction agent 105 contained in a second flexible-walled sachet 101 sealed around its edges 102. The second sachet may be formed of a laminate of polyester, aluminium foil and polyethylene. As in the embodiment illustrated in Figs. 1-4, the exothermic reaction agent 105 and the liguid for reaction therewith may, advantageously, be calcium oxide and water, respectively. Calcium oxide and calcium hydroxide have a low thermal conductivity. Consequently, the rate at which heat will flow through them from within the mixture to the outside surface is low. There can therefore be a marked difference between the temperature at the centre of the calcium oxide/calcium hydroxide and the outside surface. To assist in the rapid transfer of heat from the inside of - 1 - the mixture in the pouch to the surface of the pouch, in the embodiment of Fig. 5 the calcium oxide 105 is spread in a thin layer, approximately 5mm thick, on a sheet of aluminium foil 188 approximately 12 microns thick and bent up around its edges.

On top of the layer of calcium oxide 105 is a sheet of cellulose paper 190, the thickness of which may be approximately 1mm. When the first sachet 103 on top of the paper 190 is ruptured and the water is released therefrom, the cellulose paper 190 acts as a wick, conducting the water evenly and rapidly across the thin calcium oxide layer 105. This results in the pouch generating heat evenly and leads to rapid conduction of the heat to the exterior surface of the pouch. To help retain the calcium oxide 105 in a thin layer, the foil sheet 188 and paper 190 may be attached to one another at intervals, for example using staples 186 stapled through the foil sheet 188, the calcium oxide layer 105 and the paper 190, as shown in Fig. 5. The pouch is reasonably flexible and pliant. Furthermore, the shape of the contents of the second flexible walled sheet helps to allow excess air, which may contain undesirable moisture, to be evacuated from the second sachet prior to its sealing. In the figures the second sachets are deliberately shown as being loose fitting in the interests of clarity.

Fig. 6 shows a modified form of construction for the first sachet 103. In this modified construction the sachet 103 comprises a rectangular cellophane inner pouch 192 filled with water and heat sealed on all sides. This inner pouch 192 is enclosed in an outer pouch 194. In Fig. 6 the outer pouch is shown as being shaped as an irregular hexagon. This outer pouch 194 may be made of a laminate of polyester, aluminium foil and polythene and is impervious to water. The outer pouch 194 has a narrow opening 196 for the flow therefrom of water. When the inner pouch 192 is ruptured by external pressure, the water that was previously contained therein flows through the narrow opening 196 of the outer pouch 194 to soak into the cellulose paper 190. The shape of the outer pouch 192 helps to minimise any loss of water through evaporation into the calcium oxide layer. This enables the self- heating pouch to be used effectively even after a lengthy storage period. This modified first sachet 103 is equally usable with the embodiment of pouch illustrated in Figs. 1 to 4 as it is with the embodiment of pouch illustrated in Fig. 5.

In Fig. 5 the second embodiment of self-heating pouch is shown as being provided at one end thereof with an automatically opening vent 107. This vent 107 is of similar construction and operation to the vent 7 described above in conjunction with Figs. 3 and 4.

In the above-described embodiments the ballooning effect of the second sachet 1, 101 is utilised to open the vent means 7,107 upon mixing of the liquid with the exothermic reaction agent 5, 105. However, other valve arrangements may be used successfully. For example, the aperture 8 of the vent means 7, 107 may be, for example, closed by a membrane of plastics material that is arranged to be ruptured by heat, or be closed by a porous material impregnated with, for example, wax that will melt at a temperature below that generated by the exothermic reaction.

In Fig. 7 there is illustrated a self-heating pouch whose vent means 207 comprises a piece of material 209, such as foil, having a portion 209a stuck to the exterior of its second sachet 201 using a wax-based adhesive. The adhesive is heat sensitive and is arranged to soften when heat is generated, in use, allowing the pressure of gas generated by the exothermic reaction to lift the flap formed by the portion 209a to allow venting from the aperture 208 of the vent means 207. Another portion 209b of the material 209 may be fixed to the exterior of the second sachet 201 by a non-heat sensitive adhesive to retain the material 209.

In the embodiment illustrated in Fig. 8 the vent means 307 comprises an aperture 308 formed in the corner of one of the walls of the second sachet 301, the opposing inner surfaces of the walls in a region 309 around said aperture being glued together by a heat-sensitive adhesive. Fig. 9 illustrates a variant of the same. In this embodiment a corner of the second sachet 401 is provided with an aperture 408 and this .corner is folded over to face and be glued to another portion of the exterior of the second sachet, again using a heat-sensitive glue. When the exothermic reaction is instigated, in use, the heat- sensitive glue is softened by the heat and the increasing volume and pressure of the gas generated by the reaction causes the folded corner of the pouch to become unfolded, unblocking the aperture 408 and opening the vent means 407.

One use for the self-heating pouch is heating a beverage or foodstuff. For example, as shown in Fig. 10 the pouch 14 may be associated with a foodstuff such as a bread roll 13. The pouch 14 may advantageously be arranged, as shown, with the end of the second sachet 1 containing the first sachet 3 being accessible for squeezing, for example by being squashed between finger(s) and thumb(s) in the direction of arrows 15. The foodstuff 13 and pouch 14 may, for example, be kept together in a sealed pouch of perforated cellophane material represented in Fig. 10 by a dotted line.

To encourage the heat from the exothermic reaction to heat the foodstuff 13, rather than be wasted, the top surface 14a of the pouch, facing the foodstuff, may advantageously be blackened, for example using a food grade Black Zylon 1010. This blackening causes the top surface 14a of the pouch to reach a higher temperature (e.g. about 12"C higher) than if the surface 14a were simply silvered.

Fig. 12 is a plot of Temperature (°C) against Time (minutes) . The room temperature was 20"C. In the example of Fig. 12, Line A represents the pouch temperature and line B represents the temperature of the insulated base surface of the pouch. In the example plotted in Fig. 12, to heat a bread roll of approximately 40 grammes suitable quantities of water and calcium oxide, of the order of 10 grammes and 28 grammes respectively, were mixed together. This generated a reaction temperature of the order of 100- 105°c approximately two minutes after mixing and maintained the pouch temperature at approximately that level for 3 minutes. This led to the bread roll being heated to a desired temperature of approximately 51*C in approximately 3 minutes.

The undersurface 14b of the pouch 14, which faces away from the foodstuff 13, may be provided with an insulating jacket 25. This jacket may, for example, comprise a 3-layer sandwich of polyester mesh sheeting, a layer of polystyrene and a layer of paper or plastics material, which may be printed on. The polyester mesh sheet spaces the polystyrene layer from the external surface of the pouch, so preventing the polystyrene from being exposed to temperatures that might cause it to melt. The mesh size, which affects the volume of the pockets of air trapped by the mesh, as well as the mesh sheeting thickness may be chosen in accordance with the desired insulating effect and flexibility of the insulating jacket. Not only does this insulating layer help prevent the waste of heat, but it reduces the risk that someone handling the foodstuff during, or shortly after, the exothermic reaction of the agent 5 will be burnt by the high surface temperature of the pouch 14. Fig. 12 shows that, in the plotted example, a 3-layer sandwich jacket, comprising polyester mesh, polystyrene and paper, kept the temperature of the base of the pouch to below 45°c. - li ¬ lt will be appreciated that the reaction plotted in Fig. 12 is simply an illustrative example.

With some foodstuffs, such as bread rolls, a thin sheet of water/absorbent material 16, such as cotton interwoven with a mesh, may advantageously be placed between the food- stuff 13 and the pouch 14. When this material 16 is moistened with water and the exothermic reaction occurs, the hot surface 14a of the pouch 14 will vaporise the water soaked in the sheet 16 and the steam thereby produced will help to heat the roll 13.

In the arrangement illustrated in Fig. 10 the vent 7 is positioned so that the vapour produced by the exothermic reaction will escape from the vent past the foodstuff 13. Whilst this will help to heat the foodstuff, this is not essential. The vapour produced by the exothermic reaction may, alternatively, be vented from the pouch 14 away from the foodstuff 13.

An alternative use for the self-heating pouch 14 is in the heating of a beverage, such as soup, sake or baby's milk, prior to its consumption. For example, the pouch may be incorporated into a container for the beverage.

In the case of either of the foodstuff or beverage- heating examples, the self-heating pouch 14 may be integrally formed with the foodstuff or beverage container. Alternatively, the container may be provided with a receiving section, such as a recess, to allow a user to slip in a self-heating pouch. The container may, for example, be a jacket of plastics material with a pocket formed therein. Fig. 11 shows an embodiment of steam generator including a self-heating pouch similar to the one described above and containing a vent 7. The self-heating pouch 14 is positioned adjacent a water-containing sachet 18. The water sachet 18 may be made of heat-welded polyester/aluminium laminate material, as with the second sachet 1. The water in the sachet 18 may, advantageously be soaked in a sponge-like material. Both the pouch 14 and sachet 18 are contained in a further pouch 26 which, in the arrangement illustrated in Fig. 11, is shown as being transparent to show the internal arrangement of the .pouch 14 and sachet 18.

A straw 19 is shown extending from the water sachet 18. Prior to use of the steam generator the exit of this straw is preferably capped, for example with an elasticated cap, to prevent the escape of the water inside the sachet 18. When it is desired to generate steam, the cap may be removed from the straw 19 and the second sachet 3 in the pouch 14 ruptured to start the exothermic reaction in pouch 14. Heat from the exothermic reaction heats up the water in the water sachet 18, causing steam to be vented from straw 19. One use for the steam generator of Fig. 11 is in the heating of a beverage. In such a use, the end of the straw 19 may be submerged in the beverage and the steam exiting therefrom used to warm the beverage.

Although the arrangements shown in Figs. 10 and 11 show the first embodiment of pouch, the second embodiment of pouch may equally be used.

In the illustrated embodiments, the first sachet is shown as being a separate sachet to the second sachet and is shown as being received in the second sachet. However, this arrangement is not essential. In an alternative, non- illustrated arrangement, the first sachet may be integrally formed with the second sachet, for example by omitting the material of the first sachet 3, 103 altogether and instead forming the first sachet from the same material as the second sachet 1, 101 by welding across the second sachet 1, 101 for example in the region of dotted line 20 in Fig. 2. Provided that the weld line 20 is made weaker than the welds at the edge 2 of the pouch, when pressure is applied to the integrally-formed first sachet 3, 103 it will be the weld at line 20 that will rupture so as to mix fluid with the exothermic reaction agent 5, 105 rather than a weld 2, 102 at the edge of the pouch.

A further alternative, non-illustrated arrangement is to provide the first and second sachets separately, without the first sachet 3, 103 being provided in the second sachet 1, 101. In this arrangement, a conduit will need to be provided between the two sachets l,101;3,103 for the flow of liquid from the sachet 3, 103 to the exothermic reaction agent 5 in sachet l, 101. In this particular arrangement, both the sachets 1,101;3,103 may be provided in a common package.

In addition to avoiding the risk of explosion of the pouch, the provision of automatically opening vent means allows a range of reactions to take place in the pouch. For example, should it be desired to produce a high temperature very quickly, the amounts of the reactants in the pouch may be chosen to produce a particularly vigourous exothermic reaction. In this situation, the provision of the vent means can be very important.

Claims

1. A self-heating pouch comprising a first flexible-walled sachet of liquid and a second flexible- walled sachet containing an exothermic reaction agent, said second sachet being provided with vent means arranged to be opened automatically, after mixing of the liguid with the exothermic reaction agent, to vent from said second sachet vapour produced by the exothermic reaction of the liquid with the exothermic reaction agent.

2. A pouch as claimed in claim 1, wherein the vent means comprises aperture means provided in the wall of the second sachet and plug means for plugging said aperture means against the ingress of moisture into the second sachet prior to mixing of the liquid with the exothermic reaction agent.

3. A pouch as claimed in claim 2, wherein said plug means comprises a portion of material bonded to the wall of the second sachet around said aperture means, said portion of material being arranged to be at least partially stripped away from the wall around the aperture means by the ballooning of the second sachet during the initial stage of the exothermic reaction.

4. A pouch as claimed in claim 3, wherein said portion of material is bonded to the wall of the second sachet around said aperture means by gluing.

5. A pouch as claimed in claim 3 or claim 4, wherein a further portion of said plug means is bonded to a wall of the second sachet generally opposite to the vent means.

6. A pouch as claimed in claim 2, wherein the plug means comprises a portion of material bonded to the wall of the second sachet around the aperture means by a heat- sensitive glue arranged to soften at the temperature generated by the exothermic reaction.

7. A pouch as claimed in claim 2, wherein the plug means is a wall portion of the second sachet bonded to another portion of the wall of the second sachet around the aperture means by a heat-sensitive glue arranged to .soften at the temperature generated by the exothermic reaction.

8. A pouch as claimed in claim 2, wherein the plug means comprises a membrane of plastics material that is arranged to be ruptured by the heat generated during the initial stage of the exothermic reaction.

9. A pouch as claimed in claim 2, wherein the plug means comprises a porous material impregnated with a substance that is arranged to melt at a temperature below that generated by the exothermic reaction.

10. A pouch as claimed in any of the preceding claims, wherein means are provided between the first sachet and the exothermic reaction agent in the second sachet to encourage the mixing of released liguid from the first sachet with the exothermic reaction agent.

11. A pouch as claimed in claim 10, wherein the exothermic reaction material contained inside the second sachet is in contact with liquid absorbent and water permeable material.

12. A pouch as claimed in claim 11, wherein the exothermic reaction agent is arranged in at least one layer and is in contact with a sheet of liquid absorbent and permeable material.

13. A pouch as claimed in claim 12, wherein the at least one layer of exothermic reaction agent is sandwiched between the sheet of liquid absorbent and permeable material and a further sheet.

14. A pouch as claimed in any of claims 11 to 13, wherein the liquid absorbent and water permeable material includes at least one of muslin, cotton and cellulose paper.

15. A pouch as claimed in any of the preceding claims, wherein the first sachet is made of plastics material.

16. A pouch as claimed in claim 15, wherein the first sachet is made of cellophane.

17. A pouch as claimed in any of the preceding claims, wherein the first sachet contains a seam arranged to split, upon squeezing of the first sachet, to release the liquid contained therein.

18. A pouch as claimed in claim 17, wherein said splittable seam is a heat-welded join.

19. A pouch as claimed in any of the preceding claims, wherein the material of the second sachet comprises at least one layer of plastics material.

20. A pouch as claimed in any of the preceding claims, wherein the material of the second sachet comprises at least one layer of aluminium foil.

21. A pouch as claimed in any of the preceding claims, wherein the material of the second sachet comprises a laminate of polyester film and aluminium foil.

22. A pouch as claimed in claim 21, wherein the second sachet comprises two sheets of said laminated material sealed together around their edges.

23. A pouch as claimed in any of the preceding claims, wherein the first sachet is situated within the second sachet and is arranged to be ruptured, to release the liquid contained therein to mix with the exothermic reaction agent, by squeezing of the first sachet through the walls of the second sachet.

24. A self-heating pouch as claimed in any of the preceding claims, wherein the liquid is water and the exothermic reaction agent is calcium oxide.

25. A container associated with a self-heating pouch as claimed in any of the preceding claims.

26. A container as claimed in claim 25, wherein the container additionally comprises a layer of moisture absorbent material positioned adjacent the surface of the second sachet which is arranged to face generally towards a foodstuff.

27. A steam-generator comprising a self-heating pouch as claimed in any of claims 1 to 24, and a water- containing sachet arranged to be heated by the exothermic reaction in the self-heating pouch, said water-containing sachet being provided with a steam exit.