Abstract:
An apparatus for storing liquid air (a cryogenic mixture of about 80% liquid nitrogen and about 20% liquid oxygen) in a stable condition within a storage vessel by providing a heat exchanger in fluid communication with vaporized liquid air within vessel condense the vaporized liquid air back to liquid form. This will result in condensing the nitrogen-rich vapor into the mass as a liquid, thereby reducing ullage pressure, cooling the mass, and ultimately precluding oxygen-enrichment through boil-off. A cryocooler may be mounted externally to the vessel and in fluid communication with an interior of the vessel to condense liquid air vaporized within the vessel. The system may be used to supply air to safe haven areas of a mine or building, or piped in through a building HVAC system and/or mounted on vehicle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/471,768 filed Apr. 5, 2011, and incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to the storage and use of cryogenic liquids. More specifically, the invention pertains to systems and methods used for the storage and use of a cryogenic mixture of liquid nitrogen and liquid oxygen. 
         [0003]    Some United States government agencies utilize sub-critical liquid air backpacks rather than standard self-contained breathing apparatuses (“SCBA”) to perform work in hazardous atmospheres. These liquid air backpacks include a cryogenic mixture of about 21% liquid oxygen (“LO 2 ”) and 79% liquid nitrogen (“LN 2 ”) as a source of breathable air. Because a system or method for storing bulk quantities of liquid air is not available, a cryogenic mixture of liquid air (up to 4,000 gallons at times) is manufactured within a known time period prior to performing a task that requires the use of the liquid air backpack. A liquid air supplied backpack used in a protective suit provides a source of breathable air for up to about two hours. 
         [0004]    In comparison, a standard SCBA, used by first responders (firefighters etc.), utilizes a cylinder filled with compressed air and supplies breathable air for only one hour. Typically, the air supply in such suits will last only about thirty-five to forty minutes because the rate at which the air is consumed is dependant upon the demand. A responder, such as a firefighter, that is under stress will consume the air supply at a higher rate as compared to consumption of air under normal conditions. 
         [0005]    Storage of multi-component cryogens is difficult, due to disproportionate boil-off rates of the components. Liquid nitrogen boils at −320° F., LO 2  boils at −297° F., and liquid air has a boiling point of −317° F. Since even the best insulated vessels allow some heat leak, and since LN 2  has a lower boiling point of the two components, the liquid nitrogen will tend to boil more rapidly. This excessive LN 2  boil-off results in oxygen enrichment of the stored liquid, as the nitrogen-rich vapor vents to atmosphere. Venting is necessary to prevent an overpressure of the storage vessel, or Dewar. As the more volatile nitrogen boils and is vented, the O 2 /N 2  ratio changes. Ultimately, this increased oxygen content will render “life support grade” breathing air as an unusable fire hazard. Presently, bulk amounts of liquid air are stored for only up to about two weeks at which time any remaining liquid air must be discarded. 
         [0006]    Zero-loss systems have been used to store liquid oxygen in bulk amounts. Such a system is illustrated in  FIG. 1 , and includes a vacuum insulated vessel  10  in which LO 2  is stored. An external source of LN 2  is maintained in a second vessel  11  and is routed through a pipe  12  through the ullage space  13  of vessel  10 . As LO 2  vaporizes, as a result of the vessel  10  heat leak, the O 2  vapor condenses on the pipe  12  thereby returning the vapor to liquid phase. The pipe  10  may be configured to wind back and forth in the ullage space above the LO 2  to increase the condensing surface area and thereby increase the amount of vapor condensed. In addition, one or more valves disposed between the first vessel  10  and second vessel  11  may be automated to open when the vapor pressure in vessel  10  reaches a predetermined upper limit, and close when the pressure is reduced to a predetermined lower limit. 
         [0007]    The manufacture of liquid oxygen in air separation plants inherently produces a small amount of methane contaminants. In this case, boil-off of the LO 2  will result in methane enrichment. If the methane concentration is too high the LO 2  cannot be used for some applications. Accordingly, the O 2  vapor in the ullage space of the vessel  10  is condensed to maintain the liquid oxygen to methane ratio. However, such a system has never been used for storage of liquid air. 
         [0008]    Systems and methods for storing liquid air are disclosed in various patents including, but not limited U.S. Pat. Nos. 3,260,060; 5,571,231; and, 5,778,680. Generally, these patents disclose a cryogenic mixture of LN 2  and LO 2  stored in a vessel that is adapted to condense the vapor in the ullage space of the vessel. The liquid air is drawn from the bottom of the vessel and re-circulated in a pipe disposed in the ullage space of the storage vessel to condense the vapor and return it to its liquid phase. However, such systems may not work well for storage of bulk amounts of liquid air because the temperature difference between the liquid air and vapor may be nominal. These systems may not condense a sufficient amount of vapor over an extended time period to maintain the appropriate concentrations of LN 2  and LO 2  to serve as a source of breathable air. 
         [0009]    Inasmuch as disasters, especially manmade disasters such as a biological, chemical or radiological disaster, may occur without warning, the first responder&#39;s reaction time to the disaster is critical. First responders will not be able to wait for a cryogenic mixture of liquid air to be created. 
         [0010]    In addition, when a catastrophic event (chemical, biological, radiological, or nuclear) takes place within a city, people in occupied buildings are instructed to respond in the following manner: Close, then seal all windows and doors, turn off HVAC systems, evacuate to a safe haven, or secure space within the building, if provided, stay inside and wait for help to arrive. This could be a long wait, depending on the nature and size of the event. 
         [0011]    Refuge chambers placed within a mine are designed to keep as many as twenty miners alive for ninety-six hours, following a major mine emergency, until rescuers arrive. Oxygen requirements for that many people are enormous, much more than can be provided by compressed air cylinders in the limited amount of space these chambers afford. Present art allows the use of compressed oxygen cylinders to be used for the sole air supply within the chamber. Mine refuge chambers currently utilize high-pressure compressed oxygen cylinders as the breathing supply within the sealed, self-contained space. Oxygen is discharged into the chamber at the approximate rate that 20 miners at rest would require. Exhaled carbon dioxide is removed by scrubbing, through lithium hydroxide canisters, or some other chemical means. However, the use of compressed oxygen within a confined space is less-than-desirable, due to the increased fire hazard, but is deemed the only possible way to provide adequate oxygen to that many people for that duration. 
         [0012]    M113 Armored Personnel Carriers are examples of military vehicles that employ air purification systems referred to as NBC Systems. The NBC system provides a filter unit and gas masks for protection against Nuclear, Biological, and Chemical attacks. The NBC system will not filter carbon monoxide exhaust gases, nor will the air purifier provide oxygen to protect against asphyxiation. Carriers may be equipped differently. All of the NBC systems consist of an air purifier, hose assemblies to carry purified air to the gas masks, a circuit breaker, switch, and electric cables. In addition to the basic M8A3 NBC system, the M13 NBC system adds heaters to heat the purified air in cold weather, and the M14 NBC system provides hospital hood protectors for disabled patients. The M14 may also have heaters. However, such systems suffer from the same draw backs as identified above; namely, the systems are not available for storing bulk amounts of liquid air for extended periods of time. 
         [0013]    Accordingly, a need exists for a system and method for storing a cryogenic mixture of liquid air for an extended period of time for the purpose of making readily available to first responders a supply of liquid air to be used as an emergency response breathing supply. However, the system and method are not limited for use by first responders and may be included for any use that requires the storage of liquid air for an extended period of time. For example, the present invention may be used in refuge chambers or safe havens in mines, in buildings for providing air to people inside the building during a catastrophic event or in first responder vehicles as a source of air for the responders. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0014]    The present invention for the system and method employs the use of liquid nitrogen from an external source as the refrigerant for a condensing circuit. An apparatus for storing liquid air (a cryogenic mixture of about 80% liquid nitrogen and about 20% liquid oxygen by volume) in a stable condition within a storage vessel routes colder liquid nitrogen from an external source, through a condensing coil/heat exchanger that passes through the ullage space of the vessel. This will result in condensing the nitrogen-rich vapor into the mass as a liquid, thereby reducing ullage pressure, cooling the mass, and ultimately precluding oxygen-enrichment through boil-off. In another embodiment, a cryocooler is mounted directly to a Dewar that contains the cryogenic mixture of liquid air and serves as a condenser/heat exchanger in the ullage space of the Dewar to prevent the liquid air from boiling off. Such a system may be especially useful for instances when only a limited amount of space is available. An electric-powered cryocooler, integrated into a LAir storage Dewar will maintain the cryogen in a “zero-loss” condition until needed. Greater amounts of cryogen will require larger capacity cryocoolers, with greater power requirements. This will be the preferred storage method for the vehicle, and mining applications, due to limited space, and difficulties with liquid nitrogen replenishment. 
         [0015]    In an embodiment of a refuge chamber of a mine or secured area for a building, a Dewar having a cryogenically stored liquid air is provided and includes the above condensing coil or cryocooler is provided. A vaporizing coil external to the Dewar is in fluid communication with an interior of the Dewar and through which the liquid air is transmitted for vaporization. A regulator valve is provided for opening and closing the vaporizing coil as necessary. In addition, a re-pressurizing circuit may be provided that pumps the cryogenic liquid from the Dewar and injects the liquid into the ullage space to reduce pressure in the Dewar that may result from evaporation or vaporization of the liquid air in the Dewar. In addition, the Dewar with liquid air may be linked with a building HVAC to supply air to the building or to a secure area of the building in emergency situations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a schematic view of a prior art system for storing liquid oxygen. 
           [0017]      FIG. 2  is a schematic view of a first embodiment of the invention. 
           [0018]      FIG. 3  is a schematic view of a second embodiment of the invention. 
           [0019]      FIG. 4  is a schematic drawing of a system of the present invention that circulates liquid air through a pump and pipe to the ullage space of storage vessel. 
           [0020]      FIG. 5  is a schematic drawing of an embodiment of the invention including a refuge chamber for a mine. 
           [0021]      FIG. 6  is a schematic drawing of an embodiment of the invention including a building emergency air system. 
           [0022]      FIG. 7  is a schematic drawing of an embodiment of the invention including a refuge chamber for a mine. 
           [0023]      FIG. 8  is a schematic drawing of an embodiment of the invention including a vehicle emergency air system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    An embodiment for the present invention shown in  FIGS. 2 and 3  utilizes a first storage vessel  20  in which a cryogenic mixture  21  of liquid nitrogen (LN 2 ) and liquid oxygen (LO 2 ) is stored. The mixture  21  may comprise about twenty percent (20%) LO 2  by volume and about eighty percent (80%) LN 2  by volume so that it may serve as a source of breathable for example in use with a self-contained breathing apparatus (“SCBA”); however, the concentrations may vary. Known safety standards for using a cryogenic mixture as a source of breathable include concentrations of LN 2  ranging from to about 76.5% to about 81.5% by volume of LN 2 , and concentrations of LO 2  ranging from about 19.5% to about 23.5% by volume of LO 2 . Such a mixture  21  may be stored at a pressure of about 40 pounds per square inch absolute (psia) at −300.01° F. to about 55 psia at −293.30° F. 
         [0025]    The first vessel  20  includes an inlet/fill pipe  25  for providing the cryogenic mixture  21  therein and an outlet pipe  26  for providing the mixture  21  to a user. Control valves  27  and  28  control the flow of the mixture  21  in and out of the pipes  25  and  26  respectively. In addition, a vent pipe  29  is positioned on the first vessel  20  in communication with an ullage space or headspace  22  above the mixture  21  to vent gases to maintain the pressure in the vessel  20  within a predetermined pressure range. The vent pipe  29  may be opened and closed via flow control valve  45  However, this vent pipe  29  may be used minimally in the present system as condensing liquid air vapor in the ullage space  22  of the first vessel  20  can reduce the vapor pressure. 
         [0026]    The vessel  20  is a Dewar that is vacuum insulated. That is, the vessel  20  includes spaced apart double walls  35 A and  35 B with a vacuum  48  disposed there between for insulation of contents of the vessel  20 . Despite the insulation of the vessel  20 , there will exist some level of heat leak that will cause the mixture  21 , or components thereof to evaporate to the ullage space (or head space)  22  above the cryogenic mixture  21 . 
         [0027]    Accordingly, a refrigerant  23  supplied via an external source, relative to the cryogenic mixture  21  in the vessel  20 , is piped through the ullage space  22  of the first storage vessel  20  to condense the evaporated liquid air in the ullage space to the liquid phase. In an embodiment, the refrigerant  23  is liquid nitrogen that is stored in a second storage vessel  24 . The LN 2  is preferably stored under pressure at about 20 psia at a temperature of about −315.55° F. The second vessel  24  includes an inlet/fill pipe  30  for providing the LN 2  therein and a vent pipe  31  that vents nitrogen vapor from an ullage space  33  of the second vessel  24 . Control valves  43  and  44  control the flow of the liquid nitrogen into the vessel  24  and evaporated nitrogen out of the vessel  24  respectively. 
         [0028]    With respect to  FIG. 2 , the LN 2  flows from the second vessel  24  through the first vessel  20  via a pipe  34 . Thus the pipe  34  is in fluid flow communication with an interior of the second vessel  24  and LN 2  stored therein. That portion of the pipe  34  that extends from the second vessel  24  to the ullage space  22  of the first vessel  20  is preferably insulated in some fashion. In an embodiment shown in  FIG. 2 , the pipe  34  may include a vacuum insulated jacket  45 , or have some other insulation mechanism, surrounding that portion of the pipe  34  disposed between the first vessel  20  and the second vessel  24 . The pipe  34  is routed vertically through the vacuum insulated wall  35  of the vessel  20  for insulation of the pipe  34 . 
         [0029]    The pipe  34  may be positioned with respect to the first vessel  20  and second vessel, so the pipe  34  directly feeds from the second vessel  24  to the ullage space  22  of the first vessel  20  without routing the pipe through the vessel wall  35 . However, with larger vessels having a storing capacity of 1,000 gallons, a stored liquid is typically drawn from the bottom of a vessel, so the pipe  34  may have to be routed vertically to reach the ullage space  22 , and insulated accordingly. It may be that the second vessel  24  can be elevated with respect to the first vessel  20 , so the bottom of second vessel  24  is aligned relative to the ullage space  22  so the pipe  34  can be fed directly into the ullage space  22  without the above-described routing. 
         [0030]    With respect to  FIGS. 2 and 3 , the pipe  34  may have a cooling coil  36  (or heat exchanger) to increase the surface of the pipe  34  within the ullage space  22  in order to capture more vapor for more efficient condensation. The pipe  34  may have other configurations such as winding back and forth in the ullage space  22  to create more surface area. At least that portion of the pipe  34  disposed within the ullage space  22  may fabricated from known materials such as stainless steel or copper. That portion of the pipe  34  disposed between first vessel  20  and second vessel  24  may be similarly composed of an insulated stainless steel or copper. Alternatively, the pipe  34  may include a vacuum insulated flex pipe or line as shown in  FIG. 3 . 
         [0031]    The LN 2  is supplied through the pipe  34  on an as needed basis. More specifically, if the pressure within the first vessel  20  reaches, approaches or surpasses a predetermined upper pressure limit, the LN 2  is supplied through the pipe  34  until the pressure within the first vessel  20  reaches a predetermined lower pressure limit, or falls within an accepted pressure range. With respect to  FIG. 3 , a valve system including a solenoid  35  is positioned in communication with the pipe  34 . A first switch  37  and second switch  38 , preferably pressure switches, are placed in communication with a pressure gauge  39  that monitors the pressure within the first vessel  20  and in communication with the solenoid valve  35 . The first switch  37  is activated to open the valve  35  when the pressure gauge  39  detects/measures a pressure within vessel  20  that reaches, approaches or exceeds a predetermined upper pressure level. When LN 2  flows through the pipe  34 , and in particular through that portion of the pipe  34  that is disposed with the ullage space  22 , liquid air vapor, and/or its vapor components nitrogen and oxygen, will condense on the pipe  34  returning to liquid phase in the vessel. In this manner concentration of LN 2  and LO 2  are maintained at acceptable levels relative to one another to store liquid air for extended periods of time as a source for breathable air. 
         [0032]    As shown in  FIG. 2 , the pipe  34  exits the vessel  20  through walls  35  and is in fluid communication with the vent pipe  29 . As the LN 2  passes through the pipe  34  the heat exchange that takes place between the pipe  34 , LN 2  and air vapor in the ullage space  22  causes the LN 2  to vaporize into nitrogen gas, which is released through the vent pipe  29 . A check valve  40  is preferable mounted in the vent pipe  29  between the wall  35  of vessel  29  and the point of entry of the pipe  34  and nitrogen relative to the vent pipe  29  to prevent a back flow of nitrogen into the vessel  20 . Backflow of the nitrogen into the vessel should be avoided in order to maintain the relative concentrations of the liquid air  21  components. 
         [0033]    In another embodiment shown in  FIG. 4 , a pump  41  and re-circulating pipe, including inlet  42 A (with respect to the pump) and outlet pipe  42 B (with respect to the pump  41 ) may be added to the system to avoid stratification of the liquid air mixture. More specifically, it is thought that over time the LN 2  and LO 2  may separate and stratify. Liquid oxygen is denser than LN 2  and would separate toward a bottom of the vessel  20 , while the LN 2  migrate above the LO 2 . To avoid this potential problem a pump  41  is positioned in fluid communication with a bottom end of the vessel  20 . The pump  41  may be a typical centrifugal pump sized according to the size of the vessel. For example, for a 1,000-gallon vessel, a pump that is capable of drawing 5 gallons per minute of liquid air may be sufficient; and, for larger vessels, such as 4,000 gallon to 6,000 gallon vessels, the pump may be capable of drawing 30 gallons per minute of liquid air. 
         [0034]    In this manner, the pump  41  draws the liquid air from the bottom of the vessel  20  and re-circulates the liquid into the vessel  20  through pipe  42 B, by injecting the liquid into the ullage space  22 . A spray nozzle (not shown) may be disposed on an end of the pipe  42 B to inject the liquid air into the ullage space  22 . In this manner, the liquid air  21  may be circulated to prevent stratification of the mixture&#39;s components, LN 2  and LO 2 . In addition, the injection of the liquid air  21  into ullage space  22  may provide some immediate pressure relief because the temperature of the liquid air  21  is lower than the temperature within the vessel  10  at the ullage space  22 . The pump  41  may draw the liquid air  21  continuously or at timed intervals as determined by a user. For example, the pump  41  may linked with pressure switches  37 ,  38 , so that the pump is activated when the pressure within the first storage vessel  20  approaches, reaches or exceeds a pressure limit. In this manner, the liquid air  21  is injected into the ullage space  22  while the refrigerant  23  flows through the heat exchanger  36 , aiding the refrigerant  23  in reducing the pressure within the first vessel  20 , which may decrease the amount of time the LN 2  refrigerant is needed. When the pressure within the first storage vessel reaches or falls below the pressure limit, then the pump is deactivated. 
         [0035]    The refuge chamber liquid air breathing system shown in  FIG. 5  may replace the compressed oxygen storage and delivery system, related plumbing and components, with a cryogenic air supply system consisting of: (a) storage Dewar (b) cryocooler, to effect zero-loss storage (c) Dewar regulated pressure-building circuit; and, (d) vaporizing heat exchanger. As shown in  FIG. 5 , a liquid air storage Dewar  52  is provided with a cryocooler  54  in a safety or safe haven chamber  50  formed in a mine. The term cryocooler has used herein may be may include those systems known to those skilled in the art that included oscillating (pulse tube), acoustic or mechanical (piston pump) cryocooler systems that effect heat exchange and result in condensation of vaporized in the storage vessel. Cryocoolers sold by Cryomech, Inc. located in Syracuse, N.Y., may work with the subject invention for storage of liquid air. For example, the Gifford-McMahon AL25 cryocooler sold by Cryomech, Inc. and equipped with a cold head and compressor may be used with the subject invention. 
         [0036]    A vaporizing heat exchanger or vaporizing unit  58  is provided so external of the Dewar  52  and in fluid communication with an interior of the Dewar  52 . The vaporizing head exchanger may simply include a coiled pipe. In an embodiment, the vaporizing heat exchanger  58  may include a first section  60  in fluid communication with a second section  62 . A selector valve  64  is disposed between the two sections  60 ,  58  to control flow of the liquid air through one or both sections. If the valve is closed the liquid air will be vaporized in the first section  60  and may exit the vaporizer at a cooler temperature than if flowing through both sections  60 ,  62 . However, if the selector valve  64  is open the liquid air or gaseous air will flow through both sections causing the flow rate to slow so the air exiting the exchanger  58  is warmer. The first section  60  may be selected during warmer months of the year to provide some cooling, while both sections  60 ,  62  may be selected for cooler months of the year. 
         [0037]    The system shown in  FIG. 5  may also include a re-pressurizing circuit  56  as described above, in which liquid air is pumped from the Dewar  52  and injected into a ullage space to reduce pressure in the Dewar  52 . To the extent vaporization of liquid air may take place within the Dewar  52 , pressure within the Dewar  52  may reach or rise above a predetermined limit liquid air is circulated through the circuit. A pressure sensor (not shown) and controller may be provided to detect pressure within Dewar  52  and open valve or regulator  66  for circulation of the liquid air. 
         [0038]    The refuge chamber liquid air breathing system Dewar will be filled with LAir prior to being placed in the mine, and then remain in a static/full condition during normal mine operations. Electrical mine power is supplied to the cryocooler, enabling the Liquid Air in the Dewar to be stored in a zero-loss condition. In the event of an emergency, miners will enter the chamber and open the Vaporizer Supply Valve, activating the system. Liquid cryogen flows into the vaporizer at a pre-determined rate to deliver the prescribed amount of airflow into the chamber, and at the desired temperature. Since the breathing air originates as a cryogen, temperature control capabilities are retained. This is important because over-heating in the chamber presents a problem. This system will provide 96 hours of breathing air, and cooling to trapped miners until rescue arrives. It is estimated that 64 gallons of liquid air may serve to provide ten people with breathable air for 96 hours, if the flow rate of the liquid air is maintained at 66 ft 3  per hour. 
         [0039]    In addition, the system may include a scrubber  68  that removes carbon dioxide from the used-air in the room. As illustrated a vortex  70  is provided in fluid communication with a lithium hydroxide source  72 . The vortex  70  draws air from the chamber at a low volume rate and directs the air the LiOH source to remove CO 2  from the air. 
         [0040]    In other embodiments shown in  FIGS. 6 and 7 , the system and method for storing a cryogenic liquid is incorporated in a building emergency air system. Such a system may work in the same manner as the above described mine refuge chamber  50 , and may include a cryocooler or a source of liquid nitrogen to store the liquid air. As shown in  FIGS. 6 and 7 , the cryogenic storage system may be piped into a buildings HVAC system  76  or may include a dedicated duct and ventilation system  78 . When an emergency occurs, the building&#39;s HVAC system is isolated, and the emergency building system is activated, introducing pure air through the existing ductwork  78  ( FIG. 6 ), placing, and maintaining the entire facility  74  under positive pressure, reducing contaminant intrusion. Alternatively, the air is delivered through dedicated piping or ductwork  82 , to “secure spaces” or isolated rooms  84  within the facility or building  80  ( FIG. 7 ). Since the supplied air originates as a cryogen, temperature control capabilities are retained. 
         [0041]    The building emergency air system would work as follows: When notification is received concerning a breathing hazard in the vicinity, i.e. chemical, biological, or radiological, the system is activated. Activation may be accomplished by initiating a programmable logic controller, throwing a switch, or manually, by pulling a lever or opening a valve, and can also be triggered by toxic gas and vapor detectors. Simultaneously, the HVAC system  76  is disabled; motor controlled valves isolate the HVAC ductwork  78 , and then open the liquid air supply from the storage Dewar  52  to the vaporizer or heat exchange unit  58 , thus initiating the flow of breathing air into the ductwork  78 ,  82 . Air can be delivered in this fashion to place an entire building under positive pressure, or ducted directly into a building “safe haven.” A “safe haven,” or “secure space” is a dedicated room, usually located in the center of the building, set up for the purpose of providing food, water, and air to the building occupants, in the event of a catastrophe. Multi-story buildings would have a secure space on each floor. The building emergency air system can be customized to provide protection to occupants of all types and sizes of buildings. 
         [0042]    In another embodiment, the system and method of storing a cryogenic liquid may be used as a vehicle emergency air system. In such a system liquid air is stored in a Dewar  52  mounted on, or within the vehicle  96  ( FIG. 8 ). The Liquid Air is converted to breathable air in a vaporizer/warm-up coil  58 , and is then delivered to the occupants through a manifold  90 , with connected hoses  92  and masks  94 . Cryogenic air, manufactured from Liquid Oxygen, and Liquid Nitrogen is free from all impurities, so there is no need for filtration. The system can be adapted to suit any conveyance that might have a need for an emergency breathing supply, i.e. ground vehicle, submarine, ship, or aircraft. A cryocooler or a liquid nitrogen source may be used a condenser that is suspended in the headspace of the Dewar to store the liquid air under a “zero-loss” condition. 
         [0043]    In addition to the above described embodiments, the system and method for storing a cryogenic mixture may be incorporating as an emergency air supply to hospitals. More specifically, the system may be linked with a hospital&#39;s oxygen support system in order to provide air to devices such as ventilators, incubators etc. In case of an emergency, the conduits directing oxygen to such devices is closed and isolated, so that air is then piped in from the cryogenic storage unit. 
         [0044]    While the preferred embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.