This invention relates to an emergency oxygen rebreather system and more particularly to a lightweight, compact, closed loop rebreather for emergencies in a hostile environment, such as in a mine at the time of an explosion, fire or other disaster.
It is well known that most fatalities in mine disasters such as cave-ins, fires and explosions are not caused directly by the event. Instead, most of the miners who die in such disasters are killed either by asphyxiation when the oxygen in the environment has been consumed by the fire or they die by inhaling poisonous gases such as carbon monoxide and methane which are frequently released or generated in such disasters. In recognition of this fact, numerous proposals have been made in the prior art to provide some means to supply the miners who survive the initial disaster with sufficient oxygen to enable them either to escape from the mine or to survive until they can be reduced.
Probably the most obvious approach would be to provide bottled air or oxygen to the miners for use when a disaster occurs. However, by its very nature, a mine disaster is unpredictable, so the oxygen apparatus must be of sufficiently small size and weight that the miner can carry it with him at all times that he is in the mine. Obviously, a supply of bottled air or oxygen and the necessary pressure regulating valves and the like would be completely too heavy and bulky to be carried by all miners at all times in the mine.
The most widely accepted solution to this problem to date has been to attempt to provide some sort of closed loop rebreathing apparatus with which the miner can rebreath his own exhaled air to remain alive until he can either escape or is rescued. The common factor in most of the systems of this type proposed to date has been a canister of a suitable chemical material for "scrubbing" the carbon dioxide from the exhaled breath and replacing it with a sufficient amount of oxygen to enable the miner to stay alive. A number of chemicals of this type are known in the art, with the most commonly used one being potassium superoxide (KO2). There are presently several systems known in the art and available which utilize canisters of potassium superoxide as the key element in an emergency rebreathing system for miners.
However, there is one serious disadvantage to the use of materials such as potassium superoxide to furnish oxygen for rebreathing. The chemical reactions under which the carbon dioxide and water vapor in the breath react with the potassium superoxide to produce carbonates and free oxygen are extremely exothermic, that is, a large amount of heat is generated by the reaction. Typically, the temperature of the air leaving the potassium superoxide canister may be as high as many hundredths degrees Fahrenheit. Breathing air of this temperature, even for short periods of time, can be extremely harmful. At best, it can result in blistered lips and mouth, and at worst, it can kill the user because of lung damage. Numerous arrangements have been proposed in the prior art for cooling the air from the potassium superoxide canister, such as by providing cooling water or even ice in the unit to reduce the temperature. However, these arrangements have proven unsatisfactory because of the shelf life problems of the device and the fact that the device must be ready for instant use without notice, with no time to provide ice or coolant to the units.
It is accordingly an object of the present invention to provide an improved emergency rebreathing apparatus.
It is yet another object of the present invention to provide an improved emergency rebreathing apparatus which supplies air to the user at an acceptable temperature.
It is still another object of the present invention to provide an improved emergency rebreathing apparatus which supplies air to the user at an acceptable temperature which has an indefinite shelf life and is available for instant use.
It is still another object of the present invention to provide an improved emergency rebreather apparatus which has an improved potassium superoxide configuration.
Briefly stated, and in accordance with the presently preferred embodiment of the invention, an emergency rebreathing apparatus is provided which includes a mouth piece to be worn by the user for receiving exhaled breath from the user and for rebreathing supplying reusable air to the user. A chemical conversion unit such as a potassium superoxide bed is provided for converting the exhaled breath into air having a suitable oxygen content, and a breathing bag is provided for receiving such air from the potassium superoxide bed. A conventional check valve arrangement is provided for allowing the breath exhaled into the mouthpiece to pass into the potassium superoxide bed and for allowing inhaled breath to be drawn from the breathing bag to the mouthpiece. A hermetically sealed evaporative cooler is provided which is in thermal contact with the bed for maintaining its temperature below a predetermined maximum temperature, and control means are provided for actuating the cooling means only when it is desired to use the breathing apparatus.
For a complete understanding of the invention, together with an appreciation of other objects and advantages thereof, please refer to the attached drawings and the following detailed description of the the drawings, in which:
FIG. 1 shows a schematic representation of an emergency rebreathing apparatus in accordance with the present invention.
FIG. 2 shows a partially broken prospective view of a portion of the apparatus of FIG. 1.
FIG. 3 shows a sectional view taken along the lines III--III of FIG. 2, and
FIG. 4 shows an enlarged detail of a section of the potassium superoxide bed of FIG. 2.
FIG. 1 shows a schematic arrangement of emergency rebreathing apparatus 10 in accordance with the present invention. The apparatus 10 includes a conventional mouthpiece 12, such as is used in self-contained underwater breathing apparatus, a check valve 14, a chemical conversion unit 16, such as a bed of potassium superoxide, for converting exhaled breath into reusable air and a flexible breathing bag 18. The apparatus 10 also includes a passageway 20 for connecting the mouthpiece 12 with the check valve 14, a passageway 22 for connecting the unit 16 with the breathing bag 18, and a passageway 24 which bypass unit 16 and connects breathing bag 18 with check valve 14. Breathing bag 18 and passageways 20, 22 and 24 are preferably made from a tough lightweight flexible material such as polyvinyl chloride.
In operation, whenever it is necessary to use the emergency rebreathing apparatus 10, the user places the mouthpiece 12 in his mouth and exhales into it. His exhaled breath passes down passageway 20 and enters check valve 14. Such valves are well known to those skilled in the art, and allows the exhaled breath to enter the unit 16, in which the carbon dioxide and water components of the exhaled breath react with the potassium superoxide to form various carbonates and, more importantly, to liberate free oxygen. The "scrubbed" breath now passes out of the unit 16 and through passageway 22 into the breathing bag 18. When the user now inhales through the mouthpiece, the snow reusable breath in breathing bag 18 passes around the unit 16 through passageway 24 and through check valve 14 and passageway 20 into mouthpiece 12 for the user to rebreathe. Breathing continues in a similar manner still all of the potassium superoxide in the unit 16 has been converted into oxygen.
FIG. 2 shows a partially broken prospective view of the unit 16 and also shows the inlet passageway 20 and the outlet passageway 22. For clarity, check valve 14 and bypass passageway 24 are not shown in FIG. 2. This figure illustrates two of the important features of the present invention. As shown therein, a controlled hermetically sealed evaporative cooling unit 26 is attached in good thermal contact to one outer surface of the unit 16. As is explained in more detail in connection with the description of FIG. 3 below, the cooling unit 26 includes a portion of spongelike material which is saturated with a cooling fluid such as water and which is hermetically sealed within the unit 26. However, the cooling unit 26 is designed so that its outer surface is easily ruptured to expose the saturated sponge to the atmosphere whenever it is desired to use the unit. For example, the outer surface could be made from aluminum foil which the user could control by simply tearing away when he wanted to, or, if a stronger unit is desired in order to prevent accidental rupturing of the unit, the outer surface of unit 26 could include a pre-weakened circumference, shown schematically as 28, and a pull-ring 30 for quickly opening the outer surface, in a manner similar to the many self-opening food cans presently available.
The broken section of FIg. 2 shows the physical arrangement of the pervious bed of potassium superoxide material 32 within the unit 16. More details of this are shown and described in connection with the description of FIG. 4 below.
FIG. 3 shows a sectional view along the lines III--III of FIG. 2 taken at a time when the cooling unit 26 is in the process of being controllably opened. As shown therein, a sheet of spongelike material 34 is provided directly against and in good thermal contact with one of the outer walls of the unit 16. This sponge member 34 is saturated with a suitable coolant fluid, such as water. When the ring 30 is pulled, thereby tearing the outer surface of the cooling unit 26 away, this water-soaked sponge is exposed to the atmosphere.
At this time, the user also begins breathing through the apparatus in a manner described above, and the exothermic chemical reactions mentioned above begin occurring in the potassium superoxide bed 32. The heat from this exothermic reaction greatly increases the temperature of the air passing through the potassium superoxide 32. For example, assume that the only source of cooling is the user himself and that his exhaled breath temperature is 100° F. Assume further that the user has an average metabolic rate of 1,200 B.t.u. per hour. Under these conditions, the user will require 0.2 pounds of oxygen if he uses the device for 1 hour. The efficiency of potassium superoxide conversion into oxygen is about 30 percent, thus requiring an initial storage of 0.67 pounds of potassium superoxide. The heat of reaction of 0.67 pounds of potassium superoxide into oxygen is approximately 390 B.t.u. Under these conditions, if all of this heat had to be removed by the air passing through the bed 32, the temperature of the air would be approximately 530° F., which is well beyond the tolerable human level. Of course, some of the heat produced in the reaction would be lost by conduction and radiation to the surrounding area, but the important consideration is that some additional means must be provided for removing heat from the unit or the unit will not be acceptable for its intended purpose.
In accordance with one of the features of the present invention, this excess heat is removed by the evaporative cooling effect of the water-soaked sponge 34. For example, assume that the highest acceptable inspired breath temperature for prolonged conditions (about 1 hour) is 170° F. Thus, allowing for a 70° increase in temperature and the metabolic rates mentioned above, the body of the user can absorb 62 B.t.u. per hour. As mentioned above, in one hour the potassium superoxide will generate 390 B.t.u., leaving 328 B.t.u. to be removed by the cooler 26. Tests have been conducted using a sponge having a surface area of 23 square inches. It has been determined that at a temperature of 170° F., the temperature mentioned above, the evaporation rate of the water is 0.33 pounds per hour, thereby absorbing 330 B.t.u. per hour, which is slightly greater than the desired amount.
It is noted that this evaporative cooling effect continues even in mine conditions where the relative humidity might approach 100 percent. This is because the vapor pressure of water at the higher temperature is much greater than the vapor pressure of water in the air at the ambient temperature in the mine. For example, at 80° F., a typical mine temperature, the vapor pressure of water is 24 millimeters of mercury, while at the 170° F. temperature mentioned above, the vapor pressure of water is approximately 250 millimeters of mercury, and it is thus seen that the cooling evaporative action easily occurs even in these adverse humidity conditions.
FIG. 4 shows a detail of a portion of the previous potassium superoxide bed 32 of the unit 16. As shown therein, the bed 32 comprises a stack of a plurality of corrugated wafers 36 each formed from compressed potassium superoxide in which the top portions of the ridges o a lower wafer are pressed into the bottom portions of the ridges of an upper wafer and conversely, the bottom portions of the furrows of an upper wafer are pressed into the top portions of the furrows of a lower wafer, thereby creating a plurality of passageways 38 through the bed 32. These passageways 38 provide easy paths for the exhaled air from the user to pass through the bed 32 of potassium superoxide. In addition to providing the easy air passageways 38, the arrangement of FIG. 4 also provides easy thermal conduction paths for heat generated within the core of the bed 32 to be conducted to the outer surface of the bed where it can be removed by the evaporative action described in connection with FIGS. 2 and 3 above.
While the invention has thus been disclosed and a preferred embodiment described in detail, it is not intended that the invention be limited to this shown embodiment. Instead, many modifications will occur to those skilled in the art which lie within the spirit and scope of the invention. It is thus intended that the invention be limited in scope only by the appended claims.