Blankets are a basic yet vital tool used by medical and emergency personnel, and are therefore commonly included in emergency kits such as first responder equipment kits, search and rescue equipment kits, first aid kits and outdoor survival kits. For persons suffering from severe traumatic injuries such as broken bones, wounds that cause significant blood loss, internal bleeding and head injuries, maintaining a relatively normal body temperature is vital to preventing and managing circulatory shock during surgery or medical trauma. The critical nature of these situations is heightened when acknowledging the fact that these situations often lead to death if untreated.
Similarly, persons who are stranded outdoors without adequate shelter, clothing, sources of heat, or external power sources may be in grave danger of suffering from exposure and hypothermia. This may also lead to death without intervention to prevent heat loss felt by a victim. Other situations in which preventing a victim's heat loss may be critical include chronic care of hospital patients, the elderly, and infants, as well as veterinary care of pets, livestock and/or other animals. Furthermore, the device may be useful in keeping animals and insects alive during shipping.
For these reasons, traditional blankets are invaluable tools that may be the difference between life and death in emergencies or other situations. To be most effective at retaining a person's body heat, a traditional blanket must be sufficiently large to cover the person's entire body. Thus, many warming blankets for adults are at least 150 cm long and 90 cm wide (approximately 5 feet by 3 feet) in order to provide whole-body insulation from the neck down. However, a blanket of this size is extremely bulky if it is constructed from common insulating materials such as wool, cotton or synthetic fibers. This is particularly true if the blanket is stuffed or otherwise constructed with sufficient thickness to adequately prevent all heat loss. A bulky blanket is unacceptable for use in a first responder equipment kit, first aid kit, search and rescue kit, or outdoor survival kit where all space occupied by a blanket displaces other important medical or emergency supplies that would otherwise be included in the kit.
Accordingly, in these settings, it is required to occupy as little space as possible. This requirement has led to space blankets becoming the most commonly found blanket in the above-described kits. Space blankets are generally made from an extremely thin (e.g. about 1 mm) plastic sheet on which a microscopic layer of metal has been deposited on one or both sides. Due to this minute thickness, space blankets large enough to completely cover an adult can be folded and stored in a container the size of a deck of cards, making them ideal for use in the above-described kits.
However, space blankets suffer from many drawbacks. Most significantly, space blankets provide very little insulation and are highly thermally conductive. Although space blankets reflect nearly all heat lost by a person through radiation, are moderately effective at preventing evaporative heat loss, and provide shelter from wind in order to decrease convective heat loss, space blankets provide virtually no protection against conductive heat loss. This is a significant problem. In an outdoor survival situation, for example, when a person is forced to sleep outdoors without shelter in snow or on cold ground, conductive heat loss from the body to the snow or ground may be greater than all other forms of heat loss combined. With no protection against conductive heat loss, a victim lying on the ground wrapped in a space blanket will lose virtually as much heat through conduction as they would without the space blanket.
Another significant drawback of both traditional blankets and space blankets is that they are exclusively passive heat retention devices (i.e. not active heat retention devices). In other words, traditional blankets and space blankets at best slow down the rate a person loses heat. However, these same blankets are always incapable of actively generating heat. Therefore, a person suffering from shock may be unable to generate sufficient body heat to maintain a normal core temperature. In these situations, traditional blankets (i.e. passive heat retention devices) are often incapable of preventing the core temperature from falling. Instead, when using traditional blankets heat must be actively generated and transferred to victims in order to maintain a safe core temperature.
Attempts to solve these problems through the use of blankets configured as active heat retention have been made. Electric blankets have long been used to actively generate heat by incorporating an electrically resistive element into a blanket constructed from traditional insulating materials. However, electric blankets have the disadvantages of requiring a power source. Electric blankets also present unnecessary risks of burns, fires and even electrocution, as well as increase the already substantial bulk of a traditional blanket. Similarly, blankets incorporating thin tubing through which warm water is circulated are known. However, these blankets also suffer from being extremely bulky. They require a water source to provide the water. These blankets further require a power source and a water pump. The power source to heat the water and also drive the pump.
Heated blankets that actively generate heat through exothermic chemical reactions are also known. For example, blankets with panels containing reactants that undergo an exothermic reaction in the presence of oxygen are known (see, for example, Ready-Heat™, from TechTrade (Hoboken, N.J.) These blankets must be sealed in airtight packaging until they are ready for use. If the packaging is defective or accidentally pierced so as to permit ingress of oxygen, the exothermic chemical reaction will unintentionally initiate and continue until completion unless an oxygen-free environment is restored before exhaustion of the reactants. Thus, oxygen-activated exothermic blankets have the drawback of requiring careful handling and delicate storage to prevent damage to the packaging. Similarly, oxygen-activated blankets also have a limited shelf life once the seal is ruptured after which the exothermic reactants are unable to completely react and bring the blanket to the desired temperature.
Yet another drawback of oxygen-activated blankets is that they are a “one and done” device, meaning, once the packaging for the blanket is opened and the chemical reaction is initiated, the oxygen-activated blanket is only capable of raising its temperature to a fixed temperature and maintaining that temperature for a fixed amount of time. In other words, the user of such a blanket has no ability to regulate the blanket's temperature or to modulate the amount of time the blanket remains heated by the exothermic reaction.
Perhaps the most serious drawback of oxygen-activated blankets is that they are inherently less effective in higher altitudes such as mountainous environments where they incidentally may be most needed. Because atmospheric density decreases with altitude, there is significantly less oxygen at higher altitudes compared to sea level. For example, only 90% of the oxygen at sea level is available at 1000 m (3300 ft), and only 75% of the oxygen at sea level is available at 2800 m (9200 ft). Accordingly, the heat generation rate of oxygen-activated blankets unavoidably decreases with altitude. For victims of trauma or exposure in mountainous environments, the relatively poor performance of oxygen-activated self-heating blankets at higher altitude may represent the difference between life and death.
Finally, a related drawback of oxygen-activated blankets occurs when the blanket is placed underneath a person. This takes place when the blanket serves as a heated pad for a stretcher or bed, or as a heated ground cloth in an outdoor survival situation. The person's body may compress the blanket and this compresses the chemical reactants inside to such an extent that air cannot circulate sufficiently to intermix with the reactants. As a result, the heat generation of the blanket may slow or stop, even though the chemical reactants inside the blanket have not been exhausted. These types of blankets usually take 20 minutes or more to achieve a reasonable working temperature. Additionally, the military has been known to use a impermeable shelter called a “cocoon” in which to place wounded soldiers who await treatment, rescue, or the like. Inside the cocoon as the cocoon seals and forms a vacuum, oxygen is often depleted which decreases the efficiency of oxygen-activated blankets.
Accordingly, there remains a need for a blanket that actively generates heat that is less bulky than traditional blankets and space blankets, does not require an external power source, does not automatically and irreversibly undergo an exothermic chemical reaction when exposed to oxygen, and whose temperature and duration of heat generation can be regulated. Further, there remains a need for a self-heating exothermically-reacting blanket with reactants that are self-contained and whose heat generation capacity is not limited by the environment in which the blanket is used (e.g., an environment with reduced levels of oxygen such as high altitude or inside a protective enclosure).
There also remains a need for a blanket that actively generates heat with rapid activation and heating so that the blanket approaches its maximum heated temperature relatively quickly. However, the heat generation of the blanket also needs to be regulated so that the blanket does not reach an unsafe high temperature or stop generating heat too soon. A self-heating blanket with a short heating stage that quickly reaches a high but safe temperature, and maintains that temperature for a substantial period of time, may be the difference between life and death for a person suffering from shock, trauma, accidents, hypothermia or exposure.