Microwave burn
Encyclopedia
Microwave burns are burn
injuries
caused by thermal effects of microwave
radiation
absorbed in a living organism
.
In comparison with radiation burn
s caused by ionizing radiation
, where the dominant mechanism of tissue damage is internal cell damage caused by free radicals, the primary damage mechanism of microwave radiation is thermal, by dielectric heating
.
Microwave damage can manifest with a delay; pain and/or signs of skin damage can show some time after microwave exposure.
("pain ray") is a less-lethal directed energy weapon that employs a microwave beam at 95 GHz; a two-second burst of the 95 GHz focused beam heats the skin to a temperature of 130 °F (54 °C) at a depth of 1/64th of an inch (0.4 mm) and is claimed to cause skin pain without lasting damage. Conversely, lower frequencies penetrate deeper; at 5.8 GHz the depth most of the energy is dissipated in the first millimeter of the skin; the 2.45 GHz frequency microwaves commonly used in microwave oven
s can deliver energy deeper into the tissue; the generally accepted value is 17 mm for muscle tissue.
As lower frequencies penetrate deeper into the tissue, and as there are only few nerve endings in deeper-located parts of the body, the effects of the radio frequency waves (and the damage caused) may not be immediately noticeable. The lower frequencies at high power densities present a significant risk. The human body acts as a broadband antenna
, with a number of resonation frequencies dictated by its size and position.
The microwave absorption is directed by the dielectric constant
of the tissue. At 2.5 GHz, this ranges from about 5 for adipose tissue
to about 56 for the cardiac muscle
. As the speed of electromagnetic waves is proportional to the reciprocial value of the square root of the dielectric constant, the resulting wavelength in the tissue can drop to a fraction of the wavelength in air; e.g. at 10 GHz the wavelength can drop from 3 cm to about 3.4 mm.
The layers of the body can be approximated as a thin layer of epidermis, dermis, adipose tissue (subcutaneous fat), and muscle tissue. At dozens of gigahertz, the radiation is absorbed in the top fraction to top few millimeters of skin. Muscle tissue is a much more efficient absorber than fat, so at lower frequencies that can penetrate sufficiently deep, most energy gets deposited there. In a homogeneous medium, the energy/depth dependence is an exponential curve with the exponent depending on the frequency and tissue. For 2.5 GHz, the first millimeter of muscle tissue absorbs 11% of the heat energy, the first two millimeters together absorb 20%. For lower frequencies, the attenuation factors are much lower, the achievable heating depths are higher, and the temperature gradient within the tissue is lower.
(which depends on the distance from the source and its power output), frequency, absorption rate in the given tissue, and the tissue sensitivity. Tissues with high water (resp. electrolyte) content show higher microwave absorption.
The degree of the tissue damage depends on both the achieved temperature and the length of exposure. For short times, higher temperatures can be tolerated.
The damage can be spread over large area, when the source is a relatively distant energy radiator, or very small (though possibly fairly deep) when the body comes to a direct contact with the source (e.g. a wire or a connector pin).
The epidermis has high electrical resistance for lower frequencies; at higher frequencies, the energy penetrates through by capacitive coupling
. Damage to epidermis has low extent unless the epidermis is very moist. The characteristic depth for lower-frequency microwave injury is about 1 cm. The heating rate of adipose tissue is much slower than of muscle tissue. Frequencies in millimeter wave range are absorbed in the topmost layer of skin, rich on thermal sensors. At lower frequencies, between 1–10 GHz, most of the energy is however absorbed in deeper layers; the threshold for cellular injury there lies at 42 °C while the pain threshold is at 45 °C, so a subjective perception may not be a reliable indicator of a harmful level of exposure at those frequencies.
damage; in such cases, the damage tends to be limited to upper limb
s. Significant injury with erythema
, blister
s, pain
, nerve
damage and tissue necrosis
can occur even with exposures as short as 2–3 seconds. Due to the deep penetration of these frequencies, the skin may be minimally affected and show no signs of damage, while muscle
s, nerves, and blood vessel
s may be significantly damaged. Sensory nerve
s are particularly sensitive to such damage; cases of persistent neuritis and compression neuropathy were reported after significant microwave exposures.
s, as the tissue damage is deep instead of just superficial. Adipose tissue shows less degree of damage than muscles and other water-rich tissues. (In contrast, radiant heat, contact burns and chemical burns damage subcutaneous adipose tissue to higher extent than deeper muscle tissue.) Full-thickness biopsy
of the area between burned and unburned skin shows layers of more and less damaged tissue ("tissue sparing"), layers of undamaged fat between damaged muscles; a pattern that is not present in conventional thermal or chemical burns. Cells subjected to electrical burns show microscopic nuclear streaming on histology
examination; this feature is not present with microwave burns. Microwaves also deposit more energy to areas with low blood supply and to tissue interface
s.
Hot spots may be formed in the tissue, with a consequent higher absorption of microwave energy and even higher temperature achieved, with localized necrosis
of the affected tissue following. In some cases, the affected tissue can be even charred
.
Muscle tissue destruction can lead to myoglobinuria
, with renal failure
following in severe cases; this is similar to burns from electric current. Urinalysis
and serum CPK, BUN
and creatine
tests are used to check for this condition.
were reported after technicians looked into powered waveguide
s.
Microwave-induced cataract
s are reported in scattered and isolated partially documented cases, but these are insufficient for establishing a causal relationship of higher than only conjectural
validity; while it is possible to cause a cataract by exposure to microwaves, the required intensities would cause brain death
. Experiments on rabbit
s and dog
s, mostly in the UHF range of frequencies, shown that the ocular effects are confined to eyelid
s and conjuctiva (as e.g. anterior segment keratitis
or iritis
). Cataracts were observed at several workers exposed to radiofrequency radiation, but in some of the cases the cause was unrelated to the RF exposure and in the other cases the evidence was incomplete or inconclusive. Some sources however mention incidence of microwave-related injuries of ocular lens and retina and the possibility of thermal effects to cause cataracts or focal tissue burns (incl. keratitis
).
For the near field
2.45 GHz frequency, the minimum power density to cause cataracts in rabbits was found to be 150 mW/cm2 for 100 minutes; a retrolental temperature of 41 °C was necessary to be achieved. When the eye temperature was kept low by external cooling, cataracts were not produced by higher field intensities; that supports the hypothesis of a thermal mechanism being involved.
s are particularly sensitive to microwave damage. Cases of persistent neuritis and compression neuropathy were reported after significant microwave exposures.
When the temperature of the brain is raised to or above 42 °C, the blood-brain barrier
permeability increases.
A neuropathy due to peripheral nerve lesion
, without visible external burns, can occur when the nerve is subjected to microwaves of sufficient power density. The damage mechanism is believed to be thermal. Radiofrequency waves and ultrasound can be used for temporary blocking of peripheral nerves during neurosurgical operations.
Pulmonary burn can be present when lungs are exposed; chest x-ray is used for diagnosing.
Exposure of abdomen may lead to bowel obstruction
due to stenosis
of the affected bowel; flat and upright abdominal x-ray is used to check for this condition.
where an infant
or child
has been placed in a microwave oven. The typical feature of such injuries are well-defined burns on the skin nearest to the microwave emitter may show well-defined burns, and histology
examination shows higher damage extent in tissues with high content of water (e.g. muscle
s) than in tissues with less water (e.g. adipose tissue
).
One such case involved a teenage babysitter who admitted to having placed a child in the microwave oven for approximately sixty seconds. The child suffered a third degree burn to the back, measuring 5 inches x 6 inches. The babysitter later took the child to the emergency department, where multiple skin grafts were placed on the back. There were no signs of lasting emotional, cognitive or physical effects. CT scan of the head was normal, and there were no cataract
s.
Another case involved a five-week-old female infant that had multiple full-thickness burns totaling 11% of the body surface area. The mother claimed the infant had been near a microwave oven, but not inside it. The infant survived but required amputations of parts of one leg and one hand.
Also, there have been two alleged infant
deaths caused by microwave oven
s. In both these cases, the babies were placed within microwaves and died of subsequent injuries.
appeared on the back sides of both hands and arms. Four years later, denervation of median nerve
, ulnar nerve
, and radial nerve
in both arms was shown on an electromyography
test.
The first microwave oven injury was reported in 1973. Two women operated a microwave oven in a department store snack bar. After several years, the oven showed a malfunction manifesting by burning the food. The first woman noticed burning sensations in her fingers and very little pain or tenderness when nearby to the operating oven. A small lesion appeared on her left index finger, near the base of the fingernail. In the next four weeks, three fingers of her right hand became affected as well. Transverse ridging and deformations close to the nail base appeared on her fingernails. After five months since the initial symptoms, she visited a doctor; the examination found no abnormalities other than the nails. Topical steroid cream used over six weeks led to gradual improvement. The second woman experienced nail deformation at the same time as the first one, with the same clinical findings. The oven was returned to the manufacturer before the involvement of the doctor, and the amount of leakage could not be assessed.
On July 29, 1977, H.F., a 51-year-old teacher, was attempting to remove a casserole
dish from her new 600-watt microwave oven. The oven signaled the end of the heating cycle, but the light and the cooking blower were on. During retrieval of the dish, she inserted two thirds of her bare forearms into the oven, for a total time of about five seconds. The oven was still operating. She felt "hot pulsating sensation" and burning in fingers and fingernails and a sensation of "needles" over the exposed areas. Jabbing pain, swelling, and red-orange discoloration of dorsal sides of both hands and forearms appeared shortly afterwards. The next day she sought medical help. Since then, she has undergone treatment with oral and topical cortisone
, Grenz rays
, ultrasound, and later acupuncture, without relief. Symptoms persisted, including high sensitivity to radiant heat (sun, desk lamp, etc.) and growing intolerance to pressure of clothes and to touch in hands and forearms. Neurological examinations in 1980 and 1981 did not yield a definite diagnosis. Neuronal latencies were within norm. Electromyography discovered denervation in the median nerve
, ulnar nerve
, and radial nerve
on both arms. Severe reduction of number of sweat gland
s in the finger pulps, in comparison with a random control, was also found. The injury was determined to be caused by the full power of the magnetron; the pulsating sensation was caused either by the stirrer (a mechanical mirror distributing the microwave beam across the oven space to prevent formation of hot and cold spots), or by the arterial pulsation in combination with increased nerve sensitivity. Damage to the A beta fibers, A delta fiber
s, and group C nerve fiber
s was the cause of the burning sensation. The increased hypersensitivity to radiant heat is caused by the damage to the A beta, A delta, and polymodal nociceptor
s (the group C fibers); this damage is induced by a single-time overheating of the skin to 48.5-50 °C, and the resulting sensitivity persists for a long time. Degeneration of the alpha motor neuron
s is also caused by the exposure to heat and radiation. Most of the major nerve trunks were not affected. Damage to the A beta fibers (located in the skin), discovered by the two-point discrimination
test, is permanent; the Pacinian corpuscle
s, Meissner corpuscles, and Merkel nerve ending
s, which degenerated after denervation, do not regenerate. The sympathetic nervous system
was involved as well; the reduction in active sweat glands was caused by destruction of their innervation, the initial edema and reddening was also caused by sympathetic nerve damage.
In 1983, a 35-year-old male was heating a sandwich in a microwave oven at work. After opening the door, the magnetron did not shut off and his right hand was exposed to microwave radiation during the sandwich retrieval. After the exposition, his hand was pale and cold. 30 minutes later the man presented himself to a doctor, with paresthesia
in all fingers and the hand still being pale and cold, with Allen's test
showing return to normal color after 60 seconds (normal is 5 seconds). By 60 minutes after the exposure the hand was normal again, and the patient was discharged without treatment. A week later no paresthesias, motor weakness nor sensory deficits were found.
-damaged feed horn
of a high-power microwave antenna, a 15-meter dish at an Earth station
of a television network, using a cherry picker
. After finishing, he sent his technician to power up the transmitter, and attempted to lower the cherry picker down. The engine failed and the engineer was stuck next to the antenna, outside of its main lobe
but well within the first sidelobe. The technician, unaware that the engineer was still close to the antenna, powered it up. The engineer was exposed to an intense microwave field for about three minutes, until the error was realized. There were no immediate symptoms; the next morning the engineer detected blood and solid matter in his urine, and visited a doctor, who found blood in stool
and massive bowel adhesions
. The engineer's medical problems lasted for many years.
(diathermy
) is used in medicine; the frequencies used typically lie in the ultrasonic, shortwave
, and microwave ranges. Careless application, especially when the patient has implanted metal conductors (e.g. cardiostimulator leads), can cause burns of skin and deeper tissues and even death.
Microwave damage to tissues can be intentionally exploited as a therapeutic technique, e.g. radiofrequency ablation
and radiofrequency lesioning. Controlled destruction of tissue is performed for treatment of arrhythmia. Microwave coagulation can be used for some kinds of surgeries, e.g., stopping bleeding after a severe liver
injury.
Microwave heating seems to cause more damage to bacteria
than equivalent thermal-only heating. However food reheated in a microwave oven typically reaches lower temperature than classically reheated, therefore pathogens are more likely to survive.
Microwave heating of blood
, e.g. for transfusion
, is contraindicated, as it can cause hemolysis
and hyperkalemia
.
Microwave heating is one of the methods for inducing hyperthermia
for hyperthermia therapy
.
High-energy microwaves are used in neurobiology experiments to euthanize small laboratory animals (mice
, rat
s) in order to fix brain metabolite
s without the loss of anatomical
integrity of the tissue. The instruments used are designed to focus most of the power to the animal's head. The unconsciousness and death is nearly instant, occurring in less than one second, and the method is the most efficient one to fix brain tissue chemical activity. A 2.45 GHz, 6.5 kW source will heat the brain of a 30 g mouse to 90 °C in about 325 milliseconds; a 915 MHz, 25 kW source will heat the brain of a 300 g rat to the same temperature in a second. Special devices designed or modified for this purpose have to be used; use of kitchen-grade microwave ovens is condemned.
defines energy density
limit for exposure periods of 0.1 hours or more to 10 mW/cm2; for shorter periods the limit is 1 mW-hr/cm2 with limited excursions above 10 mW/cm2. The U.S. Food and Drug Administration
(FDA) standard for microwave oven leakage puts limit to 5 mW/cm2 at 2 inches from the oven's surface.
For 5.8 GHz, exposure to 30 mW/cm2 causes increase of facial skin temperature by 0.48 °C, cornea
l surface heats by 0.7 °C, and the temperature of retina
is estimated to increase by 0.08-0.03 °C.
Exposure of skin to microwaves can be perceived as a sensation of heat or pain. Due to lower penetration of higher frequencies, perception threshold is lower for higher frequencies as more energy is dissipated closer to the body surface. When the entire face is exposed to 10 GHz microwaves, the feeling of heat is evoked at energy densities of 4-6 mW/cm2 for 5 or more seconds, or about 10 mW/cm2 for a half second. Experiments on six volunteers exposed to 2.45 GHz microwaves shown perception thresholds on forearm skin to be at the average of 25-29 mW/cm2, ranging from 15.40 to 44.25 mW/cm2. The sensation was indistinguishable from heat delivered by infrared radiation, though the infrared radiation required about five times lower energy density. Pain threshold for 3 GHz was demonstrated to range from 0.83-3.1 W/cm2 for 9.5 cm2 of exposed area, depending on length of the exposure; other source says the dependence is not directly on the power density and exposure length, but primarily on the critical skin temperature.
Microwave energy can be focused by metal objects in the vicinity of the body or when implant
ed. Such focusing and resultant increased heating can significantly lower the perception, pain and damage thresholds. Metal-framed glasses
perturb microwave fields between 2-12 MHz; individual components were found to be resonant between 1.4 to 3.75 GHz.
A security guard with a metal plate in his leg experienced heating of the plate when patrolling near tropospheric scatter
transmitter antennas; he had to be removed from their vicinity.
In the 30–300 GHz band, dry clothing may serve as an impedance transformer
, facilitating more efficient energy coupling to the underlying skin.
Pulsed microwave radiation can be perceived by some workers as a phenomenon called "microwave hearing"; the irradiated personnel perceive auditory sensations of clicking or buzzing. The cause is thought to be thermoelastic expansion of portions of auditory apparatus. The auditory system response occurs at least from 200 MHz to at least 3 GHz. In the tests, repetition rate of 50 Hz was used, with pulse width between 10-70 microseconds. The perceived loudness was found to be linked to the peak power density instead of average power density. At 1.245 GHz, the peak power density for perception was below 80 mW/cm2. The generally accepted mechanism is rapid (but minuscule, in the range of 10−5 °C) heating of brain by each pulse, and the resulting pressure wave traveling through skull to cochlea
.
s present in microwave installations tend to generate bremsstrahlung
x-ray
s. Magnetrons and especially hydrogen thyratron
s tend to be the worst offenders.
technicians of the US Navy, who were chronically exposed to high levels of microwave radiation, did not detect increased incidence of cancer. Recent epidemiologic evidence also led to the consensus that exposure to electromagnetic fields, e.g. along power lines, did not raise incidence of leukemia
or other cancers.
Burn
A burn is an injury to flesh caused by heat, electricity, chemicals, light, radiation, or friction.Burn may also refer to:*Combustion*Burn , type of watercourses so named in Scotland and north-eastern England...
injuries
Injury
-By cause:*Traumatic injury, a body wound or shock produced by sudden physical injury, as from violence or accident*Other injuries from external physical causes, such as radiation injury, burn injury or frostbite*Injury from infection...
caused by thermal effects of microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
absorbed in a living organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
.
In comparison with radiation burn
Radiation burn
A radiation burn is damage to the skin or other biological tissue caused by exposure to radio frequency energy or ionizing radiation.The most common type of radiation burn is a sunburn caused by UV radiation. High exposure to X-rays during diagnostic medical imaging or radiotherapy can also result...
s caused by ionizing radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
, where the dominant mechanism of tissue damage is internal cell damage caused by free radicals, the primary damage mechanism of microwave radiation is thermal, by dielectric heating
Dielectric heating
Dielectric heating, also known as electronic heating, RF heating, high-frequency heating and diathermy, is the process in which a high-frequency alternating electric field, or radio wave or microwave electromagnetic radiation heats a dielectric material. At higher frequencies, this heating is...
.
Microwave damage can manifest with a delay; pain and/or signs of skin damage can show some time after microwave exposure.
Frequency vs depth
The depth of penetration depends on the frequency of the microwaves and the tissue type. The Active Denial SystemActive Denial System
The Active Denial System is a non-lethal, directed-energy weapon developed by the U.S. military. It is a strong millimeter-wave transmitter primarily used for crowd control . Some ADS such as HPEM ADS are also used to disable vehicles. Informally, the weapon is also called the heat ray...
("pain ray") is a less-lethal directed energy weapon that employs a microwave beam at 95 GHz; a two-second burst of the 95 GHz focused beam heats the skin to a temperature of 130 °F (54 °C) at a depth of 1/64th of an inch (0.4 mm) and is claimed to cause skin pain without lasting damage. Conversely, lower frequencies penetrate deeper; at 5.8 GHz the depth most of the energy is dissipated in the first millimeter of the skin; the 2.45 GHz frequency microwaves commonly used in microwave oven
Microwave oven
A microwave oven is a kitchen appliance that heats food by dielectric heating, using microwave radiation to heat polarized molecules within the food...
s can deliver energy deeper into the tissue; the generally accepted value is 17 mm for muscle tissue.
As lower frequencies penetrate deeper into the tissue, and as there are only few nerve endings in deeper-located parts of the body, the effects of the radio frequency waves (and the damage caused) may not be immediately noticeable. The lower frequencies at high power densities present a significant risk. The human body acts as a broadband antenna
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
, with a number of resonation frequencies dictated by its size and position.
The microwave absorption is directed by the dielectric constant
Dielectric constant
The relative permittivity of a material under given conditions reflects the extent to which it concentrates electrostatic lines of flux. In technical terms, it is the ratio of the amount of electrical energy stored in a material by an applied voltage, relative to that stored in a vacuum...
of the tissue. At 2.5 GHz, this ranges from about 5 for adipose tissue
Adipose tissue
In histology, adipose tissue or body fat or fat depot or just fat is loose connective tissue composed of adipocytes. It is technically composed of roughly only 80% fat; fat in its solitary state exists in the liver and muscles. Adipose tissue is derived from lipoblasts...
to about 56 for the cardiac muscle
Cardiac muscle
Cardiac muscle is a type of involuntary striated muscle found in the walls and histologic foundation of the heart, specifically the myocardium. Cardiac muscle is one of three major types of muscle, the others being skeletal and smooth muscle...
. As the speed of electromagnetic waves is proportional to the reciprocial value of the square root of the dielectric constant, the resulting wavelength in the tissue can drop to a fraction of the wavelength in air; e.g. at 10 GHz the wavelength can drop from 3 cm to about 3.4 mm.
The layers of the body can be approximated as a thin layer of epidermis, dermis, adipose tissue (subcutaneous fat), and muscle tissue. At dozens of gigahertz, the radiation is absorbed in the top fraction to top few millimeters of skin. Muscle tissue is a much more efficient absorber than fat, so at lower frequencies that can penetrate sufficiently deep, most energy gets deposited there. In a homogeneous medium, the energy/depth dependence is an exponential curve with the exponent depending on the frequency and tissue. For 2.5 GHz, the first millimeter of muscle tissue absorbs 11% of the heat energy, the first two millimeters together absorb 20%. For lower frequencies, the attenuation factors are much lower, the achievable heating depths are higher, and the temperature gradient within the tissue is lower.
Tissue damage
The tissue damage depends primarily on the absorbed energy and the tissue sensitivity; it is a function of the microwave power densityPower density
Power density is the amount of power per unit volume....
(which depends on the distance from the source and its power output), frequency, absorption rate in the given tissue, and the tissue sensitivity. Tissues with high water (resp. electrolyte) content show higher microwave absorption.
The degree of the tissue damage depends on both the achieved temperature and the length of exposure. For short times, higher temperatures can be tolerated.
The damage can be spread over large area, when the source is a relatively distant energy radiator, or very small (though possibly fairly deep) when the body comes to a direct contact with the source (e.g. a wire or a connector pin).
The epidermis has high electrical resistance for lower frequencies; at higher frequencies, the energy penetrates through by capacitive coupling
Capacitive coupling
In electronics, capacitive coupling is the transfer of energy within an electrical network by means of the capacitance between circuit nodes. This coupling can have an intentional or accidental effect...
. Damage to epidermis has low extent unless the epidermis is very moist. The characteristic depth for lower-frequency microwave injury is about 1 cm. The heating rate of adipose tissue is much slower than of muscle tissue. Frequencies in millimeter wave range are absorbed in the topmost layer of skin, rich on thermal sensors. At lower frequencies, between 1–10 GHz, most of the energy is however absorbed in deeper layers; the threshold for cellular injury there lies at 42 °C while the pain threshold is at 45 °C, so a subjective perception may not be a reliable indicator of a harmful level of exposure at those frequencies.
Skin
Exposure to frequencies common in domestic and industrial sources rarely leads to significant skinSkin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
damage; in such cases, the damage tends to be limited to upper limb
Upper limb
The upper limb or upper extremity is the region in an animal extending from the deltoid region to the hand, including the arm, axilla and shoulder.-Definition:...
s. Significant injury with erythema
Erythema
Erythema is redness of the skin, caused by hyperemia of the capillaries in the lower layers of the skin. It occurs with any skin injury, infection, or inflammation...
, blister
Blister
A blister is a small pocket of fluid within the upper layers of the skin, typically caused by forceful rubbing , burning, freezing, chemical exposure or infection. Most blisters are filled with a clear fluid called serum or plasma...
s, pain
Pain
Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."...
, nerve
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
damage and tissue necrosis
Necrosis
Necrosis is the premature death of cells in living tissue. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma. This is in contrast to apoptosis, which is a naturally occurring cause of cellular death...
can occur even with exposures as short as 2–3 seconds. Due to the deep penetration of these frequencies, the skin may be minimally affected and show no signs of damage, while muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
s, nerves, and blood vessel
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
s may be significantly damaged. Sensory nerve
Sensory nerve
Sensory nerves are nerves that receive sensory stimuli, such as how something feels and if it is painful, smooth, rough, etc.They are made up of nerve fibers, called sensory fibers .Sensory neurons are neurons that are activated by sensory input Sensory nerves are nerves that receive sensory...
s are particularly sensitive to such damage; cases of persistent neuritis and compression neuropathy were reported after significant microwave exposures.
Muscle and fat tissue
Microwave burns show some similarities with electrical burnElectrical burn
An electrical burn is a burn that results from electricity passing through the body causing rapid injury. Approximately 1,000 deaths per year due to electrical injures are reported in the United States, with a mortality rate of 3-5%. Electrical burns differ from thermal or chemical burns in that...
s, as the tissue damage is deep instead of just superficial. Adipose tissue shows less degree of damage than muscles and other water-rich tissues. (In contrast, radiant heat, contact burns and chemical burns damage subcutaneous adipose tissue to higher extent than deeper muscle tissue.) Full-thickness biopsy
Biopsy
A biopsy is a medical test involving sampling of cells or tissues for examination. It is the medical removal of tissue from a living subject to determine the presence or extent of a disease. The tissue is generally examined under a microscope by a pathologist, and can also be analyzed chemically...
of the area between burned and unburned skin shows layers of more and less damaged tissue ("tissue sparing"), layers of undamaged fat between damaged muscles; a pattern that is not present in conventional thermal or chemical burns. Cells subjected to electrical burns show microscopic nuclear streaming on histology
Histology
Histology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining cells and tissues commonly by sectioning and staining; followed by examination under a light microscope or electron microscope...
examination; this feature is not present with microwave burns. Microwaves also deposit more energy to areas with low blood supply and to tissue interface
Biointerface
A biointerface is the interface between a cell, a biological tissue or a biomaterial with another material. The motivation for biointerface science stems from the urgent need to increase the understanding of interactions between biomolecules and surfaces...
s.
Hot spots may be formed in the tissue, with a consequent higher absorption of microwave energy and even higher temperature achieved, with localized necrosis
Necrosis
Necrosis is the premature death of cells in living tissue. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma. This is in contrast to apoptosis, which is a naturally occurring cause of cellular death...
of the affected tissue following. In some cases, the affected tissue can be even charred
Charring
Charring is a chemical process of incomplete combustion of certain solids when subjected to high heat. The resulting residue matter is called Char. By the action of heat, charring removes hydrogen and oxygen from the solid, so that the remaining char is composed primarily of carbon...
.
Muscle tissue destruction can lead to myoglobinuria
Myoglobinuria
Myoglobinuria is the presence of myoglobin in the urine, usually associated with rhabdomyolysis or muscle destruction. Myoglobin is present in muscle cells as a reserve of oxygen.-Causes:...
, with renal failure
Renal failure
Renal failure or kidney failure describes a medical condition in which the kidneys fail to adequately filter toxins and waste products from the blood...
following in severe cases; this is similar to burns from electric current. Urinalysis
Urinalysis
A urinalysis , also known as Routine and Microscopy , is an array of tests performed on urine, and one of the most common methods of medical diagnosis...
and serum CPK, BUN
Blood urea nitrogen
The blood urea nitrogen test is a measure of the amount of nitrogen in the blood in the form of urea, and a measurement of renal function. Urea is a by- product from metabolism of proteins by the liver and is removed from the blood by the kidneys.-Physiology:The liver produces urea in the urea...
and creatine
Creatine
Creatine is a nitrogenous organic acid that occurs naturally in vertebrates and helps to supply energy to all cells in the body, primarily muscle. This is achieved by increasing the formation of Adenosine triphosphate...
tests are used to check for this condition.
Eyes
Cases of severe conjunctivitisConjunctivitis
Conjunctivitis refers to inflammation of the conjunctiva...
were reported after technicians looked into powered waveguide
Waveguide
A waveguide is a structure which guides waves, such as electromagnetic waves or sound waves. There are different types of waveguides for each type of wave...
s.
Microwave-induced cataract
Cataract
A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...
s are reported in scattered and isolated partially documented cases, but these are insufficient for establishing a causal relationship of higher than only conjectural
Conjecture
A conjecture is a proposition that is unproven but is thought to be true and has not been disproven. Karl Popper pioneered the use of the term "conjecture" in scientific philosophy. Conjecture is contrasted by hypothesis , which is a testable statement based on accepted grounds...
validity; while it is possible to cause a cataract by exposure to microwaves, the required intensities would cause brain death
Brain death
Brain death is the irreversible end of all brain activity due to total necrosis of the cerebral neurons following loss of brain oxygenation. It should not be confused with a persistent vegetative state...
. Experiments on rabbit
Rabbit
Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world...
s and dog
Dog
The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...
s, mostly in the UHF range of frequencies, shown that the ocular effects are confined to eyelid
Eyelid
An eyelid is a thin fold of skin that covers and protects an eye. With the exception of the prepuce and the labia minora, it has the thinnest skin of the whole body. The levator palpebrae superioris muscle retracts the eyelid to "open" the eye. This can be either voluntarily or involuntarily...
s and conjuctiva (as e.g. anterior segment keratitis
Keratitis
Keratitis is a condition in which the eye's cornea, the front part of the eye, becomes inflamed. The condition is often marked by moderate to intense pain and usually involves impaired eyesight.-Types:...
or iritis
Iritis
Iritis is a form of anterior uveitis and refers to the inflammation of the iris of the eye.-Types:There are two main types of iritis: acute and chronic. They differ in numerous ways....
). Cataracts were observed at several workers exposed to radiofrequency radiation, but in some of the cases the cause was unrelated to the RF exposure and in the other cases the evidence was incomplete or inconclusive. Some sources however mention incidence of microwave-related injuries of ocular lens and retina and the possibility of thermal effects to cause cataracts or focal tissue burns (incl. keratitis
Keratitis
Keratitis is a condition in which the eye's cornea, the front part of the eye, becomes inflamed. The condition is often marked by moderate to intense pain and usually involves impaired eyesight.-Types:...
).
For the near field
Near and far field
The near field and far field and the transition zone are regions of the electromagnetic radiation field that emanates from a transmitting antenna, or as a result of radiation scattering off an object...
2.45 GHz frequency, the minimum power density to cause cataracts in rabbits was found to be 150 mW/cm2 for 100 minutes; a retrolental temperature of 41 °C was necessary to be achieved. When the eye temperature was kept low by external cooling, cataracts were not produced by higher field intensities; that supports the hypothesis of a thermal mechanism being involved.
Nerves
Sensory nerveSensory nerve
Sensory nerves are nerves that receive sensory stimuli, such as how something feels and if it is painful, smooth, rough, etc.They are made up of nerve fibers, called sensory fibers .Sensory neurons are neurons that are activated by sensory input Sensory nerves are nerves that receive sensory...
s are particularly sensitive to microwave damage. Cases of persistent neuritis and compression neuropathy were reported after significant microwave exposures.
When the temperature of the brain is raised to or above 42 °C, the blood-brain barrier
Blood-brain barrier
The blood–brain barrier is a separation of circulating blood and the brain extracellular fluid in the central nervous system . It occurs along all capillaries and consists of tight junctions around the capillaries that do not exist in normal circulation. Endothelial cells restrict the diffusion...
permeability increases.
A neuropathy due to peripheral nerve lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
, without visible external burns, can occur when the nerve is subjected to microwaves of sufficient power density. The damage mechanism is believed to be thermal. Radiofrequency waves and ultrasound can be used for temporary blocking of peripheral nerves during neurosurgical operations.
Other tissues
The thermal effects of microwaves can cause testicular degeneration and lower sperm count.Pulmonary burn can be present when lungs are exposed; chest x-ray is used for diagnosing.
Exposure of abdomen may lead to bowel obstruction
Bowel obstruction
Bowel obstruction is a mechanical or functional obstruction of the intestines, preventing the normal transit of the products of digestion. It can occur at any level distal to the duodenum of the small intestine and is a medical emergency...
due to stenosis
Stenosis
A stenosis is an abnormal narrowing in a blood vessel or other tubular organ or structure.It is also sometimes called a stricture ....
of the affected bowel; flat and upright abdominal x-ray is used to check for this condition.
Infants and microwave ovens
There are several cases of child abuseChild abuse
Child abuse is the physical, sexual, emotional mistreatment, or neglect of a child. In the United States, the Centers for Disease Control and Prevention and the Department of Children And Families define child maltreatment as any act or series of acts of commission or omission by a parent or...
where an infant
Infant
A newborn or baby is the very young offspring of a human or other mammal. A newborn is an infant who is within hours, days, or up to a few weeks from birth. In medical contexts, newborn or neonate refers to an infant in the first 28 days after birth...
or child
Child
Biologically, a child is generally a human between the stages of birth and puberty. Some vernacular definitions of a child include the fetus, as being an unborn child. The legal definition of "child" generally refers to a minor, otherwise known as a person younger than the age of majority...
has been placed in a microwave oven. The typical feature of such injuries are well-defined burns on the skin nearest to the microwave emitter may show well-defined burns, and histology
Histology
Histology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining cells and tissues commonly by sectioning and staining; followed by examination under a light microscope or electron microscope...
examination shows higher damage extent in tissues with high content of water (e.g. muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
s) than in tissues with less water (e.g. adipose tissue
Adipose tissue
In histology, adipose tissue or body fat or fat depot or just fat is loose connective tissue composed of adipocytes. It is technically composed of roughly only 80% fat; fat in its solitary state exists in the liver and muscles. Adipose tissue is derived from lipoblasts...
).
One such case involved a teenage babysitter who admitted to having placed a child in the microwave oven for approximately sixty seconds. The child suffered a third degree burn to the back, measuring 5 inches x 6 inches. The babysitter later took the child to the emergency department, where multiple skin grafts were placed on the back. There were no signs of lasting emotional, cognitive or physical effects. CT scan of the head was normal, and there were no cataract
Cataract
A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...
s.
Another case involved a five-week-old female infant that had multiple full-thickness burns totaling 11% of the body surface area. The mother claimed the infant had been near a microwave oven, but not inside it. The infant survived but required amputations of parts of one leg and one hand.
Also, there have been two alleged infant
Infant
A newborn or baby is the very young offspring of a human or other mammal. A newborn is an infant who is within hours, days, or up to a few weeks from birth. In medical contexts, newborn or neonate refers to an infant in the first 28 days after birth...
deaths caused by microwave oven
Microwave oven
A microwave oven is a kitchen appliance that heats food by dielectric heating, using microwave radiation to heat polarized molecules within the food...
s. In both these cases, the babies were placed within microwaves and died of subsequent injuries.
Adults and microwave ovens
A case of nerve damage by an exposure to radiation from a malfunctioning 600 watt microwave oven, operated for five seconds with the door open, with both arms and hands exposed, was reported. During exposure, there was a pulsating, burning sensation in all fingers. ErythemaErythema
Erythema is redness of the skin, caused by hyperemia of the capillaries in the lower layers of the skin. It occurs with any skin injury, infection, or inflammation...
appeared on the back sides of both hands and arms. Four years later, denervation of median nerve
Median nerve
The median nerve is a nerve in humans and other animals. It is in the upper limb. It is one of the five main nerves originating from the brachial plexus....
, ulnar nerve
Ulnar nerve
In human anatomy, the ulnar nerve is a nerve which runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest unprotected nerve in the human body , so injury is common...
, and radial nerve
Radial nerve
The radial nerve is a nerve in the human body that supplies the upper limb. It supplies the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial compartment of the forearm and the associated joints and overlying skin.It...
in both arms was shown on an electromyography
Electromyography
Electromyography is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph, to produce a record called an electromyogram. An electromyograph detects the electrical potential generated by muscle...
test.
The first microwave oven injury was reported in 1973. Two women operated a microwave oven in a department store snack bar. After several years, the oven showed a malfunction manifesting by burning the food. The first woman noticed burning sensations in her fingers and very little pain or tenderness when nearby to the operating oven. A small lesion appeared on her left index finger, near the base of the fingernail. In the next four weeks, three fingers of her right hand became affected as well. Transverse ridging and deformations close to the nail base appeared on her fingernails. After five months since the initial symptoms, she visited a doctor; the examination found no abnormalities other than the nails. Topical steroid cream used over six weeks led to gradual improvement. The second woman experienced nail deformation at the same time as the first one, with the same clinical findings. The oven was returned to the manufacturer before the involvement of the doctor, and the amount of leakage could not be assessed.
On July 29, 1977, H.F., a 51-year-old teacher, was attempting to remove a casserole
Casserole
A casserole, from the French for "saucepan", is a large, deep dish used both in the oven and as a serving vessel. The word casserole is also used for the food cooked and served in such a vessel, with the cookware itself called a casserole dish or casserole pan...
dish from her new 600-watt microwave oven. The oven signaled the end of the heating cycle, but the light and the cooking blower were on. During retrieval of the dish, she inserted two thirds of her bare forearms into the oven, for a total time of about five seconds. The oven was still operating. She felt "hot pulsating sensation" and burning in fingers and fingernails and a sensation of "needles" over the exposed areas. Jabbing pain, swelling, and red-orange discoloration of dorsal sides of both hands and forearms appeared shortly afterwards. The next day she sought medical help. Since then, she has undergone treatment with oral and topical cortisone
Cortisone
Cortisone is a steroid hormone. It is one of the main hormones released by the adrenal gland in response to stress. In chemical structure, it is a corticosteroid closely related to corticosterone. It is used to treat a variety of ailments and can be administered intravenously, orally,...
, Grenz rays
Grenz Rays
Grenz Rays are part of the electromagnetic spectrum comprising low energy X-rays. These were first developed by Gustav Bucky in 1923 using a cathode vacuum tube with a Lithium borate glass window which he labeled Grenz rays as he believed that the biological effects resembled UV light &...
, ultrasound, and later acupuncture, without relief. Symptoms persisted, including high sensitivity to radiant heat (sun, desk lamp, etc.) and growing intolerance to pressure of clothes and to touch in hands and forearms. Neurological examinations in 1980 and 1981 did not yield a definite diagnosis. Neuronal latencies were within norm. Electromyography discovered denervation in the median nerve
Median nerve
The median nerve is a nerve in humans and other animals. It is in the upper limb. It is one of the five main nerves originating from the brachial plexus....
, ulnar nerve
Ulnar nerve
In human anatomy, the ulnar nerve is a nerve which runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest unprotected nerve in the human body , so injury is common...
, and radial nerve
Radial nerve
The radial nerve is a nerve in the human body that supplies the upper limb. It supplies the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial compartment of the forearm and the associated joints and overlying skin.It...
on both arms. Severe reduction of number of sweat gland
Sweat gland
Sweat glands, or sudoriferous glands, are small tubular structures of the skin that produce sweat. There are two kinds of sweat glands:...
s in the finger pulps, in comparison with a random control, was also found. The injury was determined to be caused by the full power of the magnetron; the pulsating sensation was caused either by the stirrer (a mechanical mirror distributing the microwave beam across the oven space to prevent formation of hot and cold spots), or by the arterial pulsation in combination with increased nerve sensitivity. Damage to the A beta fibers, A delta fiber
A delta fiber
A delta fibers, or Aδ fibers, are a type of sensory fiber.They are associated with cold and pressure, and as nociceptors stimulation of them is interpreted as fast/first pain information....
s, and group C nerve fiber
Group C nerve fiber
-Location:C fibers are found in the peripheral nerves of the somatic sensory system. They are afferent fibers, conveying input signals from the periphery to the central nervous system.-Structure:...
s was the cause of the burning sensation. The increased hypersensitivity to radiant heat is caused by the damage to the A beta, A delta, and polymodal nociceptor
Nociceptor
A nociceptor is a sensory receptor that responds to potentially damaging stimuli by sending nerve signals to the spinal cord and brain. This process, called nociception, usually causes the perception of pain.-History:...
s (the group C fibers); this damage is induced by a single-time overheating of the skin to 48.5-50 °C, and the resulting sensitivity persists for a long time. Degeneration of the alpha motor neuron
Alpha motor neuron
Alpha motor neurons are large lower motor neurons of the brainstem and spinal cord. They innervate extrafusal muscle fibers of skeletal muscle and are directly responsible for initiating their contraction...
s is also caused by the exposure to heat and radiation. Most of the major nerve trunks were not affected. Damage to the A beta fibers (located in the skin), discovered by the two-point discrimination
Two-point discrimination
Two-point discrimination is the ability to discern that two nearby objects touching the skin are truly two distinct points, not one. It is often tested with two sharp points during a neurological examination and reflects how finely innervated an area of skin is....
test, is permanent; the Pacinian corpuscle
Pacinian corpuscle
Lamellar corpuscles or Pacinian corpuscles are one of the four major types of mechanoreceptor. They are nerve endings in the skin, responsible for sensitivity to vibration and pressure. Vibrational role may be used to detect surface, e.g., rough vs...
s, Meissner corpuscles, and Merkel nerve ending
Merkel nerve ending
Merkel nerve endings are mechanoreceptors found in the skin and mucosa of vertebrates that provide touch information to the brain. The information they provide are those regarding pressure and texture. Each ending consists of a Merkel cell in close apposition with an enlarged nerve terminal...
s, which degenerated after denervation, do not regenerate. The sympathetic nervous system
Sympathetic nervous system
The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...
was involved as well; the reduction in active sweat glands was caused by destruction of their innervation, the initial edema and reddening was also caused by sympathetic nerve damage.
In 1983, a 35-year-old male was heating a sandwich in a microwave oven at work. After opening the door, the magnetron did not shut off and his right hand was exposed to microwave radiation during the sandwich retrieval. After the exposition, his hand was pale and cold. 30 minutes later the man presented himself to a doctor, with paresthesia
Paresthesia
Paresthesia , spelled "paraesthesia" in British English, is a sensation of tingling, burning, pricking, or numbness of a person's skin with no apparent long-term physical effect. It is more generally known as the feeling of "pins and needles" or of a limb "falling asleep"...
in all fingers and the hand still being pale and cold, with Allen's test
Allen's test
In medicine, Allen's test, also Allen test, is used to test blood supply to the hand. It is performed prior to radial arterial blood sampling or cannulation.It is named for Edgar Van Nuys Allen....
showing return to normal color after 60 seconds (normal is 5 seconds). By 60 minutes after the exposure the hand was normal again, and the patient was discharged without treatment. A week later no paresthesias, motor weakness nor sensory deficits were found.
Other
An engineer replaced a woodpeckerWoodpecker
Woodpeckers are near passerine birds of the order Piciformes. They are one subfamily in the family Picidae, which also includes the piculets and wrynecks. They are found worldwide and include about 180 species....
-damaged feed horn
Feed horn
In satellite dish and antenna design, a feedhorn is a small horn antenna used to convey radio waves between the transmitter and/or receiver and the reflector, particularly in parabolic antennas...
of a high-power microwave antenna, a 15-meter dish at an Earth station
Earth station
A ground station, earth station, or earth terminal is a terrestrial terminal station designed for extraplanetary telecommunication with spacecraft, and/or reception of radio waves from an astronomical radio source. Ground stations are located either on the surface of the Earth, or within Earth's...
of a television network, using a cherry picker
Cherry picker
A cherry picker , is a type of aerial work platform that consists of a platform or bucket at the end of a hydraulic lifting system.- Design :...
. After finishing, he sent his technician to power up the transmitter, and attempted to lower the cherry picker down. The engine failed and the engineer was stuck next to the antenna, outside of its main lobe
Main lobe
The main lobe, or main beam, of an antenna radiation pattern is the lobe containing the maximum power. This is the lobe that exhibits the greatest field strength....
but well within the first sidelobe. The technician, unaware that the engineer was still close to the antenna, powered it up. The engineer was exposed to an intense microwave field for about three minutes, until the error was realized. There were no immediate symptoms; the next morning the engineer detected blood and solid matter in his urine, and visited a doctor, who found blood in stool
Blood in stool
In medicine, when referring to human feces, blood in stool can refer to multiple conditions:* Melena, with more blackish appearance, originating in upper parts of the gastrointestinal tract...
and massive bowel adhesions
Adhesion (medicine)
Adhesions are fibrous bands that form between tissues and organs, often as a result of injury during surgery. They may be thought of as internal scar tissue that connect tissues not normally connected.-Pathophysiology:...
. The engineer's medical problems lasted for many years.
Medical uses
Dielectric heatingDielectric heating
Dielectric heating, also known as electronic heating, RF heating, high-frequency heating and diathermy, is the process in which a high-frequency alternating electric field, or radio wave or microwave electromagnetic radiation heats a dielectric material. At higher frequencies, this heating is...
(diathermy
Diathermy
In the natural sciences, the term diathermy means "electrically induced heat" and is commonly used for muscle relaxation. It is also a method of heating tissue electromagnetically or ultrasonically for therapeutic purposes in medicine.-Surgical uses:...
) is used in medicine; the frequencies used typically lie in the ultrasonic, shortwave
Shortwave
Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...
, and microwave ranges. Careless application, especially when the patient has implanted metal conductors (e.g. cardiostimulator leads), can cause burns of skin and deeper tissues and even death.
Microwave damage to tissues can be intentionally exploited as a therapeutic technique, e.g. radiofrequency ablation
Radiofrequency ablation
Radio frequency ablation is a medical procedure where part of the electrical conduction system of the heart, tumor or other dysfunctional tissue is ablated using the heat generated from the high frequency alternating current to treat a medical disorder...
and radiofrequency lesioning. Controlled destruction of tissue is performed for treatment of arrhythmia. Microwave coagulation can be used for some kinds of surgeries, e.g., stopping bleeding after a severe liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
injury.
Microwave heating seems to cause more damage to bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
than equivalent thermal-only heating. However food reheated in a microwave oven typically reaches lower temperature than classically reheated, therefore pathogens are more likely to survive.
Microwave heating of blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
, e.g. for transfusion
Blood transfusion
Blood transfusion is the process of receiving blood products into one's circulation intravenously. Transfusions are used in a variety of medical conditions to replace lost components of the blood...
, is contraindicated, as it can cause hemolysis
Hemolysis
Hemolysis —from the Greek meaning "blood" and meaning a "loosing", "setting free" or "releasing"—is the rupturing of erythrocytes and the release of their contents into surrounding fluid...
and hyperkalemia
Hyperkalemia
Hyperkalemia refers to the condition in which the concentration of the electrolyte potassium in the blood is elevated...
.
Microwave heating is one of the methods for inducing hyperthermia
Hyperthermia
Hyperthermia is an elevated body temperature due to failed thermoregulation. Hyperthermia occurs when the body produces or absorbs more heat than it can dissipate...
for hyperthermia therapy
Hyperthermia therapy
Hyperthermia therapy is a type of medical treatment in which body tissue is exposed to slightly higher temperatures to damage and kill cancer cells or to make cancer cells more sensitive to the effects of radiation and certain anti-cancer drugs...
.
High-energy microwaves are used in neurobiology experiments to euthanize small laboratory animals (mice
Mouse
A mouse is a small mammal belonging to the order of rodents. The best known mouse species is the common house mouse . It is also a popular pet. In some places, certain kinds of field mice are also common. This rodent is eaten by large birds such as hawks and eagles...
, rat
Rat
Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus...
s) in order to fix brain metabolite
Metabolite
Metabolites are the intermediates and products of metabolism. The term metabolite is usually restricted to small molecules. A primary metabolite is directly involved in normal growth, development, and reproduction. Alcohol is an example of a primary metabolite produced in large-scale by industrial...
s without the loss of anatomical
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...
integrity of the tissue. The instruments used are designed to focus most of the power to the animal's head. The unconsciousness and death is nearly instant, occurring in less than one second, and the method is the most efficient one to fix brain tissue chemical activity. A 2.45 GHz, 6.5 kW source will heat the brain of a 30 g mouse to 90 °C in about 325 milliseconds; a 915 MHz, 25 kW source will heat the brain of a 300 g rat to the same temperature in a second. Special devices designed or modified for this purpose have to be used; use of kitchen-grade microwave ovens is condemned.
Perception thresholds
Safety limits exist for microwave exposure. The U.S. Occupational Safety and Health AdministrationOccupational Safety and Health Administration
The United States Occupational Safety and Health Administration is an agency of the United States Department of Labor. It was created by Congress of the United States under the Occupational Safety and Health Act, signed by President Richard M. Nixon, on December 29, 1970...
defines energy density
Energy density
Energy density is a term used for the amount of energy stored in a given system or region of space per unit volume. Often only the useful or extractable energy is quantified, which is to say that chemically inaccessible energy such as rest mass energy is ignored...
limit for exposure periods of 0.1 hours or more to 10 mW/cm2; for shorter periods the limit is 1 mW-hr/cm2 with limited excursions above 10 mW/cm2. The U.S. Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
(FDA) standard for microwave oven leakage puts limit to 5 mW/cm2 at 2 inches from the oven's surface.
For 5.8 GHz, exposure to 30 mW/cm2 causes increase of facial skin temperature by 0.48 °C, cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
l surface heats by 0.7 °C, and the temperature of retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
is estimated to increase by 0.08-0.03 °C.
Exposure of skin to microwaves can be perceived as a sensation of heat or pain. Due to lower penetration of higher frequencies, perception threshold is lower for higher frequencies as more energy is dissipated closer to the body surface. When the entire face is exposed to 10 GHz microwaves, the feeling of heat is evoked at energy densities of 4-6 mW/cm2 for 5 or more seconds, or about 10 mW/cm2 for a half second. Experiments on six volunteers exposed to 2.45 GHz microwaves shown perception thresholds on forearm skin to be at the average of 25-29 mW/cm2, ranging from 15.40 to 44.25 mW/cm2. The sensation was indistinguishable from heat delivered by infrared radiation, though the infrared radiation required about five times lower energy density. Pain threshold for 3 GHz was demonstrated to range from 0.83-3.1 W/cm2 for 9.5 cm2 of exposed area, depending on length of the exposure; other source says the dependence is not directly on the power density and exposure length, but primarily on the critical skin temperature.
Microwave energy can be focused by metal objects in the vicinity of the body or when implant
Implant (medicine)
An implant is a medical device manufactured to replace a missing biological structure, support a damaged biological structure, or enhance an existing biological structure. Medical implants are man-made devices, in contrast to a transplant, which is a transplanted biomedical tissue...
ed. Such focusing and resultant increased heating can significantly lower the perception, pain and damage thresholds. Metal-framed glasses
Glasses
Glasses, also known as eyeglasses , spectacles or simply specs , are frames bearing lenses worn in front of the eyes. They are normally used for vision correction or eye protection. Safety glasses are a kind of eye protection against flying debris or against visible and near visible light or...
perturb microwave fields between 2-12 MHz; individual components were found to be resonant between 1.4 to 3.75 GHz.
A security guard with a metal plate in his leg experienced heating of the plate when patrolling near tropospheric scatter
Tropospheric scatter
Tropospheric scatter is a method of transmitting and receiving microwave radio signals over considerable distances – often up to 300 km...
transmitter antennas; he had to be removed from their vicinity.
In the 30–300 GHz band, dry clothing may serve as an impedance transformer
Quarter wave impedance transformer
A quarter-wave impedance transformer, often written as λ/4 impedance transformer, is a component used in electrical engineering consisting of a length of transmission line or waveguide exactly one-quarter of a wavelength long and terminated in some known impedance. The device presents at its...
, facilitating more efficient energy coupling to the underlying skin.
Pulsed microwave radiation can be perceived by some workers as a phenomenon called "microwave hearing"; the irradiated personnel perceive auditory sensations of clicking or buzzing. The cause is thought to be thermoelastic expansion of portions of auditory apparatus. The auditory system response occurs at least from 200 MHz to at least 3 GHz. In the tests, repetition rate of 50 Hz was used, with pulse width between 10-70 microseconds. The perceived loudness was found to be linked to the peak power density instead of average power density. At 1.245 GHz, the peak power density for perception was below 80 mW/cm2. The generally accepted mechanism is rapid (but minuscule, in the range of 10−5 °C) heating of brain by each pulse, and the resulting pressure wave traveling through skull to cochlea
Cochlea
The cochlea is the auditory portion of the inner ear. It is a spiral-shaped cavity in the bony labyrinth, making 2.5 turns around its axis, the modiolus....
.
Other concerns
Some vacuum tubeVacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
s present in microwave installations tend to generate bremsstrahlung
Bremsstrahlung
Bremsstrahlung is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typically an electron by an atomic nucleus. The moving particle loses kinetic energy, which is converted into a photon because energy is conserved. The term is...
x-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s. Magnetrons and especially hydrogen thyratron
Thyratron
A thyratron is a type of gas filled tube used as a high energy electrical switch and controlled rectifier. Triode, tetrode and pentode variations of the thyratron have been manufactured in the past, though most are of the triode design...
s tend to be the worst offenders.
Low-level exposure
As the energy of radio frequency waves and microwaves is insufficient to disrupt chemical bonds, the effects are limited to thermal. Energy densities that are not sufficient to overheat the tissues are not shown to cause lasting damage. A study of 20,000 radarRadar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
technicians of the US Navy, who were chronically exposed to high levels of microwave radiation, did not detect increased incidence of cancer. Recent epidemiologic evidence also led to the consensus that exposure to electromagnetic fields, e.g. along power lines, did not raise incidence of leukemia
Leukemia
Leukemia or leukaemia is a type of cancer of the blood or bone marrow characterized by an abnormal increase of immature white blood cells called "blasts". Leukemia is a broad term covering a spectrum of diseases...
or other cancers.