Approximately 8000 fire related deaths occur in the United States each year (Spitz, 2006). With recent advances in the care of burns, an expected 50% mortality rate has been reported to have improved to 98% for children and 72% for adults.(Spitz, 2006) Although every year fire caused 20 times more deaths than hurricanes, tornadoes, floods, and earthquakes combined, many of them and most of the fire-related injuries are actually preventable. Burns and fires are the third leading cause of accidental death in all age groups, the second leading cause of death in the home for all ages and the leading cause of death in the home for children and young adults. (Barillo, 1996) Males' exhibit higher rates of thermal injury have been observed in Australia, the US, England, Denmark, Israel, and Greece (Waller, 1998). These two populations (children and the elderly) are also at increased risk of non-fatal burn injury. Fire injury among the elderly is thought to be related to a decreased cognitive functioning, thinning of the dermis and an overall general frailty of health. Burns in children remain a common mechanism of injury but an uncommon cause of death. Scalds are the most common cause of burn injury in children. "Between January 1997 and December 2002, 17, 237 children (under the age of 5) were treated for burns in the ER department of approximately 100 United States hospitals. Nearly two-thirds (65.7%) of the burns were due to scalds" (Holland, 2006). Thermal injuries are frequently expensive to treat, can be very severe, and often have devastating consequences for the individual (Waller, 1998). "Annually, 1% of the United States population is burned significantly enough to prevent participation in activities of daily living. â€¦ Fire and flames cause most of the burn or inhalation injuries leading to hospital admissions and deaths (Wachtel, 2010)."
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A "burn" or "thermal injury" is a reaction that occurs when skin receives more energy than it can absorb without injury. There are several different types of thermal injuries. They are caused by heat, electricity, electricity, chemicals, light, radiation, or friction. Most burns only affect the skin. "Burns" are classified according to location depth of injury and total body surface percentage involved. First degree burns (sunburns) are superficial and only affect the epidermis. Second degree burns (scalds, burns with blisters) are burns that destroy the epidermis and some of the dermis. Third degree burns (full thickness burns) are burns that involve the entire thickness of the skin. Fourth degree burns (severe electrical injuries) are burns that also involve the entire thickness of the skin and also the underlying fat, muscle and/or bone (Wachtel, 2010). The extent of the burns is usually estimated using the rule of nines. The rule of nines is where different variants of 9% of the body. The head area of infants' accounts for 18% of their body area and each one of their lower extremities is approximately 13.5% (9% + 4.5%).
Skin is the largest organ of the human body. It protects the rest of the body from the assault by foreign bodies and infections. It is important in controlling body temperature and fluid, protein, and electrolyte balance. Factors such as the duration of contact, temperature, volume of chemical, and voltage influence the severity of the injury. Loss of the skin barrier due to thermal injury increases vulnerability to infection which is the major cause of morbidity and mortality after the burn (Kagan, 2000). It can also lead to loss of fluid, electrolytes and protein; loss of temperature controls; and pain. Systemic reactions include altered blood flow and temperature regulation, fluid and electrolyte imbalances, shock, and catabolism. (Wachtel, 2010) Other illnesses, trauma, and injuries caused by inhaling carbon monoxide, smoke, may be lethal or contribute significantly to mortality and morbidity from burns (Wachtel). Burn injuries are often followed by profound hypermetabolic responses that persist long after the injury occurred (in survivors). The extent and length of the responses depends on the extent of the original injury. The responses can be responsible for devastating dysfunctions that can last for months after the original injury. (Williams, 2009)
The severity of the injuries depends directly on the heat intensity and exposure duration. Fire temperatures vary considerable depending on what is burning. Chemical fires can rapidly reach several thousand degrees while ordinary house fires range from approximately 900 to 1200 degrees (seldom over 1300 degrees). In order to dispose of a body in a fire, the flames (temperature) must be sustainable at between 1600-1800 degrees. So, there is no way to actually cover up a homicide (by burning the body) completely in a simple house fire. Although, the body of a child in the first couple of years of life may burn completely to ash before the flames would similarly hurt an adult. The body of a newborn can even be incinerated in a normal stove in less than 2 hours. Obesity and clothes can make a body burn faster and more completely than a normal sized naked person necessarily would. After the flame gets through the skin layers to the body fat it continues to burn independently from the rest of the fire. The heat generated by the burning of the body fat will increase the flames' temperature to about 1500 degrees which helps to disintegrate the remains quicker. If adipose tissue is ignited, prolonged local smoldering can cause severe skeletal damage. The clothes on a body act similar to that of a wick of a candle supplying more complete combustion, although tight clothing (such as a belt) will actually save the skin beneath it during the early stages of a fire, by temporarily cutting off the oxygen to the fire. A body in a house fire that is devastating will be extensively charred in less than 20 minutes (Spitz, 2006). A body in an auto will undergo superficial charring in the same time (Spitz, 2006). It does take a considerable rime for a body to burn (at about 1200 degrees) before the bones are actually revealed. The rib cage and facial skeleton take about 20 minutes to become exposed; the arms/legs are charred early but the shin bones take a little longer to be exposed. The organs are protected from most of the burned body even if the burning is severe, and this helps at autopsy to get toxicology tests performed.
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Accelerants, like gasoline, burns fast causing limited body damage unless massive quantities of accelerants are used. Identification of a body is still possible even with massive quantities of accelerant. Teeth, like bones, are tough to destroy and they are protected, from the fire, for as long as the lips/face is still intact. The lips and facial skin tightens, closing the mouth, with the tongue swelled up and protruding helps to keep the teeth protected.
The rate of decomposition of a burned body is slower than that of a non-burned body in that the bacteria do not like the burned flesh (much like cooked meat deters bacteria). Estimation of PMI on a burned body is usually inaccurate and subject to great variance. To determine cause of death, the investigator must determine whether the victim was alive at the time of the fire. Low levels of carboxyhemoglobin (COHb) results from the inhalation of carbon monoxide and can be very significant. A few breaths suffice to accumulate a meaningful concentration (Spitz, 2006). The presence of COHb gives proof of life when the fire started, but its absence does not necessarily imply that death occurred before the fire. Victims of flash fires (chemical plant fires, explosions or stoking a furnace) can have no COHb present or very low levels because death is usually instantaneous. Flames that hit the face can cause death due to the inability to breath. Breathing in of superheated air, such as occurs with steam, causes the airways to swell shut and strangle the victim. Inhaling steam is more dangerous than dry air of the same temperature. The majority of deaths from fires are actually from breathing in the toxic fumes given off by the burning plastics and polymers (which are basically solidified gasoline). In the burning of the plastics/polymers there is carbon monoxide as well as hydrogen cyanide. The human lethal level of blood cyanide is 5mg/mL. During/after a fire COHb decreases and cyanide increases with time during the storage of blood sample. The effects of cyanide and COHb are additive as COHb interferes with the ability of blood to carry oxygen and cyanide interferes with the ability of cells to utilize oxygen. Combine the two and it is more toxic. Just low levels of the gases cause disorientation and confusion which interferes with escape from the fire. But the lethal effect of smoke is mainly from the carbon monoxide. COHb levels can increase rapidly with just a few breaths of smoke (especially with stress, fear and agitation) and levels can fluctuate depending on age and general state of health. In a middle-aged healthy individual who died in a fire common blood saturation is 50-60%; lower levels are found in the elderly; and in children the saturation levels are often higher than adults. Infants/children can build up to a lethal saturation faster than an adult exposed to the same saturation. This is mainly due to the children's higher metabolic rate. No significant amount of carbon monoxide will get into a body after death (even if there is large open wounds), thus a level of COHb of over 10% means that the victim was alive at the time of the fire. High COHb levels found in a person usually indicate life at the time of the fire but blisters in the skin does not necessarily indicate that the victim was alive at the time of the fire.