Burns deeper than third degree receive less attention because they are less common and have historically had mortality rates of nearly 100 percent. Advances in medical technology and better understanding about burns have led to improved chances for victims of burns this deep. Fourth degree burns penetrate entirely through the skin and begin to burn the underlying muscle and ligaments; fifth degree burns penetrate the muscle and begin to burn bone; sixth degree burns are the most severe burns which have charred bone.
Fourth, fifth, or sixth degree burns exhibit many similar symptoms to third degree burns, but with a few additional characteristics. Primarily, these burns result in charring and loss of function of the affected area.
Charring: Charring is a process where exposure to high heat burns the hydrogen and oxygen from the skin, leaving a black substance composed almost entirely of carbon. The presence of char in a burn is indicative that the burn will require grafting and leave scars. Charring is possible in third degree burns, but is more common with deeper burns that have had longer exposure to the heat source.
Loss of Function: These burns also complete destroy the skin’s protective capabilities and begin to damage the underlying muscle. The body does not regrow muscle or bone in the same manner that it regrows skin. Damage to the muscle often requires excision and leads to long-term loss of function of the affected area. Loss of function generally leads to amputation.
Fourth, fifth, and sixth degree burns generally come from the same types of sources that third degrees burns come from. They burn deeper because the victim is exposed to the heat source for an extended duration. A few of the most common sources found in the home or workplace are detailed below.
- House fires: The U.S. Fire Administration estimates that 3,400 people die every year in home fires in the United States.
- Cooking accidents: Cooking often involves dealing with extremely hot solids (contact burns) or liquids (scald burns). Hot oil is particularly dangerous and capable of causing deep burns when it is spilled on a victim causing extended contact with the heated liquid.
- Appliance disrepair: While all electrical sources should be treated with caution, appliances deserve special care. Appliances operate at nearly twice the voltage levels of normal home electrical outlets. Contact with exposed appliance electrical cords has the potential to release substantial amounts of energy into the body.
- Emergency Personnel: Home fires are not only dangerous for those living in the home. Emergency personnel who fight fires are exposed to the dangers of home fires at a much higher frequency than individuals. Additionally, emergency personnel often respond to down power lines which pose the danger of extremely high-voltage burns (in excess of 110 kilovolts).
- Cable, Construction, or Electrical Workers: While emergency personnel typically handle downed power lines, certain professions often work in close proximity to active power lines on a daily basis.
- Food Services: Like cooks in the home, professionals in food services are often exposed to thermal burn sources. The Center for Disease Control and Prevention specifically points out the dangers of deep fryers and the possibility of submerging an extremity into oil that is over 350 °F.
- Manufacturers, Medical Workers, and Scientists: The most hazardous chemicals are rarely seen outside of industrial manufacturing or labs. Even minor contact with some of these chemicals can be potentially fatal. For example, fluoroantimonic acid (the most powerful superacid) explodes on contact with water and releases toxic fumes when not properly contained.