health

Burns are injuries caused to the skin or underlying tissues by direct heat or
extreme cold; scalds are burns caused by hot liquids or gases (such as steam).
The severity of burns is measured in two ways: by the depth of the
burn (see sidebar) and by the size of the affected area. Doctors use the
“rule of nines” to evaluate how much of a person’s total body surface area
(TBSA) has been burned. In adults, the head and neck together count as
9 percent of the body; each arm also counts as 9 percent. The front of the
trunk, the back, and each leg are considered to each represent 18 percent
of the TBSA. Doctors count only second- and third-degree burns in estimating
the affected areas of the body.
Thermal burns (and scalds) are defined as burns caused directly by
heat or by chemical reactions that release heat.

They are divided into several categories according to the specific cause :

• Flame burns. This type of burn results from direct contact with
  fire. Flame burns may take the form of a sudden flash burn produced
  by a flammable liquid or gas igniting. Pouring lighter fluid
  on burning charcoal is a common cause of flash burns.
• Contact burns. These burns are caused by touching a hot object
  like a heated iron or cooking pan. Scalds are contact burns caused
  by hot liquids or gases.
• Electrical burns. These can be caused by contact with a live electrical
  wire or in rare cases by lightning. Electrical burns are serious
  because they can cause serious injury to internal organs that is not
  obvious from the size of the skin burn.
• Radiation burns. Radiation burns can be
  caused by welding equipment, radiation
  therapy for cancer, or overexposure to
  sunlight or tanning equipment. Sunburn
  is a common form of radiation burn.
• Chemical burns. Chemical burns can be
  caused by either strongly alkaline materials
  like lye, or by strong acids like sulfuric
  acid and nitric acid. Some acids are
  strong enough to eat through the skin and
  muscles down to the underlying bone.

Thermal burns affecting a person’s airway can be as dangerous as
burns affecting the surface of the body. The tissues of the airway can be burned
by breathing in superheated air from a fire, toxic gases, smoke, or steam.
In the United States, most people who die in house or office fires die from
smoke inhalation rather than from skin burns. Skin can also be burned by
exposure to cold, either by lengthy exposure to cold outdoors
(frostbite) or by brief exposure to extremely cold materials like dry ice.

Degrees of Burns :

Burns are classified according to the degree of injury that they cause.
Some doctors prefer to classify them according to the layers of skin
and muscle tissue that are injured. Both methods of classification are
outlined here:

1. First-degree burn: Also known as a
   superficial burn, this type of burn affects
   only the epidermis, the outermost layer
   of skin. It produces reddening and minor
   pain but no blisters.
2. Second-degree burn: Also called a partial-
   thickness burn, a second-degree
   burn injures the upper level of the
   dermis, the layer of skin just below the
   epidermis. Second-degree burns are
   marked by blisters filled with clear fluid
   and pain.
3. Third-degree burn: Also called a fullthickness
   burn, a third-degree burn
   destroys the dermis and some underlying
   muscle tissue or fascia. The
   damaged tissue is hard, purplish or
   white, and there is no pain because the
   nerve endings in the injured tissue have
   been destroyed. The hair on the skin is
   also destroyed in a third-degree burn.
4. Fourth-degree burn: In this type of
   severe burn, the tissue may be
   destroyed and charred down to the
   bone. Grafting is necessary in order to
   save the affected limb.