Burns and scalds are caused by exposure to intense heat, such as that generated by fire, bomb flash, sunlight, hot liquids, hot solids, and hot gases. Contact with electric current also causes burns, especially when the skin is dry. Dry skin offers about 20 times more resistance than moist skin to the passage of electric current. Therefore, when the skin is dry, the local heating effects (burns) are greater, even though the total damage to the body is less than when the skin is wet.

Note that burns and scalds are essentially the same type of heat injury. When the injury is caused by dry heat, it is called a burn; when caused by moist heat, it is called a scald. Treatment is the same in both cases.

CLASSIFICATION OF BURNS. Burns are classified in several ways: by the extent of the burned surface, by the depth of the burn, and by the cause of the burn. Of these, the extent of body surface burned is the most important factor in determining the seriousness of the burn, and it plays the greatest role in the casualty's chances for survival.

In calculating the extent of burned surface, the

RULE OF NINES is used, which is shown in figure 10-44. These figures aid in determining the correct treatment for a burned person. Shock can be expected in adults with burns over 15 percent or in small children with burns over 10 percent of the body surface area. In adults, burns involving more than 20 percent of the body surface endanger life, and 30-percent burns are usually fatal if adequate medical treatment is not received.

Figure 10-45.-First-, second-, and third-degree burns.

The depth of injury to the tissues is spoken of in degrees.

1. FIRST-DEGREE burns are the mildest. These produce redness, increased warmth, tenderness, and mild pain.

2. SECOND-DEGREE burns redden and blister the skin. They are characterized by severe pain.

3. THIRD-DEGREE burns destroy the skin. They can destroy muscle tissue and bone in severe cases. Severe pain may be absent because nerve endings have been destroyed. The color may vary from white and lifeless (scalds) to black (charred from gasoline explosions). Figure 10-45 shows the appearance of first-, second-, and third-degree burns.

It is important to remember that the size of the burned area may be far more important than the depth of the burn. A first-degree or second-degree burn that covers a large area of the body is usually more serious than a small, third-degree burn. A first-degree sunburn, for example, can cause death when a large area of the body is burned.

The causes of burns are generally classified as thermal (heat), chemical, electrical, and radiation (as discussed in chap. 9). Another type of burn (white phosphorous) is also discussed in this chapter. Whatever the cause, shock always results when the burns are extensive.