g. Severity of Injury. The percent of burn and the depth of burn determine the
severity of burn injury. Usually, burns covering more than 20 percent of the body
surface are life-threatening. Burns covering more than 30 percent of the body surface
are usually fatal to adults without immediate treatment.
3-15. BURN DEPTH ESTIMATE
a. Scald Burn. A scald on the bare skin of an adolescent or an adult is
probably superficial. The reason is that heat dissipates rapidly. In a child or an elderly
person, the burn may involve the additional dermal layers of skin.
b. Hot Grease Burn. A burn caused by hot grease is probably a full-thickness
burn. This is because grease cools slowly and is difficult to remove. Hot grease on the
skin may cause extensive and deep damage before anyone can get it off the skin.
c. Electricity/Chemical Burns. Burns caused by electricity or chemicals are
almost always full-thickness burns.
3-16. THERMAL BURNS: THE RULE OF NINES
The severity of thermal injury depends on the depth and extent of the burn.
These two factors determine not only mortality and initial treatment requirements, but
the character of healing, functional result, and the consequences on the body of the
a. The Rule of Nines. The Rule of Nines (tables 3-1 and 3-2) is a quick way to
calculate the amount of skin surface that has been burned. The name comes from the
fact that various regions of the adult anatomy are assigned nine percent of the body
surface or multiples of nine. (The Rule of Nines is also used to determine the percent of
a child's skin surface with burns. The percentages assigned to a child's legs are not
nines or multiples of nines.) See figure 3-4 for percentages assigned to an adult's body
and figure 3-5 for percentages assigned to a child's body.
Look at figure 3-4. Notice that although the upper extremities are listed as
totaling 18% of the total body surface area with each arm being 9%, the
front and back of the arms are further divided. The front of the arm is 4.5%,
and the back of the arm is 4.5%. The same is true for the lower extremities.
Each leg is 18%, but the leg front is 9%, and the leg back is 9%.
See figure 3-5. Just as the body surface of an adult can be further divided, so
can the body surface area of the small child. Notice that while each upper
extremity equals 9%, the front of the arm is 4.5%, and the back of the arm is
4.5%. Similar subdivisions are made for the lower extremities.