Burn Degrees and Burn Classification: Depth, TBSA and the Rule of Nines

A burn is classified two ways: by how deep it goes and by how much of the body it covers. Depth is described in degrees (first, second, third and fourth) or, in current terms, as superficial, partial thickness or full thickness. Extent is the percentage of total body surface area burned (%TBSA). Together they decide how serious a burn is, how much fluid a patient may need and whether a burn center should be involved.

The skin, briefly

The skin has two layers. The epidermis is the thin outer layer. The dermis beneath it is thicker and holds the nerve endings, blood vessels, hair follicles and sweat glands. Under the dermis is the subcutaneous fat, and under that muscle and bone. Each burn degree is defined by which of these layers it reaches, and what you see and what the patient feels follow from that.

Burn degrees: depth

Most burns are a mix of depths, often deeper in the middle and shallower at the edges. Depth is hard to judge in the field and is often misjudged, and a burn can deepen over the first few days. A patient saying a burn does not hurt is not reassurance: it can mean the nerve endings are gone.

Why first-degree burns are left out of %TBSA

Only partial-thickness and full-thickness burns count toward the total body surface area burned. Superficial burns, the first-degree burns, sunburn and redness alone, are excluded. A superficial burn damages only the epidermis and does not cause the large shift of fluid out of the circulation that deeper burns do. Because the %TBSA figure drives fluid resuscitation and referral decisions, counting superficial burns inflates it, and the fluid estimate built on it, by a large margin. The Rule of Nines tool states this before you pick a single region.

Estimating TBSA: the rule of nines

The rule of nines divides an adult's body surface into regions of about 9% or multiples of 9%. Add up the regions that carry a partial-thickness or full-thickness burn. A region only partly burned counts as the part that is burned, not the whole region. An infant's head is a much larger share of the body and the legs a smaller one, so the percentages change.

The infant figures are an approximation best suited to infants, and some textbooks round each infant leg to 14%. There is no band that fits a 4 to 12 year old: an adult head at 9% and an infant head at 18% are both wrong for a school-age child. For any child, the age-graded Lund-Browder chart is more accurate and is what a burn center will use.

Add up burned regions with the Rule of Nines tool

The palm method

For small or scattered burns, use the patient's own hand as a measure. The patient's hand, the palm with the fingers closed, is commonly taught as about 1% of their body surface area; the palm alone is closer to half of that. Use the patient's hand, not yours, so the method scales to children and to any body size. For a very large burn, it can be quicker to estimate the unburned skin and subtract it from 100%.

From TBSA to fluid

The %TBSA and the patient's weight are the two inputs to burn fluid formulas such as the Parkland formula. This guide gives no volume. The Parkland tool asks you to choose the coefficient, because the formula as published and current adult burn teaching use different figures, and it does not model children or electrical injury. Your protocol decides whether fluid is started in the field and how much.

Work through the Parkland formula, choosing the coefficient yourself

Special burns

Inhalation injury

Heat, smoke and toxic gases can injure the airway and the lungs, and the swelling of the upper airway can worsen over hours, so a patient who is talking normally on scene may not be later. Suspect it after any fire in an enclosed space and look for the signs below. Smoke can also carry carbon monoxide and cyanide. A pulse oximeter cannot tell carbon monoxide from oxygen on hemoglobin, so it can read normally in a poisoned patient.

• Burns to the face, singed eyebrows or nasal hair
• Soot around the nose and mouth, or in the mouth and throat
• Coughing up dark, sooty sputum
• A hoarse or changing voice
• Stridor, wheezing or difficulty breathing
• Swelling of the lips, tongue or throat
• Altered mental status, headache or vomiting, which can be carbon monoxide or cyanide

Circumferential burns

A deep burn that goes all the way around a limb forms a stiff, tight band of burned skin. As the tissue underneath swells, the band acts like a tourniquet and can cut off circulation beyond it. Around the chest, it can stop the chest expanding and make breathing and ventilation difficult. Remove rings, watches and other jewelry early, before swelling makes that impossible, and check pulses, color and sensation beyond the burn repeatedly. The release, an escharotomy, is a hospital procedure.

Electrical burns

• Scene safety first. Do not touch the patient until the power is confirmed off.
• Look for entry and exit wounds, and for more than one of each. They can be small while the current has damaged the muscle, nerves and vessels along its path inside.
• The rule of nines underestimates an electrical injury, because most of the damage is not on the skin. The Parkland tool does not model electrical injury.
• Electrical current can cause dysrhythmias and cardiac arrest. Put the patient on the monitor.
• Look for other injuries: a fall from a pole or ladder, or a patient thrown by the current.

Chemical burns

• Protect yourself and your crew first: the chemical can burn you too.
• Brush dry powder off the skin before irrigating, then remove contaminated clothing and jewelry.
• Irrigate with large amounts of water, and keep irrigating for a long time. Many chemicals keep burning until they are washed away. A few, such as some reactive metals, must not be wetted; your protocol, the safety data sheet and poison control decide.
• Do not try to neutralize an acid or an alkali with another chemical. The reaction can make the burn worse.
• Irrigate a chemical in the eye at once and continuously, including en route.
• Identify the substance if you safely can. A few chemicals need specific handling; your protocol, the safety data sheet and poison control can guide you.

Burns that may be inflicted

In a child or a dependent adult, some burn patterns suggest the injury was not an accident: sharp-edged burns from being held in hot water, burns in a stocking or glove pattern on both feet or both hands, burns in the shape of an object such as a cigarette or an iron, and a history that does not fit the injury or the patient's development. Document what you see and what you are told, in the words used, and report it as your mandatory reporting duty requires.

Cooling and covering

• Stop the burning process: put out flames, remove the patient from the source, and remove clothing and jewelry that are not stuck to the skin.
• Cool the burn with cool running water as soon as possible. US first aid guidance (AHA and Red Cross) teaches cooling with cool running water for at least 10 minutes, and some burn guidance, such as Australian first aid, uses 20 minutes, for a burn small enough to cool safely.
• Never use ice, ice water, butter or ointments. Ice deepens the injury and can cause hypothermia.
• Do not break blisters.
• Limit cooling in a large burn, in a small child and in a patient who is already cold. Cool the burn, not the patient.
• Cover the burn with clean, dry dressings or a clean sheet. Covering also reduces pain from air moving over it.

Field priorities

• Make the scene safe and stop the burning process.
• Assess and protect the airway early. Inhalation injury can close it over hours.
• Give oxygen as your protocol directs, especially after smoke exposure, where carbon monoxide may be present.
• Look for other injuries. Burn shock develops over hours, so a burn patient who is in shock early probably has another injury, such as bleeding, or carbon monoxide or cyanide poisoning after smoke exposure.
• Estimate depth and %TBSA, counting only partial-thickness and full-thickness burns.
• Cool and cover, then keep the patient warm.
• Vascular access, fluid and pain management as your protocol directs.
• Reassess the airway, breathing, circulation beyond circumferential burns and the patient's temperature.

Burn center referral criteria

The burn association's (ABA) referral guidance describes which burned patients should be discussed with a burn center, and the ABA calls it an aid to clinical judgment. Its current version sorts them into two groups: those for whom a burn center should be consulted immediately, with transfer considered, and those for whom a consultation is recommended. The immediate group includes full-thickness burns of any size, partial-thickness burns of 10% TBSA or more, and high-voltage electrical injury and lightning, among others; low-voltage electrical injury is in the consultation group. Deep burns of the face, hands, feet, genitalia, perineum or major joints, chemical and inhalation injury, and burns with other significant trauma or illness also appear in the guidance. It is guidance for the whole system, not a rule for where an ambulance goes; your protocol and medical direction decide the destination.

The short version

• Superficial (first-degree): red, dry, painful, no blisters. Superficial partial thickness (second-degree): blisters, moist, very painful. Deep partial thickness: patchy, drier, less painful. Full thickness (third-degree): white, leathery or charred, painless in the center. Fourth-degree: into fat, muscle or bone.
• Count only partial-thickness and full-thickness burns toward %TBSA. Sunburn and redness alone are left out.
• Rule of nines in an adult: head 9, each arm 9, front 18, back 18, each leg 18, perineum 1. An infant's head is 18 and each leg 13.5. For a child, a burn center uses the Lund-Browder chart.
• The patient's hand, palm and fingers, is about 1% of their body surface.
• Suspect inhalation injury after any enclosed-space fire, and remember a pulse oximeter cannot see carbon monoxide.
• Cool with running water, never ice; cover; and keep the patient warm.
• Fluid is your protocol's; the Parkland tool makes you choose the coefficient.