Burns: Classification, % BSA and Antemortem-vs-Postmortem Indicators

The classical four-degree system describes depth of thermal penetration. The ABA uses a parallel clinical system (superficial, partial-thickness, full-thickness) that maps onto the historical degrees; the degree nomenclature remains standard in medico-legal reporting.

First-degree burns (superficial epidermal) involve only the epidermis. The skin is erythematous and painful but intact. Blistering does not occur. Sunburn is the most common civilian example. In fire deaths, first-degree injury at the body periphery may be the only thermal mark on a victim who died rapidly from carbon monoxide poisoning before full-contact thermal exposure.

Second-degree burns (partial thickness) penetrate into the dermis. The ABA subdivides these into superficial partial-thickness (intact hair follicles, sensation preserved, heal without grafting in 14-21 days) and deep partial-thickness (follicles destroyed, reduced sensation, require grafting). The blistering characteristic of second-degree injury is produced by serum exudate separating the epidermis from the dermis; ante-mortem blisters contain protein-rich fluid, whereas post-mortem heat blisters contain serous or gas-filled cavities with negligible protein content. The Brinkmann-Püschel test, first published in the German forensic-pathology literature and reproduced in Madea's Handbook of Forensic Medicine, measures blister-fluid protein to separate the two categories. This blister-fluid protein finding is one of several biochemical vital-reaction markers discussed more fully in antemortem versus post-mortem injury distinction. Levels above 2 g/100 mL are consistent with ante-mortem formation.

Third-degree burns (full thickness) destroy the entire dermis and its adnexal structures. The wound surface is leathery, waxy, or charred. Nerve endings are absent, so paradoxically the wound is painless on direct examination. Third-degree burns require skin grafting; in survival cases they are the burns associated with the ABA's classification of major burns (> 20% BSA in adults, > 10% in children, any full-thickness involvement of face/hands/feet/genitalia/circumferential).

Fourth-degree burns (sub-dermal or carbonisation) extend through skin and subcutaneous fat into underlying fascia, muscle, and bone. They are the signature finding in prolonged exposure fires, high-energy accelerant fires, and in bodies recovered from residential structure fires where the body lay in a burn pool. The pugilistic (fencer's) posture, produced by heat-induced shortening of large muscle groups, develops in the context of third- and fourth-degree involvement and is a post-mortem artefact, not an antemortem defence posture.

Wallace's rule of 9s (1951, Edinburgh Royal Infirmary) divides the adult body surface into anatomical zones each approximating 9% or a multiple of 9%, with the perineum assigned 1% to close the total to 100%.

The adult distribution: head and neck 9%, each arm 9% (forearm + hand 4.5%, upper arm 4.5%), anterior trunk 18% (chest 9%, abdomen 9%), posterior trunk 18% (upper back 9%, lower back 9%), each leg 18% (thigh 9%, lower leg + foot 9%), and perineum 1%.

The Lund-Browder chart (1944, corrected by Berkow 1931 paediatric data) adjusts for the proportionally larger head and smaller legs in children. At birth, the head accounts for 19% and each lower limb for 13%. By age 10, the figures converge toward the adult ratios. The correction matters because, at AIIMS Paediatric Burn Centre (New Delhi) and at Alder Hey Children's Hospital (Liverpool, UK), paediatric BSA errors in the range of 5-10% directly affect fluid-resuscitation calculations using the Parkland formula (4 mL lactated Ringer's per kg per % BSA in the first 24 hours), and in the medico-legal setting, systematic underestimation of paediatric BSA in a suspected non-accidental injury case can conceal the true severity of the deliberate burning.

The patient's own palm (including fingers) approximates 1% BSA and is used for irregular, scattered burn patterns. This rule applies uniformly across ages and makes it practical to document scattered contact burns on a body diagram.

For the medico-legal examiner, BSA documentation serves two purposes. In a living victim, it supports the ABA severity triage: minor burns are less than 5% BSA full-thickness or less than 10% partial-thickness (US ABA criteria); moderate burns are 10-20% partial-thickness or 2-5% full-thickness; major burns are greater than 20% partial-thickness or greater than 10% full-thickness, or any full-thickness involvement of critical zones, any burn in the very young or elderly, any inhalation injury. In a deceased victim, it allows the reconstructing pathologist to assess survivability and to map the spatial pattern of burn involvement against the physical layout of the fire scene.

The central medico-legal question in every fire death is whether the decedent was alive when the fire began, or whether fire was applied to a body already dead to destroy evidence of a preceding homicide. Four lines of evidence address this question.

Carboxyhaemoglobin saturation. Carbon monoxide from combustion binds haemoglobin with 240 times the affinity of oxygen. In a living fire victim, COHb saturation accumulates as long as the cardiovascular system is functioning. Saturation above 30% measured in peripheral (femoral) blood (or 40-50% in survival cases) is strong evidence that the victim was alive and breathing in the smoke environment. A COHb of below 10% in a fire victim is suspicious: either the death preceded the fire, the fire was very brief, or there was a competing cause of death before significant smoke exposure. The mechanism of carbon monoxide toxicity and its post-mortem cherry-red livor signature is covered in the chemical asphyxia topic. The HACH spectrophotometer (DR series) and co-oximetry on blood-gas analysers (Radiometer ABL series, Siemens RAPIDPoint) provide the laboratory measurement. In the Indore acid-bath cases (2013-2015, documented in the Indian Journal of Forensic Medicine and Toxicology), post-mortem fire applied to chemically-injured bodies showed COHb below 10% in all three recovered blood specimens, inconsistent with living fire exposure. In the US, the National Fire Protection Association's Fire Investigation Handbook specifies COHb thresholds as a primary vitality indicator for fire deaths.

Soot in the airways. Soot particles in the trachea, bronchi, and lower airways indicate that the victim was breathing during the fire. Soot below the larynx is particularly significant, as post-mortem gas movement rarely carries soot that far. The histological demonstration of soot particles in alveoli, combined with early inflammatory response in the tracheal mucosa, is the most reliable combined indicator. Absent soot in the upper trachea of an extensively burned body strongly suggests the fire was post-mortem. The UK Coroner-commissioned review following the Grenfell Tower fire (2017) required explicit documentation of soot distribution in airways for every fire-death autopsy, emphasising its evidentiary primacy.

Heat haematoma vs subdural haematoma. Post-mortem heat exposure causes the epidural veins of the dura to dry, contract, and rupture, producing a biconvex collection of brownish, frothy, honey-combed material (heat haematoma) in the epidural space, most commonly over the frontal lobes. This is distinct from an antemortem subdural haematoma, which is composed of liquid or clotted red blood in the subdural space, is accompanied by cortical contusion, and has a different morphology on cut section. The distinction is critical: misidentifying a heat haematoma as a traumatic subdural can lead to a wrongful finding of assault preceding the fire. The BKA forensic pathology protocol (Germany) mandates histological confirmation with iron staining to differentiate aged traumatic haematoma from heat artefact.

Kerckring's sign (vital reaction in visceral mucosa). In bodies recovered from fires, the gastric mucosa and proximal duodenal folds (valvulae conniventes of Kerckring) may show congestion and haemorrhagic blistering consistent with antemortem heat effects. This sign is less reliable than COHb or soot-in-airways but may be the only surviving vitality indicator in extensively carbonised remains where blood is unavailable for COHb measurement.

Self-immolation, the deliberate ignition of one's own body, accounts for a significant share of fire deaths in South Asian casework. In India, AIIMS forensic pathology data and the NCRB Accidental Deaths and Suicides in India (ADSI) reports consistently document over 20,000 suicide deaths annually by fire, with a concentration among women aged 15-35, predominantly in household settings using kerosene. High COHb saturation, soot in deep airways, and burn distribution consistent with the described ignition method (kerosene poured over anterior trunk and ignited) are the expected findings.

Homicidal burning of a living victim differs in several ways. The victim may resist, producing defensive burn patterns on the dorsal hands and forearms inconsistent with accidental fire contact. Restraint marks (rope marks, zip-tie impressions) may be present but destroyed by fire; however, underlying deep-tissue haemorrhage may survive in the adipose layer. Blunt-force trauma to the head preceding the fire may be detectable in the bone even when soft tissue is carbonised: linear skull fractures, depressed skull fractures, and subdural haematoma with cortical contusion indicate ante-mortem assault that preceded the fire. The 2003 Bihar election lynching electrocution and burning case (documented in the AIIMS forensic-medicine department case register) illustrated the combined injury pattern where electrical stunning preceded burning as a method of evidence destruction.

Carbonised remains still carry recoverable vitality indicators: bone marrow for COHb when blood is unavailable, histological lung sections for soot, and DNA profiles from teeth and long-bone cortex.

Homicidal burning of a corpse, applying fire to an already-dead body to destroy evidence, has a distinct evidence signature. COHb will be absent or below 10%, soot will be absent from the lower airways, and the pattern of burn involvement may not correspond to the fire origin point in the way a living victim's movement would produce. The medico-legal reporting standard from the UK Royal College of Pathologists (2015 guidelines on fire deaths) requires that each of these indicators be explicitly addressed, not merely noted as absent.

In cases of acid-attack survivors (India's Criminal Law (Amendment) Act 2013 (Sections 326A and 326B IPC), following the Laxmi Agarwal 2005 case in Delhi, documented in National Commission for Women case files), the chemical burn distribution, the concentration of the agent on facial areas, and the absence of defensive burn patterns on the dorsal hands distinguish a targeted attack from an accidental spill. The Criminal Law (Amendment) Act 2013 introduced specific sentencing provisions for acid attacks, and the medico-legal certificate documenting burn degree, BSA, and facial involvement directly supports the charge classification.

The ABA Burn Center verification programme (US) classifies burn severity for triage purposes. Minor burns are those that can be treated as outpatients: less than 10% TBSA partial-thickness in adults (15-40 years), less than 5% TBSA in the very young (under 10) or the elderly (over 50), less than 2% full-thickness involvement, and no involvement of critical zones. Moderate burns require inpatient management at a general hospital: 10-20% TBSA partial-thickness in adults, 5-10% in the young or elderly, 2-5% full-thickness. Major burns require transfer to a verified burn centre: greater than 20% TBSA partial-thickness in adults (or greater than 10% in the young and elderly), greater than 5% full-thickness involvement, any burn of face, hands, feet, genitalia, perineum, or major joint circumferentially, any inhalation injury, any electrical burn, any chemical burn of the eyes or major joints.

The British Burn Association (UK) parallel classification uses a three-tier system (minor / moderate / major) with similar BSA thresholds but additionally specifies that any burn requiring more than 24 hours of inpatient care triggers a formal burn unit consultation, and any circumferential limb burn requires urgent escharotomy consideration, both clinical decisions that appear in the medico-legal record as evidence of the severity of the injury at first treatment.

In India, the National Burns Registry of India (NBRI), established by the Indian Council of Medical Research (ICMR), uses the ABA criteria for severity classification. Published data from burn units at Safdarjung Hospital (New Delhi) and Lokmanya Tilak Municipal General Hospital (Mumbai) document the population distribution of burn causes, with flame burns (kerosene and LPG) predominating over scalds and electrical burns, in contrast to the UK (where scalds in the under-5 age group represent the largest paediatric category) and the US (where cooking fires and residential structure fires dominate the adult category, per the NFPA fire statistics).

For the forensic pathologist, survivability assessment combines the BSA calculation with the ABA severity thresholds to assess whether death was the expected outcome of a burn of the documented extent, or whether medical treatment failure, pre-existing disease, or a concurrent non-thermal injury contributed to a death that would otherwise have been survivable.