Chemical Burns, Hypothermia and Hyperthermia

Strong acids cause coagulative necrosis: hydrogen ions denature surface proteins, forming an eschar that limits further acid penetration. In sulphuric acid (H2SO4), the coagulative layer is firm, brown-black, and leathery, documented in acid-attack autopsies at AIIMS and Safdarjung Hospital (New Delhi). The acid is exothermic on dilution with body fluids, adding a thermal component to the chemical necrosis.

Hydrochloric acid (HCl) produces a yellow-brown coagulative eschar, somewhat softer than the sulphuric acid eschar because the chloride ion has lower protein-precipitating efficiency than sulphate. The fumes from HCl are highly irritant and may produce inhalation injury with laryngeal oedema if exposure is in an enclosed space, an important finding in the reconstruction of acid-bath deaths. Nitric acid produces a yellow-brown eschar stained with xanthoproteic reaction products (nitration of aromatic amino acids in protein), providing a diagnostic chromatic clue at post-mortem.

Hydrofluoric acid (HF) is the exception to the coagulative-necrosis rule. Fluoride ion penetrates the coagulative barrier and binds intracellular calcium and magnesium, causing deep liquefactive necrosis and systemic hypocalcaemia. HF exposure is primarily occupational (glass-etching, semiconductor manufacture, petroleum refining), and the forensic significance is its capacity to produce internal organ damage at superficially minor dermal exposure areas. UK Health and Safety Laboratory toxicological case reports (HSL, Buxton) document occupational HF fatalities where the total surface area of visible dermal injury was less than 1% BSA.

In the UK, acid attacks have been prosecuted under the Offences Against the Person Act 1861 § 29 (unlawful and malicious throwing of corrosive fluid) and, since 2018, under the Offensive Weapons Act 2019, which introduced specific offences for acid possession in public places. The Perpetua Wainwright case (2004, Bradford Crown Court) established the medico-legal precedent for documenting acid-burn distribution as evidence of intent to disfigure, a different charge characterisation from grievous bodily harm. In India, the landmark case of Laxmi Agarwal (2005, Delhi) in which a 15-year-old was attacked with sulphuric acid, led directly to the Criminal Law (Amendment) Act 2013 introducing specific acid-attack provisions at BNS §§ 124-125 (replacing IPC § 326A-326B), with mandatory minimum sentences and a framework for medical documentation of burn degree and facial involvement.

Strong alkalis cause liquefactive necrosis: the hydroxide ion saponifies cell-membrane lipids and dissolves structural proteins in a reaction that has no self-limiting eschar. This is the chemical basis for the observation that alkali burns at equivalent concentrations are more destructive than acid burns: there is no protective coagulative layer.

Sodium hydroxide (NaOH, caustic soda) is the industrial alkali most frequently implicated in occupational and criminal chemical burns. At pH above 12.5, the hydroxide ion drives saponification of subcutaneous fat with the production of glycerol and fatty-acid soaps, converting the tissue into a soft, slimy, translucent mass. John George Haigh (UK, 1949) used concentrated sulphuric acid rather than sodium hydroxide in the disposal of nine victims, having found alkali too slow, and the subsequent forensic recovery demonstrated that even concentrated acid does not achieve complete tissue dissolution. The Haigh case resulted in the recovery of acrylic denture material and bone fragments from the sludge, confirming that even concentrated acid does not achieve complete tissue dissolution.

Calcium hydroxide (slaked lime, Ca(OH)2), a weak alkali used in agriculture and construction, is frequently used in mass-grave and body-disposal cases in the mistaken belief that it accelerates decomposition. Forensically, the effect is the opposite: lime raises soil pH and creates alkaline conditions that inhibit bacterial decomposition, preserving the body for longer periods. The ICMP (International Commission on Missing Persons) exhumation cases from the Balkan conflicts document lime-covered remains that were better preserved than those in lime-free graves in the same soil environment, a finding confirmed in experimental taphonomy studies at the University of Huddersfield Forensic Taphonomy Research Institute.

In occupational settings, cement burns (Ca(OH)2 from fresh concrete) are the most common alkali-burn presentation in emergency medicine globally. The delayed onset of pain (the alkaline pH anaesthetises early), combined with prolonged occlusive contact in work boots or gloves, can produce severe full-thickness burns before the worker notices the exposure. The Health and Safety Executive (UK) Skin at Work guidance and the OSHA Hazard Communication Standard (US) both specifically address cement burns as an underreported occupational injury.

Paraquat (1,1'-dimethyl-4,4'-bipyridinium dichloride) is a non-selective contact herbicide associated with thousands of deaths in South Asian agriculture, primarily through accidental ingestion from unlabelled containers, and a smaller but documented proportion of deliberate self-poisoning cases in India, Sri Lanka, and South Korea. The WHO classifies paraquat as Hazard Class II (moderately hazardous), a designation that does not reflect its clinical lethality after ingestion.

The mechanism of paraquat toxicity is redox cycling in the lung: paraquat accepts electrons from NADPH and transfers them to molecular oxygen, generating superoxide free radicals in a continuous cycle. Type I and Type II pneumocytes in the alveolar wall are particularly susceptible because they actively concentrate paraquat via the polyamine transport system. The initial lung response is haemorrhagic alveolitis within 24-48 hours; this is followed by irreversible pulmonary fibrosis over 5-10 days, during which the alveolar architecture is replaced by fibrous tissue and the patient experiences progressive respiratory failure. The fibrotic phase is resistant to all current treatment, and no effective antidote exists; lung transplantation has been attempted but paraquat recirculates from tissues to the transplanted lung.

Post-mortem findings in paraquat deaths depend on the time from ingestion to death. Early deaths (within 24-48 hours) show haemorrhagic pulmonary oedema, renal tubular necrosis, and adrenal haemorrhage. Late deaths (5-21 days) show dense bilateral pulmonary fibrosis with honeycomb lung on cross-section, a finding that on gross examination resembles idiopathic pulmonary fibrosis but occurs in a young agricultural worker with no prior respiratory history, a pattern that should trigger paraquat measurement in urine and vitreous.

The Mettler-Toledo sodium dithionite field test (the "urine blue test") is the point-of-care paraquat screening tool: a drop of urine is added to sodium dithionite in alkaline solution, and a blue colour (the reduced, radical-cation form of paraquat) confirms exposure at clinically relevant concentrations. Quantitative measurement uses HPLC or, in reference laboratories, the HACH spectrophotometric dithionite assay on urine or vitreous fluid. Vitreous paraquat is preferred in decomposed bodies because paraquat persists in vitreous longer than in blood or urine.

In Sri Lanka, paraquat accounts for approximately 14% of all poisoning fatalities (National Poisons Information Centre data, Colombo National Hospital), and the Sri Lanka College of Toxicologists has published the island's paraquat-specific protocol integrating urine screening at triage with radiological chest scoring (paraquat lung score, Ct values on day 3). In India, the Supreme Court judgment in Manubhai Nayak v. State (1997) first addressed paraquat poisoning in a medico-legal context; the AIIMS toxicology department subsequently published reference ranges for urine paraquat in living and post-mortem samples. In the UK, the Bradford Royal Infirmary Poisons Unit published a series of deliberate paraquat-poisoning cases (Hart et al., 1984), with the landmark statistical prognostic study appearing in The Lancet, establishing the UK evidentiary framework for paraquat as a homicidal agent.

Hypothermia is defined as core body temperature below 35°C (rectal or oesophageal measurement). Severe hypothermia (below 28°C) causes cardiac arrhythmia and eventual asystole. Clinical hypothermia assessment uses the Swiss staging system (HT I to HT IV), but at autopsy the core temperature is generally unrecoverable (the body has warmed or decomposed), so the diagnosis rests on circumstantial and pathological findings.

Wischnewski spots (Wischnewski haemorrhages) are small, oval, haemorrhagic erosions in the gastric mucosa, found at the tips of the gastric rugal folds. They are the most specific autopsy finding in hypothermia, reported in 56-85% of confirmed cold-exposure deaths in the German literature (Brinkmann 2004, Madea 2014) and in the UK forensic pathology literature. They are not specific to hypothermia in that they also occur rarely in other stress conditions, but their presence in the context of an outdoor or cold-environment death is strongly corroborative. They must be distinguished from the post-mortem artefactual erosions that occur in decomposed bodies; fresh Wischnewski spots have intact surrounding mucosa and well-defined haemorrhagic margins.

Pink or red livor mortis in a cold-exposure death is produced by the relative preservation of haemoglobin in its oxygenated form in cold peripheral capillaries. Cold slows the enzymatic conversion of oxyhaemoglobin to deoxyhaemoglobin, so the post-mortem livor retains a pink-red colour similar to carbon monoxide poisoning lividity. The distinction requires COHb measurement: a COHb of below 10% in a pink-livid body found outdoors in winter is consistent with cold-exposure rather than CO poisoning.

Paradoxical undressing, the phenomenon in which a hypothermia victim removes clothing in the final phase of cold exposure, is explained by peripheral vasodilatation from failure of the central temperature-regulating centres in the hypothalamus. The victim experiences a sudden subjective sensation of intense warmth and removes layers of clothing, only to accelerate the rate of heat loss. Paradoxical undressing is documented in 20-50% of hypothermia deaths (Swiss mountain-rescue post-mortem case series, 2008; Kashmir winter cold-exposure deaths documented in the 2020 AIIMS Srinagar post-mortem register for the 2020-2021 winter period) and it frequently leads to scene-examination hypotheses of sexual assault or homicide that must be excluded before the cold-exposure diagnosis is confirmed.

Terminal hide behaviour (burrowing), in which victims squeeze into confined spaces (under beds, in cupboards) in the final phase of hypothermia, is related to paradoxical undressing and similarly causes initial scene-examination confusion. The UK Coroner guidance on outdoor-death investigation (2019) specifically addresses both paradoxical undressing and burrowing as known features of cold-exposure death that require active exclusion of assault before the natural-cause hypothesis is accepted.

In the 2020 Kashmir winter deaths documented in JIAFM, seventeen deaths attributable to cold exposure over January-March 2020 were reviewed; nine showed Wischnewski spots, seven showed pink livor, and four showed partial undressing. All were confirmed by scene temperature data and corroborated by the absence of any ante-mortem physical injury on full autopsy. The Henssge rectal thermometer (for body-core temperature measurement in the field) and the Nomogram-based TSD estimation is complicated in cold environments because body cooling does not follow Newton's cooling model when ambient temperature is at or below freezing, and the pathologist should document the ambient temperature and body temperature on recovery.

Hyperthermia covers a spectrum from heat cramps (electrolyte depletion) through heat exhaustion to heat stroke. The medico-legal distinction that matters is between heat exhaustion, which is volume-depleted but cerebral-function-preserved, and heat stroke, which involves core temperature above 40°C with central nervous system failure (confusion, seizures, coma).

Heat stroke presents in two forms. Exertional heat stroke occurs in physically active individuals (military recruits, athletes, labourers) exposed to high ambient heat and humidity during prolonged physical effort. Classic heat stroke occurs in the sedentary elderly or chronically ill during ambient heat waves, without significant exertion. Both share the cardinal finding of core temperature above 40°C, altered consciousness, and, at autopsy, widespread ischaemic organ damage: hepatocellular necrosis in zone 3 of the acinar structure (centrolobular necrosis), ischaemic acute tubular necrosis in the kidney (medullary necrosis in severe cases), and, in survivors who die days to weeks later, diffuse ischaemic encephalopathy on brain histology.

India's heat-wave mortality presents a recurring medico-legal challenge. The 2015 Andhra Pradesh and Telangana heat wave (2015, peak temperatures above 47°C) caused over 2,330 deaths officially recorded by the India Meteorological Department, with the true excess mortality estimated by the London School of Hygiene and Tropical Medicine at 4,000-5,000 over the event period. The medico-legal challenge was that most of these deaths occurred at home or in the open, reached hospital dead on arrival, and were certified as cardiac arrest or unknown cause without autopsy. A post-hoc review by the AIIMS Department of Forensic Medicine (published in the Annals of Forensic Medicine and Toxicology 2016) identified hepatic centrolobular necrosis as the most reliably identifiable post-mortem marker in bodies autopsied within 48 hours of the heat event.

In the UK, the 2003 European heat wave (estimated 70,000 excess deaths across the continent per Robine et al. 2008, and approximately 2,000 in England per ONS and HPA mortality surveillance data) produced a parallel post-mortem review challenge. HM Coroner cases in South East England documented heat stroke-compatible hepatic changes in elderly nursing-home residents, with heat stroke as the contributing cause of death in over 60% of reviewed cases where core temperature had been recorded ante-mortem.

The US Centers for Disease Control (CDC) Heat-Related Illness Surveillance data document 650-700 heat-related deaths annually in the US, with the highest concentrations in the Southwest (Arizona, Nevada). US medical examiner offices in Phoenix, Arizona have published standardised protocols for heat-stroke autopsy documentation (Maricopa County Medical Examiner heat-death protocol, 2010), specifying the histological panels (hepatic H&E, PAS, and PTAH for hepatocyte necrosis; renal PAS for tubular necrosis) that separate heat-stroke death from other hyperthermia-associated natural-cause deaths.