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BURN (Physics and Forensics)

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  1. BURN(Physics and Forensics) By Ahmed Abdelmoez MSc

  2. Burn Physics

  3. Introduction • Understanding physics of the burn leads to better knowledge about the nature of the burn. • Burn physics can explain the shape, depth and progression in burn patients.


  5. Flame burn severity is determined by: • Type of flammable liquid or gas. Flammability? Combustibility? • Contact time.

  6. When The flame reaches the subcutaneous fat, the injury becomes very severe. • Human skin doesn’t support combustion in pure oxygen except in the presence of an exposed subcutaneous fat. • Flammability of subcutaneous fat is much higher than intact skin. (Robert L. Durfee; Atlantic Research Corp Alexandria VA)

  7. Contact Burn

  8. Contact burn severity is determined by: • Object temperature. • Contact time. • ‘Glowing coal without fire’ and enlightened cigarette injury is considered as a contact burn.


  10. Scald burn severity is determined by: • Fluid or steam temperature. Boiling Point? • Contact time.

  11. Hot oil scald burn is worse than boiling water scald burn. • Boiling point of different oils is between 400-500° C. On the other hand, boiling point of water is only 100° C. Simmering Point? Smoke/Flash Point?


  13. Electrical burn severity is determined by: • Current (amperage) • Voltage • Path of current flow • Type of current (alternating or direct) • Duration of contact • Resistance at the point of contact • Individual susceptibility

  14. Low voltage burns are localized to the area surrounding the injury, while at high voltage, the cutaneous burn is associated with deep tissue damage. • Alternating current causes tetanic muscle contractions, which may either draw or throw victims away.

  15. Resistance at the point of contact varies from very low values for sweat-soaked hands or in the summer. • Resistance reaches more than 100 000 ohms for heavily calloused hands or feet during very dry winter weather. • Current flow, arc injury or flame injury are the three presentations in the electrical injury.

  16. Chemical Burn

  17. Severity of a chemical burn injury is determined by several factors: • Strength (concentration). • Quantity of burning agent. • Manner and duration of skin contact (progression). • Penetration. • Mechanism of action.

  18. Strong acids have a pH ˂2. • The best predictor of ability of an acid to cause injury is the amount of neutralizing material to correct the pH of the acid to neutral. • Alkali are capable of producing injury typically has a pH >11.5. • Some weak chemicals may turn strong by heat?

  19. pH = 2.5 – 4.2

  20. Acid burns are usually more self-limiting than alkali burns. • Acid tends to ‘tan’ the skin, creating an impermeable barrier that limits further penetration of the acid. • Alkalis, on the other hand, combine with cutaneous lipids to create soap and thereby continue ‘dissolving’ the skin until they are neutralized.

  21. Attempts to neutralize alkalis with acids (and vice versa) are contraindicated. • These maneuvers are dangerous and may induce an exothermic reaction leading to a thermal injury superimposed on the chemical burn. • Water irrigation is the routine except in cases of burning by a chemical powder, brushing is advised.

  22. The most dangerous and fatal chemical agent is Hydrofluoric acid. • Fluoride ions penetrate the skin and cause deep tissue destruction by combining with cellular calcium and magnesium. • Fluoride is also a metabolic poison that inhibits key enzymes of cellular metabolism

  23. A 10% TBSA Hydrofluoric acid burn may be life threatening due to systemic hypocalcemia. • It needs urgent excision and intra-arterial infusion of calcium to the damaged area.

  24. Flash Burn • Flash burn is any burn caused by fire without ignition after flame or electrical injuries.

  25. Frost Bite • Severity of frost bite is determined by several factors: • The duration and efficiency of tissue cooling. • Moist or wet skin is more susceptible to frostbite than dry skin. • Thermal conductivity. • The velocity of movement (exposed skin may suffer similar injuries exposed to air at 0°F in calm conditions or to a 15 mile-per-hour breeze at 25°F)

  26. Frost bite is harmful through three mechanisms: • Rapid cooling results in intracellular freezing, which causes more severe cellular damage and cell death. • Slower rate of cooling produces extracellular ice crystals, which results in transmembrane osmotic shift that drives water from within the cell and produces intracellular dehydration. • Harmful impact of generalized ischemia.

  27. Radiation Injury • Severity of radiation injury is determined by several factors: • Type of the radiation (particulate or electromagnetic). • Linear energy transfer (LET): energy deposited per unit track length. • Radiation dose. • A unit of dose equivalence was derived including all variations (roentgen equivalent man or rem).

  28. Radiation Injury is harmful through three mechanisms: • Thermal effect. • Immediate radiation damage effect. • Delayed radiation damage effect by free radicals production.

  29. Burn Forensics

  30. It is an important part of a plastic surgeon’s job, either than taking a good history, to figure out the cause and time gap of the burn on case presentation. • This important ability leads to gaining patient’s trust and cooperation. • In other occasions, It may lead to revealing assault or abuse acts.

  31. Accidental, Suicidal or Homicidal?

  32. The rule in burn injury is to be mostly accidental. • Suicidal burn injuries are mostly flame injuries then chemical or electrical. • Homicidal burn injuries are classified into assault and abuse.

  33. Suicidal attempts may be intended as a threatening tool. In such cases, injuries are not serious and on not important areas, if controlled. • In other cases, self inflicted cigarette burning may result from self harming tendency. • In cases of honest attempts, injuries are extensive and mostly involving head. • Hair color may be changed in cases of using certain types of flammable fluids.

  34. Homicidal assault burn injuries are mostly chemical, flame then contact burns in order of incidence. • Homicidal abuse burn in children include contact burn, cigarettes or hot objects, or scald burn with distinguishing spared areas as a result of protective withdrawal. • In cases of intentional injuries or those due to negligence, parent or nanny pretend a fake story about the accident.