electrocution / electrical injury

see also:

• burns

• the electrical flux energy is carried in the electromagnetic fields surrounding wires and other components of an electric circuit
• most injuries occur due to becoming part of the electrical circuit by contact
• exposure to the electrical flux energy carried in the electromagnetic fields itself does not usually cause injury as:
  • the frequency is very low - 50Hz
  • it is non-ionizing
  • the electric fields are easily shielded by everyday objects like trees, fences, and buildings, and even air between transmission lines and people attenuates their strength
  • magnetic fields, while less shielded, still decrease rapidly with distance—magnetic field strength dropped to near-background levels just tens of meters from high-voltage lines
  • these fields do not have enough energy to affect biological tissues, break chemical bonds, or heat body tissues, unlike microwaves or higher-frequency radiation
  • the fields are not strong enough to induce voltages or currents in the body above natural background levels
  • EMF strength falls off rapidly (inverse square law) with distance, so standing a few meters away from a wire means exposure is negligible

• dry human skin is very resistant to electrical currents forming as its resistance is usually around 100,000 Ohms and thus injury is only likely above 30-50V if skin is dry

• this occurs when the body is exposed to a sufficient voltage to form a damaging current in the body with the body grounded to allow a current to form
• if this current passes through the chest, an immediate cardiac arrhythmia such as VF may occur or, uncommonly there may may cardiac muscle injury which may result in delayed onset arrhythmias
• if a very high current passes across the skull, theoretically it may cause seizures and/or brain tissue injury but this is mostly protected by high resistance
• generally requires high voltages at over 30V such as 240V AC or lightning, but may occur at over 30V DC
• the electrical current passing through the body generates heat and causes tissue damage along its path, with deeper structures often suffering more severe injury than what is visible on the skin
• can cause muscle spasms strong enough to dislocate joints or even fracture bones due to intense involuntary contractions
• sensory and motor nerves can be directly damaged causing acute and delayed neurological symptoms such as weakness, numbness, and coordination difficulties
• in very high currents, bone damage can occur from heat necrosis as tissue temperatures rise thousands of degrees Celsius during electrical accidents

• contact with an electrical circuit carrying sufficient voltage to form a damaging current in the body
• electrical injury occurs if part of the body becomes part of this circuit with a positive and ground route in the body

• skin can develop severe burns if within 1m of high voltage sources due to a high-energy electrical arc forming
  • the exact burn risk distance (arc flash boundary) varies depending on arc energy, duration, and system voltage, but injuries or ignition of clothing can happen up to 1.5m away from a severe arc
  • the “arc flash boundary” is defined as the distance from an arc source within which a person could receive a second-degree burn (threshold: 5 J/cm² or 1.2 cal/cm² of incident energy)
  • this can occur at radio transmission towers, especially if unauthorized persons jump the barriers
  • an industrial 480V panels with a fault current of 10,000A usually requires a safe distance of at least 1-1.8m for bare skin
  • the higher the voltage and fault current, and the longer the duration of the arc, the farther out the risk boundary for burns extends
  • even transient exposure to radiant heat during an arc flash can cause burns, ignite clothing, and trigger secondary injuries

• modes of injury
  • 50% are from ground current from a nearby strike
    • this is why whole herds of animals can be found dead - the current passes up one leg, through the heart, and down the other leg as it spreads across the ground
    • to minimize the cardiac effects of this, one should adopt the lightning position if they sense imminent lightning strike
  • 30% are from side splash jumping from a nearby strike
  • 15% are from touching an object in a circuit hit by lightning (eg. a wired house phone, taps, antenna cables, etc)
  • 5% are direct hits
  • NB. in addition, many are injured from indirect mechanisms such as flying debris from an exploding tree, etc.
  • see safety in lightning storms
• potential clinical effects
  • may have features as outlined under electrocution
  • in addition:
    • if survive the cardiac arrhythmia / arrest component, respiratory arrest may follow from paralysis of the medullary respiratory center.
    • lightning injuries predominantly affect the nervous system and can cause loss of consciousness, confusion, amnesia, seizures, paralysis (including transient keraunoparalysis—a temporary paralysis with pallor and coolness), peripheral neuropathy, and long-term neurological deficits
    • lightning burns are typically superficial and characteristic, including “Lichtenberg figures” — a fern-like branching skin discoloration caused by capillary rupture. Other burns include flash burns, punctate burns resembling cigarette burns, and contact burns.
    • tympanic membrane rupture and sensorineural hearing loss are common
    • cataracts and other eye injuries may develop months to years after the strike
    • behavioral changes, photophobia, pallor, coolness of limbs, diminished pulses, and other vascular effects may be present

• if pregnant, obtain obstetric consult as risk of placental abruption
• high voltage > 1000V
  • consider 12-24hrs cardiac monitoring and serial troponins
  • assess for burns, fractures, dislocations
  • watch for compartment syndrome and rhabdomyolysis
• low voltage asymptomatic patients
  • “Routine cardiac monitoring is not required after household voltage electrical injury if the patient is asymptomatic and has normal initial electrocardiography. Asymptomatic patients involved in minor electrical events do not require investigation or admission. ”
    • BestBets.org
• low voltage mild symptoms
  • exclude burns, fractures
  • if ECG is normal and no haemoglobinuria, discharge home after a couple of hours observation is reasonable with follow up of any injuries as indicated