INJURY DUE TO HEAT AND ELECTRICITY

The heat source may be dry or wet; where the heat is dry, the resultant injury is called a ‘burn’, whereas with moist heat from hot water, steam and other hot liquids it is known as ‘scalding’.

Burning

1 first degree – erythema and blistering (vesiculation);

2 second degree – burning of the whole thickness of the epidermis and exposure of the dermis;

3 third degree – destruction down to subdermal tissues

Where the burnt area exceeds 50 per cent, the prognosis is poor even in first-degree burns.

Clinical conditions due to high heat exposure

1.Heat cramp- miner’s cramp, fireman’s cramp due to rapid dehydration through loss of water and salt in the sweat, severe and painful paroxysmal cramp of muscles of leg, abdomen, arms.

2.Heat prostration- heat exhaustion, heat syncope, heat collapse.

Is a condition of collapse without increasing body temperature, which follows exposure to excessive heat.
Precipitated by muscular work and unsuitable clothing
Patient usually recovers if placed at rest but death may occur from heart failure.

3.Heat hyperpyrexia or stroke- characterized by rectal temperature more than 41 degree centigrade and neurological disturbance as psychosis occurs.

Term sunstroke used when direct exposure to sun is there.
High temperature, increased humidity, muscular activity and lack of acclimatization are the principle factors in initiation of stroke.
Failure of cutaneous blood flow and sweating, the factors which control the body temperature, lead to breakdown of heat regulating centre of hypothalamus.

Burns in a victim of a house fire.

Scalds:

Runs or dribbles of hot fluid will leave characteristic areas of scalding – these runs or dribbles will generally flow under the influence of gravity and this can provide a marker to the orientation of the victim at the time the fluid was moving.
Scalding is seen in industrial accidents where steam pipes or boilers burst and it is also seen in children who pull kettles and cooking pots down upon themselves.

The examination of bodies recovered from fires

The findings of soot in the airways and carbon monoxide in the blood indicate that the person was breathing after the fire began.

Post mortem findings

A.External:

Burnt fabrics
Smell of kerosene, petrol over fabrics
Postmortem hypostasis and rigor mortis can not be assessed
Face is swollen and distorted,
Tongue protruded and swollen and may be burnt
Froth at mouth and nostril due to pulmonary edema due to heat irritation of air passage and lungs
Pugilistic attitude (boxing, defense attitude)- characteristic of great heat exposure; the flexor muscles being bulkier than extensor contract more.
Heat rupture in severe burning or charring, skin contracts and heat ruptures occur
Flash burn due to sudden ignition or explosion of gases

B.Internal:

1.Heat hematoma- has the appearance of extra dural hemorrhage

Clot has honey comb appearance
Parieto-temporal region is the most common site of such hemorrhage

2.Thermal fracture of skull-

3.Laryngeal edema

Scalds of the buttocks and feet on a child who had been dipped into a bath of extremely hot water as a punishment.

Trachea showing soot and mucus following inhalation of fire fumes and smoke.

Skin splits in the victim of a house fire. These splits were initially thought to be incised wounds.

ELECTRICAL INJURY

Usually, the entry point is a hand that touches an electrical appliance or live conductor,
The exit is to earth (or ‘ground’), often via the other hand or the feet.
In either case, the current will cross the thorax, the most dangerous area for a shock because of the risks of cardiac arrest or respiratory paralysis.
When a live metal conductor is gripped by the hand, pain and muscle twitching will occur if the current reaches about 10 mA.
If the current in the arm exceeds about 30 mA, the muscles will go into spasm, which cannot be voluntarily released because the flexor muscles are stronger than the extensors; the result is for the hand to grip or to ‘hold on’.
This ‘hold on’ effect is very dangerous as it may allow the circuit to be maintained for long enough to cause cardiac arrhythmia, whereas the normal response would have been to let go so as to stop the pain.

If the current across the chest is 50 mA or more, even for only a few seconds, fatal ventricular fibrillation is likely to occur.
The victims of such an arrhythmia will be pale.
Even more rare are the instances in which the current has entered the head and caused primary brainstem paralysis, which has resulted in failure of respiration.

The electrical lesion

Where the skin is wet, there may be no signs at all, as the entrance and exit of the current may be spread over such a wide area that no focal lesion exists.
Usually, however, there is a discrete focal point of entry.
The focal electrical lesion is usually a blister, which occurs when the conductor is in firm contact with the skin and which usually collapses soon after infliction, forming a raised rim with a concave centre.

The skin is pale, often white, and an areola of pallor (due to local vasoconstriction) is a characteristic feature. The blister may vary from a few millimetres to several centimetres.
The skin often peels off the large blisters leaving a red base.
The other type of electrical mark is a ‘spark burn’, where there is an air gap between metal and skin.
Here, a central nodule of fused keratin, brown or yellow in colour, is surrounded by the typical areola of pale skin.

The electric mark (Joule burn):

It is specific and diagnostic of contact with electricity
It is found at the entry point.
These are round or oval, shallow craters, 1-3cm in diameter, and have a ridge of skin of about 1-3 mm height.
The crater floor is lined by pale flattened skin
When the contact is prolonged, there may be charring.
Produced by conversion of electricity into heat within the tissue.

Exit mark:

Variable feature, but have some of the features of entrance mark
May be more damage of tissue
Often seen as splits in the skin, continuous or interrupted
Ante mortem electric burns can not be distinguished from postmortem electric burns