Fires, smoke inhalation and burns: stages, causes, flash over, severity

By Cristiano Antonino On Apr 7, 2023

Fires are a major cause of injury, death and economic damage. Fires inside homes, which are the context in which the largest number of burns in the civilian population occur, are responsible for more than 80% of deaths

The overall mortality rate of burn victims is about 15%, but it becomes significantly higher in younger (especially children under 4 years of age) and older (over 65 years of age) people.

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In industrialised countries, fires are the third leading cause of accidental death, after road accidents and accidental falls

Both morbidity and mortality due to fires have fortunately continued to decline over the years, falling from, for example, 3.3 per 100,000 in 1970 to 2.0 per 100,000 in 1986.

These changes are most likely the result of improved mass education, the use of fire detection equipment, improved rescue techniques and greater standardisation of burn treatment.

Damage induced by smoke inhalation leads to a dramatic worsening of the mortality rate of burn patients: in these cases, smoke inhalation damage is added to burn damage, often with fatal consequences.

About 30% of people admitted to burn centres also complain of smoke inhalation injuries.

These injuries, when associated with third degree or full thickness skin burns, almost double the mortality rate.

The injuries suffered by burn victims are very complex, as they affect most of the important systems and are not limited to the skin and respiratory system.

This article is devoted to the phases and causes of burns, with particular reference to lung injuries in burn victims who have inhaled smoke.

Stages in burns and fire inhalation

Although it is useful to classify the period immediately after the burn into various phases, the complications of each phase, in reality, often overlap.

Several pulmonary complications are associated with each of the phases of the healing process:

A) the first phase, that of resuscitation (first 24 hours) is usually associated with complications related to inhalation of toxic gases, and/or high temperature;

B) in the intermediate, or post-resuscitation phase (1-5 days), complications may occur:

pulmonary oedema
retention of secretions
atelectasis,
adult respiratory distress syndrome (ARDS),
hypermetabolic ventilatory failure;

C) in the late phase (after 5 days), the most frequent respiratory problems are infectious pneumonias, sepsis, pulmonary embolisms and chronic pneumopathies.

The pathophysiological changes associated with burns and smoke inhalation make their treatment extremely difficult.

Although complex, these changes are relatively predictable, which makes the implementation of preventive measures possible.

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Aetiology

Fire, high ambient temperatures, trauma from the destruction of buildings and smoke are the main causes of all fire damage.

Here we deal with smoke in particular.

The smoke present during a large fire, produced in a hypoxic, high temperature environment, is a complex mixture of poisons in a gaseous state.

The type and extent of smoke injuries depend on the heat developed and the chemical complexity of the environment in which the fire occurs.

in which the fire takes place: for example, a small fire developed in a flat has generally lower damage potential than a large fire developed in an industry that has a storehouse of flammable chemicals.

This obviously does not mean that a small fire developed in a small domestic environment cannot be potentially lethal, quite the contrary! In an environment full of flammable substances, such as a home or an office, the air temperature can rise to over 550°C in less than 10 minutes, leading to the spontaneous combustion of carpets, furniture, upholstery, equipment, which is the basis of the so-called ‘flash over’.

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The ‘flash over’ generally appears as a fiery wall starting from the ceiling and emitting tongues of fires through doors and windows

Heat injuries caused by a fire are much more serious in the presence of vapour than when the air is dry.

At the same temperature, steam has about 500 times more caloric content than a dry gas and can burn a larger skin surface area causing deeper thermal injuries to the respiratory system.

Modern furnishings in homes and workplaces release a large number of toxic substances through combustion.

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Various types of aldehyde (such as acrolein) and organic acids (such as acetic acid), which are powerful airway irritants, are released by burning wood, cotton, paper and many acrylic fabrics.

If the fire continues, carbon dioxide (CO2) concentrations can exceed 5%, and oxygen (O2) concentrations fall below 10%.

The reduced availability of oxygen prevents complete combustion and results in the production of the lethal carbon monoxide (CO).

Polyvinyl chloride, which is a component of plastic materials widely used in homes and offices, produces more than 75 different toxic substances when burnt, including hydrochloric acid, phosgene, chlorine and CO.

Burning polyurethane materials, such as nylon and many upholstery materials, can release isocyanates, which are very irritating, and hydrogen cyanide (HCN), which is extremely toxic.

The inhalation of particles released during combustion, which carry toxic chemicals, can lead to distal lung lesions if their diameter is between 0.1 and 5 μm.

Larger particles (e.g. 30 μm in diameter) are filtered out in the upper airways.

Combustion chemicals can generally be divided into two categories: those that are absorbed and cause systemic toxic effects and those that induce inflammatory manifestations in the mucous membrane.

In summary, the type and severity of injuries depend on

on the extent of the skin burn
the degree of the skin burn;
on the type of gases inhaled (which depends on the type of substance that caught fire);
on the temperature of the inhaled gases;
the ambient temperature;
the intensity and duration of exposure to the fire;
the age of the subject;
the general state of health of the victim before the fire.