Fires: Predisposing factors for fires

Fires: Predisposing factors for fires


Factors predisposing to fires

In recent years, the problem of forest fires has taken on dramatic dimensions to say the least, so much so that it has aroused a cry of concern at all levels.

In the past decade in Italy, more than 500,000 hectares of forest have been lost for this cause, nor have the reforestation and forest reconstitution actions managed to remedy the recent devastation.

Every year, almost at pre-established deadlines, this very serious problem is repeated, with enormous damage, both directly economic and ecological, and only the preventive and extinguishing action ensures that it can be contained and limited.

It is good to remember that the gravity of the phenomenon affects the forest in all its multiple functions, causing direct and indirect damage.

The first, easy to evaluate, are represented by the value of the wood mass; the latter, more difficult to estimate, are connected to "priceless" functions, such as: hydrogeological defense, oxygen production, naturalistic conservation, tourist attraction, job opportunities for numerous categories.

The fire of the forest is a very rapid decomposition process, which occurs only in the presence of fuel, such as the vegetable material, oxygen and a small quantity of high potential heat, which determines the chain development of the process itself.

The outbreak of a fire therefore has a triggering cause, the spark, and a predisposing situation for the phenomenon, represented by the more or less pronounced dryness of the soil and vegetation.

There is no doubt that the climatic factor and the seasonal trend have a considerable influence in creating favorable conditions for the development and propagation of forest fires, and in the case of lightning, also in determining them directly, a circumstance, but not very much. frequent. Of considerable importance is the degree of humidity of the vegetation, in particular the herbaceous one of the undergrowth, which varies directly with the seasonal trend. Forest fires, while following the climatic trend, do not occur uniformly on the territory: there are areas where this danger is greater than in others, as experience and facts confirm annually. It is meant that, with the same climatic conditions and dryness coefficient, there are other different situations that favor the development of fires in the woods, such as: the influx of tourists, the rural abandonment of the countryside, the activity of particular agronomic and pastoral practices, vendettas, speculations.

Thus, depending on the location of the forest and its specific relationship with the situations mentioned, there are stands more exposed to the danger and risk of fire, compared to others, where social and human factors are less accidents. . Based on the meteorological and climatological trends, we must record two periods of serious danger: the summer one, in the months of July, August, September, more marked in the central-southern regions, including Liguria; The other winter, in the months of January, February and March located in particular in the areas of the Alps, such as Liguria, Piedmont, Lombardy, Veneto.

In both of the aforementioned periods, even if with different intensity and while varying from area to area, the dry conditions are determined, predisposing the phenomenon.

Generally, the determining cause of the forest fire is anthropogenic, except for cases due to lightning. Self-combustion, often cited inappropriately, is to be considered a very simplistic and erroneous justification, as, in our climates, it only occurs in very exceptional cases and at most limited to barns or landfills only.

The conditions that influence both the initiation and the first spread of the fire are mainly represented:

  • the amount of water found in plant tissues, which can vary from 2 to 200% in dead tissues, depending on atmospheric conditions and in particular on the relative humidity of the air;
  • from the wind, which in addition to favoring the influx of oxygen, as a comburent, determines the advancement of the fire line, provokes the preheating of the wood material and therefore new starting and continuation points of the fire;
  • the quantity, dimensions, dispositions of combustible materials, which, if thin and not pressed, offer a greater external surface to the oxidizing oxygen.

The favorable conditions for the start of the fire in the forest occur more frequently in the presence of dried dead cover, with young stands, especially of resinous lucivagus essences.

The different meteorological conditions: rainfall regime, dominance of the winds, together with the different forest types, their management and treatment, influence the seasonal frequency of fires.

N.B. The information reported was elaborated from the news published by the State Forestry Corps