EXPERIMENTAL RESEARCH OF FIRES IN GRASSY ECOSYSTEMS

Abstract

Formulation of the problem. The fire hazard of grass ecosystems depends on many factors that determine the proper condition of the combustible material and support the burning process. The most important indicators of danger are the condition and humidity of grass. The main external factors of influence on the occurrence and spread of fires in natural ecosystems are: air temperature and air relative humidity, precipitation, wind speed. The urgent task is to determine the rate of spread of fires in grassy ecosystems.

The purpose of this work is to establish the features of occurrence and spread out of grass fires in the forest-steppe conditions   of Ukraine on the basis of fire hazard analysis and experimental studies.

Research methods. The studies were conducted in the forest-steppe zone in the Vinnytsia region on November 1-3, 2019. The plots with 10 m in length and 3 m in width were chosen, taking into account the wind direction along the plot. During the studies, the wind speed was in a range of 0 to 10 meters per second, the air temperature varied from 7 to 14 Celsium degrees during the day and from -3 to 12 Celsium degrees at night. The air humidity varied from 52 to 69 per cent during the day and from 72 to 84 per cent at night. The humidity of the grass was 20-22 per cent in the daytime, and 27-30 per cent at night. The fire load on the sites was 4-5 t/ha.

The main results of the study. Combustion mostly did not happen since 19 p.m. till 10 a.m. because the grass cover during the night increased the moisture content due to the relative humidity increasing and drop of temperature. After 10 a.m. in clear conditions and in the presence of wind, the humidity of the grasses decreased, which facilitated their ignition and spread of fire. However, in the absence of wind, ignition did not happen.

The fire spreading rate depended on wind speed and grass height. For grasses 40 cm high the fire spread rate was from 2.5 m/min (wind speed 1-2 m/s) to 3.5 m/min (wind speed 6-8 m/s). For grasses 60 cm high the fire spread rate was from 3.1 m/min (wind speed 1-2 m/s) to 12.5 m/min (wind speed 6-8 m/s).

Conclusions. The rate of fire spread in grassу ecosystems depend on temperature and relative humidity, wind speed, grass humidity, height and spatial location. At night, the high humidity of grasses, caused by high relative humidity and low air temperature, hinders ignition and burning, but the fire may occur in the presence of wind in the presence of several sources of ignition with sufficient energy.