Combined Extinguishing of Class D, Class a and Class B Fires

Abstract

The scope of magnesium and aluminium and their alloys in industry, construction and life are expanding over time. As a rule, there are no clean fires of class D, which include combustion of magnesium, aluminium and their alloys. The problem is that the temperature of combustion of magnesium and its alloys can rise above 2800 Celsius degree. Magnesium burns even in the atmosphere of nitrogen and carbon dioxide and such fire is very difficult to extinguish. When water contacts the magnesium or other light metals, the area of fire expands.
 The main purpose of this work is to study the combined extinguishing of light metals fires, Class A fires and class B fires with a special dry chemical powder and high resistance foaming agent.
 The problem of extinguishing fires at objects with the using of light metals (magnesium, aluminium) and their alloys has been explored. Class D fires usually lead to class A and class B fires. They occur at high temperatures, and may cause explosions. Scenarios for the development of fires can be as follows: burning of light metals or solid combustible materials ad initium and light metal fire that requires combined extinguishing methods afterwards. Dry chemical powder formulation for extinguishing class A, B, D and and electrical installations under voltage, which includes: sodium chloride, blast furnace slag, ammophos, aerosol has been developed. Testing of this powder has been carried out in the laboratory using chips of magnesium and aluminium alloys. The combustion area in all experiments has been equal to 2.85 × 10-2 sq. m. The quality of the powder has been evaluated by the intensity of the D class fire and the extinguishing time of the B class fier. Dry chemical powder KM-2 has been tested for extinguishing fires 21B, 1A. and for magnesium alloy chips fires. Combined extinguishing tests were conducted on class D, class A and class B fires in field conditions. Method of combined extinguishing with the dry chemical powder followed by covering the entire burning area with high-expansion foam has been proposed (the fire with total area of 2.5 square meters has been extinguished for 45 s). Extinguishing methods have been tested on model fires. Safety measures for light metal extinguishing have been developed.
 Conclusions: formulation for universal KM 2 dry chemical powder for extinguishing class D, A, B fires, which consists of sodium chloride, ammophos, slag, aerosil, has been developed. Successful extinguishing of class D and B fires has been carried out succesfully; technology of combined fire fighting D and A has been substantiated.

Thermotechnical properties of the fire-extinguishing powder for extinguishing materials based on magnesium alloy chips

“…The determined values of this ratio are given in Table 2. In addition, in view of papers [16,17], we accept the corresponding magnitudes of specific thermal capacity and the density of the fire-extinguishing powder, which are also shown in Table 2.…”

“…At the first stage, there was a study of a thin layer of the extinguishing powder at a lengthy extinguishing process in order to achieve the establishment of the thermal process. In the second stage, several experiments were conducted, for which the establishment of the thermal process was not required [16,17]. After the experiment, the temperature indicators were obtained.…”

“…7) specific capacity С р and density r of the powder have constant values and do not depend on the temperature or thickness of the layer and are accepted according to the data of papers [2,16,17]. In view of the adopted basic provisions for the creation of the mathematical model, two types of processes were considered -stationary and non-stationary.…”

“…For the boundary between the layer of the fire-extinguishing powder and the air, the boundary conditions of the third kind are established [16,17]:…”

“…Using the calculation scheme in Fig. 3, the expression of the finite-differential approximation of the thermal conductivity equation (3) was obtained in accordance with [16,17], which is shown below:…”