#combustion termination
Combustion termination. The essence of the process. Methods.
The chemical combustion process
The physicochemical combustion process consists in the interaction of a combustible substance with an oxidizer, resulting in the release of thermal radiation, light and thermal energy with the conversion of the combustible mixture into combustion products.
The chemical combustion process occurs in the presence of a combustible substance, oxygen, and an ignition source. The combustible system consists of a combustible substance and oxygen, and the combustion source causes a reaction in the system.
The chemical combustion process can also occur without the participation of oxygen: chlorine, bromine, nitric acid, potassium chlorate, sodium peroxide, and other substances can cause an oxidation reaction.
The combustion system can be chemically homogeneous or heterogeneous.
A chemically homogeneous system is characterized by the fact that the molecules of the combustible substance are uniformly distributed in the air environment, while in chemically heterogeneous systems this distribution is non-uniform.
The physical and chemical combustion process can be thermal and chain.
Thermal combustion is based on a chemical reaction that can proceed with progressive self-acceleration due to the accumulation of released heat.
Chain combustion occurs in some gas-phase reactions at low pressure.
Both types of combustion can be complicated by the occurrence of thermal self-acceleration. Thermal self-acceleration conditions can be provided for all reactions with sufficiently large thermal effects and activation energies.
Combustion can start spontaneously as a result of self-ignition or be initiated by ignition. Fire safety risk calculation is also performed taking into account knowledge of the combustion process.
Combustion Cessation.
Combustion cessation of any substance is achieved by physical or chemical action on the combustion reaction, resulting in a decrease in the amount of heat released, a decrease in the combustion temperature and, ultimately, the reaction cessation.
Combustion cessation is achieved by several mechanisms.
Based on this, the following combustion termination mechanisms are distinguished: dilution of the concentrations of reactants; isolation of reactants; cooling of reactants; chemical inhibition of the combustion reaction.
In practice, several combustion termination methods are often combined simultaneously.
Combustion suppression by diluting the concentration of reactants is based on diluting the air or combustible substance entering the combustion zone with non-combustible substances until the mixture formed in the reaction zone becomes non-combustible.
The conditions for combustion suppression in this case require that the substances used for this purpose be non-combustible, have low thermal conductivity, have high heat capacity and do not support combustion.
Such substances include: nitrogen, combustion products, carbon dioxide, water vapor.
They can be introduced directly into the flame torch, as well as into the volume of the room where combustion occurs. Combustion is stopped by isolating the reacting substances.
In this case, the combustible substance or combustion zone is separated from the air.
Fire extinguishing agents: solid sheet materials (felt, asbestos, metal lids, etc.), non-combustible bulk materials (sand, talc, etc.), liquids (chemical and air-mechanical foam, water in pure form and with additives that increase its viscosity and wetting ability), gaseous substances (combustion products, nitrogen, carbon dioxide).
Extinguishing by cooling the reacting substances — to a state where the emitted vapors are unable to ignite.
The conditions for stopping combustion, which is carried out by fire extinguishing agents, consist of their high heat capacity, the value of the specific heat of fusion and vaporization, the ability to be evenly distributed over the surface of the burning substance.
Methods of extinguishing a fire.
Methods of extinguishing a fire involve the execution by fire service employees of a specified sequence of actions aimed at eliminating a fire.
Fire safety provides for the main methods used to extinguish a fire, which are divided into the following categories:
- by the place of introduction of fire extinguishing agents:
on the combustion surface;
on the surface of combustible materials protected from ignition;
in the volume of the room where the fire occurs;
in the volume of flame;
in the volume of combustible substances;
- by the time of introduction of fire extinguishing agents:
sequentially and simultaneously — foam attack.
Such methods of extinguishing a fire involve the use of water or water-based extinguishing agents as an extinguishing agent.
The method of extinguishing a fire by sequential introduction of extinguishing agents can be used to extinguish non-spreading fires.
Methods of extinguishing a fire by simultaneous introduction involve the introduction of extinguishing agents to extinguish a fire by several units.
Simultaneous introduction techniques are used to extinguish non-spreading fires when the extinguishing agent used must be supplied within a short time, since it quickly deteriorates under fire conditions or when long-term preparation is required for the application and introduction of the extinguishing agent:
— by the sequence of stopping combustion in the fire area:
this is a simultaneous stopping of combustion in the entire fire area;
sequential stopping of combustion in the fire area;
— by the introduction of the extinguishing agent to the fire area:
introduction of the extinguishing agent to one place of the fire;
introduction of the extinguishing agent to several places of the fire.
The required consumption of the extinguishing agent, for example water, to stop the fire, can be introduced into the fire area in one or more streams.
Various types of fire extinguishers are used as equipment.