It is important for firefighters to know the basic parameters of a fire - a preliminary assessment of the situation is based on them. By orienting yourself in the peculiarities of the incident, you can choose the optimal strategy for saving human lives and property. However, not only fire department workers should be guided by this topic: it is taught in the framework of comprehensive school and university courses, to improve literacy among the general population.
General Provisions
Before considering the main parameters of fire development, you should decide on a concept. What kind of phenomenon is usually denoted by this term? If the combustion process is not amenable to control and proceeds beyond a certain source, this phenomenon can be identified as a fire. The process is both chemical and physical.
Analysis of the main parameters of the fire and their determination are directly related to the essence of the process. Combustion is explained by the rapidly occurring chemical interactions of some materials and oxygen, which is contained in the atmosphere, and oxidation processes occur under its influence. In this case, carbon dioxide, carbon and hydrogen are released. Combustion can be hetero- and homogeneous.
And if in more detail?
So, when choosing a fire extinguishing strategy, the main parameters of the phenomenon include the case belonging to a homo- or heterogeneous type of combustion:
- Homogeneous - this is a fiery burning. The combustible oxidizing component is gas. This is typical for ignition of gaseous media, in the event of a household leak of a substance or an accident at work. This is also possible if flammable liquids evaporate, as well as during the decomposition of certain chemical and organic substances. Often during the decomposition, evaporation and melting of something, gaseous substances can form. The medium formed in this way may catch fire when in contact with air, which causes homogeneous combustion.
- The second type is heterogeneous. Fuel is a solid substance, the oxidizing component is gas. When burning, the substance turns red, the change in color is explained by an oxidative reaction with the release of heat.
Analyzing the main parameters of fire development, it is necessary to take into account that in most cases the oxygen component in the planet’s atmosphere is the oxidizing component. It creates an area of chemical interaction. Consequently, the intensity of the process depends not so much on chemical reactions as on the activity of oxygen inflow into the source of ignition from the surrounding space.
About Zones
The main parameters of a fire are a set of factors that describe the ongoing physical and chemical process. Three zones are distinguished, for each of which individual characteristics and characteristics are determined. Currently, it is customary to talk about the area of combustion, smoke and the influence of the thermal effect:
- Combustion zone - the area where combustible components are directly burned. They heat up, separate fractions disintegrate, evaporate, some decompose.
- The thermal effect area is the space that surrounds the combustion zone. In textbooks that consider the main parameters, zones and stages of a fire, special attention is paid to the impossibility of finding a person in this area without the use of protective equipment.
- Smoky zone - the content of harmful combustion products in the air is so high that visibility is impaired and breathing is difficult. Also, a person is at great risk of poisoning and loss of consciousness.
About specifications
The main parameters characterizing the fire are: load, process propagation activity, heating of the zone, intensity of thermal study, mass reaction rate. Each of them deserves special attention, we dwell on only the main ones.
Considering these basic fire parameters and their definitions, you should first stop at the fire load. This term is used to denote the energy potential of a combustible substance per unit area of a land plot, the floor of an object, and the localization surface of a source. For measurement, it is customary to use energy units or mass units of substances involved in the process. The indicated units are related to the size of the area. Therefore, to describe the fire process, it is necessary to calculate specific indicators in J / m 2 or kg / m 2 .
Continuing the topic of fire characteristics
Considering the main parameters and dangerous factors of the fire, it is necessary to pay attention to the high speed of the ongoing process. This is a quantitative description of how much the mass of combustible substance becomes smaller over a certain time period. The characteristic depends on the relationship of surface areal, volumetric and density parameters, as well as gas exchange capabilities and other characteristic features of the fire. On average, for furniture, the burn-up rate is estimated at 50 kg / m 2 * h, for large wood products, including logs, it is half as much, and for hot lumber stacked in stacks this parameter reaches 400 units.
The third parameter is the main fire hazard. It is about the speed of its spread. To evaluate this quantity, it is necessary to determine how quickly the flame spreads over the surface of a substance subject to combustion. The characteristic depends on the type of burning object, the possibility of ignition and the initial level of heating. The direction of air flows and the size of the individual particles forming the burning material play a role.
This is not to say that there is some characteristic case: the main fire parameter (propagation speed) varies significantly in different situations. The role of the surface angle also plays a role. For example, if it is straight, then down the fire spreads twice as slow as on horizontal planes. But in the upward direction, the burning rate will be almost ten times higher. The higher the initial level of heating of materials, the greater the speed of propagation. If the heating reaches the self-ignition bar, the surface instantly lights up.
Where is it burning?
To calculate the main parameters of a fire, determining the area is one of the main tasks. All cases can be divided into spreading fires, and those that are not. Based on the exchange of mass and heat with the environment around, each situation can be classified as a class of internal or open fires. Internal flow in a fenced area, the second class - when a fire occurs in an open area.
It is known from practice that internal fires in which solid substances burn usually begin to spread from a local flash point. After analyzing the main parameters and stages of the fire, you understand why the process is like this: soon, after the appearance of a local flame, a characteristic gas flow accumulates, due to which oxygen inflow is realized. The temperature rises gradually, the processes become more intense, the flame is more substantial, and the combustion process covers surrounding objects.
Combustion progression
When the temperature in the combustion area reaches 100 degrees (Celsius), if the processes took place inside the building, the windows protecting the window openings crack. This leads to a change in the basic geometric parameters of the fire, as the air flow sharply increases, gas exchange is activated. Burning becomes stronger, the flame spreads beyond the original premises. The risk of igniting nearby objects is increased.
In some cases, the coverage of nearby objects is explained by thermal radiation and the ejection of individual elements of burning structures from the burning area. They can cover a considerable distance in flight, thereby provoking the spread of fire on the surface.
Outside the room where the process began, the basic geometric parameters of the fire may turn out to be quite insignificant - most often this concerns the temperature, the level of which is low enough to constitute a danger to humans. At the same time, one cannot talk about the safety of the process as a whole: if the air is rich in combustion products, this is fraught with a mortal threat to humans. A well-known standard that must be considered when extinguishing fires is the main parameter associated with time. For tall buildings, it’s 5-6 minutes. To avoid human casualties, it is necessary to first organize evacuation measures, only then proceed to eliminate the source of ignition.
How dangerous is a fire?
Special devices, the installation of which is mandatory in buildings, are able to read the basic information parameters of the fire (temperature, smoke) and generate sound signals warning of the danger. As soon as the system is activated, it is urgent to organize the evacuation of people. Some systems may automatically activate priority fire extinguishing devices (sprinklers).
To determine the hazard parameters of a particular fire, it is necessary to find out after what time the situation will become critical and dangerous for human life. This is taken into account when organizing evacuation works. There is a risk of a situation in which evacuation takes longer than the period during which a fire becomes deadly.
Speaking about the main fire parameters associated with danger, they give out the temperature of the surrounding space, since it is dangerous for a person to heat the room up to 60 degrees. It is also worth paying attention to the smoke and filling of air with hazardous substances that can lead to poisoning. On average, the rate of propagation of such substances indoors is estimated at 30 m / min.
One of the main parameters of a fire is the risk of explosion, deformation, and destruction of load-bearing elements and supporting structures. It is possible boiling liquids, their release into the surrounding space. Among others, toxic compounds and rapidly flammable substances can be released in this way. This forces to carry out evacuation work as quickly as possible.
Open fires
According to this scenario, fires occur in forests and steppes, on peatlands, warehouses, open plants, oil and gas fountains. The combustion process is not limited to any structures and obstacles, which makes it intense. The main parameters of the fire, allowing to assess the dynamics of the spread of an open fire, are largely determined by the current atmospheric situation, namely: the wind, its strength and direction.
With an open form of fire, the size of the combustion zone depends on how elements that are able to catch fire are distributed in space. The flows of gases play a role, due to which a combustion zone is formed. The thermal effect depends on the radiant heat flux. Convection provides heat removal to the upper atmosphere. Smoke is only possible with fires in peatlands and forests. In other cases, it does not interfere with the extinguishing and does not create special difficulties.
Considering the main parameters of the fire, it is also necessary to clarify that the highest temperature in an open fire for gas is 1200-1350 degrees. For a substance in the liquid phase - 1100-1300 degrees. For compounds in the solid phase - about 1100-1250 degrees.
Area and duration of the fire
Speaking about the main parameters and fire assessment, it is necessary to take into account one of the basic characteristics - the duration of the fire. This term is used to denote the duration of the time interval between the initial ignition and the termination of the process.
The main parameters for extinguishing fires are precisely the area of the territory covered by fire - this is one of the main indicators. They are guided by him when choosing the optimal approach to eliminating the fire.
Area is a parameter that describes the size of the combustion zone. It is necessary to build a projection (horizontally or vertically). When a fire occurs inside a building consisting of several floors, the total area is determined by summing the parameters for each of the floors. As a rule, a horizontal projection is calculated, but in some cases a vertical description is more suitable. This is typical for a situation when a single structure caught fire, which is characterized by a small thickness and an upright position.
The main parameters include all the above phenomena, and they need to be evaluated by calculating the means and forces that need to be thrown at the localization of the source and its suppression.
Temperature and speed
Considering an internal fire, its average temperature is considered to be the one that develops directly in the source of ignition. With an open form, it is rather difficult to determine the general temperature background, and therefore the averaged values for different parts of the fire are taken as the main indicator.
Considering the main parameters of the development and extinguishing of a fire, it is necessary to take into account the linear velocity of fire propagation. This is a parameter that describes how quickly a fire will cover new areas. Linear speed and area of ignition are very closely interconnected and are determined by the characteristics of materials that can ignite and burn. The spatial arrangement of objects relative to each other plays a role. Linear speed is constantly changing. When assessing a specific fire, it is necessary to identify the average value. This will be an approximate value, but if correctly determined, it will give an idea of the speed of propagation of fire.
A detailed review of the speed of propagation of fire
The highest propagation velocity is characteristic of burning gas spaces. After all, the presence of air in the mixture is already the primary stage of preparation for combustion, and only a heating medium is needed to start a fire. When burning liquids, the speed depends on how hot the substance is.
The lowest propagation rate is characteristic of solids. In order for them to be ready for burning, it is necessary to expend more heat than for the forms of substances described above. The propagation speed is determined by the spatial position of the object, which may undergo a fire.
In addition to linear velocity, the burnup rate is also considered. This parameter allows you to evaluate the intensity of heat generation, from which temperature, activity of the development of the process and its other features follow. The values depend on the state of aggregation of the material subject to combustion.
More on burnout rate
Gases that are capable of burning easily mix with air, due to which there is a complete burnout of the substance. The speed depends on the activity of the evaporation process, the receipt of a new substance in the combustion zone, as well as the conditions under which a reaction with oxygen occurs. In the equilibrium state of a liquid-vapor system, evaporation is determined by the chemical and physical properties of the substance, vapor elasticity and the level of heating. If the system is not in equilibrium, then the intensity is determined by the heating of the upper liquid layer, which depends on the heat fluxes from the combustion region, the conditions of evaporation and heat exchange with the colder liquid layers in contact with the surface.
If a liquid formed by numerous components is burning, the composition of the vapor depends on the evaporation rate and the equilibrium parameters. Burnout is determined by how actively the liquid vapor is mixed with oxygen. This, in turn, depends on temperature, wind speed and the geometric parameters of the source of ignition.
Gases and fire
The rate of gas exchange is a parameter that describes how much air for a certain time period arrives per unit area. It is customary to talk about the required and actual parameters:
- The first reflects how much air is needed for the material to completely burn out.
- The second gives an idea of the real air flow.
The gas exchange rate is relevant for internal fires, when there are structures due to which the air flow is limited, and the gas exchange value can be calculated.
An equally important characteristic is the density of smoke. The parameter describes how much the visibility deteriorates and how dangerous and toxic air is polluted by combustion products. Visibility is worse, the denser the smoke and the greater the thickness of its layer.
Fire load
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Speaking about the fire load in relation to objects built from solid materials, it must be remembered that the structure, placement of parts in space and dispersion have a significant effect. So, different combustion dynamics will be inherent in the boxes and boxes folded in the basement located on storage racks of standard height. The second option will give a much higher fire rate, on average ten times higher.
Features of the combustion process
The openness of the combustion process depends on the particular case. For example, if we are talking about matches, then a three-millimeter gap is enough for the match to catch fire on all sides. But for a square slab of wood with a two-meter rib, even a five times greater gap is still too small for combustion to become free.
Firefighters, calculating the features of each particular case, take into account the free surface as a separate coefficient calculated by the ratio of the surface area on which the combustion is localized to the area of the phenomenon as a whole. For the liquid in the reservoir, this parameter is equal to unity, but in the case of a solid substance, the coefficient significantly exceeds unity. From practice it is known that a lot depends on the materials. On average, for example, for a furniture factory, the coefficient varies between 0.92-4.44.
About fire classification
It is customary to divide fires into groups based on the openness of the outbreak, the type of substance involved in the process, and the means applicable in a particular case to extinguish a fire. For each class, the place of burning, the reasons, the logic of development are individual. Currently, there is no unified classification system, which gives rise to a certain misunderstanding. The simplest option of dividing into groups is to evaluate the space in which the process takes place: open or closed.
Fire extinguishing means and methods
In conclusion, it is worth mentioning the means and methods of extinguishing fires. These include:
- The use of extinguishing agents (foam, sand, water, reagents).
- Use of special installations (hydrants, columns).
- Fire fighting equipment.
- Primary means of localization and elimination of fire.
- Mobile facilities (special vehicles, helicopters and airplanes).
- The means at hand used in the fight against fire in a domestic environment.
All this helps to quickly and effectively cope with fire. But it is better not to act on your own, in case of fire it is worth immediately contacting the appropriate services.