Exploration and Development of Fire Field Identification Technology

Different fire stages will send out their unique signals, and the fire conditions will change rapidly. Accurate identification of fire conditions is essential for the safest and most effective fire-fighting strategy and tactics. Australian fire commander Shan Raffel created a fire field identification method suitable for use by firefighters on the firefield to help firefighters quickly identify fire conditions. This article is streamlined in the previous article "Hard food | fire field identification technology exploration and development."

The identification method consists of five parts: Building , Smoke , Air , Heat , and Flame . The English phrase " BE SAFE " can easily be associated with this method. Fire field identification method " BE SAHF ".

I. " B " - Architectural and Environmental Factors

(I) Construction factors

Type of building and living conditions. The type of building is important information to understand the stages of fire development and the possible collapse of the building. Living conditions will provide information on trapped people and the special circumstances that may be encountered.

House interiors. Good heat-insulating interior materials will limit thermal energy to a hot room, which may accelerate fire growth. In some cases, a well-sealed building can limit the inflow of air and hinder the fire from becoming large. On the other hand, the structure of the light building causes a large amount of air to flow in, resulting in the rapid development of the fire.

Flash fire. If there is enough air, flashover will occur in most buildings. Before the indoor air is exhausted, limiting the inflow of fresh air can reduce the chance of a crash. Thicker brick or concrete walls will absorb a lot of energy, which may delay the crash.

Rekindled. In an energy-saving building, it is more likely to return to ignition because of its good thermal insulation and sealing effect.

Smoke combustion. The more open areas of a building, or structures such as pipes and wells, allow the smoke to spread and accumulate in areas close to a fire room or at a distance from it.

(b) Environmental factors

terrain. The natural terrain of the land or the built environment around the building may cause the direction of the building's wind direction and the change of wind speed, and even lead to extreme "wind-driven."

Extreme temperature. Change has a great influence on how smoke is generated from buildings. Extremely low ambient temperatures will reduce the buoyancy of the smoke. When combined with "low pressure," an inversion layer is formed that prevents the smoke from rising.

Second, " S " - Smoke

Smoke size and area. The size and area of ​​the smoke are the characteristics of the first observed by the firefighters. Sometimes, this method is not reliable, and it may even mislead firefighters to judge the location of the fire, the area of ​​the fire, and the stage of fire development.

The color of the smoke is "for reference only, not all letters." When the flammables are affected by the fire and reach the pyrolysis temperature, lighter smoke (sometimes close to white) is produced.

Brown or light yellow smoke generally occurs in the early stages of pyrolysis of wood materials.

Black smoke usually indicates that the oxygen supply conditions are not ideal.

If the oxygen supply conditions are good, some of the carbon elements will be fully burned by the flame, resulting in a lighter smoke color in the fire field and a yellow flame.

Gray smoke usually indicates that at least some of the combustibles in the room are burning or smoldering.

Smoke thickness (optical density). The thickness of the flue gas is an effective indicator of combustion efficiency. The thickness of the flue gas can also be used as a measure of the continuous burning time.

Smoke buoyancy. When the flue gas shows a rapid up-diffusion and becomes accompanied by tumbling, the temperature of the flue gas is higher. On the contrary, if the smoke rises slowly, even if the smoke flows downwards, the temperature of the smoke is lower.

The height of the neutral surface.

If the neutral surface is far from the ground, it means that the fire is in the initial stage;

If the neutral surface is very close to the ground, there is a high possibility of reversal.

If the neutral surface suddenly rises, the indoor ventilation situation has changed;

If the neutral surface gradually decreases, it usually means that the smoke is accumulating, and the situation of the fire field is shifting to the occurrence of flash fire;

If the neutral surface suddenly drops, it means that the fire is burning fast and violently.

Third, " A " - airflow

Air flow, as a sign of fire characteristics, can occasionally be observed inside the exhaust outlet or inside the fire. Air flow cannot be seen with the naked eye, but its typical characteristics can be demonstrated by comparing the flow rate of the flue gas, the state of flow, and the height of the flue gas in the room or at the smoke outlet.

(a) Bi-Directional Flow Path

When the smoke outlet of the fire site is opened, hot smoke is discharged from the top of the smoke outlet, and cool air flows in from the bottom.

If the velocity of the flue gas trajectory is slow and stable, it means that it is still a fuel-controlled fire field. In a ventilation-controlled fire field, as the development of fire expands, the discharged smoke almost occupies the entire smoke outlet, blocking fresh air from entering the fire.

(B) the unidirectional flow trajectory (Uni-Directiona Shu Smoke / Air Tracks).

Smoke exhaust. Exhaust fumes and flames occupy almost the entire vent, indicating that this is a simple exhaust vent. At this time, there should be at least one air inlet with a cross-sectional area equal to the smoke outlet or an air inlet for driving the air flow into the fire.

ventilation. Open doors and windows may cause the air to continuously flow into the fire and expand the fire. If the air intakes can be closed before the water is extinguished, it will help reduce the development of the fire.

Wind drives. The strong wind blowing into a closed room will lead to a high pressure zone in the room. There is a bi-directional air flow path when there is a vent in the room. When strong winds appear, this unique vent will frequently alternate between a simple exhaust vent and a simple air intake.

Air flow tremors and pulsations. In ventilation-controlled or ventilation-limited fires, the smoke may be pulsed “pushed out” from a small exhaust vent (or gap). If a flue gas tremor occurs, rushing to set up an exhaust port may result in the occurrence of a flashback.

The whistling sound produced by the air flow. If there is a phenomenon of gas flow pulsation and tremor in the fire, it will usually be accompanied by howling, which is a typical symptom before the occurrence of reverberation and a sign of a ventilation-controlled fire field.

IV. " H " - Heat

In general, heat conditions can be better represented in buildings, but partially sealed and well-insulated buildings are less able to show the thermal characteristics of the early stage of a fire.

window. A window that is dark in color and does not see an open flame, when the oily deposits are attached to the inside of the window will make the window black. Glass cracks or cracks. Rapidly rising heat causes cracks in the glass, and slowly rising heat causes the glass to crack (finer cracks).

The paint is blistering or discolored. This phenomenon is easily observed on the inside of lightweight doors, but it is less prone to blistering or discoloration on the outside of heavy or heat-insulated doors.

The temperature of the fire suddenly rose. This phenomenon is usually described as a sign before a flashback or reverberation occurs.

V. " F " - Flame

Putting the "flame" at the end was because firefighters generally saw the open fire and turned a blind eye to other fires.

The size and location of the fire. By observing the open fire outside the building, the location of the fire point can be determined and the direction of the possible spread of the fire can be judged.

Smoke spontaneously ignites. The external flue gas emitted from the exhaust port spontaneously burns, indicating that the internal temperature of the fire is higher than the temperature at which the flue gas spontaneously ignites, and the fire cannot be fully ignited due to too much flue gas.

Specter fire. If the intruder finds that there is a hidden fire in the smoke layer accumulated in a certain area, this may indicate that the incombustible combustibles in the smoke are tending to self-ignition.

Roll burning (Rollover). Once the incomplete combustion of combustibles in the flue gas begins to burn, the ceiling area of ​​the flame fire is tumbling and the indoor radiant heat increases rapidly. This will cause flashing or spontaneous combustion of smoke.

The color of the flame. Traditional textbooks tell us that the burning material can be judged by the color of the flame. If only one substance is burning in the fire, this should be correct. However, if certain conditions change during the combustion process, the same kind of burning material will also have different flame colors.

This article comes from Micro Signal Orange Rescue.