Dear comrades,

Every day we deal with "fire."

But do you really understand your "enemy"?

You know different smoke colors and different forms of smoke

What do you mean?

Come and follow the Australian Fire Commander

To unveil the mysterious veil of the "enemy."

Knowing yourself and knowing yourself, you can only be victorious!

First look at what the fire commander said?

During the first 14 years of my firefighters' career , I participated in a large number of fire fighting operations and discovered many unusual fire phenomena. The firefighting materials at the time were very vague about the nature of the fire . I therefore asked whether many firefighting “old drivers” could answer the meaning of different smoke colors and different forms of smoke for me . Unfortunately, no one gave me a clear and consistent answer.

I began to seek answers from the fire agencies of other countries. To my surprise, fire protection agencies in other countries also lacked relevant theoretical knowledge, except for Sweden. In the late 1970s, Krister Giselsson and Mats Rosander (Swedish firefighter and fire engineer) discovered that in the energy-saving buildings, due to the proliferation of modern furniture made of plastic materials, a new fire environment was being created. They used new research results to challenge traditional indoor fire characteristics and fire fighting tactics.

So, I started a journey of learning fire characteristics, and more importantly, these theoretical knowledge will be transformed into fire fighting tactics for use by fire fighters all over the world. In this article, I will tell you how to learn fire characteristics, especially some unusual or unexpected fire characteristics.

I. Signs and signs of flashback and rekindling

At the end of 1999 , it took me almost three years to develop and establish a fire characteristics identification training program across the country, and described the characteristics of flashover and reverberation using “signs” and “signs”.

( i) Signs and indications of a flash fire 1. A ventilated fire site;

2. The combustible surface temperature is high;

3. The flame is on the ceiling;

4. The neutral surface of smoke is reduced;

5. Increased pyrolysis rate of combustibles;

6. The irregular flow of smoke on the neutral surface is more obvious;

7. The firefighters are forced to lower their body temperature;

8. Painful radiant heat.

( b) Signs and signs of rejuvenation:

1. Flue gas emerges from the gap in the vent and is inhaled;

2. The fire is not big or the fire has no smoke;

3. Very thick black, yellow smoke or flue gas temperature is low;

4. The color of the flame is blue;

5. Door and window temperature is higher;

6. The window becomes black and black;

7. There may be no open fire or open flame that cannot be easily found;

8. Outdoor air is sucked into the room to generate whistle sound;

9. What are the effects of combustibles of different types, types, and materials?

10. The fire has burned for a long time.

These signs and signs have already been proved by actual combat, and they have been helpful in distinguishing the phenomenon of flashover and rekindling. However, I still feel that the signs corresponding to these phenomena are not yet complete. Some of the cases I have studied show that these signs and signs rarely occur before firefighters encounter sudden and accidental fire accidents.

In 2000 , a fire broke out in a restaurant converted from an old-fashioned movie theater, and I went through this fire extinguishing operation. The smoke from the basement fire passes through the floor and accumulates in a larger ceiling area. When I realized that the fire was going to develop in the area, I ordered the firefighters to evacuate quickly, but before completely withdrawing from the area, the accumulated smoke gas burned violently and the ceiling fell due to high temperature. The water jet from outside the wall delayed the spread of the fire so that we could safely evacuate. This fire has taught me that if we really understand the characteristics of fire in the fire and predict the development of fire, we still have a lot of work to do.

Second, the impact of modern fire load

At present, the main problem in the description of fire characteristics in existing fire prevention textbooks is that the theoretical research is based on the fire load of traditional materials, while modern home furniture and articles use more plastic products.

The synthetic material extracted and processed by petroleum releases 2-3 times as much energy as wood, cotton and paper products . Not only does the combustion produce more heat, its more complex molecular structure requires better oxygen supply, and at the same time, it is more prone to burning in high-temperature environments. Therefore, these changes mean that the more synthetic materials are used in the house or workplace, the higher the content of combustibles that are not fully burned in the smoke after a fire has occurred. These fumes will form a flammable gas mixture and spread around the fire point. When the conditions permit, these fumes will be ignited.

Traditional textbooks mainly emphasize the dangers of smoke, smoke, and smoke, but they ignore the smoke that is mixed with air, spreads indoors, and has a lower temperature and thinner thickness. It is easy for firefighters to create an illusion: It is not too dangerous here. But in fact, the smoke after mixing air will be more likely to burn. If the accumulated flue gas reaches the ideal mixing state, the flue gas will ignite rapidly and release a huge amount of energy, even a deflagration (explosion) of the flue gas.

Third, smoke combustion

Combustion flue (FireGas Ignition) is a broad meaning of the term fire, characterized in case of occurrence of knocking is mainly smoke and the like. Occasionally, the manifestation of smoke combustion can be erroneously considered to be flare-up or rekindling. The magnitude of the power generated by the flue gas combustion is related to the content of unburned combustibles in the flue gas and the concentration of mixed air, and the final manifestations are often very different. It is for this reason that I do not agree with any fire term that contains the word “deflagration”.

Personally, I would use the term "flue gas combustion" to define this phenomenon: the accumulation of combustible flue gas or combustion products in the flue gas is ignited, the flue gas continues to burn or is changing into a burning state . If the amount of incompletely combusted flammables in the flue gas is low, then the form of flue gas combustion will be close to flashover; if the content is high, it will be similar to backfire ( producing a fireball); if the flue gas is mixed When the air content reaches an ideal state, then there will be smoke explosion (explosion).

Therefore, the signs and symptoms of smoke combustion are mainly:

1. The smoke flows out through the smoke outlet or crevice;

2. Smoke accumulates in areas with no open flames;

3. The temperature of the flue gas is not high and thin because it is mixed with air;

4. It is difficult to find accumulated smoke in hidden or unexpected areas;

5. The areas where these smoke accumulations may show signs of low temperatures;

6. Because the temperature is not high, firefighters are mistaken for safer areas.

Fourth, the fire field identification method

After understanding why the smoke is burning, creating a simple and accurate firefield recognition model has become a challenge. Because I found it difficult to use accurate vocabulary to define the signs and symptoms of high fire conditions and rapidly changing fire conditions. Although it is useful to define "signs and symptoms" of fire characteristics in teaching, it is very difficult for firefighters to quickly and accurately recall various fire characteristics when they are in the fire. I pondered to establish a fire field identification method that is relevant and easy for firefighters to remember, to help firefighters quickly identify fire conditions, and improve firefighters' ability to anticipate fire development trends.

Eventually, firefield identification methods based on the order of importance (flue gas, air flow, heat, and flame) were born (this part of the following section is excerpted from the article recently published by the author of this article in 2017 : “The Understanding of Language of Fire: Be Safe. Think, ' Be SAHF '").

( I) Identification of smoke characteristics

1. Smoke size and area. The size and area of ​​the smoke are the characteristics of the first observed by the firefighters. Generally speaking, firefighters can use these characteristics to determine the location of the fire point and the area of ​​the fire field. But 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. Flue gas can travel through more concealed areas or inside buildings and wells, and eventually emerge in unexpected places. If a vertical smoke vent is not provided in a fire room, hot smoke will rise vertically to the roof due to buoyancy and spread horizontally around the roof area. At the same time, many firefighters have a similar experience: initially found a large amount of smoke, but later found that the fire is very small, and even the fire point is not in the smoke accumulation area. This tells us that all the characteristics of the fire are very important, firefighters should not be out of context, point of view.

2. The color of the smoke "The content of this paragraph is not absolute, different combustibles burning color is also different, the following content is for reference only." The combustibles of different types (solid, liquid, and gaseous) and materials, as well as the ventilation and smoke exhaust conditions of the fire, can affect the color of the smoke. Smoke color can usually be used as a sign to determine the fire burning rate in a room.

When combustibles reach the pyrolysis temperature due to the influence of fire, lighter-colored fumes (sometimes close to white) are produced, the volatile components of the combustibles are released, and the solid carbon is left in the combustibles to form coke. . If the heat of the fire field continues to rise, even if the internal oxygen is not enough, even smoldering, but still produce white smoke. An important understanding of the development of fires is that the heat in the fire will be transmitted to the neighboring rooms and lead to the pyrolysis and spread of combustibles. The white flue gases produced by the pyrolysis of these combustibles may flow to areas where no fire has occurred and continue to accumulate. Even though these flue gases may not be warm, their energetic energy is high, if the accumulated white smoke is cited by the fire. Burning will produce sudden and intense burning. It should be noted that after the fire is extinguished, the smoke will turn white, because the smoke is mixed with water vapor.

Brown or yellowish smoke is generally the early stage of the pyrolysis of the wood material. The tar in the wood is released, resulting in a brown or light yellow flue gas.

Black smoke usually indicates that the oxygen supply conditions are not ideal. At this time, when burning with flame or smoldering occurs, carbon in the combustible will produce black soot and enter the smoke layer, causing the color of the smoke to turn black. If the combustion process is less oxygen or the combustibles are too full, the color of the smoke will become very dark. 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. As the black smoke generated by the combustion is mixed with the pyrolysis fumes of white combustibles, the smoke is gray.

3. Thickness of smoke (visually presented density). The sign reflects the thickness of the flue gas combustion efficiency. In the early stages of a fuel-controlled fire, the amount of smoke produced is small because of the better oxygen supply conditions . If it is developed into a ventilation-controlled fire, the efficiency of combustion will be reduced and the amount of smoke generated will increase. A poorly ventilated fire will produce a lot of black smoke. At the same time, the thickness of the flue gas can also be used as a measure of the duration of continuous burning. For example, in a ventilation-controlled fire, a small fire will continue to burn for a long time and a large amount of black smoke will be produced.

4. 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 lower buoyancy of the flue gas indicates that the temperature of the fire is not high, or that the temperature of the flue gas is reduced due to the spread of flue gas to the area where no combustion occurs in the fire (the situation of the fire at this time is not necessarily safe).

5. The height of the smoke neutral surface. With the development of fire, the neutral surface of flue gas ( the boundary between hot flue gas and cold air) will gradually reduce to the ground, and the thickness of flue gas will increase. Therefore, if the flue gas neutral surface is far from the ground, it means that the fire is in the initial stage; if the flue gas neutral surface is very close to the ground, it means there is a greater chance of reversion; if the flue gas neutral surface suddenly rises , indicating that the indoor ventilation situation has changed; if the gradual reduction of the smoke neutral surface, usually shows that the smoke is accumulating, the fire situation is changing to the occurrence of flashover; if the flue gas neutral surface suddenly decreases, indicating that the fire is fast, violent combustion.

( B) identify the characteristics of air flow

Air flow as a fire characteristic can occasionally be observed inside the exhaust or fire field. 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. Combined with the characteristics of the flue gas in the previous section, we call it the flue gas trajectory / air flow trajectory. This is extremely important for firefighters to control the smoke emission in various areas of the building (including the fire smoke plan and the unplanned smoke exhaust).

Bi-directional air flow path (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.

Smooth and steady airflow. If the flue track / track velocity is slow and gentle stream stable, indicating a fire in its early stages, and it is likely to be a fuel-controlled fire.

Rapidly flowing air. In a ventilation-controlled fire field, as the fire develops , the need to supplement the oxygen while generating a large amount of high-temperature smoke (since the exhaust port is small) occupies almost the entire exhaust outlet, blocking fresh air from entering. Fire site. This will lead to a sudden surge of smoke on the neutral surface.

Unidirectional smoke / gas stream track (Uni-Directiona Shu Smoke / Air Tracks). Exhaust fumes and flames occupy almost the entire vent, indicating that the vent is a simple vent (with almost no responsibility for entering the air). Since the smoke and flame are directly discharged from this exhaust port, there should be at least one intake port with a cross-sectional area equal to the exhaust port or an inlet port for driving the airflow into the fire field.

Open doors and windows may cause the air to continuously flow into the fire and expand the fire. As previously described, each one-way vent requires at least a cross-sectional area of ​​air intake (unless the air inlet is under the influence of wind). If the air intakes can be closed before the water is extinguished, it will help reduce the development of the fire.

The strong wind blowing into a closed room will lead to a high pressure zone in the room. Normally, when there is a vent in the room, there will be a two-way air flow path, which may occur in a fuel-controlled fire field (fluid and steady air flow in the smoke exit), or in a ventilation-controlled fire (exhaust tone) Flow surged.) 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). This indicates that the pressure in the fire field has changed due to limited oxygen supply. As the oxygen content continues to decrease, the development of the fire is severely affected, and the internal temperature of the fire field will decrease, causing the volume of the flue gas to shrink. The negative pressure generated will draw air from the small smoke exhaust port (or crevice) into the fire. These air entering the fire will increase the fire and the temperature of the fire. The expanded smoke will, due to pressure, “push” the outdoor from a small exhaust vent (or gap) until the air is again drawn into the fire. The process continues to cycle. In some cases, after the above situation occurs, if a smoke vent is rushed to open, it is likely to cause a flashback.

The whistling sound produced by the air flow. If there are pulsations and tremors in the fire, it is usually accompanied by a whistling sound (due to changes in the pressure of the fire, air flow through the gap inhalation or discharge from the fire field), which is a typical sign before the occurrence of reverberation, but also ventilation Controlled fire sign. However, due to the noise in the field, firefighters may not notice the whistle produced by the air flow.

(c ) Identify thermal characteristics

After the firefighters arrive at the fire site, they should conduct investigation and judgment on the high-temperature characteristics of the site. 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.

The window is dark and there is no open flame. In many cases, the window may become black ( including potential backfires), and oily deposits are usually attached to the inside of the window. If double or triple glass windows are used, this feature is difficult to observe.

Glass cracks or cracks. Rapidly rising heat causes cracks in the glass. Slowly rising heat causes cracks in the glass (finer cracks), and is usually blackened by the presence of oily deposits on the inside of the window. This indicates that the temperature of the fire is high. , More combustibles.

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. First, firefighters can touch the surface of the door or the doorknob by hand to feel the approximate temperature in the room. Then, a little flowering water can be sprayed on the surface of the light door. If the door temperature exceeds 100 ° C , the water in the upper part of the door will quickly evaporate. In some cases, this approach can also be used to determine the general height of the smoke neutral surface.

The temperature of the fire suddenly rose. This phenomenon is usually described as a sign before a flashback or reverberation occurs. If you only rely on "abruptly rising fire temperature" in the fire to determine if flashback or rejuvenation will occur, then you are likely to overlook other fire characteristics. "Suddenly increase in the temperature of the fire field" generally occurs after the combustion of the upper-level smoke in the room (ie, after the flare-up phenomenon). For firefighters, revolving is not easy to observe and therefore cannot be pre-warned. Over time, when the firefighters wearing personal protective equipment feel the temperature rise, the fire scene has become very dangerous.

Using a thermal imager to determine the temperature of the fire is the best way. Spraying flower water on the indoor roof is another simple way to check the temperature of the fire. "However, it is very important for shooting skills." If waterdrops fall to the ground, the roof temperature is less than 100 °C . If the waterdrops do not fall, the roof temperature exceeds 100 °C . In addition, firefighters can also experience the changes in temperature with protective gloves.

If you do not feel too high a temperature through the gloves, you can flip up the lower opening of the glove to let the exposed skin feel the temperature of the upper room.

( d) Identify the characteristics of the flame

Putting the "flame" at the end was because firefighters generally saw the open fire and "turned a blind eye" on 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. This helps firefighters to find multiple ignition points in the building and realize that these open fires are likely to have spread from the initial fire point.

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. After the extremely hot flue gas is exhausted, its flammability will be reduced by (air) dilution. If the temperature of these flue gas is still higher than the auto-ignition temperature, it will still burn. When this happens, if the air inside the fire field is increased (for example, a fireman opens an exhaust fume outlet), the indoor fire suddenly ignites. At this time, the scientific safety practice is to close the door before extinguishing the fire. Prior to the implementation of smoke extraction, watering the fire area can cool the smoke below the auto-ignition temperature and greatly reduce the possibility of extreme phenomena.

Specter fire. If the intruder finds a hidden light that is present in a layer of smoke that accumulates in a certain area, this is likely to indicate that the incombustible combustibles in the smoke are tending to the state of spontaneous combustion of the smoke. Firefighters should immediately cool the smoke layer and retreat to a safe area.

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. At this point, firefighters should shoot water in the ceiling area to prevent or slow down the onset of flare-ups. If the shot cannot reduce the heat release rate, firefighters should immediately retreat to a safe area.

The color of the flame. "For reference only, the color of different combustibles may also be different." 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. But more importantly, if certain conditions change during the combustion process, the same burning substance will also have different flame colors. For example: When liquid propane is premixed with air, the flame is a blue flame when burning (because carbon dioxide is produced). If liquid propane diffuses during mixing with air, the flame will appear yellow because the carbon material produced reduces the efficiency of combustion. Liquefied petroleum gas produces a red flame when burned in an oxygen-deficient or fuel-rich environment. Another example is: particleboard burning in the room, if the oxygen supply conditions are better, the flame is yellow, whereas the flame is orange.

In an indoor fire, a yellow flame usually indicates that the indoor oxygen supply conditions are good. If the oxygen supply conditions are poor, the flame will turn orange or red. If there is more indoor combustibles (and less air), the flame will be orange and the flame will pulsate (fluctuate) more rapidly; the pyrolytic white smoke will ignite to produce a pale yellow flame, and sometimes the flame is almost transparent. in this case, the flame beating (volatility) will be more slowly down the spread of the flame will be to find more oxygen.

V. Impact of Buildings on Fire Characteristics

In 2005 , I conducted training with Ed Hartin at the National Fire Protection Research Institute in Malaysia. Ed and I work long-term, we have been compiled as a co-author with "3D firefighting tactics" (3D Firefighting), and we have conducted discussions on the details of the fire recognition. He suggested that I add the word “buildings” in the “Fume, Air, Heat, Flame” fire field identification method, namely: Buildings—Fume, Air Flow, Heat, Flame ( B-SHAF , English for Be- Safe) .

Initially, I thought this was a good idea until I realized the importance of it. While serving in Brisbane (Eastern Port City, Australia), I have accumulated a lot of practical experience. In this hot and humid subtropical climate city, keeping indoor cool in winter and cool in summer is an important part of building construction. Because the building uses single-glazed windows and light-insulated walls and doors , firefighters can easily observe open fire after a fire. At the same time, after the fire burns glass or burns through the roof, it will cause the building to be in an “independent” state of ventilation and smoke exhaust.

The focus of my discussion with Ed was on different building construction methods, which would have a significant impact on what fire characteristics. Houses built in temperate climate regions are usually insulated with double- or triple-glazed windows, which not only affects the fire characteristics in the event of a fire, but also seriously affects the development of the fire.

Looking further, the global development trend of energy-saving buildings and the extensive use of composite building materials have made it difficult for firefighters to predict the speed of fire development and the time the houses collapse. Firefield identification technology will help firefighters, but only by mastering all the key elements of a fire can an accurate judgment be made. Obviously, this is not possible for firefighters who have only arrived at the fire for a few minutes. Therefore, we need to think repeatedly, evaluate the structure of the building in the fire, and make judgments on our firefighting and rescue operations, because sometimes the characteristics of certain fire phenomena are difficult to observe.

Now, I try to describe the relationship between building structure and smoke flow and fire development. Different types of buildings will have a huge impact on fire development and structural stability: If there is sufficient oxygen supply, most buildings will have a fire. A flash fire will occur. Before the exhaustion of indoor air (due to burning), if the fresh air is restricted from flowing in, the chance of a flashover can be reduced. Thicker brick or concrete walls will absorb a lot of heat and help delay the occurrence of flashovers.

Energy-saving buildings are more likely to return to combustion due to better insulation and containment effects (usually double- or triple- glazed windows). Fire before flashover oxygen may have been depleted, the fire may be insufficient oxygen due to the fast fading, resulting in a large accumulated amount of flue gas combustion products. Good indoor thermal insulation and double-glazed windows make it difficult to eliminate indoor heat, and some of the heat characteristics will become insignificant.

In areas where the building is relatively empty, such as pipes and wells, or ball frame structures, large open spaces, high ceiling heights, and ceiling areas are more prone to flue gas combustion. The above areas or parts allow the smoke to accumulate and spread around. Due to the renovation of the house , it is possible to construct an unexpected smoke vent or an empty area. Old or damaged smoke / fire facilities can be found in the building . The incompletely combusted products in the flue gas are continuously mixed with the air, and finally the flue gas reaches a flammable and flammable state.

VI. Why Identify Fire Characteristics

Identifying fire characteristics can help firefighters determine the location of the fire point and anticipate the direction and trends of fire development. Judging whether the fire is fuel-controlled or ventilation-controlled is a key factor in identifying fire characteristics. If the building is filled with a large amount of smoke, it is likely to be a ventilated controlled fire field. If the smoke is blindly discharged (including firefighter tactical exhaust or passive exhaust due to window damage), the rapid spread of fire can easily occur. Burning violently. Firefighters must recognize the changes in the fire field after the smoke exhaust, and formulate corresponding tactical measures to minimize the potential danger of the fire. These tactical measures include: before the water guns, main lines, and water supply are ready to be put into place, keep the interior of the fire building in a restricted-air-ventilation state and delay the smoke emission; before the smoke-exit mouth is opened, water is sprayed to cool the smoke. Fuel controlled fire after opening the exhaust port, although rarely violent reaction fire, but smoke tactics to reduce or limit the build-up of flammable fumes still have an important role. At the same time, the jets before and after the entrance to the door are cooled, and a safe area is established by cooling the wall jet water in advance. The tactics of positive pressure ventilation, smoke exhaust, and cooling of the smoke layer can reduce the dangers of fuel-controlled fire sites.

Seventh, the next direction of development

Firefield identification technology is still in the development stage. Only by strengthening the cooperation with aggressive, knowledgeable and experienced global firefighters and fire scientists can we continue to improve maturity. We must not be reluctant and self-styled. We must build a bridge of knowledge between firefighters and fire scientists. In recent years, a group of "new-born" fire scientists have emerged. They do not think that fire fighting is the "low-end" science of fire prevention and control. For example: Stefan Svensson ( Sweden ) , Steve Kerber ( UL ) and Dan Madrokowski (NIST) who have been working hard to use scientific methods and methods to improve firefighters' ability to extinguish fires. Through their unremitting efforts, firefighters will gain a deeper understanding of the fire characteristics and further reduce the number of firefighter casualties. At the same time, it also requires each firefighter to devote himself to the study of this emerging science, and to adjust fire fighting and rescue tactics in real time based on fire characteristics and fir

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