@Everyone, how can people save lives by trapped fires?

1, the process of fire development

Using the schematic diagram of fire development stage, to consider the causes of each fire development stage and the connection between them is an important means to strengthen the study of fire characteristics. The traditional fire development diagram shows the initial stage of fire, development stage, complete combustion stage and extinguishing stage.

However, traditional diagrams have obvious limitations and can mislead fire fighters. If a flammable object is placed in a large room with sufficient oxygen content or placed outdoors, its combustion process will be consistent with the schematic diagram.

However, in modern houses, the indoor oxygen content is limited, the fire will show the initial stage, development stage, extinguishment stage, ventilation and smoke exhaust (either firefighters may open the exhaust vents or windows may be damaged by heat), the fire is back in Development stage, complete combustion stage and extinguishing stage.

The following figure shows the changes in the average temperature of the roof of a fire room during all phases of fire development in all single- and double-storey dwellings. The red line is a single-storey house and the blue is a double-storey house.

2, open the door to the house is also exhaust smoke

We usually tell new recruits that exhaust fumes help vent heat and fumes in the room. The definition of ventilation and smoke exhausted by the International Fire Training Association ( IFSTA ) is to systematically discharge the high-temperature toxic smoke in buildings while replacing them with fresh air.

But the problem is that, after the ventilation and smoke exhaust openings are opened, the air can enter the room and the oxygen in the three elements of the fire is re-provided to the ventilation-limited fire field. Many firefighters believe that the opening of residential gates opens up a search and rescue passage and an offensive rather than conducting exhaust ventilation.

If it is necessary to enter the room, then firefighters should realize that the air is fueling the fire. In this very short period of time, either the fire will be extinguished quickly or the fire will continue to develop. The fire environment will reach the lower limit of survival and indoor personnel will be in danger. .

In the experiment of ventilating and exhausting the smoke in the open doors of single and double-storey dwellings, the temperature in the area 5 feet ( 1.52 meters ) above the floor of the burning room was increasing along with the ventilation and smoke exhaust.

In the single-story dwelling experiment 1 (red line), the temperature rose from 180 °C at the time of exhaust ventilation ( 480 seconds) to 260 °C ( 550 seconds) where the firefighter survived , and exceeded 600 °C at 650 seconds ( Burning temperature).

In the double-storey house experiment 2 (blue line), the temperature rose from 220 °C at the exhaust ( 600 seconds) to the firefighter's 260 °C ( 680 seconds) minimum survival limit , and exceeded 600 °C ( 780 °C ) at the 780 seconds ( Flash temperature.

These two experiments tell us that firefighters should regard opening a residential door as opening a ventilation and smoke exhaust outlet, and should consider whether or not it is a correct location for ventilation and smoke exhaust.

At the same time, coordinated operations in the fire are also very critical, such as a simple action: after the firefighters arrive, if the fire door of the building is opened, the firefighters should close the door until they are ready to open the door and attack again.

This will effectively reduce the fire air content and reduce the chance of rapid development of the fire.

3, can not see the situation of smoke

In the experiment, the experimenter observed that the smoke no longer spilled out of the building gap before ventilation. Because the ventilation of the fire is limited, the indoor temperature rapidly decreases. As the temperature drops, the pressure inside the building also decreases, so the smoke no longer appears. When the fire is in the development stage, smoke can be seen around the doors and windows.

In a single-story residential experiment, when the indoor temperature reaches its peak, it begins to fall (before ventilation and smoke exhaust), and the smoke no longer overflows from the room. In the double-storey house experiment, when the fire is in an increase stage, the smoke can be seen to overflow from the building ( 390 seconds). When the fire is extinguished due to ventilation restriction, the smoke no longer overflows and the smoke cannot be seen outside. ( 510 seconds).

On a tactical level, this is very important for firefighters who arrive at the fire scene to assess the situation of the fire. If you do not see smoke outside the building, firefighters are likely to relax. It is very important that there is no smoke or smoke outside the building that does not mean that the internal situation will be more secure. Firefighters often use the characteristics of smoke to judge the situation inside the building.

In actual combat, firefighters must be careful because smoke does not fully reflect the internal conditions of the fire. Taking into account the environment and the pace of development of the modern fire house fire, we believe that if the firefighters arrived at the scene did not see the smoke gas, the fire most likely to occur in the initial stage extinguished (smoke ventilation is limited), rather than the early stages.

4. Collaboration

Many firefighting textbooks have mentioned that synergistic attack is a very effective offensive measure. We mentioned before that if the air enters the fire and the water is not shot in time, the fire will quickly expand and it will endanger the safety of firefighters.

The analysis of how long it takes to reach the lower limit of the survival temperature of the fire can tell us how the most effective synergistic attack should proceed. Combined with the experimental calculation, the average time taken for the firehouse to reach the lower limit of the firefighters' survival is 100 seconds after the ventilation and exhaust of the single-storeyed house, and the average time for the firehouse to reach the lower limit of the firefighters' survival is 200 seconds after the double-storey house is ventilated and exhausted .

In many experiments, it took less than 10 seconds to reach the minimum survival temperature for firefighters and the occurrence of flashover. Firefighters must be very careful during this time. If the occupants do not close or close the window when they flee the scene in the event of a fire, resulting in the existence of ventilated smoke vents that have already been opened in the fire, the new ventilation and smoke vents after the arrival of firefighters will make the fire develop faster, because the new Ventilation exhaust outlet, the room temperature has increased.

When to set up a ventilation and smoke exhaust outlet is a question that needs to be considered in coordinated operations. This question will be answered separately because there are no two identical fires. Consider the time it takes for the hose to reach the fire.

If the fire building is similar to the single-story house in the experiment, the hose will not be laid for a long time. Before the hose is filled with water, you may perform ventilation and exhaust. After a fire in a double-decked building in a similar experiment, it is safer for the firefighters to perform all sorts of preparations for internal attack and fire extinguishing, and then to conduct ventilation and smoke exhaust.

Failure to prepare for firefighting and fire extinguishing will open up the ventilation and smoke vents, which will lead to the rapid development of the fire, and the life of the people inside the building will be threatened by fire.

The following figure depicts simulated search and rescue operations in a single-story home fire. The red line in the figure below is a firefighter search and rescue road map.

The search and rescue team opened the door to the residence eight minutes after the fire broke out. They found that a large amount of smoke was expelled from the doorway, so they put on an empty mask.

At 8 minutes and 15 seconds, the exhaust group opened the front window of the house. The search and rescue team then entered the room and began search and rescue in the bedroom. They saw the sofa in the middle of the room burning, but the fire environment did not pose a threat to their lives. Instead of entering the bedroom, they decided to go to the left room to search for help.

In nine minutes, they entered the kitchen and into the dining room at the time of 9 minutes and 30 seconds. They searched for a lap in the dining room and returned to the entrance of the living room in 10 minutes.

In the simulated search-and-rescue operation, firefighters spent only two minutes, but the situation in the fire field quickly deteriorated.

In the chart, the temperature changes of the firefighter's crawling height area ( 3 feet : 0.91 meters ) are recorded .

When the firefighters started the search, the fire environment was relatively good. When the firemen circumvented the living room entrance, the living room was very dangerous. The firemen had to find other exits to escape, and the firemen were unsafe in the dining room and kitchen. their only option is to broken windows to escape.

5. Flue gas passages through the gate and rapid air movement

Due to the extensive use of polymer materials, modern fires generate large amounts of smoke. In all experiments, before the ventilation and smoke exhaust was implemented, the indoor smoke layer had dropped to the ground and the visibility in the room was zero.

After ventilation and smoke exhaust, the smoke layer in the room does not continuously rise from the ground, but the air quickly enters the ventilation and smoke exhausting port to form a temporary passage in the lower part of the smoke layer. Different from the traditional smoke exhaust effect, the higher smoke release rate and lower heat release rate makes it more difficult for the smoke layer to rise.

If the visibility of the fire increases, firefighters will find it easier to extinguish the fire. However, after ventilation and exhaust, the air accelerates the burning of the fire. The smoke produced by the combustion is more than the smoke emitted from the outside, so the smoke layer is difficult to rise.

When the door to the house is opened, the interior of the building can be found by observing the flow of air and smoke. In these experiments, there was a clear flow of air from the door to the fire.

In all the experiments, the door to the house was opened. Since the air entered the fire from the gate, the air velocity at the bottom of the door was 1.5 m / sec. As a result, a flue gas channel is formed at the bottom. The following images captured before the vent 5 seconds and 5 seconds after ventilation, formation of the flue gas channel.

If there is no influence from the wind, the smoke path marks that the fire is in a restricted-air condition and firefighters need to take preventive measures. Before proceeding, do not behave in a defensive manner. Make sure that the water guns, hoses, and crew members are fully prepared.

In some cases, flue gas channels may also appear in rooms adjacent to the point of ignition, but this situation hardly occurs in rooms further away from the fire point, such as the bedroom in the experiment. Once the inside of the room undergoes flashover, the smoke path will disappear.

6. Ventilation - Entry - Search ( VES )

Many firefighters use VES tactics in actual combat . This tactic was described as opening a window to vent smoke, entering the room from the window, searching in the room, and evacuating from the entry window.

Experiments have proved that even if the window of the search and rescue room is open, as long as the door of the search and rescue room is closed, it can effectively resist the threat posed by the fire environment, thus protecting firefighters and trapped persons in the search and rescue room.

The experiment also showed that the window to the farthest room away from the fire point (the door of the room was also open), the interior situation would deteriorate sharply because after the ventilation, a path of fire propagation from the fire point to the window was established.

Therefore , the key part of the VES tactics is to close the door of the search and rescue room, and to cut off the path of fire and smoke spread between the room and the fire. Therefore, the VES tactics should be upgraded to VEIS , that is, to open a window for ventilation and smoke, enter the room from the window, cut off the path of smoldering by closing the door, and search and rescue in the room.

Some firefighters may think that their search and rescue in the room will be very rapid, so did not close the door, but the newly established path of smoldering is likely to cause indoor sudden changes.

In Experiment 8 , bedroom 3 on the second floor was in a state of exhaust ventilation. We can assume that firefighters used VES tactics to search and rescue in the bedroom but did not close the bedroom door.

The figure below shows the significant changes in the time to reach the minimum survival temperature in the bedroom and the room temperature. Two minutes after the bedroom window was opened for ventilation , the temperature in the area of 1 foot ( 0.3 meters ) from the ground rose by approximately 60 °C , reaching the minimum living temperature for the occupants, and reached the lower limit of the firefighters' survival within 3 minutes of exhaust ventilation . The bedroom 2 door next to bedroom 3 is closed, and the room temperature inside the room does not exceed 60 °C because its door is closed.

In Experiment 14 , the window of bedroom 3 was opened in 8 minutes and 42 seconds to simulate firefighters using VES tactics to search and rescue in bedroom 3 , and the bedroom door was closed.

The following figure shows the room situation at 1 minute and 2 minutes after opening the bedroom window . During this period of time, the fire area outside the bedroom 3 doors has been in a state of complete combustion, but the smoke level in the bedroom 3 has gradually increased (because of window opening and exhaust), the indoor environment continues to improve and the firefighters have more. Time to search and rescue, this is the advantage of VEIS tactics.

This article is reproduced from WeChat public number: Orange Rescue.