Fifteen years ago, when I joined the fire brigade, someone introduced me to two different ways of extinguishing fires: a low-pressure fire extinguishing system composed of water hoses and a high-pressure fire extinguishing system composed of high-pressure hose reels.

High-pressure hoses are usually mounted on reels. In Belgium, hoses are usually 80 meters in length and 25 mm in inner diameter . When the pump operates according to the specification, the flow rate can reach 180 liters per minute .

It is very popular to use high-pressure hose reels for fire extinguishing during urban firefighting and rescue operations. In Brussels, an estimated 90 % of fires are extinguished with one or more high-pressure hoses.

Figure 1 High-pressure hose reel, water separator, water gun in the equipment box

(Photograph: Pierre- Henri Demeyere )

Another fire extinguishing method is to extinguish a low pressure water zone. In this type of fire extinguishing method, the water is usually placed in a double roll. In Belgium, the common diameter of the hose is 45mm and 70mm .

When used, it is necessary to throw out the rolled ribbon and then connect the ribbon. A water separator can be used to connect the 45mm hose and the 70mm hose to form the outlet pipe. The flow in the low-pressure outlet pipe is unstable and is largely affected by the type of water gun.

In the past five years, there have been major changes in the low-pressure fire extinguishing methods: the use of a single coil of water, which is also known as “Cleveland Roll” or “annular”. Another method is to lay the layers of water in layers and place them. That is stacked water.

However, in fact, the introduction of this new method has been greatly resisted. Many people who like high-pressure reels think that high-pressure hose reels can do a good job of fighting fires. They do not understand why the fire-fighting method must be changed.

In this article, I mainly talked about some of the fire extinguishing methods that we are using, mainly to enable everyone to put forward their own views on this.

One important issue we need to consider is:

“Do we want to use the existing, problem-free fire-extinguishing system all the time, or prepare for future combat operations and build a better fire-extinguishing system?”

1. Why use high pressure reel fire

So popular?

Figure 2 Using a high pressure hose reel in a car fire

( Photograph : Pierre-Henri Demeyere)

First, the high-pressure hose reel is very easy to use, and the hose can be easily pulled from the reel.

When used, when the firefighter reaches the ignition point, the driver can immediately open the water, and the speed of extinguishing the water can become very fast, which makes it very suitable for the outdoor fire fighting.

In outdoor fire fighting, the high pressure hose can be pulled from the fire truck to the fire scene.

At the same time, it has strong mobility, requiring only one firefighter to use a high-pressure reel to save small indoor fires.

Looking back on past experiences, we can summarize some important lessons. For now, the high-pressure hose reel is the best way to quickly expand inside a building.

If a fire occurs on a three-story building, the use of a high-pressure hose reel is much faster than laying a hose. However, the emergence of single-roll and cascaded hoses poses a direct challenge to the advantages of high-pressure hose reels.

Under specific circumstances, by using well-designed methods and adequate training, the laying of hoses is faster than using high-pressure hose reels.

The high-pressure hose reels can be easily closed after use, and only the hoses need to be rewinded onto the reels without taking up too much resources.

However, after the hose has been used, it must be re-circulated and returned to the car to bring it back to the fire brigade. After returning to the team, the used hoses must be brushed and dried before they can be used again.

Therefore, from the perspective of logistics, the use of high-pressure hose reels is much more convenient.

2. Cooling capacity

High-pressure hose reel, about 180 liters per minute . In other countries, the internal diameter of high-pressure hose reel used by firefighters is 19mm , and the flow rate of such hose reels is only 100 liters per minute.

180 liters per minute flow rate of 3 liters per second by means of water emitted from the nozzle, we assume 3 MJ per liter of water absorption of heat, 180 l / min flow rate of the refrigerant, but when the theoretical capacity of 9 MW at.

Of course, such cooling capacity is obtained under certain preconditions, assuming that the water jet from the nozzle is constant at 20 °C , and all water is converted to 300 °C after spraying .

In fact, this is not always the case and steam may escape the fire until it reaches 300 °C . The most important effect on cooling capacity is that water cannot absorb enough heat during the evaporation of water into water vapor.

The water flowing out of the liquid can only absorb 11 % of the energy per liter of 3 MJ . Therefore, in the actual fire field, the cooling capacity is much less than 9MW .

Then the question is: What is the ability of the water gunner?

This problem affects both high and low pressure modes and affects efficiency. This question is difficult to answer. People have conducted extensive research in this field. The efficiency of fire fighting depends largely on which equipment is used. A good water gun will produce higher fire-fighting efficiency.

Furthermore, high-pressure hose reels are often equipped with higher-efficiency high-pressure water guns, which is why high-pressure hose reels are so popular. When the high-pressure hose reel first appeared, the low-pressure fire extinguishing method was still equipped with a single old standard water gun.

The jets of these old "standardized" water guns are not very good. The use of new high-pressure water guns allows us to control the shape of the jet more precisely, which greatly increases the efficiency of fire extinguishing. It is precisely because of this that fire fighters can use high-pressure and small-flow rates to extinguish fires without using low-pressure and large-flow.

The level of fire extinguishing efficiency is related to the fire situation faced by the firefighters. When fighting a fully flaming fire, the fire extinguishing efficiency will be higher, but if it is a smoldering fire, the situation is exactly the opposite.

Figure 3 has a typical room layout. There are many separate rooms. The surface area of ​​each room is limited. (Figure: UL FSRI )

Suppose the firefighters extinguish the fire in a fiery burning room fire. The extinguishing efficiency is 75% . The high-pressure hose reel extinguishes the heat release rate of 6.75 MW . This is equal to the combustion surface area of 27 square meters , and the heat released by the combustion. ( 250MW/ ?). Kitchen in FIG. 3 (Kitchen) are 22?, Master bedroom bottom right (M.Bedroom) area is 15?.

The "burning surface area" refers to the size of the floor area of ​​a room. In the regular room, there are many empty places, the passage inside the house. Figure 3 clearly shows the space of this house. In a typical furnished room, the average heat release rate in the event of a fire is approximately 250 kW/ ?.

Assuming that the 27- square-meter room is full of mattresses, the heat release rate will be much higher than 6.75 MW (assuming there is enough air for combustion). In this case, the heat release rate can even reach 1MW/ ?.

From the above description, it is not difficult to understand why everyone likes to use a high-pressure hose reel to fight a fire. Most of the fires have a burning area of ​​less than 27 ?, especially for residential buildings. Usually the fire is confined to one room, and most rooms are less than 27 ? This means that using a high-pressure hose reel is a very good way to fight a small residential fire.

Paul Grimwood has conducted a very extensive study of the jet flow during firefighting and rescue operations. From 2009 to 2012 , he studied a total of 5,401 fires in the United Kingdom . He conducted detailed and in-depth studies of urban fires and the fires that occurred at the junction of urban and rural areas.

These studies led him to some conclusions regarding the use of high pressure hose reels for extinguishing fires. The average burning area of ​​suburban fires was 7.72 and urban fires were 11.14 .

It is important to note that under these conditions, using a high-pressure hose reel, the flow rate per minute is only 100L . If the fire extinguishing efficiency is the same, the equivalent burning area in Belgium is between 14 and 20 (. Is 180L ).

Therefore, high pressure hose reels are mainly used for small fires. For these fires, the high-pressure reel is a good fire-fighting equipment if operated properly.

two,

In the past few years, many efforts have been made to improve the efficiency of water use by fire fighters: to achieve better results with less water. This is also intangible, improving the use of high-pressure reels. However, why are more and more people promoting the use of water hose? Is there any deficiency in the above reasoning?

The above reasoning is mainly based on past experience. People often like to use current conditions and methods to find solutions to past problems and treat them as good solutions.

High-pressure hose reels are good for past fires, but are they also good for future fires?

1. Change in fire characteristics

Figure 4 shows the development trend of ventilation control type fires. The first major change in fire development is the first two phases: the initial phase and the growth phase. In 1950 , these two phases took about half an hour. Now they only need two to four minutes. (Photo: Bart Noyens )

As we all know, in the past 60 years, the fire characteristics have changed. After the Second World War, people invented synthetic materials. The extensive use of this material led to the rapid development of fires.

In 1950 , it took half an hour to go from a fire to a flash fire; now, it only takes two to four minutes. The first reaction people usually hear about this is: "Firefighters have already had a fire before they reached the fire?" Of course, this is indeed the case.

However, people who mention this issue ignore the model of a ventilation-controlled fire site that refers to a single room. The fully developed fire in the kitchen will eventually spread to the living room and other areas. Two to four minutes later, there will be a flash fire in these places.

In this case, firefighters may have arrived at the scene. Firefighters may be crawling through the bedroom and heading to the kitchen’s ignition point while they are facing the burning smoke floor.

At this time, as the burning rate exceeds expectations, extreme fire phenomena such as flashing fire will occur, and this will cause firefighters to fall into danger. So, this is the difference between past and present fire characteristics.

The second cause of changes in indoor fire characteristics is the use of large amounts of double-glazed glass and the transition of the building to insulation.

If a room is completely closed, it is difficult to have enough air to produce flash fire. Under normal circumstances, single-layer glass will burst quickly in high-temperature environments, but double-glazed glass will not be the case. At this time, there are ventilation-limited fires.

In a closed room, the heat release rate of the flame is limited by the shortage of air, but such a situation may change due to the breakage of the glass, or the fireman opening the door to the inside attack. The additional influx of air means heat. The release rate increases. In this case, the fire can easily become larger in an instant.

Finland released a study on the formation of fire pressure this year: With the improvement of the construction level, the sealing performance of the building is getting better and better, which makes the pressure in the fire room become higher than before.

When a fire occurs, as the burning time becomes longer and longer, the room temperature rises and the hot air tries to spread to other places. In a relatively closed room, smoke and hot air cannot spread, which will lead to increased pressure inside the room.

A Finnish experiment confirmed that the increase in indoor air pressure caused by a fire can cause the entire window (glass and window frames) to be blown out, which may mean a third major change in fire characteristics. During the development of the fire, a large opening may suddenly appear, providing a lot of oxygen to the fire.

This shows once again that the deterioration of the fire situation in modern buildings is getting faster and faster.

2. Wind drive

In 2009 , the United States NIST Agency released the first comprehensive study on wind-driven technologies: Under certain wind conditions, fires may behave very irregularly. The study originated from the many accidents that firefighters had in fighting high-rise building fires.

Studies have shown that wind can greatly increase the heat release rate of the fire, resulting in a very high temperature. The wind can also push the flame to the firefighters. When the strong wind blows directly to the window, the closed glass window can prevent the wind from affecting the fire. However, once the window breaks, the situation will momentarily change, and then wind and fire will be created. The completely controllable situation suddenly becomes out of control.

In the United States, every fatal accident involving firefighters is thoroughly analyzed (in contrast to the Belgian practice). In the past few years, several firefighters were killed in a fire that caused fire in ordinary buildings.

Therefore, wind-flooding can occur in any building.

3. New style of architecture

In terms of architectural structure, there have been some major changes in recent years. In the past, housing was composed of separate rooms, with a kitchen and a living room. Sometimes, the dining room and the living room were also clearly separated. Since each room is less than 27 ?, high-pressure reels are ideal for fighting fires in such rooms. Figure 3 shows this well.

When there is a fire in the living room, if there is enough air, it will quickly flash fire. Next, the fire took a while to spread and the flames were obstructed by the walls. At this time, the "door" became a key factor.

If the door is closed, the spread of fire will be delayed for some time, but if the door is open, hot smoke can flow into the adjacent room. In this case, the effect of the wall-isolated flame is not obvious.

Figure 5 The layout of a modern typical residential floor. The kitchen and living room are connected into a unified space. There is a comfortable seating area (lower right) connected to the family room. These all create a large room. (Figure: UL FSRI )

There is always an open kitchen in modernly built homes and apartments. The living room is connected to the kitchen to form a large separate room. In many homes, the open space has an area of ​​more than 27 feet. When comparing Figures 3 to 5 , it can be clearly seen.

In modern dwellings, large open rooms are commonplace, which provides residents with a more comfortable lifestyle, but the area of ​​individual rooms has greatly increased.

Therefore, it is difficult to control the fire with a high-pressure reel.

4. Summary

After the above analysis, we have summarized several different issues that have emerged in the past few years:

• Fires develop much faster than in the past.

• In the case of limited ventilation, sudden air vents can accelerate the spread of fire.

• Start to pay attention to the impact of fire pressure on fire suppression

• Wind-fighting causes high heat release rates.

• The layout of the interior of an open, large space may result in a greater fire.

For each of these issues, each of these issues means that the fire may become larger and more difficult to control. During the attack, it may take several minutes from the entrance to the place where the water can be extinguished.

During this time, the fire may have undergone dramatic changes. A fire that could have been successfully disposed of with a high-pressure reel might require more effort in a few minutes. If internal attackers do not have sufficient cooling capacity, they will be in a very dangerous situation.

Future fires will develop faster than in the past. The above problems did not exist before. Using a high-pressure reel to extinguish fire is a good method at that time. If the fire does not change much during the attack, it will still be a good fire fighting method.

We can use the security of the car as a metaphor. Now, every driver will have a seat belt, because it will increase the possibility of people living in a car accident.

In modern fires, fire extinguishing with high-pressure reels is like running a highway at a speed of 120 km / hour without a belt .

Someone will drive on the expressway at high speed without wearing seat belts, and they may not be involved in accidents. However, for a small number of people, there will be tragic high-speed accidents. For them, fastening the seat belts is crucial to their survival.

The same applies to firefighting work. Most small fires can be disposed of with high pressure reels. Only a small part of the fire can not be saved in this way. But the problem is that we do not know in advance what kind of fire has occurred.

In the future, the fire brigade will encounter more and more complicated situations. It may appear that the fire scene after the arrival is not bad. After the reconnaissance by the fire, it is found that the initial fire can be rescued with a high-pressure reel. One of the ways to fight a fire.

However, problems often occur later in the fire, and may be one of the above five conditions, or they may be some problems that have not yet been discovered. The only thing we can be sure of is that for some fires, the high-pressure reel is not the safest option because we didn't know what kind of fire it was before we reached the fire.

A good example is a fire with a very low rate of heat release. The on-site windows are still intact and there is a slight wind blowing to the side of the building. After the firefighters arrived at the fire site, they found that the fire on the scene did not become serious. The fire suppression could be done with a high-pressure reel because the cooling capacity of the high-pressure reel was higher than the heat generation rate of the combustion.

If the burning room is closed, this assessment is consistent with reality. But if the windows in the room break, all of these things will change.

Suddenly, the wind will provide a lot of fresh air for the fire, and the rate of heat release will easily double. However, the maximum flow of high pressure reels cannot be doubled.

Therefore, when firefighters perform internal attack tasks, their safety is very worrying. Some fire fighters are very proficient in how to use a high-pressure reel to extinguish fires, achieving very high efficiency, but there is no safety margin for high-pressure reels.

When you extinguish, the facility reaches the limit of the extinguishing ability. When you need more cooling capacity, you have no way.

three,

In the above section, some issues currently facing the fire brigade have been described. Of course, there are solutions. These solutions require a certain amount of investment, that is, the transformation of existing tools or the purchase of new equipment. At the same time, keep up with related training.

Usually we will ignore these two tasks. When we implement the improvement methods mentioned below, we must strengthen the initial training and subsequent retraining.

1 single roll of water

Figure 6 uses single-roller hoses and laminated hoses in different parts of the water supply system. A 70 mm hose is connected to the water separator. The figure shows the connection of the folded hose to the trap. During fire extinguishing, the yellow single-roller hose will be connected to the laminated hose. (Photo: Karel Lambert)

Single-roller hoses and cascaded hoses have been used in most parts of Belgium. They debuted in 2009 and more and more fire brigades started to use them.

The advantage of hose extinguishing is that even with higher flow requirements, the requirements can be met. The use of a 45 mm hose produces at least twice the flow of 180 litres per minute for a high pressure reel , so the cooling capacity is twice that of a high pressure reel.

When the high-pressure reel reaches its limit, the hose only uses half its water supply capacity. In this case, firefighters can choose to use twice as much water. Therefore, there is a safety margin hose that can compensate for the lack of high-pressure reel.

Of course, it needs to be recognized that the water belt does not solve all problems. Even though the cooling capacity of the hose can reach 15 to 20 MW , it is limited.

Figure 7 The folded 70mm hose is directly connected to the trap. It is a major tactical improvement that allows easy connection without changing the water pump. (Photo: Steve Viaene )

Using a single roll type laminated plate and hoses, the laying of water to provide a convenient, but using 45 mm hose, which is still lower than convenience pressure hose reel, in this case, two methods The speed of deployment is faster than that of a traditional double roll.

One important reason is that with water of 70 mm in a zigzag layer laminated on a good car, the hose is connected to a three-way trap, the spot can quickly reach a location holding trap.

This method of laying the hoses allows the use of laminated hoses within a complex building structure that will stretch faster than high-pressure reels.

When the high-pressure reel is used, the frictional force will increase as the distance of stretching increases, while the problem of laying the laminated water belt has no friction. Conversely, as the weight of the hose is reduced, firefighters are more likely to move.

When using a high-pressure reel, firefighters must use long enough hose to reach the ignition point to avoid impediments to the internal attack. Pulling the last point of length will be the most difficult and the friction will be greatest.

When the hoses are laid, they are connected to a single roll of water at the offensive position, which increases the length of the hose belt by 20 to 40 meters. The firemen can simply place the hose at the connection.

2. 38 mm water hose

It can be further enhanced with the laying of water mobility, in Belgium, people choose 45 mm and 70 mm in two different diameters of hose.

Other countries have made different choices based on actual conditions. The United Kingdom usually uses 52 mm , and Australia prefers the 38 mm hose as a shotgun hose.

The question is: “What diameter of hose do we need?” The diameter of the hose required depends on the situation: we need the length of the hose, the flow we want to reach and the power of the pump used.

The water pump must be able to provide the required flow at a sufficiently high pressure to compensate for head loss and keep the pressure at the water gun within the reach of the water gunner.

The flow rate of the 45 mm hose is between 400 and 500 litres