Assessment of the Impact of Extinguishing with a Low-Pressure Fog Lance on a Fire Environment

Abstract

A main purpose of the study was to assess the impact of extinguishing with a low-pressure fog lance on a fire environment, especially of temperature. A low-pressure fog lance has recently been recommended for fighting fires in either limited spaces or difficult to access places. Four tests were conducted in real internal fire conditions. The following lances were used in sequential tests: fognail attack, MK with attack head, fognail defense and MK with defense head. They were fed from a fire vehicle GBA 2.5/24 equipped with a pump with automatic pressure regulation and hose lines W75 and W52. The temperature was measured with thermocouples at various points of the room, including the ceiling. Photographic documentation of the tests was prepared using thermal and video cameras. The best way of using a fog lance was established from literature sources and the manufacturer’s requirements. Two main factors of effective firefighting were observed during the tests: smoke cooling and isolation of the fire by formed water vapor. The use of a fog lance significantly improves of fire-fighting operations. A proper application of water mist eliminates the risk of fire gases’ ignition. The assumed times of ensuring safe conditions in the room were confirmed.

1. Introduction

One of the most important properties of devices used by firefighters to extinguish fires is their extinguishing efficiency. A review of several fire-extinguishing techniques ensuring adequate effectiveness with minimal water consumption is presented in [1]. It discusses such manual water and foam extinguishing systems as: standard variable nozzles, water mist, cutting extinguishers, extinguishing spears, compressed air foam systems (CAFS) and fire retardant gel. Unfortunately, it does not mention the fog lance, which is increasingly used by firefighters during action.

Fire-extinguishing lances are usually associated with the extinguishing of piles and stacks. However, this situation has changed recently with the development of training in fighting internal fires and the popularization of modern techniques and tactics. Specially prepared lances are becoming more and more popular and recommended for extinguishing internal fires [2,3,4]. This mainly concerns difficult fires in places with no access for rescuers and traditional internal actions. They are, therefore, particularly suitable for extinguishing fires in apartments, basements, attics, litter bins, landfills, vehicles, ships and containers. Are lances good firefighting equipment? Are they able to replace traditional methods? These devices provide fog, which has many advantages, and such devices’ rate of flow often does not exceed 200 dm³/min, which may cause fears among firefighters that the effectiveness of such methods is low. In Poland, attempts were made to implement low-capacity fog systems without much success. It is well-known that a large amount of water will extinguish almost any fire and this is often the only idea of commanders in charge of extinguishing operations—to apply multiple extinguishing jets with the highest possible efficiency. It is worth considering whether it is not the amount of water, but the method of its administration, that determines the effectiveness of our actions. This is the starting point for the implementation of new techniques that may prove beneficial under certain conditions. It is worth expanding workshops, adding new methods and techniques to them [5,6,7,8,9,10,11]. The use of a fire-suppression lance should allow additional time to access the fire, open doors, cut openings, create openings for ventilation, etc. In today’s operations, time plays a key role, and the development of technology and the ubiquity of synthetic materials mean firefighting is becoming harder and harder. However, after the proper suppression of a fire, there is no risk that the fire will develop rapidly during this time and the actions of firefighters will not intensify its development.

There are only a few publications in the literature dealing with the testing of devices similar to those used in the following studies. One of them is an article by Szymon Kokot-Góra entitled “A new version of the fog lance”, on the use of a fire extinguishing lance to extinguish an internal fire [1]. It describes a three-day exercise carried out in a soot warehouse that was to be demolished. Five sets were used, which included: a 70 cm long fog lance made of galvanized tool steel, a tip for attack with a capacity of 260 dm³/min and a tip for defense with a capacity of 200 dm³/min with high-quality tips made of NZ3 tool steel and a ball valve with 2 × 52 caps, including one swivel. Additionally, a heavy hammer was used to pierce the walls. The exercises carried out had several objectives. Firstly, they were used to verify the lance’s ability to pierce various building materials (brick walls of different thicknesses, door, corrugated sheet, and double sheet with insulation), and, secondly, the range of water jets in the room as well as their extinguishing and cooling abilities were visually assessed. Every day, similar scenarios were carried out, consisting in piercing various types of partitions, then visually assessing the parameters of water jets fed from different heads (attack and defense) and, in the last stage, starting a fire (a tray with two stacked, cut Euro-pallets plus 1 dm³ of a mixture of gasoline and diesel oil) in a sealed room with dimensions of 2.5 m × 4 m × 3.5 m, breaking through the door and then applying water and observing the extinguishing effect. As for the lance’s ability to pierce building partitions, the exercises showed that it can cope well with various types of obstacles, except for walls thicker than 0.15 m. As for the shape, range and quality of the mist delivered from the lance, at the pump pressure of 0.8 MPa and with two hose sections, a stream of small-diameter droplets was obtained, the duration of which was sufficiently long in the air. This should ensure a sufficient cooling effect at the capacities of the individual heads. The lance with the attack head produced a cone-shaped stream with a range of about 5 m and a radius of about 2 m. A lance with an attack head produced an umbrella with the same radius as the attack head. When extinguishing a fire with a lance with an attack head, it was found that the mist stream was so well-suited to the room that almost all the water evaporated into gases, and only a small amount of it fell on the surface (the puncture occurred in the upper part of the door and the lance was directed slightly up). The cooling was so intense that, due to the negative pressure created, air was suddenly sucked inside, which caused the door to burst. On the third day, a door that matched the opening was inserted. Its tightness was so great that after applying water, due to the vacuum created, the door was torn out of the hinges and pulled inside. The conducted exercises allowed for the formulation of a conclusion of the high efficiency of cooling fires with the fog lance, despite its low efficiency. It avoids excessive flooding and the merging of smaller droplets into larger ones, which negatively affects the ability to evaporate water in fire environments.

The next work, divided into two parts, discussed the experiment which consisted of examining the temperature distribution during the extinguishing of a fire with a selected fognail lance in a single-family building intended for demolition [12,13]. The building was made of plastered bricks and had no basement. The wooden structure of the roof was covered with ceramic tiles. In most of the rooms, the walls had paneling or panels made of fiberboard with wooden elements. The combustible finish of the rooms in the house significantly influenced the dynamics of fire development and thus determined the adopted scenarios. In order to start a fire that could lead to a flashover, a combustible charge was prepared, consisting of an upholstered sofa (about 2500–4000 kW), a few chairs and wooden planks (about 2000 kW) and a certain amount of plywood (up to 5000 kW), which was a total of about 1 m³ of wood and wood-based products. There were five thermocouples in the facility, the indications of which were displayed on boards placed outside the building. They were located in the following places: above the convection column of the primary source of fire, shifted approximately 2 m horizontally from its vertical axis; approximately 0.30 m from the ceiling (T1), below thermocouple No. 1 vertically at a height of approximately 120 cm above the floor (T2); below thermocouple No. 2 at a height of about 0.30 m above the floor (T3); in a room with a fire source under a sloping roof; inserted through a hole drilled in the sloping roof, shifted about 2 m horizontally to the vertical axis of the convection column at a distance of about 30 cm from the ceiling (T4); and under the ceiling in an adjacent room, the window of which was used to extract smoke during the attack (T5). The scenario assumed that, after ignition, the fire would develop freely for about 10 min, which corresponds to the average time of the local fire brigade’s arrival to the fire, including the preparation of the extinguishing deployment. After arriving and performing a reconnaissance, the task of the firefighters was to prepare a standard attack with the use of Turbo nozzles, while feeding the water mist to the combustion zone without oxygenating it. It was carried out using a fognail lance with an attack head inserted through a hole drilled in the wall into the fire room, supplied from a rapid attack line at a pressure of approx. 22 bar (pressure losses per 60 m of hose were taken into account) and a capacity of approx. 80 dm³/min. Water was fed for about 4 min, which resulted in water consumption of about 320 dm³. On the basis of the obtained temperature, it could be concluded that practically, in about 3 min, its value dropped by half. For example, on the T4 thermocouple, which recorded the highest temperatures, its value at the start of extinguishing was about 290 °C, and at the end of the time it was about 140 °C. Similar trends were observed on all thermocouples, especially those located in the ceiling zone, where the rate of temperature drop was the highest. On the T2 thermocouple mounted at a height of 120 cm, the decrease was slightly smaller and amounted up to about 45 °C, with the maximum value of the temperature recorded on it being equal to about 125 °C. During the application of water mist, no intense emission of smoke nor gases through the leaks was noticed, which may indicate that, due to the appropriate droplet size and good application technique, most of the water evaporated in the fire gases.

A comparison of the results of experiments related to several extinguishing techniques performed by the NIFV Research Department in cooperation with fire departments in the Netherlands can be found in [14,15]. The following five techniques were used: the cold-cut system, fognail, distributor nozzle, high pressure foam exterior and interior approach, and high pressure jet exterior approach. For each of the above-mentioned technician five tests were performed. The obtained results were averaged statistically. From the point of view of the subject of this article, the most interesting study was related to the use of the fognail. The primary goal was to determine the effectiveness of the techniques used from the point of view of both cooling fire gases and extinguishing the fire. The impact of the selected technique on the safety of rescuers was also analyzed. The tests were carried out in a steel hangar measuring 15.35 m x 11.60 m x 4.5 m located at the TRONED training center in Enschede. The source of fire was pine pallets placed in two different places (two piles of eight pallets in one). In total, 32 pallets were used, the weight of which was about 512 kg. There were trays under the pallets, into which about 2 dm³ of flammable liquid was poured onto one set of pallets. During the experiment, the temperature was measured with eight thermocouples, four of which were placed about 1 m below the ceiling (No. 2, 5, 4 and 6), three at a height of about 1.8 m (No. 1, 7 and 8) above the floor, and one in the immediate vicinity of the fire sources (No. 3). Thermocouples were located in different parts of the hangar. Both mobile video cameras and thermal-imaging cameras were used to observe the fire, in particular while extinguishing it. At the moment of starting the extinguishing, a temperature of 430 °C was assumed to be reached on the thermocouple No. 5, and the moment of reaching the temperature of 150 °C on the thermocouple No. 6 was assumed to be the end of the extinguishing. In addition to these characteristic times, the time from the initiation of the fire, after which the fire was extinguished (no flames), was also measured. Based on the average temperature measured by thermocouple No. 6 (ceiling zone), it was found that the cooling effect with the lance was most effective in the initial phase of the extinguishing process (the fastest temperature drop). After extinguishing for about 50 s, the temperature practically did not change and then it began to gradually decrease. This was not observed with the cold cutter or distributor nozzle. This may have been because the lance has a reignition effect unlike the other extinguishing devices used. The analysis of the temperature also showed that the highest average coefficient of its decrease, equal to −0.49, was obtained for the lance. For the cold-cut system and distributor nozzle it was −0.31 and −0.24, respectively. On the other hand, based on the analysis of the average temperature courses measured at a height of 1.8 m by thermocouple No. 8, it was found that the fastest temperature drop in the first phase of the extinguishing process was observed for the distributor nozzle, while the lowest temperature of below 50 °C was obtained for the lance. As for the time of a temperature drop below 150 °C, it was the shortest (58 s) for the lance, slightly longer for the cold cutter (74 s) and significantly longer for the distributor nozzle (119 s). In the case of other devices, it was over 200 s for the high-pressure foam exterior approach—296 s, high pressure foam interior approach—213 s and high pressure jet exterior approach—207 s. It turned out that the difference between these values was the greatest for the cold cutter and interior high pressure foam. For fognail and distributor nozzle it was small and it did not exceed 200 s. This may be because the cold cutter required a hole to be drilled at the start of the test, which took some time. One of the values taken into account during the tests was the average water consumption. This were determined on the basis of the average expenditure and extinguishing time. It was, respectively, in dm³: 74 for the cold cut system, 133 for fognail, 660 for the distributor nozzle, 839 for high pressure foam—exterior, 603 for high pressure foam—interior and 435 for high pressure jet—exterior.

The scientific purposes of this work not previously reported in world literature are:

(a)

Assessment of the extinguishing effectiveness of fognail and MK lances with attack and defense nozzles in full-scale fire conditions;

(b)

Comparing the extinguishing performance of both types of lances, taking into account two types of heads, one for attack and the other for defense;

(c)

Formulating conclusions based on the analysis of the temperature obtained during fire extinguishing with the use of the above-mentioned types of lances with two types of changeable heads: attack and defense.

2. Materials and Methods

2.1. Subject of the Study

The subject of the research were two types of lances used by the Fire Brigade. The first was a fognail lance built in 1988 by the Swedish firefighter Lennart Strand. It is usually supplied with flat-folded hoses with a diameter of 0.025 m with Storz D25 couplings or semi-rigid hoses with 1″ couplings (popular 0.019 m or 0.022 m quick attack lines). The two most popular versions of fognail lances are shown in Figure 1. There are two versions of the lance head, for attack and defense. The attack head has 18 holes directed perpendicular to the direction of water flow, and the water stream is smashed by a properly profiled element (Figure 2a). The defense head (Figure 2b) has two rows of six nozzles directed at different angles in the direction of water flow (approx. 45 °C and 60 °C).

Lances are made of stainless steel, equipped with permanently installed brass, and with chrome valves designed to work with a maximum pressure of 0.4 MPa. This makes it possible to also supply high-pressure systems used in firefighting vehicles in Poland. The use of quick couplings adapted to pressures up to 0.4 MPa allows for better use of the potential of the high-pressure line, the so-called quick attack. Fog delivered at a pressure of about 0.2 MPa at the end of such a line will have better parameters than fog fed with low-pressure fittings (working pressure up to 0.12 MPa). The water droplets will be smaller and the stream will be more dispersed and will have more kinetic energy. Figure 3 shows a proposal to extend the tactical capabilities of the standard rapid attack line with the use of high-pressure quick couplers.

Dafo company offers various types of extinguishing lances, but the most common are fognail lances in two versions, standard and XL (0.52 m and 1.50 m).

Technical data of fognail lances [16]:

(a)

Material: stainless steel lance, chrome plated brass valve and connections;

(b)

Length: 0.52 m or 1.50 m;

(c)

Hole diameter: 0.019 m;

(d)

Weight: 1.2 kg in the 0.52 m version;

(e)

Working pressure: up to 0.40 MPa;

(f)

Flow rate: 72 dm³/min for 0.8 MPa (in accordance with the manufacturer’s declaration), 80 dm³/min for 0.31 MPa;

(g)

Dimensions of the defense stream: 5 × 2 m;

(h)

Dimensions of the attack stream: horizontal range of 8 m;

(i)

No possibility to change the head;

(j)

No rotating attachment.

MK series extinguishing lances were designed and manufactured in Poland by Miko Rescue Tech from Mosina. Specialists in the field of extinguishing internal fires from Poland and abroad were involved in the work on the creation of the lance. The manufacturer declares that it is an effective device for extinguishing and preventing the spread of internal fires in confined spaces that are difficult to access and pose a threat to rescuers. The general view of the lance is shown in Figure 4. The lances are made of high-quality materials in accordance with the standards of mechanical, heat and galvanic treatment. The lance is characterized by high mechanical resistance and has been repeatedly tested while piercing walls and roofs. The design makes it impossible to damage the feeding tube. It is characterized as a demolition lance, which in practice means it has the possibility of piercing roof, door and wall sheathing. The lance is designed to hit with a hammer and overcome various obstacles. In a fire condition, making a 0.035 m hole during a fire could be embarrassing, and hand-held demolition equipment is more readily available. The set includes two wrenches for changing the nozzle and head. It is possible to replace the nozzle, tip and the element in contact with the driving hammer.

It is preferable to use an attack head by default, which creates a cone-shaped jet from nozzles directed at an angle of about 60°, but a 90° angle on the second row of nozzles also produces an umbrella. The defensive head has two rows of nozzles creating an umbrella-shaped stream with a large area (about 20 m², according to the manufacturer’s declaration). Each head has 16 holes in two rows. The shaft of the lance is equipped with special ribs ensuring the stability of the lance when driving into the roof, for example, creating resistance when opening and closing the water flow. It is advisable to use the lance with a pressure of about 0.8 MPa; therefore, in order to minimize the phenomenon of water hammer, the valve should be opened slowly and smoothly. The lance has ergonomically shaped handles that ensure operation in various conditions. Due to the size of the lance, it should be operated by two rescuers while driving. The use of an attached linear valve with a swivel attachment allows you to connect the extinguishing line only after the lance has been driven in; the irrigated line will significantly complicate the operation of the lance. Flow rate up to 250 dm³/min, however, allows the use of hoses with C-type connectors with diameters smaller than 0.052 m, i.e., 0.038 m or 0.042 m, the capacities of which provide the required flow, but generate higher pressure losses, which should be taken into account during operations. Water pressure affects the size of the droplets of the resulting stream: the greater the pressure, the smaller the droplets and the greater the energy of the stream. Lances have been introduced for use in many fire protection units in Poland, e.g., in the Warmian-Masurian province, each rescue and firefighting unit received an MK type lance for equipment.

Technical data of MK lance [19]:

(a)

Material: structural steel S355 JR and tool steel for cold work 1.2550, quenched and tempered, all protected with galvanic coatings;

(b)

Length: 1 m;

(c)

Hole diameter: 0.035 m;

(d)

Weight: 9 kg in the 0.7 m version, 10 kg in the 1 m version;

(e)

Working pressure: up to 1.2 MPa;

(f)

Airflow efficiency: 165 dm³/min for 0.6 MPa, 201 dm³/min for 0.8 MPa (the manufacturer currently declares 260 dm³/min at 0.8 MPa);

(g)

Stream efficiency attack: 125 dm³/min for 0.6 MPa, 154 dm³/min for 0.8 MPa (the manufacturer currently declares 200 dm³/min at 0.8 MPa);

(h)

The manufacturer declares the possibility of preparing a lance with a flow rate from 70 dm³/min to 250 dm³/min, in two different diameters and three different lengths (in addition to the described one, available diameter 0.030 m and length 0.5 m and 0.7 m);

(i)

Dimensions of the defensive stream: umbrella with a diameter of 5 m;

(j)

Attack stream dimensions: cone 5 m in diameter and 5 m high;

(k)

The ability to change the head and tip (twisting wrenches included);

(l)

The possibility of equipping the lance with a 0.7 m long extension without the possibility of piercing;

(m)

No rotary attachment (installed in the optional linear valve with C52 adapters).

2.2. Measurement System

The tests were carried out in a room prepared for this purpose, with a reinforced concrete structure and walls made of burnt brick, 4.5 m × 5.5 m × 2.4 m in size, used for exercises in extinguishing internal fires by the Municipal Headquarters of the State Fire Training Center in Warsaw. Its preparation consisted of installing doors with dimensions of 0.9 m × 1.8 m and sealing the windows. There are ten sheathed thermocouples in the room, the technical data of which are given below [20]:

(a)

Sheathed thermocouple: NiCr—NiAl (K);

(b)

Sheath: Inconel (T, J, K);

(c)

Thermocouple diameter: 0.001 m;

(d)

Maximum measurement temperature: 900 °C;

(e)

Thermocouple length: 0.25 m;

(f)

Measurement accuracy: 1.5 °C (−40 °C) or 0.4% (1150 °C).

The floor plan of the room with a diagram of the location of thermocouples (numbered from 1 to 10) and the location of the combustible material (rectangle in the lower right corner) and the extinguishing lance with attack head (filled red arrow) or with defense head (empty red arrow) during extinguishing are shown in Figure 5. Nine thermocouples (no. 1–9) are positioned symmetrically just below the ceiling at a height of 2.3 m (see Figure 5). The last thermocouple (no. 10) was installed at a height of 1 m to check the conditions in which firefighters carry out extinguishing operations. Temperature values converted from analog form to figures using appropriate analog-to-digital converters were recorded and saved in the computer memory.

Two fires were recorded with the Drager UCF 9000 thermal-imaging camera. All measurements were recorded with a video camera placed in a special housing.

2.3. Description of the Experiment

About 200 kg of wood and chipboard were used for each of the fire tests in accordance with the recommendations given in the training program in the field of internal fire extinguishing approved by the Commander-in-Chief of the State Fire Service. The combustible material was placed on the floor in the corner of the room and two adjacent walls in accordance with the recommendations for this type of training. After reaching about 200 °C on the T10 thermocouple, the door was closed and the extinguishing was started for 15 s with the help of the extinguishing lance. Then, after waiting for about 2 min, the room with a fire line ended with a torch was searched and the fire was extinguished according to the tactics of fighting internal fires. The extinguishing lances were fed from a GBA 2.5/24 fire-extinguishing vehicle with an autopump with automatic pressure regulation. The extinguishing line was made of one section of the W75 hose and one section of the W42 hose (in the case of the MK lance) or W25 (in the case of the fognail lance). The feed pressure was 0.8 MPa during all experiments. The efficiency of the MK lance was approximately three times that of the fognail lance. Four test fires were carried out. The first was extinguished with a fognail attack lance, the second with an MK lance with an attack head, the third with a fognail defense lance and the fourth with an MK lance with a defense head. The lances with the attack heads were pierced through the shorter wall in the middle at a height of about 1.3 m. The lances with the defense heads were pierced through the ceiling in the center of the room with a hammer drill and placed perpendicular to the floor plane at a height of 2 m from the floor. During each of the experiments, the temperature distribution in the room, and in particular its changes during the application of water mist from the extinguishing lance, were recorded.

3. Results

Figure 6, Figure 7, Figure 8 and Figure 9 show the temperature curves measured at the selected six measurement points (see Figure 5) obtained in the individual tests discussed in Section 2.3. The time in which the water-mist stream from the extinguishing lance took place (15 s) is marked on the graphs with a blue rectangle. From the point of view of the fire suppression efficiency of the extinguishing lances, important are values such as the rate of temperature decrease after starting the stream of supplied water, the average temperature that is established after the end of its delivery, as well as the difference between the maximum temperature and the set temperature. For individual detectors and the tests performed, these values are summarized in

Table 1. Average temperature drop rates in °C/s after extinguishing for individual tests and thermocouple sensors.

Test No (Lance Name)	Thermocouple No
	T2	T3	T4	T5	T6	T7	T8	T9	T10
1 (Fognail attack)	12.5	8.2	10.9	-	-	-	7.4	9.0	7.0
2 (MK attack)	11.8	2.3	9.7	-	-	-	7.4	11.9	5.4
3 (Fognail defense)	5.4	-	10.6	-	11.7	-	6.2	5.5	3.6
4 (MK defense)	-	-	22.5	23.7	11.3	5.6	5.5	-	3.6

,

Table 2. Average temperature value in °C fixed after the end of extinguishing for individual tests and thermocouple sensors.

Test No (Lance Name)	Thermocouple No
	T2	T3	T4	T5	T6	T7	T8	T9	T10
1 (Fognail attack)	105	108	100	-	-	-	76	78	56
2 (MK attack)	350	200	160	-	-	-	150	67	50
3 (Fognail defense)	172	-	75	-	63	-	136	140	74
4 (MK defense)	-	-	69	60	128	120	120	-	72

and

Table 3. The temperature difference in °C between the maximum value and the one fixed after the extinguishing for individual tests and thermocouple sensors.

Test No (Lance Name)	Thermocouple No
	T2	T3	T4	T5	T6	T7	T8	T9	T10
1 (Fognail attack)	405	239	345	-	-	-	247	216	147
2 (MK attack)	202	421	352	-	-	-	186	287	173
3 (Fognail defense)	299	-	335	-	280	-	172	172	133
4 (MK defense)	-	-	437	341	222	236	196	-	142

. The most favorable values are marked in green, and the least favorable, from the point of view of extinguishing efficiency, in red.

4. Discussion

4.1. Extinguishing with Fognail Attack Lance

Based on the temperature measured by the thermocouples T2, T3, T4, T8, T9 and T10, whose curves are shown in Figure 6, it can be concluded that the sensors installed under the ceiling, which were closer to the source of the fire (T2 and T3), registered a fast increase in temperature in the interval between 400 s and 450 s (approximately 6 °C/s for T2 and 4.2 °C/s for T3). After this time, the temperature was relatively stabilized, oscillating around the higher value, the closer the sensor was to the source of the fire. For example, for thermocouple T2 it was about 450 °C, for thermocouple T3 about 300 °C. Thermocouple T2 also recorded the highest maximum temperature value, exceeding 500 °C. For ceiling thermocouples located further from the fire source (T8 and T9), the temperature increase was much slower (about 1 °C/s for T9 and 1.44 °C/s for T8) and practically continued until extinguishing began. As for the T10 thermocouple installed at a height of 1 m, a significant increase in temperature recorded by it with an average speed of about 1.4 °C/s can be observed only after about 450 s of fire duration. In accordance with the adopted assumption, the extinguishing process with the lance was started after the temperature of 200 °C on the T10 thermocouple was exceeded (in this case it was 203 °C in 568 s of the fire) and after about 15 s, i.e., in 583 s of the fire, the extinguishing was stopped. As a result of extinguishing with the fognail attack lance, all thermocouples showed a rapid drop in the temperature value to a level ranging from 50 °C to 108 °C (see Table 2). The maximum mean temperature drop rate of about 12.5 °C/s was observed for the T2 thermocouple, and the lowest one, about 7 °C/s for the T10 thermocouple (see Table 1). As expected, based on Table 3, it can be concluded that the maximum difference between the maximum value and the value determined after the extinguishing process was recorded on the T2 sensor (approximately 405 °C) and the smallest one on the T10 sensor (approximately 147 °C). It can also be seen that the sensor T3 furthest from the lance head registered the drop with a delay of about 20 s. This is due to the shape of the fog stream, which is narrow and long in relation to the firebox. Its horizontal range is about 8 m with a low-pressure supply, and the greatest width is about 2 m. After the water was evaporated and the fire gases mixed, this sensor also recorded a drop to less than 100 °C. In the room at a height of 1 m, a temperature of about 50 °C is maintained for a long time, which allows the rescuers to enter the room and extinguish the fire using conventional methods, e.g., a Turbo water nozzle.

Study participants observed a violent tug on the firebox door as the only vent. Air was sucked in through the leaks, with a characteristic whistle. This is evidence that negative pressure was created in the room as a result of the rapid cooling of the fire gases. As a result of the mist application, water vapor was formed, which filled the room; however, after opening the front door, the visibility and comfort of the rescuers’ work improved significantly.

4.2. Extinguishing with MK Attack Lance

On the basis of the temperature measured by the thermocouples T2, T3, T4, T8, T9 and T10, whose curves are shown in Figure 7, it can be concluded that the nature of temperature changes until the start of extinguishing (at about 1000 s from the moment of recording) was similar for all analyzed sensors. Up to about 680 s, an increase in temperature was recorded, then a decrease to about 750 s due to the closing of the door to the room, then an increase again to about 850 s. After this time, the temperature measured by sensors located closer to the source of the fire slowly decreased, while, on the other sensors, it stabilized at the level of about 300 °C in the case of T8 and T9 sensors and 200 °C in the case of the T10 sensor. As expected, as in the case of the first test, the maximum temperatures measured by sensors T2, T3 and T4 are significantly higher than the temperatures measured by sensors T8 and T9. For example, it exceeds 600 °C for sensor T3 and 500 °C for sensors T2 and T4, while for sensors T8 and T9 it does not exceed 355 °C. In this test, the extinguishing in the form of the fog stream produced by the MK attack lance was started later than in other cases, only after reaching a temperature stabilization of a few minutes at the level of 200 °C measured by the T10 thermocouple (after about 1000 s counted from the moment of recording). After its administration, the temperature measured on all sensors dropped almost immediately (on the T2 and T3 thermocouples located closest to the fire source after slight fluctuations). The rate of this decrease was different and, further, it was in ascending order: 2.3 °C/s for T3, 5.4 °C/s for T10, 7.4 °C/s for T8, 9.7 °C/s for T4, 11.8 °C/s for T2 and 11.9 °C/s for T9 (see Table 1). After extinguishing for 15 s, the following temperature values were obtained on individual sensors (given in order from the highest to the lowest): 350 °C for T2, 160 °C for T4, 150 °C for T8, 67 °C for T9 and 50 °C for T10 (see Table 2). In the case of the T3 thermocouple farthest from the lance head, the temperature drop was much slower than in the case of the other sensors and only after about 150 s from the end of extinguishing did it reach the level of about 200 °C. This is due to the shape of the fog stream, which is narrow and long in relation to the firebox. Its horizontal range is about 8 m with a low-pressure supply, and the maximum width is about 2 m. About 100 s after the application of the fog, the temperature readings began to increase again, but did not exceed 300 °C. The safe waiting time for taking fire-fighting measures was maintained. The fire was abruptly suppressed and safe conditions were created for internal operations. In a room at a height of 1 m, a temperature of around 45 °C was maintained.

4.3. Extinguishing with Fognail Defense Lance

On the basis of the temperature curves shown in Figure 8, as in the previous tests, it is possible to distinguish the range in which the temperate stabilized at an appropriate level depending on the distance from the fire source (fire controlled by ventilation). After closing the door to the room for about 325 s (the temperature measured on the T10 thermocouple was then about 150 °C), a gradual drop in temperature was observed on all sensors mounted under the ceiling (anti-ventilation). After reaching a stable level of 200 °C on the T10 thermocouple, extinguishing was started by applying water mist to the ceiling zone using the fognail defense lance (after about 350 s from the beginning of recording). As a result, a rapid drop in temperature was obtained on all sensors, with the highest value equal to 11.7 °C/s being obtained for the T6 thermocouple, and the lowest, equal to 3.6 °C/s, for the T10 thermocouple (see Table 1). After the extinguishing ceased, depending on the sensor, the temperature was either stabilized at a certain level for a longer or shorter time (approximately 60–80 °C in the case of T4, T6 and T10 sensors and approximately 140 °C in the case of T8 and T9 sensors) or it gradual decreased to the value of about 170 °C in the case of the T2 sensor (see Table 2). If firefighters do not take action to extinguish the suppressed fire within 525 s, the temperature rises again to the maximum values comparable to those before the extinguishing process. The maximum differences between the maximum value and the set temperature after the end of extinguishing were, respectively, in descending order: 335 °C for T4, 299 °C for T2, 280 °C for T6, 172 °C for T6 and T9 and 133 °C for T10 (see Table 3). The use of a lance above the fire by feeding for 15 s to the ceiling zone allowed the temperature to drop at a height of 1 m to a level of about 70 °C. This created safe conditions for firefighters to enter the room and the direct extinguishing of the fire, e.g., with a Turbo water nozzle.

4.4. Extinguishing with MK Defense Lance

On the basis of the temperature curves shown in Figure 9, it can be concluded that, after about 300 s from the start of the recording, the temperature measured by all the analyzed sensors stabilized. As in the previously discussed tests, the highest temperatures were obtained for the thermocouples closest to the fire source (in the case of this test, the indications of the T1, T2 and T3 sensors were omitted due to their damage during the measurement). For example, the maximum temperature values before quenching were: 510 °C for T4, 400 °C for T5, 365 °C for T7, 350 °C for T6, and 316 °C for T8. The temperature value on sensor T10 exceeded 200 °C after 413 s from the start of recording and then stabilized at an average level of about 210 °C. After approximately 465 s, a water umbrella with a diameter of approximately 5 m was applied from the ceiling zone for 15 s using a defense head located in the center of the room. On all analyzed thermocouples, a sharp decrease in values was recorded with the following average velocities: 3.6 °C/s for T10, 5.5 °C/s for T8, 5.6 °C/s for T7, 11.3 °C/s for T6, 22.5 °C/s for T4 and 23.7 °C/s for T5 (see Table 1). After the extinguishing was finished, after a longer or shorter time (the T4 and T5 thermocouples closest to the head showed the greatest drops, to about 60 °C, but after about a minute they increased to the same level as the other thermocouples) all the temperatures measured by the thermocouples in the zone ceiling stabilized at the level of 120–130 °C (see Table 2). The maximum differences between the maximum value and the set temperature after the end of extinguishing were, respectively, in descending order: 437 °C for T4, 341 °C for T5, 236 °C for T7, 222 °C for T6, 196 °C for T8 and 142 °C for T10 (see Table 3). Most importantly from the point of view of safety, the average temperature that was recorded on the T10 thermocouple was about 72 °C, which allows firefighters in appropriate clothing to enter the room and extinguish the fire (see Table 2). If this had not happened, the temperature would have started to increase again, similarly to the third test described above, because after several-dozen seconds from the end of extinguishing, a gradual re-ignition of the fire would be noticed.

5. Conclusions

The intention of the authors of this study was to investigate the methods of suppressing fires using fog lances and to show to what extent they are effective in conditions of difficult to access rooms with the source of a fire. For this purpose, four full-scale fire extinguishing experiments with different types of extinguishing lances were discussed. Two of them were intended for attack and the other two for defense. They show a number of advantages, the greatest of which is the low cost of purchase and operation compared to available high-pressure water-mist-delivery devices. They are powered by commonly available fittings and have the possibility of piercing. The extension of the equipment with a multi-purpose drill (19 mm for fognail lances, 35 mm for MK lances) with a dedicated drill provides further possibilities of using the extinguishing lance. The possibility of piercing the MK lance with a hammer is limited; during the tests it was necessary to make a hole with a drill. Fognail lances, however, have a low mechanical strength, but are characterized by low weight; smaller mist droplets and greater mobility during operations compared to the MK lance.

During the tests covering both the development of the fire and the extinguishing process itself, the temperature was measured at several points in the ceiling zone and at a height of 1 m.

Based on the analysis of the obtained results in the form of temperature curves, with particular emphasis on the time interval in which the extinguishing was carried out, the following conclusions were formulated:

• Extinguishing with each of the tested lances, regardless of whether it was a lance intended for attack or defense, effectively suppressed the fire, which was associated with a rapid drop in temperature both in the ceiling zone and at a height of 1 m. The lowest temperature determined there after the end of extinguishing was 50 °C obtained for the MK attack lance and the highest was about 74 °C for the fognail defense lance.
• The higher efficiency of the MK lance had a very insignificant effect on the fire-suppression efficiency, because the difference between the obtained temperature level after the extinguishing process was completed did not exceed 6 °C. Hence, it can be concluded that the fognail lance is characterized by several times less water consumption and thus losses associated with flooding with a comparable extinguishing effect. Moreover, it is much lighter and easier to use than the MK lance. The MK lance can only be recommended if you need to pierce it through a thicker and harder wall, for which the fognail lance is too fragile.
• Suppression of fires with a fog lance, which reduces the temperature at a height of 1 m to a level below 80 °C, allows firefighters dressed in appropriate protective clothing to undertake traditional extinguishing activities, e.g., using a Turbo nozzle, which would not be possible before its use. It should be performed no later than a few minutes after the 15-s extinguishing cycle with the lance, otherwise the temperature would rise again, even exceeding the level of 400 °C in the ceiling zone.

To sum up, it can be stated that the use of fog lances in the suppression of developed fires, to which the access of firefighters is limited, is as effective as possible. It increases the safety of rescuers by administering fog outside the room with the fire and reducing the amount of oxygen in this room, thanks to closed ventilation openings (e.g., doors). They are opened only after the fire has been adequately suppressed, when the conditions in the room can be considered safe.