Innovation – Water mist
A modern tactic of extinguishing urban rail vehicles with the use of water mist
Putting out rail vehicles is not a light, easy and pleasant task. The main threat and difficulty in the implementation of the tactical intention of the conducted action is the presence of high voltages of the overhead contact line supplying the devices and driving elements. It might seem that it is absolutely unacceptable to supply water or foam before disconnecting the power supply – but is it really?
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Tram fire statistics show a small number of this type of hazardous event.
The circumstances of the fire of the 105N high-floor tram in November 2019, which occurred at the Okęcie terminus in Warsaw, are described in the Internet media. The cause of the incident was the ignition of the converter in the first car, which resulted in the appearance of thick smoke inside. As part of the activities performed, the technical services disconnected the voltage in the traction network for safety reasons. Three teams of firefighters equipped with a thermal imaging camera worked on the site.
Another interesting case was a fire of a tram of the same type on the Śląsko-Dąbrowski Bridge in December 2018. It was caused by a short-circuit in the electrical system (the distribution box behind the driver’s seat caught fire). The tram driver stopped the train and released all passengers (two windows in the tram were broken during the evacuation), but traffic on the Vistula crossing was blocked for over half an hour.
Both events concerned old-type vehicles. According to the information obtained from the Warsaw Trams, none of the most modern trams have fired yet.
The classification of the rolling stock of the company Warsaw Trams is as follows:
- high-floor (historic trams, 105Na and derivatives, 123N, technical)
- low-floor (116Na, 120N, 120Na, 120Na DUO, 128N, 134N)
As of December 27, 2020 information on the number of trams operated in Warsaw shows that in the company Warsaw Trams there are 311 low-floor articulated carriages from the various groups: 112N – 1, 116N – 29, 120N – 201, 128N – 50, 134N – 30.
In the case of city trams, the issues of organizing and conducting a rescue operation include the entire surroundings of the accident site, evacuation of passengers, the use of clothing and personal protective equipment to prevent electrocution, as well as significant restrictions on the use of the basic extinguishing agent, which is water. Not only the Warsaw metro, but also some of the tram lines in Poland run underground, such as the Krakow Fast Tram Tunnel. Extinguishing fires in such places requires the use of ventilation tactics (Fig. 1), additional lighting and the choice of evacuation methods other than in the case of overground lines.
Being aware of the specific hazards and conditions of the operation, the tool facilitating operational activities may be fog lances (Fig. 2).
Specific threats in public transport by rail
As mentioned, a particular threat to firefighters during rescue operations related to extinguishing rail vehicles is the possibility of electric shock. Therefore, one of the basic activities that should be performed before taking other actions is the emergency catenary sewing, which consists in connecting the electric cable with a single rail with a metal line. Its purpose is to equalize the potentials of the contact line and the return line to bring the residual charge to the ground. In the case of traffic accidents related to the breaking of the traction line supplying rail vehicles, the situation becomes even more complicated. Be aware that the minimum safe distance from the line on the ground is 10 meters.
Table 1. Voltage in the supply network of selected rail vehicles
|No.||Type of rail transport||Voltage|
|3.||Warsaw Commuter Railway||3000 V|
Source: own study
Safety systems of selected city trams
One of the basic duties of a tram driver during emergency events related to a fire is to lower the current collector (pantograph). In modern trams, this operation is performed using buttons on the panel in the cabin. It is important to turn off the batteries after lowering the pantograph. It is also possible to lower the current collector in an emergency using the crank located behind the driver’s seat (the crank should be inserted into a special socket and by turning it the pantograph is lowered). It should be taken into account that the steel structure of the raised current collector in contact with the overhead contact line is at high voltage (approx. 600 V).
Rescue cards for selected trams: 128N and 134N are shown in Fig. 3.
Modern electric traction vehicles, apart from batteries, are equipped with recuperation and electric energy storage systems, enabling partial recovery of kinetic energy of a speeding vehicle during braking (Giziński 2007). Fig. 4 shows the appearance of the battery box and the supercapacitor (both components are located on the roof of the tram).
The power supply to the batteries can be cut off using special disconnectors. Disconnecting the battery does not disconnect the supercapacitor, therefore its disconnect should be used. Both disconnectors are shown in fig. 5.
It should be added that the 128N and 134N trams are equipped with two dangerous voltage signals located on the vehicle roof.
Principles of organization of rescue operations
Apart from KSRG units, specialist technical services at the disposal of the management board of a communication company are among the necessary forces and resources to carry out rescue operations to eliminate hazards arising from the use of rail vehicles. They include track, rail, energy and crane emergency services. It is they who will provide professional support during rescue operations. Thanks to the knowledge of the rolling stock, they have knowledge of the construction and design possibilities. They are able to assemble the pantograph, carry out sewing (if necessary), and after the completion of the activities, they will enable the restoration of the communication line, e.g. by re-railing. The first action performed by the fire brigade should be to try to lower the pantographs and disconnect the main circuit breaker.
As part of the basic training for rescuers available for action as a first-line unit, particular attention should be paid to the safety of operations.
The applied tactic of extinguishing rail vehicle fires
The UK has developed National Operational Guidelines as the basis for the development of operational principles, procedures and training for firefighters to deal effectively and safely with incidents. It is a “good industry practice” that can be used by all fire-fighting services. The tactical intentions for this type of event, developed by the National Operational Guidance expert team, include three elements:
- Fire extinguishing and elimination of all ignition sources.
- Ensuring the safety of all people in the danger zone (staff, passengers, bystanders, firefighters and rescuers).
- Evacuation, reduction of material and environmental losses.
Further objectives of the activities include: preventing the spread of the effects of the incident, minimizing the effects of the incident (including fire brigade activities) on the environment, securing the scene (preserving material evidence and traces for fire investigations), restoring the operation of the communication line to the state before the fire.
Priorities for tactical firefighting activities include: disconnecting and earthing the overhead line (including verifying that there is no voltage at the site of action) prior to commencing firefighting, and ensuring a safe working environment for firefighters and other emergency services.
The remaining elements of the tactic were: protection of the environment and infrastructure against heat radiation and the spread of fire (e.g. with the use of water curtains), and in the event of a need to evacuate – determining the number of people and developing a plan for their relocation to safe zones, as well as ensuring appropriate living conditions and medical care (including the establishment of a first aid point for victims).
In the British solution, the tactical scope also included the preparation of documentation (report) from the action carried out, including the planned activities, methods of communication and the applied fire tactics.
Operational activities in the elimination of fires on rail vehicles consist of:
– developing the most effective tactics to limit the development of a fire by selecting the appropriate extinguishing method, appropriate extinguishing agents (e.g. water or water fog, foam, extinguishing powder, CO2),
– creating access to the source of fire by cutting or cutting out elements and partitions of the vehicle, and at a later stage gaining access to the interior of the vehicle through doors, connectors and windows (if necessary, cutting out additional escape passages in construction elements of wagons).
In the case of a larger scale of the event, a forward control point should be organized.
Alternative fire protection solutions and extinguishing techniques
In developed tram fires, the most combustible material may come from passenger seats (Hohenwarter 2016). One of the methods of fire protection for this type of rolling stock are active fire extinguishing systems using water mist under high pressure (Barbagli 2016).
An effective system for extinguishing rail vehicle fires can also be a cutting and extinguishing device. It provides safer work for firefighters and is approved for extinguishing live equipment up to 420 kV. The properly ground water mist is fed under high pressure (200-300 bar) through a special nozzle, which allows it to penetrate the fire and instantly transforms water into water vapor. The water evaporation reaction removes huge amounts of heat from the fire, which is very effective in inhibiting the development of the most difficult fires that occur inside vehicles. The cutting function enables a quick start of an effective extinguishing operation from a safe place outside the wagon (Fig. 6).
Tests carried out at the training ground of the PSP Aspirant School in Poznań showed that:
– it takes 2 seconds for the stream of water to break through the side of the tram,
– the generated water mist fills the entire volume of the wagon in a few seconds,
– it is possible to carry out safe activities from outside the vehicle.
Incidents involving trams are not frequent, but require specialist knowledge and the preparation of appropriate procedures precisely because they are not routine activities carried out by the State Fire Service. The use of quenching and cutting lances with an extinguishing medium in the form of high-pressure water mist can significantly improve the safety of rescuers. However, the variety of rolling stock and different locations of elements that may constitute additional threats to those conducting rescue operations requires the development of detailed procedures depending on the model and type of rail vehicle, taking into account the specificity of the rolling stock in a given city. Therefore, the author of the article asks companies managing public transport and tram producers (PESA Bydgoszcz SA, Stadler Polska Sp. z o.o.).
Barbagli M., Active fire extinguishing systems with the use of high pressure water mist: first test experience according to the Italian standard UNI 11565 (Low Noise Barriers – High-pressure Water Mist Active Firefighting Systems: First Testing Experiences According to Italian Standard UNI 11565). “Railway Problems” 2016, No. 171.
Giziński P., Condenser energy storage for electric traction vehicles. “Technika Transportu Szynowego” 2007, No. 1-2.
Hohenwarter D., Experience gained in the fire tests of seats carried out in accordance with the standards EN 45 545-2 and DIN 5510-2 (Experience Gained from Fire Tests According to EN 45 545-2 and DIN 5510-2 for Testing of Seats). “Railway Problems” 2016, No. 171.
Ksyna Ł., Characteristics of the Warsaw Trams Rolling Stock. Training material for rescue and firefighting units of the State Fire Service. Warsaw Trams, Warsaw 2018.
Podlasiński R., Karabin P., Basic script for technical rescue training carried out by KSRG. Warsaw 2018.
The film “Tram – possible to put out through the wall of the wagon – CutLanca”, https://www.youtube.com/watch?v=MAcL5MQ0S-k
National Center for Coordination of Rescue and Civil Protection, A set of test questions to be used in checking the knowledge of combat division casts and management positions during operational readiness inspections. KG PSP, Warsaw 2017.
High Voltage Laboratory, Test report no. EWN / 132 / E / 20. LancePro1 mist lance. Institute of Power Engineering – Research Institute, Warsaw 2020.
National Operational Guidance, Railway or tram fire. Website https://www.ukfrs.com/scenarios/railway-or-tram-fire
A fire on a tram. “Thick smoke inside one of the carriages”. Website https://tvn24.pl/tvnwarszawa/najnowsze/warszawa-petla-okecie-pozar-tramwaju-gesty-dym-wewnetrz-wagonu-2022081
A fire of a tram on the Śląsko-Dąbrowski Bridge. Traffic has stopped, traffic jams have formed. Website https://warszawa.wyborcza.pl/warszawa/7,54420,24295006,pozar-tramwaju-na-moscie-slasko-dabrowskim-wstrzymano-ruch.html
Regulation of the Minister of Infrastructure of 2 March 2011 on the technical conditions of trams and trolleybuses and the scope of their necessary equipment. Journal of Laws of 2011, no. 65, item 344.
Tramwaje Warszawskie Sp. z o.o. Low-floor wagons. Website http://tramwar.pl/tram116n.html
For more information please see article:
Tuśnio N., Wolny P., New Techniques and a New Approach to the Effective Extinguishing of Fully Developed Fires in Enclosed Spaces. “INTERNAL SECURITY” 2016, 8 (1), 213-224.