PRELIMINARY RISK ANALYSIS OF LOW PRESSURE RAILWAY TRANSPORT

: The subject of this study is a preliminary risk analysis during travel by the low pressure railway Hyperloop. The main objective was to formulate recommendations related to the development of the project of the new transport mode. The main analysis was preceded by the identification of Man – Machine - Environment system. Undesirable events were identified for each of the specified steps of a ride. For each event, a risk assessment was performed using Risk Score based method. The causes, effects and preventive actions were also listed. Events with the highest risk score were indicated. The need to develop procedures for safety checks and emergency situations was pointed out. It was shown that the safety analysis of the transport system should be extended after a final project development of the railway system and the necessary infrastructure.


Introduction
Safety activities concern many aspects of man life and his functioning in the Man-Machine-Environment (M-M-E) system. The development of safety science is related to the ability of better hazard identification, considering safety issues at the stage of designing technical devices and progress in counteracting threats by developing existing and proposing new methods of risk and reliability analysis [12].
One system whose concepts are being developed around the world is the "Hyperloop". It is a mode of transport that can be classified between the aircraft and the train. It involves travelling at very high speed in a special prepared capsule inside a reduced pressure tunnel [10]. Although the concept of passing a vehicle inside a tube with reduced pressure has been considered for years, the author of the name and assumptions of the "Hyperloop" vehicle is the American entrepreneur and multi-billionaire Elon Musk. According to his idea, the vehicle is supposed to be, compared to other means of transport, safer, faster, cheaper, more comfortable, resistant to weather conditions and earthquakes, sustainable in terms of energy and collision-free [8]. It should be noted that in some countries -the USA and South Korea studies and works are so advanced that test runs are already taking place. In Korea, test runs without passengers were conducted at speeds of about 700 and 1000 km/h [13]. In the USA, a test ride with two passengers was carried out on a 500 meters test track at a speed of 160 km/h, there was also a series of test runs at approx. 400 km/h without passengers. Ultimately, it is planned to exceed 1000 km/h over a longer distance [14]. In Poland tests have taken place in a mechanical and virtual low pressure railway simulator [15]. A description of the main principles of operation of the low-pressure railway of which the simulator was built can be found in the study [9].
In all projects about this new mode of transport, safety analyses play an important role. Due to the lack of relevant standards and regulations in this field, it is necessary to refer to universal standards for the safety of technical equipment [16], as well as regulations [17,18] and standards (e.g. [19]) related to traditional railway. Normative acts on the principles of conducting safety checks in air transport [20,21] may be useful, a possibility of using lightweight materials used in aviation should be considered. Original concepts and solutions related to risk analysis and management in transport [6,11] are also important. Attempts are made to develop appropriate recommendations related to the "Hyperloop" technology also in the context of safety system management. It is realized on the basis of risk analyses with the use of: detailed description and assessment of individual properties, characteristics and components of the transport system [5], risk maps and SWIFT (Structured What If Technique) method [7], HAZOP (Hazard and Operability Study) based model [2]. In ongoing research, comparisons and references to existing transport systems can often be found. Issues related to the potential for technological development and commercialization of investments [4] and public acceptance of the new transport mode [1] are also considered.
The risk analysis to be carried out in this paper will address aspects related to the safety of use and ergonomics of the low pressure rail system using a qualitative indicator (scoring) method similar to Risk Score [3,12]. The economic or social issues associated with implementing the low pressure rail system will not be studied.

M-M-E system identification
Before starting the identification of hazards and searching for possible undesirable events, it will be important to identify the analyzed Man -Machine -Environment (M-M-E) system. The identification of individual system segments is presented in table 1. Table 1 M-M-E system identification

Man
Machine Environment  low pressure rail passengers;  persons responsible for the management of rail traffic;  other staff of railway and station.
 "Hyperloop" low pressure railway consisting of three modules: passenger, safety and locomotion (transport).
 tube system located largely underground (pipe tunnels);  necessary infrastructure in the form of stations, airlocks, cross conveyors, technical areas, emergency chambers.
The concept of low pressure railway was developed within the framework of the implemented project. Its main assumption is its modularity. It is assumed that the vehicle is divided into the following modules: passenger/freight, safety and locomotion. The vehicle according to this concept would have one or both ends of the safety module opened, through which passenger or freight modules are inserted into its interior. This is shown in fig. 1. The main author of the railroad concept, detailed technical solutions and aerodynamic analyses carried out [9] is professor Janusz Piechna. The main design and maintenance assumptions are as follows:  pressure in the tunnel: 1000 Pa, in the vehicle: atmospheric;  maximum speed of the capsule: 720 km/h;  maximum linear acceleration: 0.25 g (2.5 m/s 2 );  separation between vehicles: 24 km (2 min);  wheel unit: standard wheel system with rolling bearings;  maximum number of passengers in one vehicle: 30 or 56. The station concept assumes the separation of the following zones: safety control zone, platform hall, atmospheric pressure zone, low pressure zone. In addition, it is assumed to use special airlocks and cross conveyors to move the vehicle to the low pressure zone and then the appropriate tube (tunnel). During the rail ride, it was assumed that the acceleration and braking of the railroad will be carried out using linear motors and brakes. According to the developed concept, the vehicle will be accelerated to the maximum speed, then after the speed decreases to half of the maximum value, the vehicle will be accelerated using linear motors spaced every 300 km. Moreover, emergency chambers will be used in the event of a system failure. In contrast to the other concepts considered [10], very high speeds (above 0.6 Ma) are not assumed. In such a case, it will be possible to use a traditional locomotion system and there will be no significant problems in ensuring the stability of the capsule movement. This will significantly reduce the construction complexity and cost of the project. A detailed description of the station concept and the technical infrastructure used can be found in [9].

Hazard identification
Hazard identification is the recognition of undesirable events that may occur at the workplace or while conducting a project, study, experiment, or using technical devices. Relevant here will be events that may occur during a railway ride and activities immediately before and after travel.
To initially identify hazards, undesirable events that may occur during the various stages of a low pressure railway vehicle ride were determined:  Steps 1 and 11: Moving around the station;  Step 2: Passing the security check;  Steps 3 and 9: Entering/exiting the vehicle (passenger module) and taking up/leaving seats;  Steps 4 and 8: Passenger module insertion/ejection from the safety capsule, crossing the airlock and low pressure zone;  Steps 5 and 7: Accelerating or braking the vehicle;  Step 6: Rail travel. Steps (tasks) were divided into activities in order to be able to more precisely select undesirable events.
Possible undesirable events for each step and activity were identified in table 2. For each event the probable causes, effects, and suggested actions to eliminate or reduce the negative effects of the specified event were listed in table 3.  Attention should be paid to events related to failure of vehicles or conveyors -primarily events E16, E17, E28. In case of event E16: Blocked entry to the station, two scenarios can be distinguished: a) failure of another vehicle while still in the tunnel -in this case, the conception of "safety buffer" is developed; b) failure of another vehicle in the low pressure zone or its conveyorin this case, a solution must be devised to allow emergency transfer of the capsule to another cross conveyor (perhaps using a technical crane). In the case of event E17: Vehicle stopping while riding in the low pressure zone, a scenario can be distinguished that coincides with scenario b for event E16.
In case of event E28: Vehicle stopping during travel (e.g. bearings failure, failure of the low pressure maintenance system) the concept of using emergency stations, emergency vehicles and carrying out evacuation is provided.
Event E29: Loss of safety capsule containment forces the vehicle to be equipped with oxygen cylinders and masks and actions as in the previous event. However, it can be assumed that with high care in the design and construction of this capsule, the probability of this event occurrence is negligible.
Similarly, for event E30: Tube damage, procedures for conducting rescue and evacuation should be refined. Geodynamic monitoring of the earth should also be undertaken and the area should be secured against any unauthorized excavation works and the occurrence of a terrorist attack.

Development of indicator method
In this study, a proprietary indicator method is developed to assess the risk of low pressure railway transport. The defined risk indicator was based on the Risk Score method. Due to the fact that the analysis is conducted for one railway ride, the exposure factor was not considered (as opposed to the classical method). The risk score is as follows: where: nundesirable event index (from 1 to 31); risk score for the n th undesirable event; probability of occurrence factor for the n th undesirable event occurring during a single ride, taking values from 1 to 100; consequences (injuries severity) factor with values from 1 to 100.
For all undesirable events the values of and were estimated by experts using the descriptive values provided in table 4. The estimates were performed independently by the authors of the paper and are presented in table 5.  No risk score was obtained for any event to conclude that it is high (significant) and drastic preventive action is required. The events that need special attention in the final design of the railway transport system, the necessary infrastructure and their construction are the following:  Contact with bacteria and viruses during rail travel;  Vehicle stopping while riding in the low pressure zone 1 ;  Loss of safety capsule containment during rail travel;  Fire during rail travel;  Nausea, feeling of claustrophobia during rail travel;  Contact with bacteria and viruses at the train station;  Feeling of boredom, weariness, irritability during rail travel;  Aggressive behavior / attack of a other passenger, terrorist attack;  Impatience, weariness during the security check; It can be noticed that the events with the highest risk score are usually associated with high potential consequences (loss of safety capsule containment, fire during travel, vehicle stopping while riding in the low pressure zone) or with high probability of occurrence (contact with viruses, fatigue, malaise). An exception is the event related to aggressive behavior of another passenger. In this case, the final score was evenly influenced by the probability and consequences factors. The experts showed a relatively high risk associated with the event involving contact with viruses and bacteria. This is mainly related to the epidemiological situation in Poland and in the world during the research work related to the Hyperloop project.

Recommendations related to the development of the railway project
Based on the conducted risk analysis, recommendations related to the development of the "Hyperloop" low pressure railway can be listed.
For the sake of ensuring an appropriate level of safety during the travel, it is necessary to provide appropriate systems and equipment components and take the following preventive measures:  video/thermovision monitoring, use of appropriate smoke detectors and fire safety measures both at the station and in the vehicle;  choosing appropriate materials for the seats (avoiding flammable materials);  providing voice messages and an ability to communicate with staff;  requiring staff and passengers to be equipped with personal protective equipment, installing hand disinfection dispensers at railway stations, frequent ventilation and disinfection of the station and vehicles;  use of redundancy in the selection of mechanical systems, utmost care in the design of travel system and infrastructure;  use of module tracking / traffic management system;  equipping passenger modules with oxygen cylinders in case of loss of containment;  developing procedures for conducting evacuation and rescue operations;  developing a concept for transfer a vehicle in the event of a vehicle or conveyor failure in the low pressure zone;  avoiding high steps and slippery surfaces in the station area, protecting against the possibility of falling under the vehicle;  developing checking procedures. In order to ensure an appropriate level of comfort during the use of the low pressure train in the context of minimizing the occurrence of fatigue, boredom, irritability or poor well-being, it is important to provide the following systems and equipment:  ventilation and air conditioning system, ensuring fresh air supply and temperature comfort on the station and in the vehicle;  selection of appropriate lighting inside the cabin;  display system with monitors;  mobile and/or Wi-Fi network ability;  cabin interior layout to minimize the feeling of claustrophobia. The above recommendations were developed primarily on the basis of the conducted detailed hazard identification. The conducted risk analysis showed the necessity to develop assumptions for proceeding in case of a failure of a vehicle locomotion system or a failure of a cross conveyor on which the vehicle is located in a low pressure zone.

Summary and conclusions
The analysis conducted was aimed at a preliminary risk assessment of the low pressure railway "Hyperloop", providing recommendations in the formation of the final design and construction of the railway system and the necessary infrastructure (stations, technical areas, tube system). The analysis to a significant extent was carried out in a classical way. It started with an analysis of the M-M-E system, identified undesirable events that could occur during moving around the station and during travel. Then, using a proprietary indicator method based on Risk Score, the potentially most dangerous events were selected. The events ranked with the highest risk score were: contact with viruses and bacteria during travel and at the station, loss of safety capsule containment, occurrence of fire, feeling of boredom, fatigue, irritability during the ride and security checks, aggressive behavior of another passenger, nausea, feeling of claustrophobia during the ride. It was also noticed that there is no concept of what to do in case of failure of the vehicle locomotion system or the conveyor on which the vehicle is located in the low pressure zone. Attention was drawn to the need for refinement of rescue and evacuation procedures in case of a failure during the ride.
The safety analysis of the "Hyperloop" system should be extended after developing the detailed project of the railway system and the necessary infrastructure. This project should take considering the recommendations developed in this study.