Risk and Safety Management for Surveying Work in Underground Cavities that Are Difficult to Access

On 28th and 29th August 2023, scientists from the Research Center of Post-Mining (FZN) at the TH Georg Agricola University (THGA), Bochum/Germany, carried out a special task. The Paasbach piping, a tunnel structure under and in the area of the Hattingen Henrichshütte, was surveyed above and below ground. The tunnel was relocated several times over the years as the Henrichshütte grew, and the exact course was not known. The City of Hattingen’s Departments of Public Works and Civil Engineering feared structural damage that could lead to severe consequences of parts of the piping, e. g. in the area of roadways. In order to plan the necessary renovation measures, it was first necessary to obtain an accurate picture of the exact course of the piping under the city and the smelting works.

The special nature of the tunnel and the underground conditions made this a challenging task, which meant that conventional surveying companies were not willing to carry out the work in accordance with the tender. In contrast, the FZN saw a problem from the outset that addressed several research questions. A tunnel survey under constantly changing conditions in a pipe system that was actively used for decades, was constructed using a wide range of materials, has various inlets from branch tunnels and unknown inlets and has no means of communication with the outside world, offered a wide range of activities, particularly for the surveying aspects. These aspects led to a research cooperation between FZN and the city of Hattingen, within which the work was planned and finally carried out.

This article deals with the aspect of safety before and during the work. At peak times, up to 14 people were in the piping, which was characterised by complete darkness, difficult communication options, e. g. no mobile phone reception, and flowing water up to chest height over a distance of approximately 575 m. In addition, the ground is completely uneven, beams force you to bend down and the transport of any injured persons can become an obstacle course in case of doubt. From the first inspection in 2021 to the actual execution, various aspects had to be addressed in the form of a risk assessment or a hazard assessment with an associated rescue concept. Together with the Hattingen fire brigade and the mine rescue team of RAG Aktiengesellschaft, Essen/Germany, the topics were identified and the procedure for a safety concept was presented, which enabled the work to be carried out.

Authors/Autoren: Dr. rer. nat. Bodo Bernsdorf, Prof. Dr. rer. nat. Tobias Rudolph, Prof. Dr.-Ing. Peter Goerke-Mallet, Forschungszentrum Nachberg­bau (FZN), Technische Hochschule Georg Agricola (THGA), Bochum/Germany, Melanie Gendrullis, Thomas Adam, Abteilung Feuerwehr und Rettungsdienst, Stadt Hattingen/Germany, Christoph Uphues, Fachbereich Stadtbetriebe und Tiefbau, Stadt Hattingen/Germany, Dipl.-Ing. Andreas Koschare, RAG Aktiengesellschaft, Essen/Germany, Benjamin Haske M. Eng., Marcin Pawlik M. Sc., Forschungszentrum Nachbergbau (FZN), Technische Hochschule Georg Agricola (THGA), Bochum/Germany, und TU Bergakademie Freiberg, Freiberg/Germany

1  Introduction

The Paasbach is a left tributary of the Ruhr, a stream in the low mountain range that reaches the town of Hattingen from the hilly area of the Bergisches Land. Its catchment area, including all tributaries, is about 33.6 km². Since the beginning of the construction of the Hattinger Hütte in 1854 (1), hydraulic engineering has always been a challenge in the confined spaces along the Ruhr. The stream had to be relocated and increasingly piped as the Henrichshütte was expanded. The most significant conversion took place between 1882 and 1894 (1). Major changes also occurred in the course of the Ruhr relocation in 1959, which primarily affected the stream’s mouth. It can be assumed that such relocations occurred repeatedly in the course of various expansions of the smelting works, but were sometimes only inaccurately documented. The role of the adit tunnels running through the pipework is also unclear in some cases.

Safe passage through the current piping is possible at an average discharge of < 0.2 m³/s. Due to the catchment area and its location in the Bergisches Land, the water level rises quickly even during precipitation in the hinterland. The level analyses showed considerable increases in two examples. In the first case, the level rose from 0.026 m³/s to 13.6 m³/s in 1:45 h, in the second case from 0.124 m³/s to 7.79 m³/s in just 40 min (measurements by the city of Hattingen). Due to a not inconsiderable inflow of mine water from various adits, e. g. the Braut, Edeltraut, Vereinigte Wildenberg and Vogelbruch adits, estimated at between 63.3 m ³/s to 155 m³/s, the flow rate is relatively high even in times of low rainfall (own measurements by the Research Center of Post-Mining (FZN) at the TH Georg Agricola University (THGA), Bochum/Germany).

The reason for the project was that the city of Hattingen had a good idea of the course of the piping, but was unable to locate the exact position under the city, streets and smelting works. In particular, the assumedly small but largely unknown distance between the tunnel ceiling and the ground surface offered a high risk of accidents and was therefore the focus of the survey. The first joint inspections in June 2021 revealed structural damage, which also led to uncertainty as to the extent to which the covering material was sufficiently stable, especially in the area of roads that can be used by lorries.

This prompted the city of Hattingen to invite tenders for the precise measurement of the piping, which several companies responded to. However, the challenges became clear at the latest when the detailed task description was provided or after an initial inspection, so that none of the companies expressing interest placed a bid in response to the subsequent invitation to tender.

In its search for suitable partners, the city came across the activities of the FZN. The FZN is made up of a diverse team of specialists who were considered capable of performing the task. In addition to mining surveying and surveying capacities, the team includes mining engineers and safety experts. Fire and mine rescue training is available, but the necessary technical skills are also available at a university of applied sciences and are repeatedly trained, especially in the field of geomonitoring in old and post-mining, due to the extensive field work.

For the FZN, the enquiry resulted in various synergies with the work that the researchers are pursuing. In particular, the research area of geomonitoring in old and post-mining recognised scientifically challenging aspects that promised a steep learning curve in the team, but also opportunities for final theses in the Master’s programme in geoengineering and post-mining (MGN). Aspects of surveying a pipe system in different materials and ceiling heights with beams at high humidity, where it is not possible to find a secure surface on which to set up the measuring instruments, questions of laser scanning for 3D modelling and the resulting accuracy in relation to the reflective properties of the materials or water, with uncertain pathways at the same time, the number of necessary connection points for the polygon and other aspects led to the formulation of a research cooperation between the city of Hattingen and the FZN.

Once this cooperation had been established, there were ultimately two branches of work. In addition to planning the tunnel survey as the actual task, it had to be ensured that the highest conceivable safety standard for the teams deployed was implemented in the described environment and that no accidents occurred in the unsafe environment during the work. If an incident should occur, questions arose as to how an alarm could be raised and the person affected rescued in the absence of communication, and how the teams could bridge the gap for a while until the Hattingen fire brigade arrived to provide assistance. Solutions were developed in conjunction with the fire brigade and the mine rescue team, and these were subsequently incorporated into the development of the safety concept.

2  Preparations

The authors first had to get a clear picture of the location and its conditions. Although the Hattingen fire brigade was familiar with the tunnel, the conditions in the piping were more or less unknown. To this end, there was an initial inspection with the Public Works and Civil Engineering Departments on 9th June 2021. A small team led by the Public Works Department inspected the piping under optimal conditions with an extremely low water level. The team found a complex structural situation (Figure 1).

The height of the piping was generally comfortable for the inspection, except for a few beams that could become an obstacle at higher water levels. In contrast, the floor was problematic, as some scouring with higher water levels alternated with gravel from the Paasbach with sandbanks and muddy areas. Improperly disposed of rubbish, ranging from small items to shopping trolleys and even a scooter, also made it difficult to make progress. The unsafe walk was exacerbated by the complete darkness, as the helmet and hand lamps we carried did not always provide the best possible illumination. A basket stretcher provided only suboptimal conditions for rescuing injured persons. One of the main conclusions was that in future inspections and, at the latest, when a larger team is working in the piping, there must be a way to communicate with the outside world, e. g. to make emergency calls. After a few metres, there is no mobile phone contact with any of the available networks. And with a length of 570 m between the openings, even a sprained ankle could become a challenge.

2.1  Consequences of the first inspection

These findings led to several conclusions. One of the main consequences was that the Hattingen fire brigade and mine rescue team were to be involved in any further inspections. Any further inspections were to be carried out with the support of the specialists, in order to make the investigations safer when drawing up the safety concept, on the one hand, and to discuss rescue options directly with the potential rescuers, on the other.

On the other hand, additional rescue options were sought immediately along the long route. Access to the water tunnel for assistance/rescue and material supply is either via the two openings – roughly 570 m apart according to rough measurements by the mine rescue team of RAG Aktiengesellschaft, Essen/Germany – or via two known openings (manholes) that can be accessed at about one quarter and three quarters of the waterway (Figures 2, 3, 4). However, the access points appear to be unsafe and are partly characterised by the remains of rusty steps (especially S002), which pose a high risk of injury during a potential rescue.

The heights from the piping to the respective manhole are very different. On 2nd May 2023, the water surfaces in shaft S002 were about 6 m below the day opening, in shaft S008 about 2.5 m.

After the research cooperation was signed by all parties in mid-December 2022, the planning could begin. Due to the high water levels, it took until spring 2023 for a second safety inspection to be carried out for the concrete planning. This was not possible until 2nd May 2023.

As a consequence of the first impressions, the second inspection was carried out with the support of the RAG mine rescue team, the Hattingen fire brigade and the City of Hattingen’s Department of Civil Engineering (Figures 5, 6).

The fire brigade and mine rescue team contributed their expertise and commitment. This ensured that, in addition to the colleagues from the civil engineering office, only trained rescue workers were in the piping, which had a very positive effect on the creation of the safety concept.

At this point, we would like to mention the commitment of the equipment supplier Dönges GmbH & Co. KG, Wermelskirchen. The company provided a colleague who is also a member of the fire brigade to accompany the team. His task was to evaluate which type of personal protective equipment (PPE) is suitable for the underground work environment, even for those who are inexperienced in underground work. However, as the procurement of the PPE had to be put out to tender, there was no certainty at that time that the company would be awarded the contract. The focus here was on the interest in the topic.

The main finding from the second inspection was that the water depth had changed significantly at various points due to scouring after the heavy rainfall on 14th/15th July 2021. Even at low water levels, water depths of up to 1.30 m were sometimes observed. In particular, there appeared to be more abrupt changes in water depth.

Another finding was made for the communication concept. With the analogue 2 m radio equipment of the mine rescue team and the positioning of remote stations at the mine openings or the designated shafts S002 and S008, continuous communication with the outside world was ensured. It would have been possible to make an emergency call at any time.

2.2  Recognised hazards

Intrinsic hazards are recognisable in the project. Certain causes have certain effects. If employees are exposed to cause and effect, hazards arise. All work in the Paasbach water tunnel therefore poses risks to personnel, which had to be assessed before the work was carried out. The following aspects emerged from the two inspections for consideration in a risk assessment:

• Communication:
  • Communication is essential, at least in an emergency.
  • There is no secure mobile phone reception in the tunnel.
  • Communication with the outside world is therefore not guaranteed by the use of mobile phones, and requests for help may be impossible.
  • Communication during the day is also important for coordinating work, which may also become a disruptive factor when calling for help.
• Lighting:
  • There is no lighting in the tunnel.
• Subsoil/pathways:
  • The tunnel is assumed to have an extremely inhomogeneous subsoil with debris and rubbish deposits.
  • The scouring described above means that different water depths can be found in a small area, some of which are difficult to recognise.
  • These may change in position and extent between two inspections due to currents.
  • Even solid surfaces are damp and may be slippery.
• Running water:
  • The Paasbach stream flows actively through the water tunnel (current).
  • The Paasbach has a catchment area that extends well beyond the city limits of Hattingen. Even without precipitation in Hattingen or the immediate vicinity, the water level and current can rise rapidly.
  • Depending on the position in the tunnel, the time it takes for the water level to rise may be less than the time needed to escape.
  • Ten feeder tunnels flow into the upper reaches of the catchment area. At least one of them flows into the piping. High inflow rates from the feeder tunnels ensure a minimum water flow even in times of drought.
  • Flowing water with a corresponding current even at low water levels at narrow points due to structural measures, water barriers or debris.
  • Potholes and structural depressions with known water depths of up to 1.30 m (possibly deeper at higher water levels!).
  • Running water builds up a lot of pressure, especially due to the nozzle effect.
  • Objects carried along by the water, e.g. branches.
• Hygienic conditions (chemical and biological hazards):
  • The Paasbach is a body of water with “pure water”, i.e. spring water and surface water from precipitation.
  • It is not possible to rule out discharges of unknown origin (faeces, road grime, hydrocarbons, etc.).
  • Bats, various species of spiders and crayfish have been sighted in the Paasbach tunnel – all of them harmless species (eye protection may be necessary due to bat faeces).
  • There is no vegetation (climbing plants that could cause tripping hazards) inside the pipes.
• Atmosphere/weather (respiratory toxins):
  • The Paasbach is a flowing stream. Due to the constant movement of water and shafts that act as ventilation shafts due to the chimney effect, good ventilation seems to be provided.
  • No foul gases etc. (typical of standing water) are to be expected (lack of sapropel/foul sludge).
  • The sources of the emissions are unknown and pose a risk (O₂deficiency, harmful gases/respiratory poisons), which could not be determined during several inspections with measuring instruments.
  • The water tunnel is characterised by high humidity, presumably all year round.
• Temperature/water temperature:
  • The stream is not expected to exceed 10 to 12 °C even in summer, which means that work will be carried out in cool conditions.
  • The outside temperature is balanced and adapts only slowly to the conditions above ground.
• Manual work/building materials:
  • During the work, impact marks are applied using angle grinders and wall brackets are mounted on the joints using hammer drills.
  • In addition to the classic risk of injury when working with such equipment, the various building materials of unknown condition pose a risk (spalling, shattering, backfill¹, etc.).
  • In addition, the (measuring) instruments used, such as lasers, etc., pose a risk.
  • The tools are battery-powered and may cause problems if they come into contact with water (IP protection classes).
  • Noise is generated when using angle grinders and impact drills in particular. If this noise can be minimised with ear protection, there is a risk that warning signals or communication in general will also be blocked.
• Long distances:
  • Material transport must be carried out from the mouth holes (approximately 288 m distance from inlet and outlet in optimal condition, max. 575 m if the current does not allow otherwise).
  • The same applies to the rescue of people in a lying position (grinding basket).
  • If necessary, the manholes (approximately Ø 60 cm) can be used (Figures 2, 3, 4).
• Access/remaining journeys in the shafts:
  • Access is only possible via comparatively steep slopes at both entrances.
  • Both areas are densely overgrown with vegetation and impassable.
  • The shafts at the manholes are narrowed by rusty remains of ladders.
• Personnel deployed:
  • Working underground in unfamiliar surroundings is frightening for employees (possible panic reactions, claustrophobia, known or unknown).
  • Depending on their physical fitness and experience, employees may be better or worse able to cope with the demands.
  • Manual work and the use of machinery pose intrinsic dangers.
  • The use of equipment and the associated noise, reverberation and sound transmission/distortion through the variously structured tunnel walls mean that employees are exposed to unfamiliar situations even in places where they are not directly working.

¹ Backfillings are used here as a synonym for the unknown state, e.g. soil may be fluid, water/water bubbles may be under pressure, etc., which could be set in motion by the activities or could escape through the work site. Therefore, drilling through the support should be avoided during all work.

3  Procedure and concept development

3.1  Definitions

3.1.1  Danger

A hazard arises from the triad of cause, effect and exposure of the latter to a subject or object. For example: the flowing water of the Paasbach has a kinetic energy that erodes a stream bed and displaces sediments. This causes objects to be pulled under the surface (sinking, flooding). This is intrinsic and a natural process that is not dangerous at first. This process becomes a hazard when employees are exposed to this situation and, for example, step into the stream.

A hazard is therefore a situation in which, from an objective point of view, the occurrence of damage is likely unless preventive measures are taken (2, 3, 4).

3.1.2  Risk

The term risk is characterised by additional components.

First of all, there is the probability of occurrence. The risk of an accident in the Paasbach is low if the employees are NOT exposed to the intrinsic danger. The probability of occurrence increases if the employees enter the water tunnel and becomes even more likely if they also cross the stream in the dark and in unfamiliar surroundings.

The conscious increase in the probability of occurrence is described in the specialist literature as a risk, i.e. a conscious decision to expose oneself to a danger (5).

The second component is the extent of the damage. In the event of an incident, there are a number of possible scenarios. Crossing the stream can result in minor damage (“wet socks” from defective waders) or, if the waders fill up after a fall, e. g., it can also lead to serious injuries or even drowning.

Risk is therefore understood to mean the conscious, accidental or unintentional occurrence of the three-way constellation of cause, effect and exposure of an object or subject to an intrinsic hazard. This increases the probability of damage occurring and the potential amount of damage (4, 5, 6).

3.2  Project-specific risk matrix

It can be seen that working under the described conditions represents a hazard, as employees are exposed to cause and effect. However, it is necessary to take this risk in order to determine the exact location and condition of the tunnel and thus to avert other risks (partial collapse, etc.), the extent of damage of which may be higher. The risk with an as yet unforeseeable extent of damage and due to the higher probability of occurrence is therefore given.

In principle, an assessment is carried out according to the scheme presented, in which an assessment matrix is created for the aspects to be assessed, consisting of the extent of damage and the probability of occurrence (Table 1).

In essence, this already shows whether the work can be carried out or not. All aspects with the assessment criterion “1” carry only a low risk with a very low to low probability of occurrence and a tolerable extent of damage. Such risks can be taken without any problems. On the other hand, there are aspects with at least a high probability of occurrence that also cause a high level of damage. Ultimately, these are the risks that should not be taken.

However, there are always ways to take appropriate countermeasures. This is not shown in the diagram. In the above example of the use of waders, e. g., it is conceivable that a potential risk of injury or even death could be categorised as “wet socks” with the appropriate measure, and the risk could be taken if the countermeasure is, in all probability, easy to implement and is used. In the present case, waders that have filled with water would create an extremely heavy weight, which would result in the employees being unable to move. However, if the measure of giving the colleagues, who only work in teams, a rescue knife with which, for example, the waders can be cut and escape made easy, the use of the waders is only an acceptable risk.

The aim must therefore be to seriously assess all the risk aspects to which employees are exposed (see section 3.1) and to reduce the probability of occurrence and/or the extent of damage by means of suitable countermeasures. This ensures that employees have the safest possible working environment. This in turn makes it possible to reduce other – perhaps greater – risks with high levels of damage (partial collapse of the pipework). In order to take account of local conditions and the tasks involved in the project, a more detailed assessment matrix with five categories was introduced (Table 2). The project-specific risk is calculated by multiplying the values for the probability of occurrence and the extent of damage.

The extent of damage is measured in terms of the potential risk of injury to the workers deployed. All the countermeasures described must at least minimise the risk of injury or even eliminate it completely (optimal scenario). If this risk of injury exists, the situation is assessed at least with the score “20 – high risk”. A catastrophic event – permanent injury or death of a worker – was not assumed based on the knowledge of the situation, since the preliminary investigations did not reveal any risk of collapse, for example, that could lead to a worker being buried in the piping.

Table 3 shows an example of how the evaluation matrix is applied to the hazards described. All the aspects described above were evaluated in this way and examined for opportunities to minimise risk. The result was iteratively revised by all the organisations involved, and thus from different perspectives, until a result was achieved that was acceptable to all parties.

3.3  Team approach

An important preventive measure in an environment such as the piping is, in particular for personnel without extensive underground experience or experience with moving in rough terrain, not to use it alone. A team-based approach was therefore prescribed as an essential safety measure. This emphasises immediate mutual assistance, but also mutual observation and the early detection of possible problems. “Being alone” is always avoided. In the context of the fire brigade, the term “Trupp” (team) refers to a team of at least two people, unlike the mine rescue team, which consists of five people. In the project, the fire brigade-specific team approach was prescribed in every phase of the work.

3.4  Personal protective equipment

In principle, it was specified after the inspections and risk assessment that the work should be carried out using suitable personal protective equipment. Depending on the hazards identified, this includes (Figure 7):

• waterproof or water-repellent work jacket;
• high-visibility jacket or work jacket in signal colours;
• waders in suitable sizes (especially in relation to the boots):
• puncture-resistant, category 5, steel toe cap;
• waders in a signal colour;
  • warm boot liners;
  • depending on the outside temperature, supplemented by warm underwear;
• protective helmets with chin straps;
• adjustable helmet lamps;
• additional hand lamps/torches;
• lightweight work gloves (to be worn throughout the pipework);
• whistles on stable lanyards;
• rescue knives;
• 2 m analogue radio for each team.

The following PPE (personal protective equipment) is worn for special tasks:

• work gloves for special tasks (using tools);
• close-fitting protective goggles with seal (suitable for people who wear glasses, but also because of the potential for dust/shards and bat excrement);
• ear protection for work such as drilling, grinding;
• carrying straps or shoulder bags for tools/materials.
• A floating basket was used as a transport container and as a storage container during the work.

3.5  Radio concept

In a first approach, the radio concept was developed using the fire brigade’s digital radio devices, so-called hand radio terminals (HRT). Due to the range problems and the experience of a rather abrupt radio breakdown in the so-called direct mode operation (DMO), the use of repeaters was considered. From the outset, the problem was that the operation was not the work of the non-police emergency services, the fire brigade or an aid organisation and therefore had to be specially requested. The use of repeaters is also generally subject to authorisation.

During the first inspection of the piping in June 2021, it became clear that there was no continuous mobile phone coverage. Even the partial coverage reliably shielded the radio connection. It was assumed that this would also apply to digital radio in network operation, i.e. trunked mode operation (TMO). This meant that there was no way for a large group of workers to call for help quickly in the event of an emergency.

During a tour of inspection, the RAG mine rescue team was able to test four analogue radio devices, so-called 2 metre devices, i.e. handheld radios for authorities and organisations with security tasks (BOS) in the 2 m band around 150 MHz. The communication concept envisaged that as the work in the tunnel progressed, the respective closer rescue routes (mouth holes, shafts) would be occupied as communication points. The planned work was to be carried out against the direction of flow from the outlet to the inlet, i. e. this mouth and the western shaft 008, then the western (008) and eastern shaft (002) and finally the eastern shaft and the mouth inlet. Internally, these positions were given the following designations in accordance with the above-ground measurements:

• S001 – mouth hole outlet (west);
• S008 – western shaft, near the outlet of the mouth hole;
• S002 – eastern shaft, near the inlet mouth;
• S004 – mouth hole inlet (east).

A team remaining above ground (team 5) had to occupy these positions as work progressed in order to ensure communication between the underground teams and the outside world and, if necessary, to send an emergency call to the Hattingen fire brigade.

With the 2 m devices of the RAG mine rescue team, continuous communication could be ensured in this way during the inspection on 2nd May 2023. Therefore, an easy-to-understand graphic was created for each section and integrated into a simply described radio concept.

It is essential that rules be established for the implementation of secure communication. Based on the well-proven procedures of the fire brigades, corresponding guidelines for radio discipline were defined. For this purpose, the teams were clearly named and communication was explained using concrete examples. Excerpt from the radio concept:

• To ensure disciplined communication, only necessary information is exchanged.
• When addressing someone, first the person being called is addressed, then the caller is named:
  • Example of squad communication:
    • “Team 2 from team 5 – come in, please”.
    • Report: “This is team 2 – come in”.

The concept also includes emergency communication, which is also closely modelled on that of the fire services. Excerpt from the radio concept:

• In an emergency, proceed as follows:
  • The person making the emergency call reports “Mayday, Mayday, Mayday – team 5, over”.
  • Team 5 is the surface squad responsible for ensuring that emergency calls are made (Hattingen fire brigade). The member of squad 5 who receives this radio message replies: “This is team 5 – over”.
  • “Attention!” With this message, all other radio traffic ceases and only team 5 and the calling squad communicate afterwards.
  • “Attention!” Since team 5 is divided and positioned at two locations, problems may arise here. The person who receives the radio message in good quality should respond. If both respond, there must be a brief coordination as to who will continue the conversation.

The content of the actual message was based on the well-known “five Ws” (Wer, Wo, Was, Wie, Warten – Who, Where, What, How, Wait):

• Who (person) is calling? (e. g. “This is Gabriele”).
• Where did it happen? (Give your position as precisely as possible, e. g., “We are in the area S008/S002, near shaft S008”).
• What happened? (“George fell and injured his leg, he can’t walk”).
• If the problem affects several people: How many are affected? (“A beam has collapsed and three people are trapped.”)
• Wait for further questions from team 5! ( Important: Team 5 repeats the information and has it confirmed!)
• Gabriele: “Georg is injured and unable to walk. You are in the area S008/S002, near shaft S008. We will alert the fire brigade and get back to you!”
• Gabriele’s reply: “Correct, over and out.”

The procedure is not familiar to inexperienced people. The same applies to the operation of the 2 m devices via a push-to-talk button. Therefore, the procedure was extensively practised in small workshops before the survey was carried out. All participants had several opportunities to familiarise themselves with the processes.

4  Implementation

The safety concept that had been developed was reviewed and improved by the Hattingen fire brigade, the RAG mine rescue team and the city of Hattingen. After a final check of the safety concept by a specialist in occupational safety from the THGA, it was approved by the management of DMT-LB GmbH, Essen/Germany. This meant that the recommended PPE could be tendered and procured. The same applied to the necessary equipment, such as replacement batteries for the 2 m devices. The latter were provided by the Hattingen fire brigade (eight 2 m devices). Subsequently, the planned forces were familiarised with the PPE in workshops and trained in its use and the communication concept in corresponding training units. The exercise was finally carried out on 28th and 29th August 2023. The water level in the piping was higher than hoped for, but the work was assessed as feasible.

The problem was that the colleagues from the RAG mine rescue team were not available on the date. The Hattingen fire brigade stepped in here by providing personnel from the area of voluntary work. A colleague from the main fire station accompanied the work, partly above ground and partly underground. Since a trained mine rescue worker and a trained firefighter worked in the team, the concept was adapted to the new personnel situation. In addition to the firemen, the two team members were also responsible for the rescue tasks, so that the original plan of four trained rescue workers underground could be implemented at any time, although two of them were also assigned other tasks at the same time.

On site, the first tasks were to organise and set up the break facilities and to organise the work equipment. The set-up phase was followed on both days by a comprehensive safety briefing for the entire team, so that the changing Hattingen fire brigade colleagues could be included in the planning. The distribution of the radio equipment and the obligatory function tests were completed positively in each case.

With the start of the piping at the mouth hole outlet (S001), the work was essentially carried out as planned. Two aspects of the concept proved to be problematic:

• On the one hand, the coordination of the working teams was problematic, as they did not work synchronously due to the individual progress of their work. With regard to the occupation of the openings and shafts by the external team (team 5), it was necessary to act more flexibly than planned.
• In the middle section of the piping, unexpected problems with the radio connection arose. Not only was contact with the surface teams more difficult than planned, but also with those in the piping. One reason for this was the significantly higher water level in the piping than that recorded during the inspection on 2nd May 2023. This probably resulted in different reflection and absorption conditions with a major impact on the 2 m communication. These were also intensified by the now significantly narrower passages under several beams. Since the beams are metallic, consisting of double-T girders, e. g., there was effective shielding of the 2 m radio waves (Figure 8).

Since communication from the piping was considered to be the most important criterion, particularly in an emergency, the concept had to be adapted flexibly. In this respect, it was again an advantage that the procedures were somewhat less organised than planned. This meant that the teams were distributed over longer distances in the piping and a reporting chain could be established. The teams were explicitly made aware of the fallback solution of using their signal whistles. An additional surface position could also be occupied by the Hattingen fire brigade. This ensured that communication with the surface team 5, now reinforced by the Hattingen fire brigade and consisting of three people, could be maintained. Another positive aspect was that the piping in the area of the S004 intake consists of a DN 3600 concrete pipe. This pipe, which ultimately connects shaft S002 to the S004 intake, provided an acoustic connection, and a simple call for help or the use of the signal whistle could have been used to request help even without a radio. This fact had already been noticed by the Hattingen fire brigade during the inspection in May 2023, but had not been included in the concept.

Another change during the work was that shaft S002 was ruled out as a possible daytime opening for a rescue. It became clear that setting up a turntable ladder or a tripod over the shaft with the correct integration of an injured person in the basket stretcher would take considerably longer than the rescue in the basket stretcher through the comparatively easily accessible DN 3600 pipe. The ground here was firm and safe, and the constant flow of the Paasbach with its corresponding speed also meant that it was clean and free of obstacles.

With these adjustments, the concept, the PPE and, in particular, the training of the deployed forces proved their worth. Uncertainties in the radio concept were able to be compensated for by the accompanying firefighters. All work was able to be carried out safely and without incident. A result that was also achieved because all employees internalised and lived the concept.

5  Conclusion

Overall, the creation of a comprehensive safety concept with several inspections, planning, formulation and several iterations with the security forces and the occupational safety specialist was time-consuming. Nevertheless, in the authors’ view, it was essential to be able to react to all eventualities and to remain capable of acting at all times. The goal must always be to ensure the safety of the deployed forces and to exclude or minimise possible personal injury in the event of an incident. An important aspect of the planning was the necessary deployment of personnel without extensive underground experience. In this case, reactions to unforeseen events were not necessarily predictable. The formation of teams increased the sense of security, as did the active safety and the presence of professional rescue workers.

The process of comprehensive hazard analysis and detailed risk assessment proved its worth. In particular, the specific naming of hazards made it possible to recognise the dangers and to describe suitable risk reduction measures for each aspect. The mere naming of the recognised hazards made it possible for all the deployed forces to deal with the situation in advance of the work and to consider conceivable scenarios.

The support provided by trained safety experts, in particular the Hattingen fire brigade during the mapping, but also the RAG mine rescue team in the preparation, is an added value that can hardly be described. On the one hand, many aspects would have been overlooked and not addressed. On the other hand, the accompanying safety forces were able to deal with and think through possible rescue scenarios in advance. In addition, the Hattingen fire brigade was always ready to intervene by being involved in the planning and implementation. For coordination reasons, a specific rescue exercise could not be carried out with the participants. However, this offer from the Hattingen fire brigade could have significantly improved the processes if actual problems had occurred and is recommended for similar work.

The detailed discussion of the topic within the team, as well as the preliminary workshops and exercises, e. g. on the use of PPE or the application of the radio concept, can also be seen as positive for the optimisation of the processes. This sensitisation of the team was able to achieve a high level of attention. The sum of the measures resulted in a safe and accident-free execution of the surveying work.

6  Acknowledgements

The project was supported by the City of Hattingen, and in particular we would like to thank our colleagues in the City Works and Civil Engineering Departments for their support and for giving us the opportunity to implement this project.

Thanks are also due to the colleagues at the FZN who were involved. Any safety concept can only work if it is lived.

Dönges GmbH & Co. KG, Wermelskirchen, provided personal protective equipment for the underground work. The company went well beyond the simple customer/supplier relationship by accompanying a preparatory inspection to gain a very concrete picture of the requirements and necessities.

The RAG mine rescue team supported several underground inspections and provided its expertise in the development of the safety concept. The colleagues were important partners in the preparation.

A special thank you goes to the Hattingen fire brigade. In addition to providing the communication technology, the colleagues and comrades were always ready to accompany the work. In particular, the provision of underground safety personnel to accompany the actual surveying work was more than self-evident – a good feeling! The Hattingen fire brigade was always available as a contact and discussion partner

7  Video

The video by THGA photographer Volker Wiciok gives a somewhat idealised impression. The extremely light-sensitive cameras used paint a somewhat “brighter” picture than those involved experienced on site:

https://vimeo.com/vowiausbo/review/891426305/140133b07a
©Volker Wiciok/THGA.

Authors/Autoren: Dr. rer. nat. Bodo Bernsdorf, Prof. Dr. rer. nat. Tobias Rudolph, Prof. Dr.-Ing. Peter Goerke-Mallet, Forschungszentrum Nachberg­bau (FZN), Technische Hochschule Georg Agricola (THGA), Bochum/Germany, Melanie Gendrullis, Thomas Adam, Abteilung Feuerwehr und Rettungsdienst, Stadt Hattingen/Germany, Christoph Uphues, Fachbereich Stadtbetriebe und Tiefbau, Stadt Hattingen/Germany, Dipl.-Ing. Andreas Koschare, RAG Aktiengesellschaft, Essen/Germany, Benjamin Haske M. Eng., Marcin Pawlik M. Sc., Forschungszentrum Nachbergbau (FZN), Technische Hochschule Georg Agricola (THGA), Bochum/Germany, und TU Bergakademie Freiberg, Freiberg/Germany