Mitigating risks in railway tunnel maintenance: A pilot study on air quality management during drainage flushing

Abstract

This article examines the challenges and solutions associated with protecting railway workers from the negative effects of exposure to diesel emissions and dangerous dust emissions during tunnel maintenance works. A major difficulty in this matter is the increased risk of respiratory and cardiovascular diseases for railway workers due to exposure to diesel and gasoline-powered vehicles and dangerous dust emissions, which is further compounded in enclosed spaces such as tunnels. The article analyses the feasibility of renouncing the currently imposed use of ventilation systems during certain railway maintenance work in Germany while still ensuring occupational safety of the employees. The research methodology involves a comprehensive investigation of the applicable national legislation and limit values for dangerous carcinogenic chemicals. The hypothesis is then validated by interpreting the measured values for elementary carbon and for the gases CO, CO2, NO and NO2 during a pilot project conducted in 2022. The findings indicate that it is theoretically possible to forego the technical ventilation system in certain cases of railway maintenance, such as cleaning and flushing a railway drainage located in a tunnel, without jeopardising the occupational safety of employees if an alternative and less expensive fallback measure (face masks for employees) is implemented. The implications of these findings for railway workers and rail maintenance projects are discussed. In the conclusion of the article, recommendations for conducting additional research and improving the current understanding of the topic are provided.

Keywords:

• railway maintenance
• railway tunnel
• ventilation system
• workforce protection
• air quality
• occupational safety

1. Literature review and methodology

When maintenance works are carried out on railway tracks and points, there are two important, often less considered hazards for the occupational safety of employees. Firstly, there are a variety of diesel and petrol-powered vehicles, machines, and tools in use, and their emissions can lead to respiratory and cardiovascular diseases. In addition, dangerous dust emissions, such as mineral dust and quartz dust, occur during repair work on the ballasted superstructure, which can result in lung disorders such as silicosis or lung cancer.

These risks are even higher when railway maintenance works are carried out in tunnels, as generated emissions and dust accumulate in confined space (see (Bakke, 2004) or (Ulvestad, 2000)). Several factors influence the number of gases registered in the tunnel—for example, a 2020 study found that generated gases are considerably higher during winter (Li et al., 2020), while an Austrian study has shown that emissions from freight trains are on average 6.68 times higher than those from passenger trains (Sturm et al., 2022). The consequences of these emissions have been thoroughly investigated: a study based on spirometry tests conducted on dust-exposed railway tunnel workers has found a decrease in lung function in direct correlation with the period of exposure of employees (Mahmoud et al., 2018), while another generally establishes lung cancer as the predominant disease in personnel subjected during work hours to diesel exhausts (Bhatia et al., 1998).

Another danger concerns the effect of welding fumes in an enclosed space such as a tunnel, as studies have clearly shown that exposure to toxic fumes can cause lung cancer or other serious diseases (Abbasi et al., 2013; European Union, 2016). Welding is an important part of railroad maintenance, for example, in rail replacement or the renewal of track switch components.

Therefore, it is crucial to protect railway workers from the negative effects of exposure to dust and diesel emissions. Reducing particle emissions is undoubtedly the most effective method and the first solution in this matter. This first step is followed by ventilation systems for tunnels and enclosures designed to manage and restrict concentrations (Abbasi et al., 2013).

This article aims to establish whether it is possible to renounce the technical ventilation system in select cases of railway maintenance in Germany, such as cleaning and flushing of a railway drainage located in a tunnel. The methodology used for this research is shown in Figure 1.

Figure 1. Research methodology of the article (own representation).

A comprehensive investigation of applicable national legislation was the first step in the research process. The EU Directive 2016/1628/EC (European Union, 2016) requires the limitation and reduction of diesel and other traction vehicle exhaust emissions from locomotives and vehicles in all member countries. To this effect, EU countries have corresponding regulations; in Germany, these are TRGS 554 (Bundesanstalt für Arbeitsschutz und Arbeitsmedizin, 2019), stipulating, for instance, that diesel particle filters (DPFs) must be used for all machines and vehicles, or TRGS 559 (Bundesanstalt für Arbeitsschutz und Arbeitsmedizin, 2020).

TRGS559 differentiates between harmful dust released, by defining the two subtypes of dust emissions—their limit values are shown in Table 1:

• E-dust—dust fraction that can be absorbed through the respiratory tract;

• A dust fraction—dust that can reach the alveoli and bronchioles.

Table 1. Limit values for E-dust and A-dust

Type of dust	General dust limit value	Fine quartz dust limit value
E-dust	10 mg/m^3	-
A-dust	1,25 mg/m^3	50 μg/m^3

Harmful dust emission occurs during railway maintenance works, foremost when shifting track ballast using heavy machinery (such as a ballast tamper or a ballast cleaning machine). The gravel is compacted and transported, resulting in a certain friction between the gravel stones; this friction then releases the harmful dust. This is mostly the case when the following maintenance works take place: ballast tamping, ballast cleaning, ballast processing (recycling), complete track renewal—manual or by using a track renewal train. Changes in paradigm from corrective railway maintenance (repairing damage to infrastructure) to predictive railway maintenance (preventing damage, for example, with models such as those shown in (Seraco & Ratton Neto, 2023) or (Bouhlal et al., 2022)) can increase the volume and frequency of tamping works; this also applies to tunnels, thus exacerbating the highlighted challenges for employees.

In Directive 2004/37/EG, as revised by Directive (EU) 2017/2398, the EU established mandatory limit values for some dangerous carcinogenic chemicals, which cannot be exceeded. The EU limit value for diesel soot particles is expressed as an EC value (elemental carbon). The German regulation TRGS 900 also contains other limit values for diesel emissions—for the gases CO, CO₂, NO, and NO₂ as shown in Table 2 (Bundesanstalt für Arbeitsschutz und Arbeitsmedizin, 2006).

Table 2. Limit values for diesel emissions

Type of emission	Limit value
Elemental carbon (EC)	0,05 mg/m^3
Carbon monoxide (CO)	35 mg/m^3
Carbon dioxide (CO2)	9100 mg/m^3
Nitric oxide (NO)	2,5 mg/m^3
Nitrogen dioxide (NO2)	0,95 mg/m^3

2. Air quality management during railway maintenance in German tunnels—current state

Following the aspects shown in the first paragraph, it becomes clear that every railway maintenance site in a tunnel requires a careful planning of occupational safety under consideration of all safety hazards. Priority must be given to the dangers posed by maintenance activity itself and ongoing train operations on the adjacent track, as these pose immediate dangers to the well-being of personnel, but the issue of air quality must be addressed in addition. To be effective, air quality management must include reducing the effects of both diesel/petroleum emissions and harmful dust emissions.

It should be noted that every employer is required to ensure the occupational safety of its own employees—this includes compliance with the limit values shown in Tables 1 and 2, which poses a significant challenge not only for DB Netz AG, as the largest operator of German railway infrastructure with over 33,000 km (Statista.de, 2022), but also for its subcontractors. This is no trivial task as there is no general solution that can be deployed to ensure compliance with these values.

Several options can be used to limit the dust and diesel/petrol emission values, while performing railway maintenance works. The option used depends mostly on the type of maintenance work carried out and thus on the machines and devices employed. To establish criteria based on which the correct course of action can be identified, DB Netz AG carried out several pilot projects with various types of railway maintenance works. During these pilot projects, the effectiveness of several options was analysed for the limitation of the relevant values.

In one of the initial pilot projects, solutions were studied to reduce emissions during tunnel ballast cleaning operations using a ballast cleaning machine (Brill, 2019). For the Munich Feldmoching 2017 test pilot, the solution used was a suction system installed on a work train that was moving in parallel on the neighbouring track. The test could disprove the initial hypothesis, which was that the suction on the clearing chain of the ballast cleaning machine could remove so much dust that there would be no substantial dust development elsewhere in the tunnel.

Another milestone pilot project was a tunnel ballast cleaning operation in the Kaibachtunnel of the high-speed line Hannover-Würzburg in 2018. In this case, the suction system was further developed by allowing suction to take place not only in the clearing chain; additionally, the track ballast was wetted. This combination of actions was deemed successful as the limit values were respected. The pilot project in the Wildsbergtunnel on the same track in the same year further confirmed that the wetting of the track ballast is highly effective in containing dust emissions. The pilot project in the Rollenbergtunnel on the high-speed line Mannheim-Stuttgart was used to validate the necessary quantity of water to be used when wetting the track ballast. It was concluded that a quantity of 20 litres/m3 is sufficient to maintain the limit values of the dust emissions.

Diesel/petrol emission management is usually the simpler task of the two and it is mostly achieved by two courses of action: satisfying the requirement of the TRGS 554 regarding the use of machines and tools with DPF and the use of ventilation systems. The preferred use of emission-free power technology, such as electric or battery-powered machines and tools, is an increasingly viable and cost-effective alternative. If petrol-powered hand machines are unavoidable, then catalytic converter-equipped engines should be used (Bau, 2021).

In some cases, tunnels can be contaminated with other substances as well—not originating from dust or diesel/petrol. This was the case in the Hoffnungsthaler tunnel on the main line 2655 (Köln-Kalk-Overath) where arsenic contaminations caused by economically exploited ore deposits were discovered in the past (Brockmeier, 2020). Construction work stopped after the discovery of arsenic contaminations and continued after several months with supplementary precautions in the form of special protective clothing and masks for the employees.

Although the first objective in managing air quality in tunnels is, as stated above, reduction of emissions, a mobile or fixed ventilation system (shown in Figure 2) is almost always used to provide tunnel workers with fresh air. These ventilation systems must be calculated, so that a certain speed is achieved—the TRGS 554 imposes a fresh air supply of 4.0 m3/min per kW of every tool, machine, or vehicle used, a value that must be supplemented with an air supply of 2.0 m3/min for every employee present. As a 2017 article (Gehring et al., 2017) proposes, air supply can be calculated starting from the number of vehicles and machines present at the same time on the construction site and not from the total number of machines planned for the ongoing project. This allows for lower ventilation speeds, which have lower negative effects on the health and comfort of employees.

Figure 2. Mobile ventilation system by CFT GmbH (GmbH, 2017).

Through analysis of the pilot projects, an application matrix was defined. This application matrix serves as a simplified decision support system in the planning phase of railway maintenance works—it lists common railway maintenance works such as rail replacements, rail grinding, ballast work, track renewal, and the courses of action deemed necessary.

Therefore, the application matrix in use today stipulates, for instance:

• a ventilation system is almost always necessary (exception here are two rail-grinding procedures known as high-speed grinding and two-pass grinding);

• ballast wetting is required for all complex maintenance works regarding the track ballast (not for rail replacement, rail grinding);

• DPF and/or Euro 5/Euro 6 compatibility is required for all machines and tools in use;

• in some cases, the driver’s cabin of a vehicle must be protected, for instance, through an encasement.

If diesel emissions can be avoided using vehicles and tools powered by alternative fuels and if dust emissions can be safely excluded (based on the type of railway maintenance work), then the matrix clearly states that costly ventilation systems can be eliminated from the work site. Additional organisational measures, such as the use of a construction site coordinator and a contingency plan, are expected for all types of work currently covered in the application matrix—this is a further improvement of the occupational safety of the employees.

3. Case study—waiver of the ventilation system during railway tunnel drainage flushing

Although the current application matrix covers most common railway maintenance works, there was no pilot project to analyse air quality during equally important but less prioritised tunnel drainage flushing. Over time, sintering and deposits—most dangerously calcium carbonate, as shown in (Dietzel et al., 2008)- occur in tunnel drainage, which consequently can impair the function of groundwater drainage (Girmscheid et al., 2003). To prevent this—and the ensuing track stability problems—the tunnel drainage must be cleaned and flushed regularly.

To carry out the tunnel drainage flushing, a work train (shown in Figure 3) is driven into the tunnel. This consists of a locomotive (BR203), a high-pressure unit, a control car, and two flushing trucks, one of which is only used as a reserve. Under high pressure, the tunnel drainage is cleared of deposits with the help of the truck. The locomotive is switched off during the work phase and, in addition to arrival and departure, is used for the transfer to the subsequent flushing section.

Figure 3. Work train used in tunnel drainage flushing (Ullrich, 2022).

For this case, dust emissions are not relevant as the track ballast is not moved or changed. However, diesel/petrol emissions must be considered, as many vehicles and tools are used during this type of rail maintenance. For example, the BR203 locomotive used boasts an installed capacity of 900 kW, requiring a corresponding supply of fresh air of more than 3600 m³/min only to counterbalance the diesel emissions of this vehicle.

To analyse air quality and occupational safety of workers during tunnel drainage flushing works, DB Netz AG conducted a pilot project on three consecutive days in mid-July 2022 in the Landrückentunnel—a 10,779 metres long tunnel with two railway tracks, built between 1981 and 1988 and situated on the high-speed line Hannover-Würzburg (track number 1733). The choice is not random, as the Landrückentunnel is to date Germany’s longest railroad tunnel.

An important aspect is the fact that tunnel drainage flushing was part of a larger project, the complete track renewal conducted in 2021 in the Fulda-Würzburg section of the Hannover-Würzburg high-speed line. This meant that while the tunnel drainage flushing was carried out in the Landrückentunnel, other track renewal works took place outside of the tunnel. This factor led to the necessity of allowing several work train movements in the neighbouring track, as these were needed, for instance, for the supply of other work sites along the track section.

Financial (exploding project costs as a result of hiring specialised subcontractors for the installation and operation of the ventilation system) and organisational considerations (difficulty in planning the construction site, possibly a required declaration of intent before every maintenance of the railway in a tunnel greater than 80 m to the German Federal Railway Authority EBA as intended by a general decree in 2019 (Eisenbahn-Bundesamt, 2019)) contribute to the need to examine the possibility of the elimination of the technical ventilation system.

The design of the study stipulated that the project would be accompanied by measurement technology. This included, on the one hand, the measurement of the components of the diesel engine emissions by the accredited environmental measuring station of the DB Engineering & Consulting (a DIN EN ISO/IEC 17,025 certified laboratory—see (DB E&C, 2023)), as well as the entrainment of gas warning devices for the detection of acute limit value violations. To obtain a statistically reliable finding, the workplace measurements were carried out in three shifts with the ventilation system present and installed but switched off. As part of the workplace measurements, one mobile, one person-carried (or personal) and one stationary measuring point (MP) on the flushing truck were agreed. The following ground rules were established for this pilot project:

• If the limit value should be exceeded when the ventilation system is off, work must be immediately halted and the ventilation system must be turned back on;

• The personnel are ordered to leave the worksite until the warning equipment is no longer emitting its signal;

• If the ventilation system must be turned on during a shift because a limit has been exceeded, it is not turned off again so as not to further impede operations.

The study was carried out by measuring and then aggregating values for elementary carbon (EC) and for the gases CO, CO₂, NO and NO₂ through three measuring points daily. Concerning the selection of this particular set of parameters, it was determined during the study design phase to analyse these values, as these are the elements designated by the TRGS 900 - see Table 2. As their limit values are defined as time-weighted 8-hour averages, the individual concentration measurement findings c_j and the accompanying exposure times t_j must also be linked to an 8-hour period. Consequently, the mean shift value C is calculated as follows (Bundesanstalt für Arbeitsschutz und Arbeitsmedizin, 2006):

(1) $\mathit{C}=\frac{{\sum }_{j=1}^n{c}_j\cdot t_j}{8}=\frac{c_1\cdot t_1+\mathit{\hspace{0.17em}}{c}_2\cdot t_2+\dots +c_n\cdot t_n}{8}$(1)

To allow a comparison of the results obtained, the substance index I is calculated for each item by dividing the mean concentration shift value C by the specific limit value GW (Bundesanstalt für Arbeitsschutz und Arbeitsmedizin, 2010):

(2) $\mathit{I}=\mathit{\hspace{0.17em}}\frac{C}{\mathit{GW}}$(2)

According to TRGS 402, a rating index is calculated if several substances contribute to exposure in the work area simultaneously or sequentially during a shift (Bundesanstalt für Arbeitsschutz und Arbeitsmedizin, 2010):

(3) $\mathit{B}{I}_{\mathit{AGW}}=\mathit{\hspace{0.17em}}\sum I_i=\frac{C_1}{\mathit{AG}{W}_1}+\frac{C_2}{\mathit{AG}{W}_2}+\dots +\frac{C_n}{\mathit{AG}{W}_n}\mathit{\hspace{0.17em}}$(3)

According to DIN EN 689 (Workplace exposure, 2020), the statement “Protective measures adequate” can be made if

1. the assessment index $\mathit{BI}\le 0.1$ or if

2. The results of the determination results for at least three shifts are available and all assessment indices $\mathit{BI}\le 0.25$.

The limit value of the BI assessment index is 1 – between the values 0.25 and 1, the finding is not necessarily “protective measures adequate”, but is determined after a competent assessment, considering all other important factors regarding the work site. The measurement results obtained through the study were interpreted according to DIN EN 689 and are represented in Table 3.

Table 3. Interpretation of the measurement results obtained (own representation)

Type of MP	Elementary carbon values	CO values	CO2 values	NO values	NO2 values
Day 1	Protective measures deemed:
Personal MP	Adequate	Adequate	Adequate	Adequate	Inadequate
Stationary MP	Adequate	Adequate	Adequate	Adequate	Inadequate
Mobile MP	Adequate	Adequate	Adequate	Adequate	Inadequate
Day 2	Protective measures deemed:
Person	Inadequate	Adequate	Adequate	Adequate	Adequate
Stationary MP	Inadequate	Adequate	Adequate	Not detected	Not detected
Mobile MP	Inadequate	Adequate	Adequate	Adequate	Not detected
Day 3	Protective measures deemed:
Personal MP	Inadequate	Adequate	Adequate	Inadequate	Not detected
Stationary MP	Adequate	Adequate	Adequate	Not detected	Not detected
Mobile MP	Adequate	Adequate	Adequate	Adequate	Not detected

For a further interpretation of the results, it is important to take note of the operational movements on the neighbouring track. On the first day, there were two train passages on the adjacent track (one diesel locomotive, one excavator), on the second day there were five passages (Unimogs and baggers), while on the third day there were three passages from two cranes and one Unimog.

The analysis of the results shown in Table 3 reveals that compliance with the emission limit values is not immediately guaranteed for all elements and gases. However, it can be assumed that the development of the emissions was mainly caused by further traffic on the neighbouring track (especially on the second day of the pilot project).

4. Conclusions

It does not suffice to concentrate on the work and train traffic-related aspects of railroad maintenance works when planning the occupational safety of railroad workers. Furthermore, air quality must be ensured to keep workers healthy and safe. For this reason, it is of paramount importance that emissions from fuels such as diesel or petrol, as well as emissions generated from dust, be minimised or countered through appropriate courses of action.

There are multiple actions that can efficiently reduce the negative effects of both dust and diesel emissions; these have been centralised in an application matrix that contains the most common maintenance works of the railway tracks of the German infrastructure company DB Netz AG. There are, however, still some blind spots in the matrix, as not all possible use cases are represented. In these cases, the decision lies solely with the employee tasked with the planning of the works, without the aid of a decision support system.

This gap must be closed with knowledge from further pilot projects, such as the project on the high-speed line Hannover-Würzburg in July 2022 presented in this article offering insights on possible solutions for air management quality during railway tunnel drainage flushing and cleaning works.

Due to the specifics of the project, implementation as part of a major track renewal, there was unfortunately interference in the form of an increased volume of journeys on the neighbouring track, which had a negative impact on the measurements results. Therefore, the conclusion is that further measurements under maintenance conditions (without further construction traffic on the adjacent track) are required. The DB E&C environmental office recommendation is to carry out an annual repeat measurement. Repeat measurements are used to compile reliable results before ventilation can be avoided in the tunnel.

Another possible solution was formulated after this first project on the management of air quality during the drainage maintenance works of the railway tunnel—a waiver of the technical ventilation system seems plausible if employees wear FFP3 masks during working hours. This option is certainly highly recommended from an employer’s perspective because of the substantial cost savings achieved by eliminating ventilation, but it may create a certain discomfort for the employees. Whether or not this solution is feasible must be further analysed through a test run in subsequent measurements.

It is crucial that the current application matrix be extended to also include other less frequently occurring railway maintenance works, such as the case with important tunnel drainage flushing. This would provide personnel tasked with planning these maintenance activities with confidence in their decisions, as no individual investigation or choices would be required.

Finally, since the use of the ventilation system will still be necessary for several maintenance works, even in the eventuality of a waiver for the tunnel drainage flushing, railway infrastructure companies would be well advised to use already installed fixed ventilation systems where they are in place and consider installing such technical tunnel equipment for current and future railway projects. Although the initial installation costs are high, this will be beneficial in the long run.

Acknowledgments

This research did not receive any specific grants from funding agencies in the public, commercial or non-profit sectors.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

Vladimir Voicu

Vladimir VOICU, Ph.D. Stud Eng., is the Head of Railroad Maintenance for the Deutsche Bahn Netz AG in Kassel, Germany. He has been active as a railway specialist and manager for the last 10 years.

Anca Draghici

Anca DRAGHICI, Ph.D. Eng. is a full professor at the Faculty of Management in Production and Transports, Politehnica University in Timisoara; President of the Romanian Ergonomics and Workplace Management Society, https://ergoworksociety.com/blog-feed/