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Fires in tunnels can cause severe damage, leading to long closures for repairs, sometimes lasting months. These closures often have a significant negative impact because tunnels are crucial parts of the transport network. As a result, alternative routes become overloaded with traffic, and access to certain areas is limited. To minimize the impact of fires, passive fire protection boards (PFP boards) are being installed on tunnel walls and ceilings to shield the structure from high temperatures.
This study not only shows the costs of installing these fire barriers but also highlights the benefits. For example, using fireproof boards in a tunnel can be a cost-effective solution.
In recent years, vehicle fires have repeatedly occurred in tunnels in German-speaking countries. Examples are fires in the Gleinalm tunnel (Austria, 2016 and 2018), in the Königshainer Berge tunnel (Germany, 2013) and in the Elbe tunnel (Germany, 2018). Besides the actual repair costs, tunnel operators also face losses from lost toll revenues, which can be much higher than the repair costs. For instance, the structural repair of the Gleinalm Tunnel fire in August 2016 cost €0.5 million, but the lost toll revenues were €3.5 million [1]. Additionally, tunnel closures for repairs lead to significant economic costs due to longer routes and travel times caused by detours. For example, the closure of the Königshainer Berge tunnel caused about €6 million [2] in damage to alternative routes not designed for heavy traffic, while the total repair cost for the tunnel was only about €2.2 million [3].
Tunnel Fire statistics – rail and road tunnels as per IFA-SWISS
According to ASFINAG's tunnel fire statistics from 2006 to 2012, there are an average of 6.5 fires in Austrian highway and expressway tunnels for every 1 billion vehicle kilometres travelled. The likelihood of truck fires (≥ 3.5 tons) is much higher, with 25 fires per 1 billion tunnel kilometres, compared to fires for passenger cars (4.2). Statistically, a truck fire occurs every 40 million kilometres travelled in a tunnel [4]. Swiss International Fire Academy (IFA) published also their statistics from tunnel fires in German speaking countries from 2012 until 2023.
Additionally, Institute of Transport Economics Norwegian Centre of Transport Research also presented their finding and statistics from tunnel fires in Norway. On average, there’s 27 vehicle fires in Norwegian road tunnels. Whereas French CETU - Centre d’Études des Tunnels (Centre for Tunnel Studies) shared in February 2022 their reports regarding Breakdowns, accidents and fires in road tunnels – statistics. The study investigated 177 incidents and revealed a fire rate in tunnels of 1.1 per 100,000,000 vehicle kilometres. Unfortunately, only ASFINAG data was available during preparation of the Economic possibility study between Aestuver and STUVA. Therefore, the information below excludes findings from Switzerland, Norway and France.
At the time of writing the study the key interest rate (mid-2019) was kept at a record low of 0.0 % by the European Central Bank since March 2016. Due to numerous factors like COVID-19 pandemic and war between Russia and Ukraine, we have experienced significant increase of interest rates. Over long periods, like 100 years in this case, inflation affects price development. However, if all prices change at the same rate, inflation doesn't need to be considered because the price level changes uniformly for all payment variables. Moreover, estimating the inflation rate introduces more uncertainty than the potential accuracy gained. Therefore, this study uses the "actual value approach" and does not account for inflation. The different lifespans (or re-investment intervals) of various components are factored into the life cycle cost calculation using the annuity factor. The interest rate and the useful life are considered as follows: 𝑎𝑓 = (1+𝑖)𝑛∗𝑖 (1+𝑖)𝑛−1 (1) With the calculation interest rate (i = 1.7 %) and the useful life of the fire protection panels (n = 30 years), for example, the annuity factor for the production and installation of fire resistive boards is calculated at af = 0.043.
The extra maintenance cost, based on a shorter six-year interval, gives an annuity factor of af = 0.177. To find the annual construction costs, multiply the investment costs of the components by this annuity factor. To calculate the present value of all costs over this period, multiply the total annual building costs by the present value factor bf = 1/af for any useful life n. For example, with an interest rate of 1.7% and a useful life of 100 years, the present value factor is bf = 47.923.
This article focuses only on the profitability of fireproof boards. Therefore, when comparing a tunnel with passive fire protection system to one without, other construction costs are not considered in this analysis. The ongoing maintenance costs for the tunnel are almost the same for both options. However, the additional cost for maintenance and repair of the tunnel fire protection must be considered, as they may need to be removed and reinstalled during structural inspections.
For the economic efficiency calculation, we consider a two-way tunnel with a circular cross-section RQ 10.5 T and a length of 1,000 meters. Depending on the tunnel design (e.g., circular or rectangular, with or without smoke extraction), the circumference to be protected ranges from about 12 to 19 meters. In this example, we assume 16.5 meters. The calculation parameters needed are summarized in Table 1:
The average daily traffic is assumed to be 24,900 vehicles, similar to the Gleinalm tunnel [9]. Of these, 3,700 vehicles have a total mass over 3.5 tons. This means trucks travel 3,700 kilometres per day in the 1-kilometer-long example tunnel, totalling 1,350,500 kilometres per year. According to ASFINAG's tunnel fire statistics, which show an average of 25 fires per 1 billion truck kilometres, a truck fire is expected to occur every 30 years in the example tunnel. It is assumed that there will be at least one fire during the tunnel's lifetime, occurring in the first year of the study. The fire is assumed to be caused by two burning trucks standing directly behind each other. As a result, 70% of the reinforced concrete inner shell over an 80-meter length is damaged to category 4.
The life cycle costs of the tunnel fire protection are calculated for a tunnel service life of 100 years. In this example, the cost is estimated at €72/m² for the procurement and disposal of the boards and €70/m² for the installation of the fire protection systems, including fire protection mastic. Please take into consideration that this number is quite conservative. Installation costs depend on a lot of factors. The total cost can be also reduced with Aestuver set in concrete fire protection system. Sometimes, also referred to as lost formwork fire barrier. Aestuver fire boards do not require regular maintenance. However, tunnel operators might want to clean the fire cladding panels or inspect the structure behind them.
Based on expert interviews, the additional maintenance cost is estimated at €1.5/m² per maintenance interval. This is because the fireproof boards need to be randomly removed during a main inspection of the tunnel, according to DIN 1076 (every six years), to inspect the inner shell. Video presenting these requirements for tunnel maintenance is available here.
The main advantage of tunnel fire boards is that they prevent structural damage from fires. Therefore, it's important to consider the potential repair costs for a damaged inner surface with and without these fire barriers.For the calculations here, data from the "Protection of critical bridges and tunnels in the course of roads" (SKRIBT) project, funded by the Federal Ministry of Education and Research (BMBF, Germany), were used. Five damage levels were defined for assessing fire damage. Levels 1 to 3 involve isolated to large-area spalling with depths of 5 to 50 mm. Level 4 is large-area spalling with exposed reinforcement, and level 5 is spalling beyond the centre of the cross-section. Table 2 summarizes the essential repair work and costs for each damage level. According to the damage scenario, level 4 is assumed for a tunnel without fireproofing boards. For a tunnel with fire protective boards, the costs mentioned above are used:
Repairing fire damage to a tunnel's inner lining usually requires closing the tunnel. For structures without tunnel fireproof boards, the closure duration is estimated to be about 7.3 months for level 4 damage, based on SKRIBT project data, reduced by one-third due to shorter refurbishment times observed in past fires. For tunnels with fire proofing boards, the closure duration after a fire is estimated at 1.5 months, based on manufacturer and operator experience. This includes removing damaged boards and installing new ones. Depending on the damage, this work can be done in stages during off-peak hours to minimize traffic disruption. Overall, tunnels with fireproof boards typically have shorter closure times compared to those without, due to quicker planning and tendering processes.
Closing the tunnel for fire damage repairs requires local traffic control near the tunnel. Cost estimates based on the SKRIBT project are listed in Table 1.To estimate diversion costs, the extra costs for road users due to the diversion (increased time and longer distance) are included. The calculation distinguishes between vehicles under and over 3.5 tons, considering the extra travel time based on the average speed on the diversion route and possible traffic jams. Table 1 lists the availability and operating costs for cars on business and private trips, as well as truck costs, based on the Federal Transport Infrastructure Plan 2030 manual.
The average speed without traffic jams, also shown in Table 1, is set relatively high, positively affecting the time needed to cover the diversion route and leading to lower costs. The manual provides values for time-dependent costs, determined through a willingness-to-pay analysis, depending on the distance and vehicle occupancy rate.
Assumptions for traffic and cost calculations
For simplification it was assumed in the study that cars are occupied by only one person and that the statutory minimum wage (2018) of € 8.84 per hour is to be calculated for this person. For trucks (over 3.5 t) that are generally used for commercial purposes, the hourly rate for the driver was set at € 20. The length of the diversion is based on the diversion route for the Gleinalm tunnel and was set at 28 km. Due to the traffic volume shifted from a motorway to federal/state roads, traffic jams can occur, especially at peak times. It is so assumed that 50 % of road users are stuck in traffic jams for 30 minutes.
Similar to the Gleinalm tunnel, a special toll of €9 per vehicle is assumed for this example [11]. Since many vehicles using the tunnel are from the nearby area, their owners often have annual season tickets, which are much cheaper than single trips.Therefore, only 50% of the lost toll revenue is considered during the closure. For comparison, in Germany, the toll for the Warnow Tunnel in Rostock is €3.80 for a car and €16.50 for a truck.
Besides the parameters listed above, there are other cost factors that are difficult or costly to quantify. Therefore, the following impacts on diversion routes were not considered in this study:
The initial cost to install tunnel fire barrier panels is about €2.34 million. Including the extra cost for building inspections (maintenance), the annual construction costs are approximately €105,000 at an interest rate of 1.7%. Over 100 years, the life cycle costs are about €5.0 million. At interest rates of 0.0% and 3.0%, these costs are about €8.2 million and €3.9 million, respectively (Fig. 1). Figure 1. Life cycle costs (initial and maintenance costs) of fire protection boars for different interest rates i Table 3 compares the costs for tunnels with and without tunnel fire protection safety system, considering one fire at the start of the tunnel's life. The total costs avoided by using tunnel protection boards are about €88 million, which is 17 times the life cycle costs of the boards. In both cases, repair and traffic safety costs after the fire are relatively low.
However, diversion costs and lost toll revenue make up most of the extra costs.For the tunnel operator, the lost toll revenue from one fire (€19.6 million) more than covers the life cycle costs of the tunnel reinforced concrete protection boards (about €5 million) due to faster reopening. From the , and from the tunnel users' perspective and economically, the savings from avoiding diversion costs with tunnel fire and safety system even with just one fire, are even greater, amounting to around €73 million.
Table with study results The cost difference for extra kilometres travelled is around € 31 million for cars and € 12 million for trucks, while the cost difference for extra travel time is around € 20 million for cars and € 10 million for trucks. Table 3. Comparison of costs resulting from a fire in a tunnel with and without fire protection boards