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Design Fire Curves in Tunnel Fire Protection

27/01/2025

Time-temperature fire curves are commonly used in tunnel fire protection. Fire safety in tunnels is a critical aspect of civil engineering and fire engineering. Tunnels, whether for road or rail present unique challenges due to their confined nature and the potential for high heat and smoke accumulation.

 

One of the key tools in designing effective fire protection systems for tunnels is the time-temperature fire curve. This article will delve into the importance of these design fire curves, their types, and their application in tunnel fire protection.


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The Importance of Time-Temperature Design Fire Curves

Time-temperature fire curves are graphical representations that show the relationship between temperature and time during a fire. These curves are essential for understanding the thermal exposure that tunnel structures and materials will face during a fire. By analyzing these curves, engineers can design fire protection systems that ensure the structural integrity of the tunnel and the safety of its occupants.



Types of Time-Temperature Fire Curves

There are several standard time-temperature fire curves used in tunnel fire protection design, each representing different fire scenarios. The most commonly used curves include:

  1. Standard Fire Curve (ISO 834)

  2. Hydrocarbon Fire Curve (HC)

  3. Rijkswaterstaat (RWS) Curve

  4. Modified Hydrocarbon Curve (HCM)

  5. ZTV-ING/RABT Curve

  6. EBA Curve (EUREKA)

Let's explore each of these in detail:


1. Standard Fire Curve (ISO 834)

The Standard Fire Curve, also known as the ISO 834 curve, is the most widely used fire curve in building design. Sometimes, it is also applied in the tunnel fire protection. It represents a typical building fire scenario by cellulosic fire and is defined by the following equation 

 

T(t)=T0​+345log10(8t+1) where:

  • ( T(t) ) is the temperature at time ( t ),

  • ( T_0 ) is the initial temperature (usually 20°C),

  • ( t ) is the time in minutes.

 

This curve is characterized by a gradual increase in temperature, reaching approximately 1,000°C after 120 minutes. While it is useful for general fire protection design like fire protection of steel, it may not accurately represent the more severe fire conditions that can occur in tunnels.



2. Hydrocarbon Fire Curve (HC)

The Hydrocarbon Fire Curve is used to represent fires involving hydrocarbon fuels, such as gasoline or diesel, which are common in road tunnels. This curve is defined by a much more rapid temperature rise compared to the Standard Fire Curve, reaching temperatures of around 1,100°C within the first few minutes. The equation for the HC curve is:

 

 T(t)=1080(1−0.325e−0.167t−0.675e−2.5t)+20


3. Rijkswaterstaat (RWS) Curve

The Rijkswaterstaat (RWS) curve is specifically designed for road tunnels and represents a very severe fire scenario. It was developed by the Dutch Ministry of Infrastructure and Water Management (Rijkswaterstaat) and is characterized by an extremely rapid temperature rise, reaching 1,350°C within the first few minutes and maintaining this temperature for a prolonged period. The RWS curve is defined by:

 

  T(t)=1535(1−0.324e−0.2t−0.676e−2.5t)+20


This curve is particularly useful for designing fire protection systems in tunnels with high traffic volumes and the potential for large vehicle fires.

 

4. Modified Hydrocarbon Curve (HCM)

The Modified Hydrocarbon Curve (HCM) is a variation of the HC curve, tailored for specific tunnel fire scenarios. It accounts for the unique conditions in tunnels, such as ventilation and the presence of multiple fuel sources. The HCM curve is defined by:

 

 T(t)=1200(1−0.325e−0.167t−0.675e−2.5t)+20


This curve provides a more accurate representation of tunnel fires involving hydrocarbons and is used in conjunction with other fire curves to design comprehensive fire protection systems. According to the CETU guideline In France, there are more far-reaching requirements for fire-protection in road tunnels. Depending on the size and infrastructural importance, in accordance with the CETU guideline. There are four categories: N0, N1, N2 and N3.


The categories represent a combination of the different time-temperature curves and have the following meanings:

  • N0 = no requirement
  • N1 = HCM 60 minutes and ISO 120 minutes
  • N2 = HCM 120 minutes
  • N3 = HCM 120 minutes and ISO 240 minutes

 

5. ZTV-ING/RABT Curve

The ZTV-ING curve, also known as the RABT curve, is used for road tunnels in Germany. This curve ensures that the supporting reinforcement of the tunnel structure does not exceed 300°C. It also mandates the use of building materials that do not release harmful substances during a fire. This curve is crucial for maintaining the structural integrity of tunnels under severe fire conditions.

 

6. EBA Curve (EUREKA)

The EBA curve is used for railroad tunnels and is defined by the German Federal Railroad Authority (Eisenbahn-Bundesamt, EBA). This curve simulates the temperature profile of fire gases in railroad tunnels, reaching 1,200°C within just 5 minutes. It is based on extensive fire tests and is essential for designing fire protection systems in railroad tunnels.

 

Application of Time-Temperature Fire Curves in Tunnel Design

Time-temperature fire curves are used in various aspects of tunnel fire protection design, including:

  1. Structural Fire Protection

  2. Fire Suppression Systems

  3. Ventilation Systems

  4. Evacuation Planning
     

1. Structural Fire Protection

The primary application of time-temperature fire curves is in the design of structural fire protection systems.

Engineers use these curves to determine the thermal exposure that tunnel structures will face during a fire.

This information is crucial for selecting appropriate fire-resistant materials and designing structural elements that can withstand high temperatures without losing their integrity.

For example, concrete linings in tunnels must be designed to resist concrete spalling effect during tunnel fire and under high temperatures.

By analyzing the time-temperature fire curves, engineers can specify the thickness and composition of concrete linings to ensure they remain intact during a fire.

This is the same approach taken by our Aestuver team. In order to advice customers, engineers and consultants on the selection of suitable tunnel fire protection system we review fire curve requirements.

Based on that information, we are able to verify reports from hundreds of fire tests and suggest the thickness for the tunnel fire protection boards. Aestuver fire boards are regularly and rigorously tested for all of the above mentioned fire curves.

You can find out more about why we need fire protection in tunnels.

 

2. Fire Suppression Systems

Time-temperature fire curves also play a vital role in the design of fire suppression systems, such as sprinklers and deluge systems. These systems must be capable of controlling or extinguishing fires within the temperature ranges represented by the fire curves. Engineers use the curves to determine the required response times and water flow rates for fire suppression systems to be effective in tunnel environments.

 

3. Ventilation Systems

Effective ventilation is critical in tunnel fire safety to control smoke and heat. Time-temperature fire curves help engineers design ventilation systems that can maintain tenable conditions for evacuation and firefighting. By understanding the expected temperature rise and duration of a fire, engineers can specify the capacity and configuration of ventilation systems to ensure they can handle the thermal and smoke loads during a fire.

 

4. Evacuation Planning

Finally, time-temperature fire curves are used in evacuation planning to ensure the safety of tunnel occupants. Engineers use these curves to model the spread of heat and smoke during a fire, allowing them to design evacuation routes and procedures that minimize exposure to hazardous conditions. This includes specifying the locations of emergency exits, signage, and communication systems to guide occupants to safety.

 

Conclusion

Time-temperature fire curves are a fundamental tool in tunnel fire protection design. They provide critical information on the thermal exposure that tunnel structures and systems will face during a fire, allowing engineers to design effective fire protection measures.By understanding and applying these curves, engineers can enhance the safety and resilience of tunnels, ensuring they can withstand severe fire scenarios and protect both the structure and its occupants.


In summary, the use of time-temperature fire curves in tunnel fire protection design is essential for creating safe and resilient tunnel environments. By leveraging these curves, engineers can design fire protection systems that address the unique challenges of tunnel fires, ultimately safeguarding lives and infrastructure.
 

If you have any specific enquiry related to fire protection systems designed to tunnel fire curves, please contact our Aestuver team.

Do you want to learn more about the passive fire protection? Head over to our knowledge centre for more documents, data sheets, white papers, brochures. 

 

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