Due to the nature of their design and uses, tunnels have particularly unique fire risks, and any fire can spread quickly, risking damage to assets or injuries to teams. Mining, cable and communication tunnels are subject to significantly high risks, as they utilize heavy-duty machinery, flammable materials and cables, which are all subject to the production of excess heat.
Here we discuss the prevalent fire risks in tunnels and explain how businesses operating within them can assess and mitigate these risks.
What causes the heightened fire safety risks in tunnels?
- Lack of natural ventilation: The enclosed design of tunnels results in a lack of natural ventilation, making it incredibly difficult to regulate temperatures. As heavy-duty machinery operates for long period of time within tunnels, this causes a significant fire risk.
- Smoke spread across curved ceilings: Tunnels are generally built with a curved ceiling structure. This enhances the spread of smoke along the ceiling, resulting in the entire surface area of the ceiling being covered. When the temperature of smoke decreases – once fire has been extinguished – it can sink to human eye-level, increasing the risk of smoke inhalation.
- Limited access: Tunnels are often well-sealed and confined, with limited access. This means that if a fire breaks out in a particular area of the tunnel, access points can be restricted, proving evacuation to be challenging. As a result, evacuation may be limited to a singular route – the same route for people and smoke.
- Heightened risk of structural damage: The sealed and confined nature of tunnels means that temperatures, caused by uncontrolled fires, can reach up to 140°C. These severe temperatures can cause structural damage to tunnels if left unresolved.
What are the fire risks in tunnels?
- Ignition sources: Ignition sources are commonplace in tunnel environments. Vehicles (powered by lithium-ion batteries), heaters and electrical sources, which power equipment and machinery, such as conveyor belts, all present significant fire risks if not correctly monitored.
- Overheating: Nearly half of all fires in industrial environments are caused by the overheating of electrical equipment. This can be as a result of overuse or even poor maintenance. In manufacturing tunnels, machinery, such as conveyor belts, is continuously used to support operations. If unmonitored, the friction in belts can begin to heat, potentially igniting the materials they carry. Additionally, if industrial machinery reaches high temperatures, it can speed up the propagation process of a fire, especially when in contact with flammable materials, such as coal, wood or dust.
- Maintenance of equipment: Tunnels of all kinds use machinery to support operations, such as mining, transportation of goods or maintenance work. Due to the lack of ventilation, dust is commonplace, and its build-up can cause clogging in this machinery, amplifying the risk of overheating. Depending on its material, dust can be highly flammable.
- Combustible materials: Combustible materials are frequently present in tunnels, particularly in mining tunnels. These materials create a prominent fire risk, due to their extremely flammable natural, making it crucial to ensure they are transported and stored safely.
- Electrical faults: Some tunnels, such as cable tunnels, store lengthy networks of cables, which have the potential to cause fires. A lack of maintenance or heat can increase this risk significantly. So, how can you reduce fire risks in tunnels?
Regular risk assessments
By conducting regular risk assessments, you can identify any potential fire risks and put the appropriate measures in place to control these. Once a risk assessment has been conducted, it is important to share the results with team members, so they are aware and can act safely to further reduce risk.
As overheating is a considerable risk in tunnels, it’s crucial to ensure temperature is continually monitored. This allows you to act to reduce temperatures if they reach or exceed a certain limit, before a fire breaks out.
Regular equipment maintenance
Regular maintenance of all electrical equipment within a tunnel is key
Equipment should be subject to regular maintenance and testing to HSE standards. This will ensure you identify any issues early, allowing you to rectify problems to reduce fire risk. Equipment should also be regularly cleaned to decrease the risk of dust build-up.
Any electrical equipment used to support operations should be subject to regular PAT testing (portable appliance testing) and checked for any loose cables or damage.
Temperature regulation within the tunnel can also limit the effects of exterior heating on cabling. In cable tunnels, where there is a lot of electrical equipment present, these regular checks are paramount to ensuring safety.
Storage and transportation of materials
When combustible materials are transported, they should be subject to appropriate controls and measures to ensure they do not present fire risks. For example, combustible materials should be safely stored during transport and subject to regular temperature monitoring to quickly identify the occurrence of any hot spots.
Regular maintenance of all electrical equipment within a tunnel is key for mitigating fire risk, as if a fire is to begin within a ‘hidden area’, such as in cable ducts, it can be difficult to access or control the flames.
To reduce the risk of cables overheating, the temperature should be consistently monitored to highlight any high temperatures which may result in a fire.
Using fire detection and suppression equipment to enhance safety
Putting appropriate measures in place can actively reduce fire risks within tunnels. However, unnoticed hotspots, overheating between regular maintenance or combustion of flammable materials are all still prevalent fire risks. As such, supporting your fire prevention measures with a rigorous fire detection and suppression system is key.
Overheating is a considerable risk in tunnels
If a fire were to break out, detection it early is crucial for allowing the safe evacuation of teams and decreasing the risk of structural and equipment damage.
As every tunnel is unique, the fire detection and suppression system must be bespoke and tailored to the site’s individual uses and risks. There is no ‘one-size-fits-all’ approach.