Since the beginning of civilization, the underground tunnels play important roles, not only shaping the landscapes, but also connecting peoples and bringing advancements to the society in several areas.
Current Times
Today, there is a significant increase in tunnel construction. This growth stems from the high demand for mobility, mineral extraction, the development of electrical infrastructure, sanitation and other diverse needs of society.
As this process of expansion progresses, it is necessary to establish specific standards and procedures due to the risks involved in these constructions. As a result, the first public and private organizations dedicated to standardization emerged, to reduce or control the existing risks in tunnel construction and operations.
The main risks of tunnels
Over time, as tunnel construction progressed, several accidents occurred which, as they happened, allowed solutions and standards to emerge to avoid accidents in future constructions.
Among the risks, which are now more controlled, are the following:
Collapse: Tunneling in a variety of soils, from ordinary soil to rocky and unstable formations, represents a significant challenge. Before modern tunnel construction techniques and support systems, the risk of collapse was a constant concern. This scenario could result in significant consequences, including serious injuries and even fatalities, with workers potentially becoming trapped under tons of rubble.
Photo: Tunnel Collapse in India – Source: AFP
Flooding: In underground tunnels, especially those that pass through waterbodies or areas with high water tables, there is a constant threat of flooding. If a sudden influx of water floods the tunnel, it could endanger workers and cause damage to equipment.
Photo: Collapse at Line 6 Metro Construction on Marginal Tietê – Source: Estadão Conteúdo
Accumulation of gases and explosions: The accumulation of toxic gases, such as carbon monoxide and hydrogen sulphide, represents a great danger to workers. In tunnels where mines are operating or which are close to volatile materials, such as coal or other flammable substances, the risk of explosion becomes greater. In addition, inadequate ventilation contributes to further increasing this risk, allowing harmful gases to accumulate in confined spaces.
Photo: BENXI, Liaoning, June 6 – Source: People's Daily Online
The importance of underground ventilation
Ventilation in tunnel constructions is essential to ensure the safety of workers. In addition to keeping the air clean, underground ventilation controls harmful gases and cleans up the residues of controlled explosions.
The advances in ventilation technology over time have been remarkable. Initially, rudimentary methods were used, such as fires lit in shafts to generate rising air currents in the tunnels. However, these methods have evolved into more advanced systems, such as steam-powered fans. Despite this, the working conditions in the tunnels remained extremely dangerous, resulting in the loss of many lives among the workers.
These events highlighted the importance of efficient and safe ventilation systems in tunnel constructions, and directly influenced the safety standards and engineering practices that would be adopted in future projects.
Evolution of Ventilation Equipment in Tunnel Excavation
In the early stages of tunnel construction, ventilation was usually carried out naturally, through natural air currents or using simpler methods such as building chimneys to circulate the air.
The first fans were operated manually, using cranks or other forms of human drive, and had limited power and ventilation capacity. With the advent of electricity, it was possible to create electric fans, but initially they also had low power and ventilation capacity. It was only then, with the advancement of technology, that electric motors were improved and allowed for new, more powerful and efficient fans.
Throughout the 20th century, axial and centrifugal fans specific to tunnel applications were developed, providing the right air flows and pressures to ensure ventilation in confined environments, such as tunnels.
Definitive Ventilation in Urban and Road Tunnels
The definitive fans, resistant to high temperatures, are essential in urban and road tunnels once they have been built, guaranteeing the safety of users in various situations, including daily traffic and emergencies such as fires or explosions.
How is the definitive ventilation determined?
Determining the need for and type of ventilation takes some complex considerations. Parameters such as tunnel length and section, traffic probability, number of lanes and permitted vehicles are the main information to be taken into account. In addition, factors such as the slope, height and cross-section of the tunnel, along with the distance of each of the fans that will be installed in the ceiling, also influence the calculation of ventilation in normal operation.
In the context of emergency ventilation, it is essential to assess the maximum power of the fire, which is directly influenced by the type of fuel involved, the extent and the rate of heat release from the fire. These elements are fundamental for determining the amount of heat generated by the fire and, consequently, establishing its maximum power.
After determining the power of the fire and the air speed needed to avoid the smoke back-layer, the next step is to calculate the total thrust required to direct the smoke as desired. Based on these analyses, it is possible to select the number and the appropriate type of fan for the ventilation system.
In Brazil, there is no obligation to renovate existing tunnels to install adequate ventilation systems. However, in the event of renovation, it is mandatory to reassess ventilation and firefighting projects to ensure compliance with the new safety criteria.
Want to know more?
This text is designed to provide an overview of the aspects related to the final ventilation of tunnels, aiming to facilitate the understanding of the subject without going into complex technical details.
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