Methods of Ventilation in Tunnels
Following methods are implemented for ventilation in tunnels:
- Natural Method
- Mechanical Method
1. Natural Ventilation
When a tunnel receives fresh air and automatically removes the dust without the use of mechanical appliances, this sort of ventilation is called natural ventilation. This type of ventilation can be improved by providing shafts in regular intervals along the length of the tunnel during its construction.
2. Mechanical Ventilation
When the ventilation in tunnels is done with the help of mechanical devices is known as mechanical ventilation. Mechanical ventilation is done by any one of the following methods:
This type of ventilation method is suitable for short-length tunnels. In this system of ventilation, Fresh air is blown by a blower installed in the input shaft. Blowers provide a uniform distribution of fresh air at the workplace, and the vitiated air is pushed out through the portals.
In this method of ventilation, vitiated air is sucked from the tunnel by using exhaust fans, and fresh air is drawn into the tunnel through the inlet shaft. This method rapidly removes dust and foul air from the working face of the tunnel but does not provide proper ventilation.
(iii) Combination of Blowing and exhausting
A combination of blower and exhaust fan is the most reliable ventilation system. This combined system utilizes the advantages of both blowing and exhausting. Immediately after blasting, the exhaust system is operated for 10 to 25 min to drop smoke and dust, and then the fan is reversed for blowing fresh air.
Method of ventilation depends on the following factors:
- Length of tunnels
- Size of Tunnels.
- Frequency of blasting and the amount of explosive.
- Amount of the heat which are produces by human, animals and light.
- Amount of carbon dioxide present in the atmosphere due to human breathing and explosives.
- The temperature inside the tunnels.
- Percentage of humidity present inside the tunnels.