Ventilation Management in long tunnels is the most important requirement not only for the working of machines but also for the sustenance of the personnel. Poisonous gases are generated by blasts in tunnel, exhaust of diesel operated machines, Carbon Dioxide generated by human breathing and besides, a tunnel may cut through strata with trapped foul poisonous gases which would be released on excavation.
Arrangement for speedy evacuation of such gases to avoid serious mishaps and sufficient ventilation to counter the effects of heat released by the rocks, exhaust gases, electrical transformers and cables is absolutely necessary. All these factors demand highest standard in design and performance of the ventilation system. Any shortcoming in the ventilation system can be disastrous and produce long term demoralizing effect on workmen subjected to suffocation resulting in inordinate delay in project execution, ultimately causing huge financial losses. Therefore, ventilation management is the most important aspect of underground works during construction phase.
An effective Ventilation System has to ensure the following :
- Air quality
- Air quantity at the right place
- High reliability
- Ventilation theory
- Effective ventilation is expensive
- Ineffective ventilation, much more expensive
- Expenses include both capital cost and operation cost
- Operation cost is often much higher than capital cost
The quantity of air to be moved is obviously the first choice. At the time of deciding this aspect, one should also consider acceptable tolerances. In general, one may design ventilation for a certain number of air changes at a given situation with considerable range. It is best to assess the resistance of the air system on the assumption that air of standard density is being handled (i.e. 0.0764 lb. per cu. ft., UK) Usually, a Return Velocity between 0.3 M/Sec to 0.6 M/Sec is maintained, depending on the length and cross section of the tunnel.
A ventilation system primarily consists of the following :
A suitable fan with Silencer & Accessories.
- Electrical equipments like Frequency Converter and Control Panel.
- Ducting of correct size and type with necessary accessories for installation.
Source: The Masterbuilder – May 2010