---
title: "Short note: importance of ventilation in tunnelling"
subject: "Transportation Engineering II"
chapter: 5
key: "semester_7/transportation_engineering_ii:short-note-tunnel-ventilation-importance"
source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/short-note-tunnel-ventilation-importance
site: BCT Engineering
---

# Short note: importance of ventilation in tunnelling

Transportation Engineering II · Chapter 5: Introduction to Bridge and Tunnel Engineering

- Asked in: 2070 Chaitra (old course), 4 marks
- Video: [Transportation Engineering-II U-4 L-5 Tunnel Ventilation](https://www.youtube.com/watch?v=u976BC4cyc0) — Namrata Singh
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/short-note-tunnel-ventilation-importance
- Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-5

## Question

Write a short note on importance of ventilation in tunnelling.

## Short answer

Ventilation removes harmful gases (CO, NOx, methane), supplies oxygen, clears dust and smoke, controls temperature and humidity, prevents explosive gas build-up, and aids firefighting. In operating road tunnels it dilutes vehicle emissions to permissible limits and maintains visibility.

## Answer

Ventilation is essential in tunnelling because the air in a tunnel quickly becomes unsafe.
- **Removes harmful gases:** blasting fumes, CO, NOx, diesel exhaust and natural gases (methane, H2S, CO2) are diluted or exhausted.
- **Supplies oxygen** for workers and combustion engines, protecting health and life.
- **Clears dust and smoke** after blasting and drilling, improving visibility and the speed of work.
- **Controls temperature and humidity**, which rise at depth, and reduces worker fatigue.
- **Prevents the build-up of explosive gas** and helps in firefighting and rescue.
- In an operating road tunnel, it dilutes vehicle emissions to permissible limits (IRC:SP:91, PIARC), maintains visibility and controls smoke during a fire.

Methods include natural ventilation, longitudinal (jet fan), semi-transverse and transverse systems, and ducted forced or exhaust ventilation during construction.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which of the following is a main reason ventilation is provided during tunnel construction?
   A. To dilute or exhaust blasting fumes, CO, NOx and natural gases such as methane
   B. To increase the strength of the lining concrete
   C. To lower the water table around the tunnel
   D. To reduce the weight of the rock above the tunnel
   Answer: A. Ventilation dilutes or exhausts blasting fumes, CO, NOx, diesel exhaust and natural gases so the air stays safe. (Key point: Removing harmful gases)

2. Why is continuous ventilation needed where methane may seep into a tunnel?
   A. Methane makes the air too humid
   B. It stops gas accumulating to explosive concentration
   C. It makes methane heavier so it settles on the floor
   D. It cools the rock so methane cannot form
   Answer: B. Ventilation prevents explosive gas build-up by diluting or removing it, and also helps in firefighting and rescue. (Key point: Preventing explosive build-up)

3. In an operating road tunnel, ventilation is mainly used to:
   A. Supply compressed air to drilling machines
   B. Cool the tunnel lining after concreting
   C. Dilute vehicle emissions to permissible limits, keep visibility and control smoke in fire
   D. Remove blasting fumes after every round of drilling
   Answer: C. In service, ventilation dilutes vehicle emissions to limits (IRC:SP:91, PIARC), maintains visibility and controls smoke in a fire. (Key point: Ventilation in the operating road tunnel)