Ventilation Type Selection in Tunnels

Input by User

Select Guidelines to Compare:

Type of traffic

Length L [m]

Lanes (per tube)

Total AADT [veh/day]~10,000 / lane

HGV Allowed?

HGV share [%]

Flammable Cargo Permitted?

Congestion (RVS/RABT)

Environment (French)

Traffic Level (French)

OUTPUT

Final Analysis

ASTRA matrix

RVS TVS guideline

RABT (German)

French classification See Help

AASHTO Guideline (Reference Only)

Input Parameters

Tunnel Length (meters)

Peak Hourly Traffic (vehicles/hour/lane)

Traffic Direction

Vehicle Types Present

Tunnel Category

91 - 305 m (lower traffic)

X: <91m

A: 91-244m

B: High traffic

C: 244-914m

D: >914m

Classification Graph

Click anywhere on graph to see values. Red pin shows your tunnel location.

Uni-directional Traffic

Bi-directional Traffic

Your Recommendation:

NFPA 502 Table A.7.2 - Fire Protection Requirements

Fire Protection System	Section	X	A	B	C	D

MR = Mandatory CMR = Conditional - = Not Required

Input Parameters

Risk Assessment Calculator - Purpose & Usage

Purpose: This calculator performs Quantitative Risk Assessment (QRA) for tunnel safety, evaluating the risk of deaths from accidents and fires per vehicle-kilometer traveled. It compares calculated risks against ALARP (As Low As Reasonably Practicable) thresholds to determine if the tunnel design meets safety requirements.

How to Use:

Step 1: Enter tunnel parameters (length, speed limit, traffic volume) in the left panel.
Step 2: Adjust baseline rates and safety factors (AMF, FMF, probability of death) based on your project conditions.
Step 3: Set ALARP thresholds (GI and GII) according to your regulatory requirements.
Step 4: Click "Calculate" to compute risk values and view results.
Step 5: Review the ALARP graph in the center panel - data points should be below the red dashed line (GII) for acceptable risk.
Step 6: Check ALARP validation results in the right panel to see if your design meets safety requirements.
Step 7: Use "Report" button to generate a comprehensive risk assessment report.

Legend:

Green dashed line = ALARP GI threshold (best practice)
Red dashed line = ALARP GII threshold (maximum acceptable)
Blue circle = Deaths from accidents per vehicle.km
Red square = Deaths from fires per vehicle.km

Tunnel Length (m)

Speed Limit (km/h)

Traffic Volume (veh/day)

AMF

Baseline Death Rate (deaths/vehicle-km)

Baseline Accident Rate (accidents/vehicle-km)

Baseline Fire Rate (fires/vehicle-km)

ALARP GI

ALARP GII

Fire Outbreak Time (s)

Persons per Vehicle

Traffic Direction Factor

FMF

Probability of Death

ALARP Graph

ALARP GI

ALARP GII

Deaths (Accidents)

Deaths (Fires)

Accidents

Exposition —

Accidents / yr —

Deaths / yr —

Deaths / veh·km —

Fires

Fires / yr —

Deaths / yr —

Deaths / veh·km —

ALARP Validation

Accidents —

Fires —

Input Parameters

NFPA 502 Annex D — Eq. [D.1] V_c = K₁ · K_g · (g · H · Q / (ρ · C_p · A · T_f))^1/3
T_f = Q / (ρ · C_p · A · V_c) + T (iterated)

Tunnel Height H (m)

Tunnel Width W (m)

Grade / Slope (%)+ uphill − downhill

Approach Air Temp T (°C)

Design Fire Size Q (MW)

Results

Critical Velocity V_c

m/s

Mass Flow

kg/s

Avg Gas Temp T_f

°C

Temp Rise ΔT

°C

K₁ (Froude factor)

K_g (Grade factor)

Cross-section A

m²

Table D.1 — K₁ Values

Q (MW)	K₁
> 100	0.606
90	0.62
70	0.64
50	0.68
30	0.74
< 10	0.87

Fig. D.1 — K_g Grade Factor

Grade (%)	K_g
+6 (uphill)	0.80
+4	0.88
+2	0.95
0 (flat)	1.00
-2	1.05
-4	1.12
-6 (downhill)	1.20

Fire Growth Model

Growth Method

Peak HRR Q_max (kW)

Fire Diameter D (m)

Target Distance R (m)

t_growth (s)

t_steady (s)

t_decay (s)

Fire Growth Rate

α_g,q (kW/s²)

t_steady (s)

Decay α_D,q (s⁻¹)

Steady State

Decay

t_max (s)

E_tot (MJ)

Summary & Results

Peak HRR

Total Energy

Max Radiation

kW/m²

STATUS: NOMINAL OPERATION

HRR vs Time

Phase Log

Time (s)	HRR (kW)	Phase

Cat	Length (m)	Unidirectional			Bidirectional
Cat	Length (m)	w/HGV; w/FLC	w/HGV; no FLC	no HGV; no FLC	w/HGV; w/FLC	w/HGV; no FLC	no HGV; no FLC
X	<90	No Ventilation; No Fire Suppression
A	90-240	Ventilation	No Supp (Vent?)	No Supp; No Vent	Ventilation	No Supp (Vent?)	No Supp (Vent?)
B	240-300	Ventilation	No Supp (Vent)	No Supp (Vent?)	Vent, Supp	Ventilation	No Supp; Vent Req
C	300-1000	Vent, Supp	Ventilation	No Supp (Vent)	Vent, Supp	Ventilation	No Supp; Vent Req
D	>1000	Vent, Supp	Vent, Supp	No Supp; Vent Req	Vent, Supp	Vent, Supp	No Supp; Vent Req

Traffic	AADT/lane	Congestion	Length [m]	Result
Unidirectional	-	-	≤ 500	Natural ventilation
Unidirectional	< 5000	Low	≤ 700	Natural ventilation
Unidirectional	5000-10000	Mean	500-3000	Longitudinal ventilation
Unidirectional	≥ 5000	High	500-1500	Longitudinal ventilation
Unidirectional	≥ 5000	High	1500-3000	Longitudinal ventilation with point extraction
Unidirectional	-	-	> 3000	Exhaust air suction with suspended ceiling
Bidirectional	-	-	≤ 500	Natural ventilation
Bidirectional	< 2000	-	≤ 700	Natural ventilation
Bidirectional	< 5000	Low	500-2000	Longitudinal ventilation
Bidirectional	< 5000	Mean	500-1500	Longitudinal ventilation
Bidirectional	≥ 5000	-	1500-3000	Longitudinal ventilation with point extraction
Bidirectional	-	-	> 3000	Exhaust air suction with suspended ceiling

Length (m)	Two-way OR One-way (Stagnant)	One-way (Exception)
≤ 400	Natural longitudinal	Natural ventilation
400 - 600	Mechanical longitudinal	Natural ventilation
600 - 1200	Risk Analysis	Mechanical longitudinal
1200 - 3000	Smoke extraction	Mechanical longitudinal
> 3000	Smoke extraction	Longitudinal w/ spot / Ceiling

Category	Length [m]	Natural	Longitudinal	Transverse
Non-Urban Bi (High)	300-500	Possible	Possible	Possible
	500-800	Forbidden(3)	Possible(1')	Possible
	800-1000	Forbidden	Possible(1')	Possible
	1000-3000	Forbidden	Forbidden	Possible
	>3000	Forbidden	Forbidden	Possible(2')
Non-Urban Bi (Low)	300-1000	Possible	Possible	Possible
	1000-1500	Forbidden	Possible	Possible
	1500-3000	Forbidden	Forbidden(4)	Possible
	>3000	Forbidden	Forbidden(4)	Possible(2')
Urban Uni	300-500	Forbidden	Possible(1)	Possible
	500-1500	Forbidden	Possible(1)	Possible
	1500-3000	Forbidden	Possible(1)	Possible(2)
	>3000	Forbidden	Possible(1)	Possible(2')
Urban Bi	300-1500	Forbidden	Forbidden	Possible
	1500-3000	Forbidden	Forbidden	Possible(2')
	>3000	Forbidden	Forbidden	Possible(2')
Non-Urban Uni (High)	300-500	Possible	Possible	Possible
	500-800	Forbidden(3)	Recommended	Possible
	800-3000	Forbidden	Recommended	Possible
	3000-5000	Forbidden	Recommended	Possible(2')
	>5000	Forbidden	Recommended(1)	Possible(2')

Traffic	Length L [m]	Total DTV	HGV %	System
Unidirectional	≤ 500	≤ 30000	≤ 25	Natural ventilation
Unidirectional	500-3000	≤ 40000	≤ 25	Longitudinal ventilation
Unidirectional	> 3000 / High	> 40000	-	Transverse ventilation
Bidirectional	≤ 700	≤ 10000	≤ 20	Natural ventilation
Bidirectional	700-3000	≤ 30000	≤ 20	Longitudinal ventilation
Bidirectional	> 3000 / High	> 30000	-	Transverse ventilation

Risk Assessment Parameters

Type of Traffic

Ventilation System

Tunnel Length [m]

Compliance Check

Fire Detection Time [s]

Emergency Response Time [min]

Evacuation Time [min]

Tenable Conditions Duration [min]

NOTE: The application of the matrix is only admissible, if a set of requirements is fulfilled.

Traffic	System	Length	Risk Matrix

💨

Critical Velocity Calculator

NFPA 502 2017 Kennedy Method

Critical Velocity Calculator - NFPA 502 2017 Kennedy Method

What is Critical Velocity? The critical velocity (Vc) is the minimum longitudinal air velocity required to prevent smoke backlayering in tunnel fires. Backlayering occurs when hot gases from a fire flow upstream against the ventilation, potentially blocking escape routes and increasing fire growth.

NFPA 502 2017 Method: This calculator implements the Kennedy formula from NFPA 502, Annex D:

                                Vc = K · Kg · √(g·H) · [Q / (ρ · Cp · A · Tg)]1/3
                                
                                Where:
                                
• K = 0.61 (Critical Froude constant per NFPA 502)
                                
• Kg = 1 + 0.0375·grade (Grade factor)
                                
• g = 9.81 m/s² (Gravitational acceleration)
                                
• H = Tunnel height (m)
                                
• Q = Heat release rate (kW)
                                
• ρ = 1.2 kg/m³ (Air density)
                                
• Cp = 1.005 kJ/kg·K (Specific heat capacity)
                                
• A = Cross-sectional area (m²)
                                
• Tg = Average gas temperature (K)

Iterative Solution: Since Vc depends on Tg, and Tg depends on the mass flow rate (which depends on Vc), the solution requires iteration. The algorithm uses an initial guess for Tg, calculates Vc, computes the resulting Tg, and iterates until convergence.

📐 Tunnel Geometry

Tunnel Height, H (m) Clear height from road to ceiling

Tunnel Width, W (m) Clear width of tunnel cross-section

Grade/Slope (%) Positive = uphill, Negative = downhill

🌡️ Environmental Conditions

Ambient Temperature (°C) Standard range: -20°C to 50°C

Maximum Fire Size (MW) Design fire HRR for analysis

m/s

Critical Velocity (V_c)

Mass Flow Rate (kg/s)

Avg Gas Temperature (°C)

Temperature Rise (°C)

⚡ Calculated using NFPA 502 Equation D.1

K₁ = -- (Froude factor)

K_g = -- (Grade factor)

📈

Critical Velocity vs Heat Release Rate

📊 Chart Explanation

This chart shows how the critical velocity varies with fire size. As the heat release rate increases, higher air velocities are required to prevent backlayering. The curve typically shows a power-law relationship, with velocity increasing at a decreasing rate at higher fire intensities.

🚗

Quick Reference Presets

Welcome to the Ventilation Type Selection in Tunnels - Decision support tool.
This application assists engineers in evaluating tunnel ventilation system requirements by comparing multiple international standards, enabling faster and more consistent decision-making during early design stages.

Capabilities & Workflow

Multi-Standard Evaluation: Compare tunnel geometry, fire loads, and traffic composition against ASTRA (Swiss), RVS (Austrian), RABT (German), French, and AASHTO/NFPA guidelines.
NFPA 502 Automatic Categorization: The system automatically determines tunnel category (A, B, C, or D) based on length criteria.
Integrated Engineering Tools: Includes calculators for critical velocity and Austrian risk assessment.
Decision & Reporting Output: Generates concise text summaries indicating alignment with standards and key recommendations.

How to Use

Input Project Data: Enter tunnel dimensions, traffic class, and other required parameters into the input section.
Select Standards: Enable the guideline checkboxes to activate comparative assessment.
Review Analysis: The tool highlights applicable matrix values and displays results in the OUTPUT panel.
View Detailed Matrices: Access guideline tables through options like “View ASTRA Matrix”.
Explore Additional Tools: Use the “MORE” menu for risk calculation modules and additional engineering assessment features.

Acronyms & Abbreviations

TVS: Tunnel Ventilation System

AADT: Annual Average Daily Traffic

HGV: Heavy Goods Vehicle

FLC: Flammable Cargo

HRR: Heat Release Rate

AMF: Accident Modification Factor

FMF: Fire Modification Factor

ALARP: As Low As Reasonably Practicable

Uni: Unidirectional Traffic

Bi: Bidirectional Traffic

Supp: Fire Suppression System

Vent: Ventilation

Cong: Congestion

DTV: Average Daily Traffic

Nat: Natural Ventilation

Mech: Mechanical Ventilation

Trans: Transverse Ventilation

French Classification Notes

(1): Massive Extraction required
(1'): Compensatory Measures required
(2): Desirable Airflow Control
(2'): Mandatory Airflow Control
(3): Forbidden Except with Compensatory Measures
(4): Only if transverse system is ineffective

Credits & Contact

Developed by:

SMH Adil — adil@geedsim.com

Mohd Ahsan Khan — ahsan@geedsim.com

For support, clarifications, or feature requests, please contact the developers.

Legal Disclaimer
This tool utilizes information from international standards and is intended exclusively for preliminary assessment purposes; it does not constitute certified engineering advice. All outputs must be independently verified and approved by qualified tunnel ventilation specialists before any application or reliance. The authors assume no responsibility or liability for loss, damage, or consequences arising from use or interpretation of this tool. The tool and its results are inadmissible as evidence in any legal, regulatory, or contractual dispute.

Growth Definition

Fire Growth Method

Q_max (kW)

Time Interval (s)

t_growth (s)

t_steady (s)

t_decay (s)

Fire Growth Rate

α_g,q (kW/s²)

t_peak (s)

t_steady (s)

Decay Coef α_D,q (s⁻¹)

Steady State Required

Decay Required

t_max (s)

Total Energy E_tot (MJ)

Reference Information

Quick Reference

Linear: Q(t) = α_g,L × t

Quadratic: Q(t) = α_g,q × t²

Exponential: Q(t) = Q_max × n × r × (1-e^-kt)^n-1 × e^-kt

Flame Height: L = -1.02D + 0.235Q^0.4

1. Linear Curve Method

Linear fire growth model with steady state and linear decay phase.

Growth Rate Coefficient:

α_g,L = Q_max / t_growth [kW/s]

Linear Decay Rate:

α_D,L = Q_max / t_decay [kW/s]

Growth (0 ≤ t ≤ t_growth) Q(t) = α_g,L × t

Steady (t_growth < t < t_D) Q(t) = Q_max

Decay (t ≥ t_D) Q(t) = Q_max - α_D,L × (t - t_D)

2. Quadratic Curve Method

Standard t² fire growth model (NFPA/PIE) with exponential decay.

Quadratic Growth Coefficient:

α_g,q = Q_max / t_growth² [kW/s²]

Growth (0 ≤ t ≤ t_growth) Q(t) = α_g,q × t²

Steady (t_growth < t < t_D) Q(t) = Q_max

Decay (t ≥ t_D) Q(t) = Q_max × e^{-α_D,q × (t - t_D)}

3. Exponential Curve Method

Continuous function describing entire fire duration without distinct phases.

Q(t) = Q_max · n · r · (1 - e^-kt)^n-1 · e^-kt

Time to Peak t_max = ln(n) / k

Rate Constant k = Q_max / E_tot × r

Shape Factor r = (1 - 1/n)^1-n

Standard Growth Rates (α_g,q)

Fire Category	α (kW/s²)	Time to 1 MW	Description
Slow	0.00293	~584 s	Cellulose materials, archival storage
Medium	0.01172	~292 s	Wood products, residential furniture
Fast	0.04689	~146 s	Office furniture, retail combustibles
Ultra-Fast	0.18780	~73 s	Plastics, liquid fires, industrial

Physical Correlations

Flame Height (Heskestad, 1984)

L = -1.02 × D + 0.235 × Q^0.4

Radiant Heat Flux (Point Source Model)

q'' = χ × Q / (4πR²)

Parameter	Symbol	Unit	Description
Flame Height	L	m	Vertical distance from fire base to flame tip
Source Diameter	D	m	Characteristic diameter of fire source
Heat Release Rate	Q	kW	Total heat release rate of fire
Radiation Fraction	χ	-	Fraction of HRR radiated (typically 0.3-0.4)
Target Distance	R	m	Radial distance from flame center to target
Heat Flux	q''	kW/m²	Radiant heat flux at target location

Reference Notes

All HRR values are in kilowatts (kW)
Energy values should be converted to kilojoules (kJ) for calculations
Time values must be in seconds (s) for all equations
For tunnel applications, NFPA 502 recommends using Quadratic method with appropriate safety factors
Critical velocity calculations use iterative solution of Kennedy equation

HRR Power Curve

DETAILED TIME-SERIES ENGINE LOG STEP: 60s

Time(s)	HRR(kW)	Phase

Physics Summary

Time to Peak

Total Energy

0MJ

Peak Radiation

0.0

Max HRR

STATUS: CALCULATING

Ventilation Type Selection in Tunnels

Input by User

OUTPUT

Input Parameters

Classification Graph

Uni-directional Traffic

Bi-directional Traffic

NFPA 502 Table A.7.2 - Fire Protection Requirements

Input Parameters ?

Risk Assessment Calculator - Purpose & Usage

ALARP Graph

Input Parameters

Results

Table D.1 — K1 Values

Fig. D.1 — Kg Grade Factor

Fire Growth Model

Summary & Results

HRR vs Time

Phase Log

AASHTO / NFPA 502 Matrix

RVS TVS Guideline

RABT (German Guideline)

French Classification

ASTRA Matrix

Austrian Risk Assessment with Compliance Tool

Risk Assessment Parameters

Compliance Check

Critical Velocity Calculator (NFPA 502)

Critical Velocity Calculator

Critical Velocity Calculator - NFPA 502 2017 Kennedy Method

📐 Tunnel Geometry

🌡️ Environmental Conditions

Critical Velocity vs Heat Release Rate

📊 Chart Explanation

Quick Reference Presets

Guide & Application Overview

Capabilities & Workflow

How to Use

Acronyms & Abbreviations

French Classification Notes

Credits & Contact

French Code Notes

Fire Dynamics Analyser

Growth Definition

Reference Information

Quick Reference

Fire Dynamics Reference Guide

1. Linear Curve Method

2. Quadratic Curve Method

3. Exponential Curve Method

Standard Growth Rates (αg,q)

Physical Correlations

Reference Notes

HRR Power Curve

Physics Summary

Generated Report

Input Parameters

Table D.1 — K₁ Values

Fig. D.1 — K_g Grade Factor

Standard Growth Rates (α_g,q)