Transit Vehicle Design Standards and Risk Analysis on Fire Development in Rapid

Transit Vehicles

Adrian Milford

Sereca - a Jensen Hughes Company, Project Engineer

Vancouver, BC, Canada

Motivation

● Design fire size: important parameter in the design of emergency ventilation systems

Factors: materials, train geometry, ignition source characteristics, ventilation conditions, suppression…

Potential impact on life safety (system performance)

Construction and equipment costs

Important Factors: Fire Development

● 1. Material ignition and burning properties

Flame spread, smoke development characteristics

● 2. Ignition source characteristics

Potential severity, locations, exposure to combustibles

Likelihood of occurrence

● 3. Conditions for fire development

Configuration of materials, ventilation conditions

Operational response, detection/intervention

1. Material Fire Properties

● Transit vehicle design standards

ie: NFPA 130, EN 45545

Testing methodology, performance criteria based upon material function

Flame spread, smoke developed – Fire hardened materials

1. Material Fire Properties - Example

● EN 45545

3 hazard levels assigned based upon 4 operational categories and 4 design categories

1. Material Fire PropertiesSide Walls Example

EN 45545 NFPA 130

Flame spread

Heat release – cone calorimeter

Smoke generation

Flame spread – radiant panel

Smoke generation

2. Ignition Sources

● Exterior fire development

Train equipment, vehicle systems separated from interior

● Interior fire development

Train equipment/systems not separated from interior

Limited by vehicle design standard requirements

Introduced combustibles/ignition sources

Generally – potential for greatest fire size

● Severity and likelihood - Risk

2. Ignition Sources - Interior

● Range ~1 kW to 350 kW, most likely sources are minor

● Extreme ignition sources – flammable liquids

Item Peak HRR [kW] Approximate Peak Burning

Duration [s]

Lighter or match < 1 -Polyethylene wastebasket (0.6 kg) filled

with shredded paper (0.2 kg)

15 100 - 200

Pillow with 0.65kg of polyurethane foam 40 100

Luggage filled with clothes 120 (hard suitcase)

25 (soft suitcase)

300

1000

Two men’s jackets 75 - 85 10 - 20

Trash bags filled with paper (1.17kg total) 140 (1 bag - 1.17 kg)

280 (2 bags - 2.34 kg)

350 (3 bags - 3.51 kg)

100

20

100

Amtrak trash bags from overnight trains

(1.8 - 9.5 kg)

30 – 260 10 - 400

3. Conditions for Fire Development

● Ignition source sufficient to ignite exposed materials

● Fire development undetected/no intervention occurs in incipient stages

● Material configuration and ventilation conditions facilitate spread

● Operational response

Train remains operational or is disabled?

Fuel configuration, ventilation, suppression response

How are Design Fire Sizes Estimated?

● Traditional methods

Typically assume 1 car is fully burning

Summation of all vehicle material heat release rates or available ventilation (post-flashover)

Assumptions based upon historical events and testing

● Advanced methods – pyrolysis, prescribed material burning rate modelling

Skilled user knowledge, important material inputs required

Model parameter uncertainty, limitations, validation

Traditional Fire Estimation

● Limitations relative to key factors:

1. Historical fire events/testing largely involve materials that do not comply with current design standards

2. No ignition source context

3. Propensity for fire spread not included, no risk context

● Further limitations

Fire dynamics in interconnected vehicles?

Influence of train configuration, interaction of ventilation conditions with fire development, …

Advanced Methods of Fire Estimation

● Objective: obtain better understanding of influence of key factors on fire development

● Limitations

Uncertainty in model input parameters, sub-models

Impact of simplifying assumptions (ie: prescribed burning rates)

Further work would be beneficial in evaluating/validating prediction methodology flame spread at assembly and full scale for modern fire-hardened materials

Advanced Methods – Example 1

● Prescribed burning rate methodology with interconnected trains

● FDS 5.5.3, material burning properties from cone calorimeter testing

Reference: Milford A, Senez P, Calder K, Coles A (2014) Computational Analysis of Ignition Source

Characteristics on Fire Development in Rapid Transit Vehicles, 3rd International Conference on Fire in

Vehicles (FIVE), 131-142

Advanced Methods – Example 1

Ignition location: floor beneath

seats

No fire development

One portion of incident car● Objective:

estimation of fire development trends relative to:

Forced ventilation (open doors)

Ignition source strength and location

Reference: Milford A, Senez P, Calder K, Coles A (2014) Computational Analysis of Ignition Source

Characteristics on Fire Development in Rapid Transit Vehicles, 3rd International Conference on Fire in

Vehicles (FIVE), 131-142

Advanced Methods – Example 2

● Assembly scale testing of rapid transit vehicle materials with large initiating source (500 kW)

● Pyrolysis modelling and comparison: FDS 5

Reference: Coles A, Wolski A, Lautenberger C (2009) Predicting Design Fires in Rail Vehicles, 13th

International Symposium on Aerodynamics and Ventilation of Vehicle Tunnels, 819-833

Advanced Methods – Example 2

● Comparison of model with experiment (500 KW burner)

● Evaluation of other ignition source: 300 kW (peak) trash bag

Reference: Coles A, Wolski A, Lautenberger C (2009) Predicting Design Fires in Rail Vehicles, 13th

International Symposium on Aerodynamics and Ventilation of Vehicle Tunnels, 819-833

Advanced Methods: Example Findings

● Small localized ignition sources unlikely to lead to fire development beyond the immediate area under natural ventilation

Most common ‘nuisance’ ignition sources (trash, minor introduced combustibles): minimal risk

● Extreme ignition scenarios (ie: flammable liquids) have potential for fire spread beyond initiating area

Remote event, disproportionate to materials typically present, security and risk implications

Risk Considerations

● Risk philosophy: What is ‘acceptable’ and what constitutes acceptance?

Owners/operators, authorities/regulators, public

● Likelihood of occurrence for the key factors vs potential severity

Event Tree Analysis

Type of Incident Type of Fire Spread Detection Extinguished Probability

0.1 1.608E-05

0.99

0.9 1.447E-040.05

0.01 1 1.624E-06

0.56

0.93 2.841E-030.0058

0.99

0.95 0.07 2.138E-04

0.01 1 3.086E-05

0.44 2.552E-03

0.9942 0.9942

1.000000

Incident

P(fire)=0.0058

P(other)=0.9942

P(arson)=0.56

P(mech/elec)=0.44

P(det)=0.99

P(det')=0.01

P(ext)=0.10

P(ext')=0.90

P(ext')=1.0

P(spread')=0.95

P(spread)=0.05

P(det)=0.99

P(det')=0.01

P(ext)=0.93

P(ext')=0.07

P(ext')=1.0

Full Vehicle Involvement

Localized Damage

Evaluation of Risk Context

● Probabilistic assessment

What is credible?

Statistical data

Uncertainty?

● Evaluation

Risk scoring

Cost-benefit analysis

Thank you!

Questions?