With the rapid growth of cities it is considered that around 75% of the world's population will live in cities by 2050. Estimates are that the population moving to cities are approximately 172,800 persons per day [1]. This increased demand on cities has resulted in further technological advancement in terms of infrastructure. Although the rail industry has significantly advanced in terms of driverless capability, open gangway train systems and real time monitoring it is important that our awareness of fire safety advances at the same rate.In the past, tunnel and operational fire strategies considered assisted evacuation for persons with reduced mobility (PRM) by on-board staff members, while allowing able bodied persons the ability to self-evacuate to a point of safety outside the incident tunnel. As we move into a future with further automation and less on-board train staff, it may be time to re-evaluate our current thinking in terms of tunnel evacuation strategies for Persons with Reduced Mobility.The aim of this paper is to open the discussion in terms of fire safety in tunnel systems, in particular provision of walkways and the effect on egress within tunnels. The widths of walkways are key factors in the pace at which passengers can disembark from a train onto a walkway.Although there is an active effort to improve walkway provisions within tunnels, the minimum acceptable width limit is still open for debate. This ultimately comes down to a balance between cost (monetary, environmental) and level of acceptable risk.

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Influence of walkway design on the evacuation of passengers

within a fixed guideway transit system

Aaron Mc Daid1

1Arup

Dubai, UAE

aaron.mcdaid@Arup.com

Keyword: Underground Structures, Evacuation strategy, Person with Reduced Mobility, Fire

Engineering, Ethics, Tunnels.

Abstract

With the rapid growth of cities it is considered that around 75% of the world's population

will live in cities by 2050. Estimates are that the population moving to cities are

approximately 172,800 persons per day [1]. This increased demand on cities has resulted in

further technological advancement in terms of infrastructure. Although the rail industry has

significantly advanced in terms of driverless capability, open gangway train systems and real

time monitoring it is important that our awareness of fire safety advances at the same rate.

In the past, tunnel and operational fire strategies considered assisted evacuation for persons

with reduced mobility (PRM) by on-board staff members, while allowing able bodied persons

the ability to self-evacuate to a point of safety outside the incident tunnel. As we move into a

future with further automation and less on-board train staff, it may be time to re-evaluate our

current thinking in terms of tunnel evacuation strategies for Persons with Reduced Mobility.

The aim of this paper is to open the discussion in terms of fire safety in tunnel systems, in

particular provision of walkways and the effect on egress within tunnels. The widths of

walkways are key factors in the pace at which passengers can disembark from a train onto a

walkway.

Although there is an active effort to improve walkway provisions within tunnels, the

minimum acceptable width limit is still open for debate. This ultimately comes down to a

balance between cost (monetary, environmental) and level of acceptable risk.

Introduction

With the latest updates of TSI (Technical Specification for Interoperability) there is a trend

for walkway widths to increase (750mm to 850mm) [3]. However, in terms of other

international practice, NFPA (National Fire Protection Association) 130 walkway widths

remain at 610mm [4]. This is something which is contested among some members of the fire

safety community. Particularly, given that the life safety code (NFPA 101) requires a

minimum width of 1120mm for corridors within buildings [5], which would be considered to

have a lower level of risk.

NFPA 130 has largely become the generally accepted international standard for most train

systems throughout the world, in particular the Middle Eastern regions, Asia and throughout

the United States of America. The code provides requirements for passenger egress

provisions within tunnels and stations. The NFPA 130 minimum width requirement for

walkways within tunnels are below that which would be provided within a conventional

building, we ask ourselves what are the key influences on the choice of walkway width and

are the current provisions acceptable given the trend for un-staffed trains.

Objectives

The paper has the following objectives:

1. Evaluate current and industry practice in terms of design guidance of walkways.

2. Investigate current drivers for choosing walkway widths and the implication on cost

and risk

3. Discuss the impact of walkway width on evacuation.

4. Provide a simple case study for discussion.

5. Discuss some measures which can reduce risk in existing tunnels

6. Make some conclusions and recommendations for further research.

Industry Practice and factors Influencing Walkway Width

Most design guidance around the world for tunnel design has limited provision for

accessibility for persons with reduced mobility in the event of an evacuation scenario. Instead

a reliance is placed on the resilience of the train system to continue to the next station.

Although trains will generally make it successfully to the station in most cases, the ability for

a train to make it safely to the station cannot always be relied upon. A recent event illustrates

this, where a train was immobilized in Washington DC and 1 person was killed and 84

persons hospitalised [6].

As design engineers we must consider the event of the train stopping within the tunnel.

Currently, this is addressed in various ways such as the provision for tunnel smoke

ventilation, traction power isolation (blue light stations), and intervention shafts.

The expectation of the fire and operational strategy for un-staffed train systems, is that the

fire service will assist in the evacuation of persons with reduced mobility which may result in

delays to evacuation and take a considerable amount of time.

Although current walkway widths within most tunnels throughout the world have the NFPA

130 compliant walkways, history has shown that the level of risk to passenger is relatively

low. This may be due to the advancement in reliability and technology or improved material

properties within trains.

Current Industry practice which is commonly followed to select an appropriate walkway

width is based on code compliance. This prescriptive based approach may not fully consider

the bespoke nature of individual transit systems and there specific operational and fire safety

objectives, which may result in increased operational risk during the whole life cycle of the

transit system.

Drivers for selecting walkway widths

Given the nature of infrastructure projects such as fixed guideway transit systems, large

capital investment is required by nation states or Public Private Partnerships in order to

finance such projects. As such, it is important to maintain a balance between the capital cost

of a project and the ongoing operational risk. It is widely understood that there is a point of

diminishing return in terms of risk reduction as investment increases. This is because it is not

possible to eliminate risk all together.

The below hypothetical graph attempts to visualize the relationship between reduction of

ongoing risk versus capital investment.

Figure 1 Hypothetical Risk Vs Cost

With a higher capital investment it is possible to significantly reduce the risk within tunnels,

however there is a point of diminishing return where, as the investment in safety reduces the

amount of risk reduced becomes disproportional to the benefit. Thus, the investment would

be better made to achieve more safety in other areas. This is due to the exponential impact of

walkway width on the amount of excavation, concrete required and Tunnel boring machine

diameter.

Currently these metrics are not fully understood and there is a tendency to opt for the

prescribed values, particularly in terms of walkway width.

To further examine this issue, a risk based approach could be undertaken to evaluate, the

optimal cost point in terms of walkway width with respect to other key metrics such as cost,

risk reduction, life safety and fire exposure.

In conducting such research, possible considerations could include;

Fire Service Response times

Distance between stations

Specification of rolling stock

Open or closed gangway trains

Smoke Control provisions

Table 1 further outlines some of the influences of increasing or decreasing the tunnel

walkway widths in terms of cost implication and evacuation timing.

Table 1 Effects of changing walkway widths

Provision for two lanes of passenger

flow

Provision for self-evacuation for

Persons With Reduced Mobility

Increased Evacuation Time

Walking speed controlled by slowest

person in lane

Lack of provision for Persons with

Reduced Mobility

Cost impact on project

Increased Excavation

Increased Ventilation

Increased Concrete

Larger Tunnel Boring Machines

Cost impact on project

Reduced Excavation

Reduced Ventilation

Reduced Concrete

Smaller Tunnel Boring Machines

No Change to Risk of Fire Starting

In the event of fire scenario within a train in a tunnel, stopping the train within the tunnel is

the last option, this is largely due to lack of familiarity of the tunnel environment and the

increased risk, compared to a station or the open air. If a train must stop within a tunnel, per

most operational strategies the operator will attempt to stop the train such that the train is near

to a cross passage. This is intended to reduce the amount of time for passengers within the

incident tunnel.

When considering tunnel evacuation we must also examine conventional thinking in terms of

longitudinal smoke control. Such tunnel ventilation design philosophies result in an upstream

(fresh air) and a downstream (smoke). The downstream condition is generally untenable for

the evacuating passenger. Depending on the location of the fire within the train there is

potential for passengers to be both upstream and downstream of the fire during an evacuation

scenario. As such, it is beneficial to provide every opportunity for a quick evacuation in such

an event. However, the benefit is not yet quantified in general terms. It is considered that a

wider walkway would allow for a reduced evacuation time and would consequently reduce

the overall downstream passenger smoke exposure [7, 8]. Increasing the walkway width

would provide a potential two fold advantage by allowing potentially double lanes of

passengers and allowing wheelchair users the ability to effectively self-evacuate.

Hypothetical Tunnel Fire Evacuation Scenario

A simple case study is assessed to demonstrate the possible sequence of operation for a train

fire scenario in an NFPA 130 compliant tunnel; see figure 1. The selected scenario considers

a fully automated driverless train with open gangways (no carriage separation).

Figure 1(Hypothetical Train Fire Scenario)

The case study considers the possible timeline of escape for a wheelchair user in the event of

a fire scenario. The sequence of operation is based on previous project experience; see Table

2

Sequence of Operation (Hypothetical Example)

Hypothetical

Timeline

(Cumulative)

Fire Detected onboard and automatic notification to Operational

Control Centre

Train Fire verification using CCTV System

Passengers informed over Public Address and Voice Alarm

(PAVA)

Train begins to come to a halt and able bodied passengers begin to

self-evacuate via the fixed walkway to the non-incident tunnel.

NFPA 130 Compliant Walkway

Persons with reduced mobility are assisted by other passengers

(Removed from wheelchair and carried to the non-incident tunnel)

Persons with reduced mobility await first responders to assist in

evacuation (Removed from wheelchair and carried to the non-

incident tunnel)

In both of the above possible evacuation outcomes, persons with

reduced mobility would likely be negatively affected by the

610mm walkway width resulting in reduced travel speed traveling

along walkways.

Likely to be in

excess of 30 minutes

depending on

response time

Table 2: Hypothetical Train Fire Scenario

The above hypothetical example illustrates that the evacuation timeline for able bodied

persons are largely functional in the current design philosophy. The same arguably cannot be

said for the evacuation of persons with reduced mobility. As such, there may be the

opportunity to provide further innovation in terms of fire safety systems, operational

procedures and awareness for evacuation within tunnels, firstly to educate members of the

public to assist passengers with reduced mobility and secondly to improve the overall

evacuation flow in tunnels.

Measures for Reducing Risk in Existing Tunnels

Current tunnel design trends note that there is a willingness to make provision for wider

walkways and further provisions for those with different level of ability. However, apart from

walkway width, there are other areas which can assist in minimizing the effect of tunnel fire

evacuation in particular for driverless train systems;

Specially designed easy to use tunnel evacuation chairs provided within trains

Regularly updated operational fire strategy

Increased training and education for passengers while waiting for trains

Enhanced monitoring (Real time fire detection)

Safer trains (Reduced ignition sources and combustibility)

Self-closing smoke barriers between carriages to reduce smoke spread

Conclusions

Widely accepted practice within the fire safety community is to rely on other passengers to

assist in evacuation of persons with reduced mobility to a point of safety. If passenger

assistance is not available then persons with reduced mobility would be required to await

assistance from first responders, which may take a long period of time. In the event of a train

fire scenario this may have a negative impact on the survivability of those train users given

the level of fire and smoke that would be expected. This is largely due to such train users not

having the ability to self-evacuate due to limited walkway widths. The overall implication of

this is not fully understood as events where trains are immobilised are rare and very

infrequent.

Whether assessing an existing rail transit system or designing a new one, as designers it is

important we understand the level of risk for a given design item in terms of prescriptive

requirements. This is particularly relevant when assessing the walkway width in tunnels. As

such, when providing guidance in terms of fire strategy, we must consider the potential

impact of the minimum provisions not meeting the holistic fire safety objectives of the

design.

The following list provides some further research and measures that can be considered;

1. Consideration is required to the adequacy of prescriptive code requirements to ensure

they meet the fire safety objectives.

2. Given the significant cost implications of increasing tunnel diameters, the increased

level of safety must be balanced with the potential for disproportional benefit in terms

of risk reduction.

3. Walkway has been demonstrated as a key factor in the overall evacuation time to a

point of safety.

4. Existing tunnels may not meet the demands for a modern railway system given the

trend of un-staffed trains and as such may not meet the required fire safety objective.

5. Investigate the relationship between tunnel diameter and acceptable level of risk to

establish the optimal cost point for tunnel walkway width.

6. Investigate the impact of Persons with reduced mobility on able bodied evacuation

flow

References

[1]Siemens (2013). Como – Facts, Trends and Stories on Integrated Mobility. The future of

getting around. Issue 10. May 2013.

[3] Official Journal of the European Union (2014) Safety in railway tunnels of rail systems

of the European Union

[4] NFPA 130 (2014) Standard for Fixed Guideway Transit and Passenger Rail Systems

[5] NFPA 101 (2015) Life Safety Code

[6] News Report from Washington post on https://www.washingtonpost.com/news/dr-

gridlock/wp/2015/01/12/lenfant-plaza-station-evacuated-for-smoke/

[7] Justin M. Edenbaum, (20016). Subway Tunnel Cross Passage Spacing A Performance

Based Approach

[8] Kohl B., Bauer F.,Hödl R., (2004). Self-rescue in railway tunnels - Evacuation simulation

results

ResearchGate has not been able to resolve any citations for this publication.

Como -Facts, Trends and Stories on Integrated Mobility. The future of getting around. Issue 10

  • Siemens

Siemens (2013). Como -Facts, Trends and Stories on Integrated Mobility. The future of getting around. Issue 10. May 2013.

Safety in railway tunnels of rail systems of the European Union

Official Journal of the European Union (2014) Safety in railway tunnels of rail systems of the European Union

Standard for Fixed Guideway Transit and Passenger Rail Systems

NFPA 130 (2014) Standard for Fixed Guideway Transit and Passenger Rail Systems

Subway Tunnel Cross Passage Spacing A Performance Based Approach

  • Justin M Edenbaum

Justin M. Edenbaum, (20016). Subway Tunnel Cross Passage Spacing A Performance Based Approach

Self-rescue in railway tunnels -Evacuation simulation results

  • B Kohl
  • F Bauer
  • R Hödl

Kohl B., Bauer F.,Hödl R., (2004). Self-rescue in railway tunnels -Evacuation simulation results