Jane Embury explains how skybridges, along with modern glazing systems, play a significant role in evacuations.

The Bridge of Sighs and Evacuation Models

Skybridges, along with modern glazing systems, play a significant role in evacuations.

Legend has it that prisoners would sigh as they crossed it, on their short journey to a life behind bars.  Nowadays, the Ponte dei Sospiri, or Bridge of Sighs, is one of Venice’s star tourist attractions. Built in 1600, the bridge joins what was the Prigioni Nuove, or new prison, to interrogation rooms in the Doge’s Palace across the canal.  The view from the bridge was the last glimpse of the outside world that prisoners would see, prompting Lord Byron to poetically name the bridge.

But the Bridge of Sighs, built for the mundane purpose of transporting people from one building to another, also has one further claim to fame.  It is the world’s first skybridge.But the Bridge of Sighs, built for the mundane purpose of transporting people from one building to another, also has one further claim to fame.  It is the world’s first skybridge.

Once a common architectural feature joining skyscrapers in New York, they not only joined tall buildings – often owned by the same company – but provided a horizontal means of escape in the event of fire.

Nowadays, we think solely about escape in vertical terms, usually downwards to street level.  But, the skybridge concept has not been totally forgotten; Manhattan still boasts a number of the historic structures.

The best current example is between the Petronas Towers in Kuala Lumpur, Malaysia.  They were the tallest buildings in the world between 1998 and 2004, and remain the tallest twin towers internationally. A double-deck skybridge connects the two towers on the 41st and 42nd floors.  The skybridge isn’t actually joined to either tower, being designed to slide in and out of them as the towers sway several feet in strong winds. For the Petronas Towers, the skybridge provides an innovative fire safety feature, while also being an iconic feature of the conjoined buildings.

Simply, as we build higher into the sky, with super-tall buildings set to dwarf anything constructed today, designers and fire engineers have to look again at features like skybridges in evacuation planning. More than anything, they have to revisit the computational models used to predict how a building can be safely evacuated in the event of a fire.

Those models test design configurations to determine whether a building’s safety characteristics are adequate, from the number of evacuation routes to the width of exit doors.  The trouble, of course, is that evacuation involves the movement of people – and the behaviour of flesh-and-blood humans can’t so easily be predicted.

It’s all about psychology and how we process information.  We respond to information from our physical and social environments and, based on what we perceive, we then decide what to do.  In other words, hearing a fire alarm is not enough to make everyone in a building immediately move to an exit.

Office buildings are generally the easiest to evacuate.  Staff have typically been trained in evacuation procedures, are dressed and awake, and able to make informed decisions.  On the downside, many modern office buildings are open plan, making it harder to contain the fire within a small area.

Residential buildings, which include hotels, pose a different dynamic.  People can be asleep, not dressed, and have only limited knowledge of escape routes.  That can seriously extend evacuation times and, worse, lead to re-entry behaviour – for example, to retrieve valuables.

Most challenging are escape strategies for healthcare facilities where the occupant population will include people of limited mobility and therefore unable to perform self-rescue.

Nor is physical impediment simply about age or infirmity.  As buildings are increasing in height, our physical abilities are diminishing.  The buildings in which we live and work are getting taller, while we are getting fatter and more unfit.  That has ramifications for evacuation procedures, and the length of time to exit a building – something that designers and fire engineers will be researching further.

Evacuation models have been used for some time to estimate the time taken to evacuate a building and are a requirement of fire safety and building approval.  But research at the US National Institute of Standards and Technology (NIST), among others, demonstrates that those computer models don’t necessarily reflect the variable nature of human reaction.

In other words, computer modelling can only take us so far in designing in safety.  What is also needed is an understanding of human behaviour in an emergency situation, particularly the factors that have been shown to influence our decision-making processes.  By understanding those factors and processes, a fire safety team can develop a more comprehensive – and predictive – behaviour model for a building’s fire evacuation.

Those predictions have to cover “exit choice behaviour” – the different exits that people will choose to leave by, often because they’re also the entrances and routes by which they arrive at work.  In other words, not maybe the closest exit.

Nor does it model “pre-movement times” – the period immediately following a fire alarm, when the fire has been detected but doesn’t yet pose a threat.  Simply, people don’t always regard an alarm as an immediate call to action.  Many will assume it’s a false alarm or a fire drill, and do nothing.

It adds up to a building evacuation that may be greatly delayed, or patchy in nature.  Recent research indicates that this “pre-movement time” is a more significant evacuation factor than the length of time taken to reach an exit.  As much as two-thirds of the time it takes people to exit a building after an alarm is start-up time – time wasted in looking for more information.

 All of those factors, and many other variables, can influence estimates of evacuation times, and therefore the level of protection within a building to safely allow the occupant population to escape.

Those calculations have never been more important, with a whole raft of super-tall buildings being built, mostly in the Middle East and Asia.  The tallest of them all, on which work has begun, is the £780 million Kingdom Tower in Jeddah, Saudi Arabia which will stand at just over 1,000 metres and have 200 storeys.  It will be three times higher than London’s Shard, Europe’s tallest building, and 173 metres taller than Dubai’s Burj Khalifa, currently the world’s tallest building – with 160 storeys.

Modern glazing systems are now an integral part of fire protection strategy, providing up to 120 minutes of protection against radiant heat or toxic gases – giving everyone, however infirm or slow, more than enough time to exit a building.  Building in time is what glazing systems can do; and time-to-exit saves lives.

High-tech fire suppression systems, refuge floors, protected elevators and well-designed staircases all have a part to play in modern evacuation planning.  But the role that advanced glazing systems have is also a vital element, and we’re pleased that our systems can now be found in buildings great and small across the world.

Maybe, sometime, we’ll also supply systems for a new generation of skybridges.


Bridge of Sighs image courtesy of www.bridgeofsighs.info


  • 12 Commercial Crime Sites to Do Your Research

    12 Commercial Crime Sites to Do Your Research

    Understanding crime statistics in your industry and area is crucial for making important decisions about your security budget. With so much information out there, how can you know which statistics to trust? Read Now

  • Boosting Safety and Efficiency

    Boosting Safety and Efficiency

    In alignment with the state of Mississippi’s mission of “Empowering Mississippi citizens to stay connected and engaged with their government,” Salient's CompleteView VMS is being installed throughout more than 150 state boards, commissions and agencies in order to ensure safety for thousands of constituents who access state services daily. Read Now

  • Live From GSX: Post-Show Review

    Live From GSX: Post-Show Review

    This year’s Live From GSX program was a rousing success! Again, we’d like to thank our partners, and IPVideo, for working with us and letting us broadcast their solutions to the industry. You can follow our Live From GSX 2023 page to keep up with post-show developments and announcements. And if you’re interested in working with us in 2024, please don’t hesitate to ask about our Live From programs for ISC West in March or next year’s GSX. Read Now

    • Industry Events
    • GSX
  • People Say the Funniest Things

    People Say the Funniest Things

    By all accounts, GSX version 2023 was completely successful. Apparently, there were plenty of mix-ups with the airlines and getting aircraft from the East Coast into Big D. I am all ears when I am in a gathering of people. You never know when a nugget of information might flip out. Read Now

    • Industry Events
    • GSX

Featured Cybersecurity


New Products

  • PE80 Series

    PE80 Series by SARGENT / ED4000/PED5000 Series by Corbin Russwin

    ASSA ABLOY, a global leader in access solutions, has announced the launch of two next generation exit devices from long-standing leaders in the premium exit device market: the PE80 Series by SARGENT and the PED4000/PED5000 Series by Corbin Russwin. These new exit devices boast industry-first features that are specifically designed to provide enhanced safety, security and convenience, setting new standards for exit solutions. The SARGENT PE80 and Corbin Russwin PED4000/PED5000 Series exit devices are engineered to meet the ever-evolving needs of modern buildings. Featuring the high strength, security and durability that ASSA ABLOY is known for, the new exit devices deliver several innovative, industry-first features in addition to elegant design finishes for every opening. 3

  • Connect ONE’s powerful cloud-hosted management platform provides the means to tailor lockdowns and emergency mass notifications throughout a facility – while simultaneously alerting occupants to hazards or next steps, like evacuation.

    Connect ONE®

    Connect ONE’s powerful cloud-hosted management platform provides the means to tailor lockdowns and emergency mass notifications throughout a facility – while simultaneously alerting occupants to hazards or next steps, like evacuation. 3

  • Camden CV-7600 High Security Card Readers

    Camden CV-7600 High Security Card Readers

    Camden Door Controls has relaunched its CV-7600 card readers in response to growing market demand for a more secure alternative to standard proximity credentials that can be easily cloned. CV-7600 readers support MIFARE DESFire EV1 & EV2 encryption technology credentials, making them virtually clone-proof and highly secure. 3