When It Comes to Smoke Control, Are Depressurisation Systems Fit For Purpose?

We have known for many years that pressurisation is the most effective method for keeping protected escape routes clear of smoke and heat:

• BS 5588-4: 1978: Smoke Control in Protected Escape Routes Using Pressurisation was the industry standard until 1998.
• BS 9991:2015: Fire Safety in the Design, Management and Use of Residential Buildings is the current standard. Recent revisions state that pressurisation systems should be used in all new single staircase residential buildings taller than 18 metres.
• BS12101-13 Pressure Differential Systems. Design & calculation methods, installation, acceptance testing, routine testing & maintenance. This standard is currently in draft form, but, with public consultation being terminated in August 2020, publication is expected soon

But these are standards, not laws. And of course, there’s also Building Regulations Approved Document B, which deals with the aspects of fire safety in buildings. The introduction of this document says:

“Those with responsibility for meeting the requirements of the regulations will need to consider for themselves whether following the guidance in the approved documents is likely to meet those requirements in the particular circumstances of their case.”

So in other words, it’s up to designers to decide on the most appropriate fire safety systems for their projects. And most designers seem to choose depressurisation systems.

It’s easy to see why. Depressurisation systems have a reputation for being simple and inexpensive to install. Also, pressurisation systems sometimes depend on an air release shaft, which can cost developers up to 0.5m² of real estate per floor.

It’s not the fire that kills. It’s the smoke.

According to government statistics, since 2017 there have been over 8,000 fires in buildings taller than four storeys. And sometimes, such fires can be catastrophic:

• July 2009 – Lakanal House, Camberwell, London – six deaths.
• June 2017 – Grenfell Tower, London – 72 deaths.
• January 2022 – East 181st Street, the Bronx, New York – 19 deaths.

In each of these tragedies, either the majority of the victims died due to smoke inhalation, or smoke made a bad situation even worse.

In Grenfell Tower, for example, structural issues caused the fire to spread rapidly. But many residents were unable to escape as the building’s single stairwell filled with thick, toxic and suffocating smoke. A similar situation occurred with Lakanal House – a central stairwell was the only way in and out of the building, but it quickly filled with smoke.

Each of these tragedies is the result of a long list of systemic failures. But in each instance, it’s clear that there would have been significantly fewer casualties had the residents been able to access a safe and reliable means of escape.

This is what needs to change. Tall residential buildings need a dependable smoke control system that’s capable of keeping stairwells smoke-free in the event of a fire. Not only does this make it easy for residents to escape, it also makes it much easier for fire and rescue services to enter the building.

The problem is that depressurisation systems can only manage fires on single levels. But in each of these tragedies, the fires spread to multiple levels.

For tall buildings, depressurisation systems are simply not fit for purpose.

All buildings use some form of smoke control. Each system has its benefits. But once a building reaches a certain height, certain smoke control systems no longer offer a level of protection you can depend on.

Let’s look at three of the most common forms of smoke control systems, and assess the benefits and limitations of each.

This involves using wind and the natural thermal buoyancy effect – whereby hot air rises to be replaced by colder, denser air – to encourage smoke to escape through windows or vents. When an external wall isn’t available, a natural ventilation system will instead use a dedicated smoke escape shaft.

This is by far the cheapest smoke control system to install. However, architects rarely adopt natural ventilation as a smoke control system these days, largely because the ventilation shafts take up so much space – they can be between 1.5 and 3m², depending on whether the system is protecting a fire fighting shaft.

Also, given the specific requirements it would involve to accounting for atmospheric and structural conditions, natural ventilation systems are not suitable for use in buildings with extended travel distances.

So natural ventilation systems are almost exclusively used in smaller buildings, or in certain public areas of larger buildings, such as lobbies and atriums.

This is currently the most popular method for smoke control in contemporary building design. If hot, dense smoke enters the common escape area, the depressurisation system will use extractor fans to discharge the harmful gases to the atmosphere via a smoke extract shaft.

As the name suggests, depressurisation systems work to depressurise stairwells in the event of a fire. They create a predetermined air velocity across the fire door that links the protected space and the stairwell, before inducing fresh air into the stairwell via an automatic opening vent (AOV) at the head of the stairs. In this way, they work to create “tenable conditions” within the stairwell and escape corridor, allowing the building’s occupants to escape safely.

Picture the scene: A fire breaks out in a flat in a tall residential building. The depressurisation system detects the fire, and immediately gets to work protecting the common escape areas from the effects of heat and smoke.

But depressurisation systems are designed to manage a single fire on a single floor. If the fire spreads across multiple floors – as it did during the Grenfell tragedy – then the system can quickly get overwhelmed.

As soon as the fire spreads to more than one level of the building, rather than protecting the stairwells from heat and smoke, the depressurisation system may instead induce smoke from the additional levels into the escape stairs.

But even if the fire remains on one level of the building, there are still certain problems associated with depressurisation systems.

BSEN12101-6: 2005, the British Standards for smoke and heat control systems, warns about the limitations of depressurisation systems, it states: “It is important to note that there is no protection of any part of an escape route within the depressurised space itself, or may even be fully involved in a fire.” It is quite obvious of course that, if there is no protection to any part of an escape route, then that part is likely to be entirely filled by smoke!

Fire doors are designed to contain heat and smoke, yet the majority of depressurisation systems work on the basis of drawing make up air into the escape route by “sucking open” the fire door that links the common corridor with the stairwell. This breaks the containment, and increase the risk that smoke will migrate into the stairwell.

Above all, the issue with depressurisation systems is that they’re designed to remove smoke from an escape route that’s already contaminated. Yet the very act of depressurising a stairwell can increase the risk that the system will actively induce more smoke into the protected space.

Surely it would be better to use a system that actively prevents heat and smoke from entering the protected space in the first place?

After all, prevention is better than a cure…

Instead of extracting smoke from a protected area, a pressurisation system instead actively prevents smoke from entering the area in the first place.

It does this through forcing cool, clean air into buildings. This creates a positive pressure difference between the area afflicted by fire, and the essential escape and access routes such as the stairwell, lobbies, and common corridors.

Pressurisation systems are specifically designed to protect a building’s primary escape route – the stairwell. Through continuously forcing fresh air into the escape route, it either reduces or outright prevents the migration of smoke into the protected space.

So rather than working to remove smoke from an already-compromised space, a pressurisation system will instead work to keep the protected space safe from the start.

A major benefit pressurisation systems have over depressurisation systems is that they can manage fires on more than a single level. So even if the fire starts to spread, and even if several stairwell doors are opened at the same time, the pressurisation system will continue to supply cool fresh air to the critical stairwell escape route at all times.

Hi-Protect is our advanced intelligent pressurisation smoke control system. It’s designed to resist the flow of smoke into a high-rise building’s common escape routes.

Why do we call it “intelligent”? Because it’s all managed by a sophisticated control system we call The Doormon.

The Doormon constantly provides the Hi-Protect system with real-time data, meaning it can react instantly to changing conditions. And at the same time, the Doormon is constantly monitoring its own smoke control and system component status. You can view all the relevant data and make key adjustments remotely – such as from the concierge management office.

So you can easily access an up-to-date overview of exactly how the Hi-Protect pressurisation system is performing, while receiving advanced notifications whenever routine maintenance is due. This way, you can rest assured that you’ll be able to depend on your Hi-Protect system when you need it most.

Depressurisation systems extract smoke from areas that are already contaminated. This feels counterproductive. And as we’ve seen, in some cases depressurisation systems can actually induce more smoke into a protected area.

Our pressurisation system instead prevents smoke from entering the protected space in the first place. It does this through forcing a constant supply of fresh air into the stairwell, thereby creating a pressure difference which ensures that smoke migration into the protected space  will be resisted even if somebody opens a fire door.

Many pressurisation systems use pressure sensors and pressure relief terminals to control and monitor the airflow. These components can be costly and complicated to install and run maintain – which might partially explain why many designers distrust pressurisation systems.

But the Hi-Protect system instead relies on door proximity sensors (DPS). They’re small, discreet, very easy to install, yet they’re more reliable – than pressure sensors and relief terminals and provide real-time control of the pressurisation system. They don’t just monitor whether a door is open or closed. They also monitor how far a door’s open.

The DPS will send this information to the Doormon control system, which will in turn adjust the speed of the pressurisation fan to maintain the positive pressurised environment in the protected space.

This happens in real-time. The Doormon will respond to any changes in conditions within two seconds. Meanwhile, a breaking system in the fan inverter control allows for rapid acceleration or deceleration of the pressurisation fan, helping to keep the pressurisation levels constant.

• Keep stairways free from heat and smoke, even if fire spreads to more than a single floor and multiple fire doors are open at once. So you can give the building occupants a safe and clear escape route while allowing fire and rescue services unobstructed access.
• Small and unobtrusive door proximity sensors are simple and inexpensive to install. This makes the system just as simple and cost-effective as a depressurisation system – yet it’s significantly more effective.
• Remotely monitor every moving part of the pressurisation system and make automatic routine maintenance checks to give you smoke control you can depend on for the long-term.
• Self-diagnostic processes allow you to carry out routine maintenance and act on any faults long before they become problematic, helping to extend the lifespan of the system.

An effective pressurisation system cannot be retrofitted. It must be embedded into the building’s design so as to optimise smoke ventilation and air release, and to reduce the risks of air leakage and smoke recirculation or re-entry.

During the design stage, for example, the architect should make certain considerations to maximise the pressurisation system’s efficiency, such as placing pressurisation fans at ground or basement level to reduce the risks of smoke recirculation.

As a result, if you want to install the Hi-Protect smoke control system in your building, you must get Advanced Smoke Group involved as early in the project as possible.

We’ll liaise with your architect Design Team to ensure that your building’s designed with for optimum pressurisation. We’ll also advise on wind load, air density, all the relevant standards and regulations, and any other considerations that could influence the design and installation of an effective smoke control system.

And during the construction process, our engineers will be onsite to install all three aspects of our smoke control system:

• The Hi-Protect pressurisation system, including all fans, dampers, ductwork and smoke detection system.
• The Doormon control system, including the system control panel, the door proximity and pressure sensors, and all fire service monitoring and control stations.
• Set-up and configuration of the Doormon Service Control system.

The Doorman control system will automatically notify you when any part of your smoke control system requires attention, or when any routine maintenance is due. And at this point, we’ll be on-hand to ensure that any maintenance is carried out to the optimum standards, to ensure you can depend on your Hi-Protect system for the long-term.

For more than 30 years, Advanced Smoke Group has provided innovative technical solutions in smoke ventilation across the UK and Europe.

Our mission is to deliver reliable, compliant, and cost-effective smoke control solutions, and you can depend on us to be onsite whenever you need us, at any stage of your project.

From initial consultancy and design, to installation and commissioning and ongoing maintenance, we’ll be with you every step of the way to ensure your project meets all the most up-to-date standards of smoke control and fire safety.

We’ve had more than 600 major smoke control systems completed and certified. We’ve helped make some of Britain’s busiest public buildings safer, including Glasgow Royal Infirmary, London Paddington Station, Bradford Broadway, Palace of Westminster, and Blackwall Tunnel.

Several of our company’s employees have been actively involved in the development of British and European standards, ranging from car park ventilation systems to Pressurisation systems for tall buildings. They have also been involved in the creation of industry guidance documents such as those published by the smoke control industry’s trade association, the SCA. The company has also run numerous seminars for clients and colleges and published books on the subjects of car park ventilation and smoke control.

Hi-Protect is our latest ground breaking innovation, and it’s the result of many, many years spent assessing and perfecting pressurisation systems. In the very near future, pressurisation will once again become the industry standard for smoke control, and we believe the Hi-Protect system is the last word in effective smoke control pressurisation systems.