The world of smoke ventilation is complex — there’s no doubt about it. From natural to mechanical, there are many intricacies to designing a system that is capable of protecting people in the case of a fire. Another such system, called a pressurisation system, relies on pressure differentials between various parts of the building. Recently, the draft BS 9991 has proposed to mandate these in single stair buildings over 18m in height, which is resulting in an increase in their popularity.
So, what are pressurisation systems and how do they work? Read on to find out.
A pressurisation system, AKA a stair pressurisation system, is a type of smoke ventilation system that protects areas by increasing the air pressure in the protected zone — for example, a staircase — relative to the fire zone. This essentially blocks elements like smoke from entering the protected zones, allowing people to evacuate and firefighters to safely manoeuvre through the building and extinguish the fire.
The primary document for the design and specification of pressurisation systems is BS EN 12101-6. Currently, this contains both the specification of the system components and guidance on how to design a system. However, in January 2022, the European Committee for Standardisation voted to approve BS EN 12101-13, which will replace the design element of BS EN 12101-6. The document was then released in April, and the Declaration of Performance requirements will be enforced from 31st October 2022. Part six will still be used for kit and component specification.
There are three main areas of a building that you might protect using a pressurisation system:
The areas you pressurise and the performance of the system are based on classes which range from A through to F, as laid out in BS EN 12101-6. These classes help relevant persons choose the most appropriate system by considering the main use of the building, the evacuation policy and the firefighting policy.
There are two core scenarios which change the objectives of a pressurisation system: when the door to the fire floor is closed, and when it’s open.
In a scenario where the door to the fire floor is closed, we are trying to maintain a pressure differential between the protected zone and the fire zone to prevent products of combustion (like carbon monoxide) leaking into the protected zone.
If the door to the fire floor is open, the goal is to maintain airflow at a certain velocity through the open door to prevent products of combustion flowing into the protected zone.
Without over simplifying this complex topic, the three main components of a pressurisation system are:
Supply air is oxygen pumped into the pressurised zones. This is ideally supplied from ground level, but can also be supplied at roof level subject to inlet locations.
If pressures are too high in the pressurised zones, it can force doors shut and occupants could struggle to evacuate. This is why we need overpressure relief, which will prevent the pressure from reaching unsafe levels.
Air release is needed to make sure we have an airflow passage away from the protected zones. Firstly, this ensures we keep the fire zone as close to atmospheric pressure as possible (so we maintain our pressure differential). Secondly, it ensures that we have a strong airflow through any open doors, which would be difficult to achieve without sufficient air release. Air release can come in the form of facade AOVs, natural smoke shafts or a small amount of mechanical extract.
If you have any questions or want to discuss the system that would work best for you, contact us.