Can we Protect the Building Envelope from Fire?

The building envelope can be thought of as the barrier between the inside and the outside of a building. The envelope surrounds the conditioned living space and separates it from the unconditioned elements and the outside.

Parts of the Building Envelope[1]


Diagram of a modern house, with a purple line going around the entire inner walls. This is the conditioned area

The building envelope is separated from the conditioned and unconditioned environment, as evidenced by the navy-blue outline above. Conditioned spaces have been designed and built to develop resistance to the negative effects of air, water, heat, light, and noise transfer.

Below Grade

This below ground, basement, level section can hold functional spaces such as storage, offices, mechanical, and electrical, rooms, parking, tunnels, and crawlspaces. Here the focus on durability of design is mandatory as it holds much of the structural elements of building construction, for example foundation walls and slabs on grade, which support the walls and the rest of the building, and potential plaza decks with support elements such as parking or pathways.


Walls

These elements function predominantly to separate the indoor from the outdoor and their function consists of predominantly environmental control, security, privacy, fire control, and aesthetics.

Walls can be further classified into the further categories to that reflect the permeability possibilities, or the structural strength.


Fenestration

These elements function to provide access, ventilation or light for the building, and centre around windows, doors, and skylights. These features improve the environment, air quality and condensation levels.


Atria

Atria are large open air, or skylight covered spaces surrounded by a building. The impact of having open air or skylights provide light and ventilation for the building and bring a connection to the outside.

All sections of the building envelope will be considered by the client and architect when designing a structure, as they will have an awareness of building, and fire regulations. If the plans did not showcase how the building and users were to be protected, it would not be granted planning permission, and would have to go back to the architect, which would extend the time frame of the project, and increase costs.

How does Building Envelope relate to Fire Safety?

Much of Passive Fire Protection (PFP) is built into the walls, floors, and ceilings of the building itself.


These can include:

  • Fire doors

  • Fire-resisting walls, floors, ceilings, and ducts

  • Firestopping and fire protection for structural members

  • Fire-resistant epoxy coatings that can be spray applied

  • Fire-protective boxes or wardrobes

  • Protection for vital equipment such as first-aid boxes, oil or gas tanks, or other volatile sites to prevent the risk of explosion.

  • Compartment walls and floors

  • Fire-resisting walls and partitions

  • Suspended ceilings

  • Fire-resisting glazing

  • Fire doors and hardware

  • Firefighting shafts and stairwells

  • Fire-resisting dampers (mechanical or intumescent) used in horizontal or vertical air distribution ducts

  • Fire-resisting ductwork

  • Fire-resisting service ducts and shafts

  • Linear gap seals

  • Penetration seals for pipes, cables, and other services

  • Cavity barriers

  • Fire-resisting air transfer grilles (mechanical or intumescent)[2]


As you can see, typical Passive Fire Protection is considered alongside the design process, as they are installed when constructing the building itself, and their implied use will be evident on the plans for the building from the outset.

Is Fire Protection Always included from the Beginning of a project?

Traditional Passive Fire Protection methods, such as those outlined above, are planned from the earliest design stages with the architect, as this is when wall positions and building construction elements are considered, such as which materials to use, and what fire rating they will achieve, to ensure it passes fire regulations. Similarly, the architect and client will decide how they are going to ensure adequate fire protection, be that from a fire door or a fire curtain, for example.

How Traditional Passive Fire Protection Methods Provide Fire- Resistance.

Fire- resistant walls, floors, and roofs can be constructed from materials such as reinforced concrete and protected steel, which provides structural support, as well as being naturally fire-resistant. These can then be clad in materials such as tilt-slab construction or reinforced masonry, which is also non-combustible. This provides them with the structural integrity needed to maintain the structure of the building if a fire does occur and prevents fire spread.

The building shall be designed and constructed so that there are […] appropriate means of escape in case of fire from the building to a place of safety outside the building capable of being safely and effectively used at all material times.

[3] ApprovedDocument B Volume 1, 2019 ed., Requirement B1.

Construction materials that provide fire resistance will also be considered carefully when protected escape routes are planned into the building. Protected escape routes will provide inhabitants with longer, safer evacuation opportunities, as they can be certain that the building will support itself for far longer than it takes for inhabitants to exit,[4] because it ‘is adequately protected from fire in adjoining areas by fire resisting construction.’[5] Depending on the layout of the house, this corridor or lobby may take you to an emergency exit, or ‘leads to a final exit to a place of safety and that is adequately enclosed with fire resisting construction. Included in the definition is any exit passageway between the foot of the stair and the final exit.’[6] These stairways will adhere to minimum fire resisting construction, and specific fire doors- see below.[7]

Diagram showing different possible arrangements for exits.


Fire Doors

Fire-proof doors and fire-resistant glazing also provide a strategy for providing PFP, a category in which Active Fire Curtains are making vast inroads.


Fire doors are commonly built with layers of wood, steel, gypsum products and aluminium, and may contain windows, often made from borosilicate or ceramic glass, which may also contain an anti-shattering wire mesh. The construction of the fire door is as such to aid compartmentation and allow inhabitants longer to evacuate as they hold the fire back. They have a variety of gradings, which is based on how long they will withstand fire for, commonly either 30 or 60- minutes. They also have self- closing mechanisms which ensure they swing shut if a fire is noted by fire, or smoke detectors and are ‘fitted with intumescent strips in a groove on every edge of the door or fire doorframe. If a fire ignites, the intumescent strips expand in the heat to fill the gap between the fire door and the frame. This seals the room and stops the spread of fire for a given time.’[8]


Fire doors are necessary for:

  • all non-domestic properties,

  • flats, and houses of multiple occupancy,

  • domestic properties of three or more floors-fitted to every habitable room that leads from a stairwell, and

  • any door from a domestic home into an internal garage. [9]

A white fire door, in a white tiled wall, with a pathway and two bollards in front.


Fire-Resistant Glazing

Fire-resistant glazing can be used to ‘ensure that, along with other elements such as walls and doors, fire and smoke does not spread to other parts of a building for a prescribed period’[10] of time. If chosen, installed, and maintained correctly, fire-resistant glazing can provide good compartmentation for the building it is installed within.


The answer to the problem of open plan layouts is Active Fire and Smoke curtains.


Open-Plan? Open for Solutions.
In recent years, building designers are increasingly considering the use of Active Fire Curtains as an alternative to conventional compartmentation elements such as walls and floors. The use of Active Fire Curtains allows the use of more open plan building where traditional compartmentation solutions would impose inconvenient restrictions […] (on) the building.[11]

Due to uptake of Fire Curtains as a viable alternative being considered slow in the industry, and a previous lack of dedicated fire tests to determine fire performance, Fire curtains are still a relatively green option for fire protection. However, with the publication of the ASFP Black Book in 2020, Fire Curtains have enjoyed a developing grip on the industry and have begun to reveal themselves as the build to order solution for the commercial and domestic market.[12]


Active Fire and Smoke curtains can be considered an effective replacement for non-loadbearing walls that split the space into smaller compartmentalised sections, and for the doors that sit within these spaces.


Fire Curtains can also replace corridors designed to form protected routes of escape, essential for the safe egress of inhabitants, and allow safe access for firefighters.


Another useful application of Fire Curtains is to provide boundary protection to cease fire and smoke spread, from one room, or building, to another. This is especially helpful if you have whole walls of glass, increasingly common in commercial and domestic properties in local beauty spots, or those built with a modern design.[13]

Corridor lined with floor to ceiling windows, showing the grass and sunshine outside

Fire and Smoke Curtains can be designed into initial plans with architects and can also provide flexible solutions for retrofitting existing spaces; an increasingly common, and encouraged, option as a way to ‘save between 50 and 75 of the embodied carbon emissions compared to constructing a new building.’[14] As the construction industry begins to turn towards greener, less wasteful methods of developing the built-environment, Active Fire Curtains provide yet another solution.

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[1] Original image from Freepik.com, courtesy of Pikisuperstar (Cityvector created by pikisuperstar - www.freepik.com

[2] IFSEC Global, ‘A Beginner's guide to passive fire protection,’ <https://www.ifsecglobal.com/fire/beginners-guide-to-passive-fire-protection/>19.11.2021

[3] H M Government, 'Approved Document B' Volume 1, 2019 edition, Requirement B1, page 8.

[4] H M Government, ‘ApprovedDocument B,’ Volume 1, 2019 edition, Requirement B1, diagram 2.1, page 12.

[5] H M Government, 'Approved Document B,' Volume 1, 20219 edition, definition of protected corridor or lobby, page. 126.

[6] H M Government, ‘Approved Document B,’ Volume 1, 2019 edition,definition of a protected stairway, page 126.

[7] H M Government, ‘ApprovedDocument B,’ Volume 1, 2019 edition, Requirement B1, diagram 2.2, page 13.

[8]Safelincs.co.uk, Blog ‘10 things You Should Know About Fire Doors,’ <https://www.safelincs.co.uk/blog/2021/07/07/10-fire-door-questions-answered/>26.11.2021

[9] Image from Pexels.com, courtesy of The Creative Exchange.

[10] IFSECGlobal.com, ‘Yourguide to fire-resistant glass and glazing,’ <https://www.ifsecglobal.com/fire-protection/guide-to-fire-resistant-glass-and-glazing/>22.11.2021

[11] ASFP, Black Book: Active Fire curtains 1stedition, 2020, page.6

[12] Theblack square indicates the RAL powder-coated bottom bar, which is pictured slightly lowered. When fully retracted, the bottom bar would not be visible andwould be hidden by the ceiling panel at the top left of the shape. You can also see the galvanised steel side guides, which can also be RAL powder-coated to blend in more with the décor of your room.

[13]Image from Pexels.com, courtesy of of Max Vakhtbovych.

[14] AIA.org,‘10 steps to reducing embodied carbon,’ <https://www.aia.org/articles/70446-ten-steps-to-reducing-embodied-carbon>25.11.2021

Cover image from Pexels.com, courtesy of Binyamin Mellish.

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