Fire-Resistant Glazing: An End to Design Compromises?

When glass is required to stand up to fire, this has traditionally been associated with aesthetic and other design compromises. But have the latest advances in fire-resistant glazing technology consigned these to the past?

Arguably the first consideration for designers of the built environment, before aesthetics or even functionality, is to provide safe space for a building’s occupants and contents.

When it comes to defending a property against fire, design plays a crucial role, ensuring that a blaze is not able to spread but is instead contained in a single area, limiting damage while allowing safe egress for occupants and entry for emergency services personnel.

Achieving this means placing fire-resistant physical barriers throughout a building, and especially around exit and entry routes.

The challenge for designers and specifiers is that this need for robust physical barriers can seem to contradict some of the principles of contemporary building design, which often call for light, airy spaces that provide a sense of openness by providing extensive lines of sight through buildings.

Glass has become ubiquitous in modern building design precisely because it offers a barrier to the elements and to external sounds while still allowing light to flood into interior spaces and uninterrupted views to be had both outwards and inwards. However, it is now often required to play the same role from a fire-safety perspective, and this places much higher demands on glazing in terms of its physical properties.

Flame resistance and insulation
Fire spreads through a building via three distinct means: convection, conduction and radiation.

Convection – whereby very hot air from the source fire moves upwards and outwards, potentially igniting surrounding materials – is the primary route and therefore the most dangerous of the three.

However, conduction and radiation can be equally hazardous if the right precautions are not taken. Conductive materials, especially metals, can absorb heat and transmit it to other rooms where it can cause new fires to break out, while radiation transmits heat through rays similar to sunrays, requiring no physical contact in order to transfer large amounts of heat.

Modern fire-resistant glazing systems can provide complete protection against convection, conduction and radiation – whether as curtain walling, or internal doors or fire screens – for up to three hours.

There are two main performance categories for fire-resistant glass: integrity and insulation.

Integrity is a measure of the length of time over which the glass can prevent flames, smoke or hot air from travelling from one space to another.

This is tested by subjecting glazing systems to a standard time/temperature curve according to either British Standard BS 476-Part 20-22 or European Standard BS EN 1363 series. Depending on its performance in these tests, each system is classified as having attained an integrity test time of 30, 60, 90, 120 or even 180 minutes.

Insulation, meanwhile, assesses the ability of the glass to prevent significant heat transfer from the fire side to the non-fire side, with the surface presented towards the non-fire side not exceeding given thresholds for average and point temperatures on the unexposed face.

This is particularly important in spaces such as stairwells and corridors, where not only does the space need to be protected from sources of flame, but also be kept as cool as possible to allow safe passage for escaping occupants.

The whole picture
There is no hard and fast rule for the fire resistance requirements of any particular piece of glass in any given setting. Instead, the appropriate level of protection must be provided in line with the detailed fire strategy for the building in question. As well as the more obvious considerations such as providing separation between different floors and areas within a property to contain the spread of fire, the strategy will also take into account things like the mobility of the people that need to escape a blaze.

For example, for a corridor in an office building where all occupants will be mobile and able to evacuate the building quickly, a lower level of protection may be needed than for an escape route in a hospital or care home where those exiting are likely to need much more time for a safe egress.

Getting these decisions right is up to the designated ‘responsible person’. This is an individual that is nominated to take responsibility for ensuring the building is safe by design. The role is typically taken on by a facilities manager or health and safety officer.

This individual assumes liability should the strategy be inappropriate or incorrectly implemented. While the person themselves does not need to be an expert in fire safety, they take responsibility for consulting with those who are in order to ensure that a robust and reliable strategy is in place for every eventuality.

Aesthetics
Traditionally, by far the most common form of fire safety glass was wired glass, in which a mesh of metal wires are embedded in a pane of glass to ensure it maintains integrity in the face of high temperatures.

This product is a common sight in many older buildings and still sells in high volumes thanks to its affordability and long-standing association with safety-sensitive projects. However, few would claim it is the best-looking or best performing solution.

Today, fire resistant glass is mostly completely transparent and makes use of intumescent interlayers placed between two or more panes of glass to provide integrity and insulation.

In more basic clear glazing products, they serve the same basic purpose as wired glass – to maintain integrity. Some provide an enhanced level of integrity using intumescent technology while also providing an intermediate level of insulation. In more advanced insulating products, the multi layers are designed to expand sequentially when exposed to heat to provide an opaque, robust and heat-resistant layer.

There can be benefits in some scenarios to using the more basic systems which maintain transparency when exposed to fire. For example, where insulation is not a concern and only integrity matters, glass that stays clear when hot can give emergency services crews a better view
of the inside of the building.

However, for more robust protection, intumescent interlayers become necessary. Interlayer technology has progressed to the extent that large panes of glass which are completely transparent when cool can provide insulation against very high temperatures for up to three hours while permitting a very low level of heat transmission.

This means that floor-to-ceiling transparent glass screen can now serve effectively the same purpose as a brick wall, and the design implications are significant. No longer is there a need to visually screen off areas in order to protect them in the event of fire, even where critical escape routes are involved.

Of course, it is important to ensure that tested and appropriate framing is used, as the fire rating is based not only on the glass but on the performance of the system as a whole. However, as technology in glass has advanced, so has that of frames so that specifiers and designers now have a wide variety of different designs at their disposal to achieve the right appearance.

All-round performance
There is a lot more to selecting the right pane of glass than simply the way it looks and energy performance is also a key concern. Where large areas of glass are to be used in a building, careful consideration must be given to the amount of heat it will allow to leave the building and the amount of the sun’s energy it will let enter, as these properties have a significant effect on the ease and cost of maintaining a comfortable environment for occupants.

Modern fire-resistant glass has also removed the need for compromise in these areas when it comes to delivering fire-safe buildings, as it is now available with the latest low-emissivity and solar control coatings to ensure it also delivers excellent energy performance.

The impact of these advances can already be seen in many high-profile projects around the world, including at the Bundestag building in Berlin and the refurbished Dusseldorf airport. The glazing for such prestigious landmark buildings is expected to be long-lasting and of the highest quality and, in today’s age of instant digital communications, appearance has never been more important.

The benefits are not limited to high-end architecture either, as the proliferation of glass as an option for safety-sensitive settings has made these products available in high-quantities for mainstream use. The result? Lighter, brighter, more energy efficient spaces that also deliver high levels of protection should a fire break out.

Pilkington Pyrostop® helps deliver fire-protection package at parcel hub
A good example of the design applications of clear fire resistant-glass came when a major logistics company commissioned a new multimillion-pound parcel hub.

The business wanted to ensure a close connection between the office workers at the facility and those working on the warehouse floor. A key part of this was allowing lines of sight between the two spaces so that all employees have a feeling of belonging to the same operation.

Of course, warehouses such as this are subject to strict safety regulations, which require that they be separated from adjoining areas by fire-resistant screening.

Because the offices are part of an escape route from the main warehouse, there needed to be a fire resistant barrier between the two spaces that could stand up to exposure to fire for at least 30 minutes to allow safe evacuation in the event of a blaze. This meant that the wall of glazing the architect wanted to place between the two spaces would need to be able to maintain integrity and act as a protective shield for more than half an hour.

The solution specified was Pilkington Pyrostop® fire-resistant double glazing units, glazed in steel frames, which were also rated to ensure the system would maintain integrity and insulation for the required period.

The level of protection this screen needed to provide presented a significant challenge from a materials technology perspective. The wall of glazing is 215 sq metres in size, and it needed to maintain integrity against extremely high temperatures and flames for more than half an hour.

The units used in the project consisted of a pane of 6mm toughened Pilkington Optitherm™, a 12mm argon-filled cavity with fire-resistant steel spacers, and a 15mm laminated layer of Pilkington Pyrostop® 30-10 glass, classified to deliver protection from fire, smoke and radiant heat for at least 30 minutes, chosen for the performance achieved after rigorous testing and quality control.

Pilkington Pyrostop® glass is a multi-layer laminated glass, comprising intumescent interlayers sandwiched in between glass layers, which expands and becomes opaque when exposed to heat. This intumescent interlayer means that the glass becomes highly resistant to flames and the passage of heat as soon as it is exposed to fire.

As well as offering fire protection, the glass also needed to be thermally insulating, as temperatures on the warehouse floor are often lower than those in the adjoining office space.

The layer of Pilkington Optitherm™ is included to help with energy saving as it is optimised for thermal insulation, featuring a low emissivity coating that delivers a low U value, reducing the rate at which energy passes from the warm to the cold side of the glass.

The wide availability of such advanced materials has opened up a huge number of options from a design standpoint. As a result, facilities such as this – where safety is obviously the number one concern – can benefit from added natural light and improved integration of spaces that would otherwise not have been possible.

For more information, go to www.pilkington.co.uk