Glass is an increasingly popular construction material. It maximises the use of natural light and helps to create a feeling of space. In high-footfall areas, glass can enhance visibility immensely – often desirable for safety reasons. The benefits are clear to see. So, when it comes to fire-resisting doors, designers and architects are often specifying much larger glass panes and complex shapes. Glass technology is being pushed to the maximum.
This prompts a clear question: how must this trend be addressed within a fire-safety strategy? There’s little documented advice on the specification of glazing for fire doors. And yet it’s imperative to get it right.
Before focusing on fire doors, let’s quickly touch on the principle of compartmentalisation, and how the increased use of glass has an impact.
Dividing the building into fire-safe compartments
You might well be familiar with the principle of dividing a building into distinct zones to slow fire spread. Walls and floors are obvious natural divisions. Any cavities must therefore be effectively sealed to reduce the spread of flame and smoke. This might necessitate the incorporation of components such as flame-retardant foams, pipe collars and wraps.
The importance of developing a firestopping strategy such as this cannot be understated. Dependent on the specification of materials installed, it will slow the spread of fire for 30 or 60 minutes, perhaps longer. And the outcome will be less damage to the building, and most importantly, more time for people to evacuate safely, prior to the fire brigade getting the risk under control.
Alongside walls and floors, fire-resisting doors are a critical factor in compartmentalisation. But what impact does an increased amount of glass – both in fire doors and glass screens – have on the situation?
Fire-safety technology must develop at the same pace as design. It must always be possible to specify certified materials and safeguards to manage the fire risk of all building materials. Thankfully, leading manufacturers of passive fire-protection products are reacting swiftly to these changing trends. The challenge is now to educate specifiers and architects, so that specification is appropriate and risk-managing. The tools and methods exist, but they must be communicated.
Avoiding a weak spot in the fire door
The fire-resisting door is not new and it’s a key factor in any fire-safety strategy, helping to divide a building into compartments and slow the spread of any fire and smoke.
However, a fire door is only as good as the sum of its parts. Whether it’s the timber, the seal or the glass, no single part must let all the others down. And this can be what happens when specification is ill-informed.
Indeed, the Fire Door Inspection Scheme cites evidence of installed fire doors with countless deficiencies, most notably to do with excessive gaps and insufficient sealing. Poorly specified glass is also a serious contender on the list of concerns.
Whilst gaps and poor sealing will present a problem even for 30 minutes of fire resistance, glazing specification is of particular importance when looking for fire resistance of 60 minutes or more. Small changes in specified components can have a dramatic effect on the fire performance of the resisting door.
And so, correct specification of glass within the door and surrounding panels is of paramount importance. We’ve seen countless examples in heavily populated buildings such as schools, hospitals and care homes, where glazed apertures in doors and adjacent screens are considered ineffective. Put simply, their protection would ultimately fail in the event of a fire.
Another factor that can let the fire door down is poor installation. If not assembled and fitted in accordance with the manufacturer’s instructions, the fire-resisting door will be the failing link in the entire passive fire system.
Insulated or uninsulated: know the difference
When it comes to glass specification, there’s lots of choice and it can seem daunting for many. A competent supplier will be able to discuss the various options, keeping fire-safety requirements at the fore.
A key decision is whether to opt for uninsulated or insulated glass.
European standards for all fire-resistant glass are classified as E, EW or EI. The structure and end-use of the building will generally determine the correct specification.
E-classified glass (uninsulated)
At one end of the spectrum, glass that has been classified as E will stop the spread of fire and smoke from the fire side to the non-fire side. This might seem sufficient to many, but there are two further risks to consider.
E glass does not prevent intense radiant heat passing through the glass after a short time. In turn, this radiant heat can easily ignite something on the non-fire side. It can also burn human skin intensely, should it come into close contact or indeed touch.
The higher the fire resistance required, the less likely should E glass be specified as it will let down the entire firestopping system.
EW-classified glass (insulated)
A more protective material, glass classified as EW will stop the spread of fire and smoke, plus the transfer of radiant heat from one side to the other. Technically speaking, it does this by emitting a heat transfer of less than 15kW per m2, when measured at 1m for a stipulated period of fire resistance.
EW-glass is constructed from multiple layers. Most importantly, an intumescent material is embedded in the centre and it is this construction that provides such a robust barrier in the event of fire.
What is radiant heat?
Invisible and extremely intense electromagnetic waves travel at the speed of light. This is radiant heat. In testing, radiant heat will be measured on the non-fire side of the glass, at 1m distance.
On striking an object, the waves are absorbed, and their energy converted into heat. Combustible materials such as paper and wood will auto-ignite after a period of time.
Determining your choice
E-classified glass should not be used in many types of building – for example, in public buildings where a high volume of people might need to escape through corridors. E glass is generally suitable for vision panels and areas where combustible items are not in the vicinity.
EW-classified glass offers far greater protection. It should be specified for fully glazed doors, escape corridors and internal partitions. The final choice will be determined by the National or Local Building Code requirements and the relevant building authority.
It’s interesting to note that the cost premium for EW glass is generally no more than 10%, but this marginal additional cost makes a far greater impact on the fire-safety strategy.
Symmetrical or asymmetrical?
Another decision for glazing specification is whether to specify symmetrical or asymmetrical glass. Ignorance and cost advantages are no reason to make the wrong choice.
If fire-resistant glass is symmetrical, it offers fire protection on both sides of the glass. Conversely, asymmetrical glass will provide protection on only one side.
As ever, testing and certification are paramount here. The choice must be accompanied by proper test evidence of its performance. This must also concern the intended fire-door system. Each component of a fire-resisting door and the assembled door must possess testing evidence and third-party certification if the firestopping strategy is to deliver.
Should asymmetrical glass be specified, ensure that the fire-protecting side of the glass is clearly marked and oriented as intended.
Don’t forget the seal…
Correctly specified glass will perform only with correctly specified glazing seal. Broadly speaking, this is determined by the design and components of the fire door system, coupled with the level of fire resistance required. High-specification glass is useless if a gap remains for fire and smoke to penetrate. A reputable fire-door manufacturer should be able to provide guidance.
Wider use of large glass panels and an increased variety of glass thickness has led Pyroplex to complete further testing, in compliance with BS476: Parts 20 and 22. Certifire approved products, such as our 60-minute fire-glazing seal system, offer immense versatility. This is welcome news to architects and specifiers looking for fire-safety components to accompany more ambitious designs.
Remember that effective firestopping is all about sealing, and thus eliminating, gaps that fire can take advantage of. Just like walls and floors, it’s incredibly important for doors, and a vulnerable point is always around glazing.
Intumescent technology now leads the field in fire-resisting seals, expanding to create a firm seal the moment heat is detected. Leading passive fire manufacturers have invested heavily in development and testing to deliver incredibly effective products, even at 60-minutes fire resistance.
It’s clear that design trends and fire safety must work hand in hand. What’s less clear is that those responsible for the design must have the knowledge to specify appropriately and effectively. They must appreciate how essential this is, and as an industry we must ensure it happens.
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