Featured in Industrial Fire Journal, January 2010
Yes, we do need to raise the competency and knowledge of fire resistant glazing in the fire industry, says Peter Barker of Chiltern International Fire.
Introduction
It would be near impossible to find a public building or place of work that does not incorporate fire resisting glazed elements somewhere within its structure, whether it is a large glazed screen enclosing a protected escape route or a small area of glazing within a fire door.
It follows, therefore, that anybody involved with the management of a building will need to have at least a basic knowledge of fire resistant glass, to understand why the correct specification, installation and maintenance are so important, if the glass is to provide the required level of fire protection.
The focus of this article is the use of fire resistant glazing within a building and to highlight why competency and education within the fire industry needs to be advanced / have its profile raised. It will address:
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The role of fire resistant glass
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Fire resistant glass technology
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Installation of fire resistant glass
The Role of Fire Resistant Glass
The role of fire resistant glass within a building is a crucial one. It provides both form and function as a life safety product that can be integrated into the fabric of the building to meet architectural and regulatory requirements.
Unlike some other methods of fire protection e.g. pipe collars, fire dampers and sprinklers; fire resistant glass may have a multitude of functions to perform, and standards to meet, depending on its location and use within a building. The table below summarises the potential functions of fire resisting glass and the relevant Approved Document guidance (practical guidance for meeting the functional requirements of the building regulations as created by the Department for Communities and Local Government).
| Glazing Application* |
Location of Glazing* |
Approved Document |
| As a fire barrier within a fire resisting compartment lin |
On an escape route, within a fire door, enclosing a protected stair well |
Approved Document B - Fire safety: 2000, 2006 Edition |
| Sound attenuation/control |
Meeting rooms, circulation spaces |
Approved Document E - Resistance to the passage of sound: 2004 |
| Safety barriers/balustrades |
Atriums, elevators |
Approved Document K - Protection from falling, collision and impact: 1998, amended 2000 |
| Reducing heat loss, light transmission |
Double glazed units, roof lights, facades |
Approved Document L - Conversation of fuel and power: 2006 Edition |
| Clear sight lines for oncoming persons, protection from collision and impact |
Doors, side lights |
Approved Document M - Access to and use of buildings: 2004 |
| Protection from collision and impact |
Doors, side lights |
Approved Document N - Glazing - safety in relation to impact, opening and cleaning: 1998, amended 2000 |
* Not exhaustive
The above list demonstrates that it is likely fire resisting glass will need to meet at least one of the functional requirements of the building regulations, in addition to its principle role of compartmentation, ie maintaining fire separation within the building. Meeting the functional requirements of one building regulation cannot be to the detriment of another and this extra level of complexity must be considered before building work starts.
Fire resisting glass, when used as part of a complete system, sub-divides a building into fire resistant compartments and has the following objectives:
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It prevents rapid fire spread which could trap occupants of the building
- It reduces the chance of fires becoming large and therefore more dangerous to occupants, fire safety personnel and people within the vicinity of the building
- It minimises the damage to the building by isolating the fire to its origin and is therefore critical for business continuity should a fire event occur
There are many types of fire resistant glazed systems, based on a wide range of fire resistant glasses, governed by numerous codes of practice and standards in addition to the approved documents listed above.
The key is selecting the correct glass for the end use requirement for use as part of complete fire resisting system and ensuring that this is correctly installed, so that the fire resistance performance of the system is not compromised.
Fire Resistant Glass Technology
There are a number of different glass technologies, with each glass type having its own characteristics, differences in behaviour and fire resistance capabilities. To better understand what these differences mean when it comes to specifying the correct glass type, it is necessary to clarify how fire resistance is classified in terms of the UK building regulations.
| Classification |
Description |
| Integrity |
The ability of a material to withstand fire exposure from one side without the transmission of fire as a result of the passage of flames or hot gases. |
| Insulation* |
The ability of a material to withstand fire exposure on one side without the transmission of fire to the unexposed side by limiting heat transfer due to conduction, convection and radiation (in addition to integrity) |
| Radiation (European classification) |
The ability of a material to withstand fire exposure on one side and reduce the probability f transmission of fire by significant heat radiation to adjacent materials |
| Integrity and Insulation |
The ability of a material to provide both integrity and insulation |
| Integrity and Radiation (European classification) |
The ability of a material to provide both integrity and radiation control |
* Partial insulation is a term used occasionally in the UK glazing industry to describe a fire resistant glass which does not achieve the insulation performance for the required time in a standard test (e.g. 15 minutes instead of 30). This is different to the use of the term as outlined in BS476: pt22: 1987.
The above performances are defined as a standard time period (in minutes) according to the building type, the application and location: 20, 30, 60, 90 or 120. Currently in the UK, the performance times are determined by testing to the relevant British Standard or European Norm. Both test methods have a standard time temperature curve that essentially produces standardised conditions similar to the fully developed phase of a fire.
The following table summarises the different glass types and how they provide fire resistance (adapted from Table 3 in A Guide to Best Practice in the Specification and Use of Fire Resistant Glazed Systems – GGF):
| Glass type |
Fire resistance |
Method of providing fire resistance |
| Wired |
Integrity |
Due to thermal stress the glass breaks early on in the fire but is securly held together by the integral wire mesh |
| Ceramic |
Integrity |
Due to its composition and micro crystalline structure this glass type has a near zero thermal expansion coefficient. The glass remains intact and performance is not edge cover dependant. This glass has a very high softening point so its integrity limit is not normally reached. |
| Modified toughened soda lime silicate |
Integrity
|
Relatively high toughening stresses in the glass are intended to retain integrity on exposure to fire, but edge cover and edge clearance are critical to avoid failure. The integrity limit is reached when the glass reaches its softening point or if the glass shatters prematurely. |
| Resin laminated |
Integrity |
The integrity of these types of glass is achieved through the use of a resin-based interlayer formulated to have resistance against fire and flaming. In a fire, the glasslayers creack and the interlayer carbonizes to give an opaque layer, which holds the glass together and reduces heat radiation. Its integrity limit is reached when the interlayer breaks down and/or glass layers develop open cracks. |
| Laminated intumescent |
Integrity and partial insulation or integrity and insulation (depending on number of interlayers) |
These types of glass have a sodium silicate-based interlayer formulated to turn opaque and swell on exposure t fire and provide a known level of insulation. The glass layers crack but are bonded together by the interlayer. The performance limit is reached when the interlayer breaks down, and this progresses as each layer intumesces. The products are based on a glass interlayer sandwich structure. This allows a wide performance reange to be achieved by building up the structure based on alternate sheets of glass and interlayer. |
| Laminated intumescent |
Integrity and insulation |
These products are composed of gel-filled dhouble or multiple-glazed units using toughened glass. The gel is formulated to release water on exposure to fire to provide a known level of insulation. |
| Gel laminated |
Integrity and insulation |
These products are composed of gel-filled double or multiple-glazed units using toughened glass. The gel is formulated to release water on exposure to fire to provide a known level of insulation. The integrity and insulation limit is reached when the interlayer breaks down and/or the glass shatters. The performance range is achieved by varying the thickness of the gel. |
| Toughened borosilicate |
Integrity |
On exposure to fire, the glass remains intact due primarily to its composition and low thermal expansion. Manufacturer's specified edge cover requirements must be complied with, but this type is much less sensitive to edge cover than modified toughened soda lime glass. The integrity limit is reached when the glass passes its softening point and pulls out of the glazing 'pocket'. |
It can be seen from the above table that there are many glass types with different compositions and performance capabilities and it becomes easier to appreciate that each glass type has to be treated separately from another in terms of:
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Installation – glazing system, screen type, aspect ratio, permitted pane size
- Decorative treatments and manifestation
- Multi functional performance – impact safety, barrier loading, thermal insulation, solar control, acoustics
Even different glasses that fall within the same generic glass type must be treated separately from one another as they are likely to have different supporting test evidence for different applications.
It is therefore of the utmost importance that the performance specification is defined before the glass is selected and that the manufacturer of the glass has the appropriate test evidence in place to support the required performance specification.
However, the glass alone will not provide the required performance unless it is correctly installed using the appropriate screen specification, materials and fixing details.
Installation of Fire Resistant Glass
Any scrupulous company having electrical or gas installation work would use a registered tradesman that would be expected to have the requisite minimum level of knowledge to carry out the work to a safe standard. Unfortunately, when it comes to fire safety products, all too often it is assumed that because a product is ‘fire rated’ it will do the job no matter how it is installed. This is a surprisingly common and most definitely dangerous assumption as the incorrect installation of fire resistant glass can significantly reduce the fire resistance capabilities of a glazed element.
Common issues with fire resisting glass installation are as follows:
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Incorrect glazing seal – for example using a high-pressure door edge intumescent seal instead of the correct glazing seal. These seals are engineered to expand with a high pressure and could easily force the beads away from the glass causing premature failure.
- Incorrect glazing beads/framing material – for example using softwood for glazing beads that become quickly charred allowing the perimeter of the glass to become exploited.
- Incorrect glass expansion allowance – can be particularly problematic for modified toughened glasses as the thermal shock can cause the glass to shatter within a matter of minutes
- Cutting apertures into existing doors – increasingly common as a result of the Disability Discrimination Act (DDA) where glazed apertures are required below the waist line of the leaf. Even if the correct glass and glazing system are used, it may be that the door is not suitable for glazing due to its construction.
- Decorative finishes and manifestation can significantly affect the performance of the glazing unless there is evidence to support its use
The best way to ensure that fire resistant glazing is correctly installed is to use an appropriately qualified fire resistant glazier or a company that has demonstrable competence in glazing fire resistant elements.
The need for education and competency within the fire resistant glazing industry has been recognised by the Fire Resistant Glazing Group of the Glass and Glazing Federation which has developed an eight-module QCF (formerly an NVQ). The QCF is currently in draft and when it is formally agreed and published it will provide a mechanism for glaziers to gain a nationally recognised qualification that can be used as evidence of an individual’s knowledge. It is expected that the individual or company will still be backed by a suitable third-party certification scheme.
Apart from the obvious reassurance that the glazing installation will be able to provide the required fire protection to life safety, the building and business, using a specialist contractor, can also save a significant amount of time, effort and money.
References:
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A Guide to Best Practice in the Specification and Use of Fire Resistant Glazed Systems – Glass and Glazing Federation
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Approved Document B – Fire Safety 2006 Edition
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BS 9999: 2008 – Code of practice for fire safety in the design, management and use of buildings
PDF: A Window to Survival
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