There have been three main developments in fire resistant glass, all of which rely on adapted / specialist intumescent glazing systems and for different reasons:
1. Composite doors
There has been a growth in the use of composite doors (GRP faced mineral/foam core doors), typically as entrance doors for flats, with a corresponding increase in use of insulated glass units (IGU’s) within them. Door assemblies based on plastics and foams require a completely different approach to the more traditional timber or steel based constructions. There have been developments in glazing systems for these types of units within composite doors, which must be strictly followed if the IGU is to provide required level of fire resistance. Fire rated composite doors is a rapidly growing industry and there is a significant level of malpractice at the installation stage arising from a lack of understanding or appreciation of the glazing system.
2. Toughened glass technology
Fire resistant glass is a vital part of building design and there are two basic types, insulated and uninsulated. The insulated glass has more than one glass layer interleaved with another material which provides insulation to the required level by increasing the number of layers. Uninsulated glass was traditionally made fire resistant by the use of embedded wires forming a grid. This is very effective but has the disadvantage that the wires are visible. Later it was found that clear modified toughened glass was able to withstand the fire resistance test but only toughened borosilicate glass was sufficiently reliable since it benefitted from low thermal expansion compared with soda lime glass. Insufficiently toughened soda lime glass can fail quite quickly in a fire test, around 6 to 10 minutes being commonplace. However, recently there have been significant developments in toughened soda lime glass and a number of glass manufacturers are now able to produce reliable fire-rated toughened glass products.
These newer, more reliable modified toughened glass types still require appropriate intumescent seals around the perimeter in order to consistently work. Edge cover and temperature difference across the face of the glass is still critical to performance, as is protection to the beads from the heat of the glass and ensuring the pocket around the glass is adequately protected when the glass begins to expand and move. Intumescent seals help to accommodate the distortion of the soda lime glass and the consequent movement of the beads. Some intumescent glazing tapes are better than others in this respect so it is important to use the product that has been proven to work for the particular glass in question. Interchangeability of the intumescent glazing tape is not usually possible in fire glazing applications when using modified toughened soda lime glass.
3.Higher performance doorsets
There has been an increase in the use and specification of higher performance doorsets, which has required the development of innovative glazing systems that can accommodate different design features, bead materials, aperture sizes, as well as cope with other types of glass (other than ceramic which is the normal ‘go to’ glass at this level of performance). These types of glazing systems are highly specialist and must be installed correctly to cope with the extreme demands of 90 and 120 minute tests.
Further guidance on fire resistant glazing systems may be sought from the Intumescent Fire Seals Association:
Tel: +44 (0) 1844 276928
Fax: +44 (0) 1844 274002