Insulating glasses are manufactured from float glass laminated with either intumescent or gel materials. Intumescent laminated glass has clear interlayers, which on exposure to fire expand to a white opaque material, inhibiting the passage of conductive and radiant heat (Fig. 7.13). The glass layers adjacent to the fire crack but retain integrity owing to their adhesion with the interlayers. The fire resistance, ranging between 30 and 120 minutes for insulation and integrity, depends on the number of laminations, usually between 3 and 5. To avoid the green tint associated with thick laminated glass, a reduced iron-content glass may be used to maintain optimum light transmission. For exterior use the external grade has an additional glass laminate with a protective ultraviolet filter interlayer. Laminates may be manufactured with tinted glass or combined with other patterned or solar control glasses. Insulating glass is supplied cut to size and should not be worked on site.
Double-glazed units with two leaves of intumescent laminated glass give insulation and integrity ratings of 120 minutes; alternatively, units may be formed with one intumescent laminate in conjunction with specialist solar control glasses. The fire-resistant laminated glasses conform to the requirements of BS 6206: 1981, in respect of Class A impact resistance. Whilst most fire-resistant materials are relatively thick, one 7 mm product, with a single clear intumescent layer, giving
both fire and impact resistance, achieves a rating of E30/EW30/EI20, i.e. 30 minutes' integrity, 30 minutes' reduced heat radiation and 20 minutes' insulation.
Gel insulated glasses are manufactured from laminated toughened glass with the gel layer sandwiched between two or more glass layers. In the event of fire, the gel interlayer, which is composed of a polymer-containing aqueous inorganic salt solution, absorbs heat by the evaporation of water and produces an insulating crust. The process is repeated layer by layer. Depending upon the thickness of the gel layer, fire resistance times of 30, 60 or 90 minutes are achieved.
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