STRUCTURAL GLASS FACADES - USC School of Architecture

Table 2-8 Data compiled from the websites of Viracon and Pilkington regarding distortion resulting from
heat-treatment (Viracon 2008b) (Pilkington n.d.).
Published
Type of distortion
Tolerance
Viracon Pilkington Standards*
Overall bow – in/linear ft 0.031 0.024 0.062
Overall bow – mm/305mm 0.787 0.61 1.575
Roller wave
(peak to trough in inches) 0.003 0.0008 no standard
(peak to trough in mm) 0.076 0.02
Edge lift – inches ** 0.008 0.009
Edge lift – mm ** 0.20 0.229
* ASTM C1048 Standard for
Heat-treated Flat Glass
** within 10.5 in (267mm) of
leading and trailing edges
2.4.2.5 Nickel Sulfide Inclusions and Spontaneous
Breakage
Nickel Sulfide is a contaminant, a small stone or crystal that can be present in float glass. In
annealed glass it presents no problem, but in tempered glass has been identified as the
source for rare occurrences of spontaneous breakage, whereby the glass shatters for no
apparent reason. Low quality glass production may result in a higher occurrence of the
contaminant.
Interestingly, in Asia and other developing areas of the world where local glass supply may
be of lesser quality, some structural glass façade designers are moving away from the use of
tempered glass, regarding the spontaneous breakage problem as simply too risky to
tolerate. Instead, they are using heat-strengthened laminated glass panels (see laminated
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