Since the publication of the ANSI Z97.1-2015 standard, there have been requests for interpretations of how to best test vacuum insulating glass (VIG) for safety performance. One is that the glass should be tested as a final product, another is that the unit should be tested as individual glazing lites.

On January 13, 2016, the ANSI Z97 Accredited Standards Committee released a technical interpretation to clarify the impact test specimen evaluation criteria for diverse types of safety glazings.

It reads, “There is no reference to vacuum insulating glass (VIG) in ANSI Z97. 1-2015. It is unclear how to test safety glazing used in VIG products to this standard.”

The request rationale explains that each lite of safety glazing required for insulating glass units (IGU) are tested and labelled independently to the standard prior to the IGU’s assembly. However, the vacuum process required for a VIG could alter the safety characteristics of the glass, possible “de-tempering” the glass.

The committee responded by saying that VIG is a manufactured assembly of at least two lites of glass separated by pillars, sealed at the edges with the gap between the glass lites under vacuum. VIG units shall be tested in accordance with section 5.1. Specimens shall be tested as a final product. Specimens shall be impacted in accordance with the protocol for asymmetrical glazing.

John Kent, ASC Z97 committee chair, explained the decision to

“Because of the unique construction of some VIG, multi-panes of glass are permanently fused together. In 2016, the ANSI Z97.1 committee was asked if a safety VIG should be tested monolithically or as a final product. The ANSI Z97.1 Steering Committee took, what they believed as the more conservative position, and stated that VIG shall be tested ‘as a final product,’” he says.

On February 23, 2017, the committee released another technical interpretation to ensure consistent reporting of results from various laboratories.

“After several test programs it was recognized that due to the edge bonding conditions of a VIG, further clarification was needed to interpret results in the perimeter edge area of the sample. The 2017 TI is the result of that interpretation,” says Kent.

The committee interpreted that an effort should be made to separate any crack-free particles suspected to be in the “ten largest” search. If not possible, the crack-free fragments in the perimeter should be measure for area. That measured area should then be added to the selected ten largest crack-free particles to determine if the test specimen did or did not comply with the standard. As an alternated, some form of digital photography and/or calculation method is acceptable.

The rationale reads, “Per [the previous technical interpretation], VIG units shall be tested as final product units. The permanently bonded nature of the unit causes the break pattern to be somewhat hybrid in nature between tempered glass and laminates. The edges of the systems tend to break as composite perimeter edge fragments, while the rest of the glass falls away in particles that are rated in the same manner as tempered. It is the consensus of the steering committee that the edge sections need to be evaluated for particle size after breakage. Glass shards that are not separated by a break pattern which are in the one-inch marked border area are the concern from a cutting and laceration and test evaluation standpoint. The language above is deemed to address the characterization of the composite perimeter edge fragments and provide a method of evaluation after impact for VIG evaluation. This interpretation applies to VIG units only.”