What Makes Tempered Glass Shatter? Here Are 5 Possible Factors

You’ve just had your brand new smartphone reinforced with tempered glass. You’re feeling really great about it. “Now nothing can possibly hurt my precious phone screen,” you reckon. “I’m invincible.” Cackling to yourself, you walk five steps before you realize that your “invincible” tempered glass has just shattered.

“WTF?” you go. “BUT WHY?”

At that moment, a bespectacled kid introduces himself as Mr Wee Kee Pia and proceeds to explain:

“Tempered glass may be ideal for most scenarios, but there are situations in which they may spontaneously break for seemingly no reason whatsoever.”

Perplexed, you beget: “Pray tell, what reasons do thou speaketh?”

You watch as the kid opens his mouth:

What Makes Tempered Glass Shatter? Here Are 5 Possible Factors

1. Installation damage

According to Wikipedia, it’s relatively easy for the glaziers to nick or even chip the edges of the glass (with various tools) while glass is being moved and installed. Fasteners such as nails and screws (that’re used to attach glass stops) are also liable to nick the glass edges if they’re installed at an improper angle.

Granted, these minor nicks might not cause immediate breakage, but as the glass expands and contracts over time, stress concentrations could potentially form around the nick, leading to breakage.

It’s worth noting that should tempered glass receive such a fate, the entire unit usually ends up breaking altogether.

2. Binding in the frame

Lest you’re unaware, glass actually expands and contracts with changes in temperature and wind deflections. As such, almost all modern glass is situated upon resilient blocks at the base with space for expansion at the sides and top. It’s worth noting that the gaskets that hold the glass in the frame are also usually tough, in order to support the glass against wind buffeting.

However, if no space is catered to the perimeter of the unit, the glass will ultimately bind against the frame, causing internal stresses to accumulate in the glass. If the pressure manages to exceed the strength of the glass, the tempered glass will ultimately break.

3. Inadequate glass thickness

If a pane lacks the adequate amount of glass thickness, it’ll ultimately be susceptible to breakage. This is because it hasn’t been properly engineered for wind loads on the site, which makes it vulnerable to external stresses.

4. Thermal stresses

Thermal stress is also an indisputable factor, and it’s most common in large pieces of “sealed insulating glass with heavy-absorbing (reflective) coatings.” As the coating’s commonly applied to the “number two” surface (the inside face of the outside lite), the outside lite of glass will tend to heat up more than the inside lite, as the coating turns radiant heat from the Sun into sensible heat.

As a result, the outer lite will expand due to the heat, and the entire unit starts to bend outwards. This might ultimately lead to the development of bending stresses, which may prove too powerful for the glass and cause breakage.

The John Hancock Tower in Boston, for one, faced extensive glass breakage the same exact way. And more recently, a tempered glass table fell prey to this factor as well.

5. Internal defects and inclusions in the glass

Tempered glass? For all you know, it might well be tampered glass. According to Wikipedia, nickel sulfide inclusions, also referred to as “stones”, can be present in the glass, commonly when stainless-steel machinery is used in the glass making and handling process.

Over time, these small quantities of stainless steel tend to change structure and grow, causing internal stresses in the glass as a result. When the stresses overload the resilience of the glass, breakage occurs.

Apparently, this type of breakage’s “almost always” found in tempered glass, and is recognisable by a distinct “figure eight” pattern, with each “loop” of the figure eight approx. 30mm in diameter.

Tempered Glass

And there you have it folks. Tempered glass might be quality material for various apparel, but it’s by no means the perfect one. Though as long as you keep the aforementioned points in mind…

Your tempered glass should serve you just fine.