Why does Glass Shatter Unexpectedly

Why does Glass Shatter Unexpectedly

Why does glass shatter unexpectedly?

Glass from high-rise buildings has broken unexpectedly and fallen from such heights several times. 

There have been several reports surfacing from different sources, and they are dangerous.

The use of the right type of glass has thus been reconsidered by builders and glaziers to ensure safety. 

A new term has been introduced as a result: safety glazing. 

Glass that has been engineered to minimise the possibility of injury is considered safety glazing, and it is necessary for glass doors, skylights, shower doors and even car windshields.

In London, there are many glazing companies. 

The three types of safety glazing employed by these glazing companies are tempered glass, laminated glass, and laminated safety glass. 

The best safety feature is that if it breaks, it shatters into tiny pieces that are not dangerous. Glass rapidly warms and cools because it is heated and cooled rapidly. 

Other types of safety glazing include laminated and heat-strengthened glass, the latter of which cannot be safely broken since long fragments will result, which can cause serious injury.

It is important to hire a company that is equipped with the best glaziers to install your windows safely and to assist you in case of an emergency. 

There might be a reason for the breakage of glasses in the house, but one might not know it.

There are instances when spontaneous glass breaks even with toughened glass being four to five times stronger. 

Despite the rarity of this event, we wanted to share some information on what it is, what causes it, and what can be done to limit its consequences.

Have you ever wondered why the glass shattered on its own. It is rare that glass spontaneously breaks but it is  possible.

There are reasons that breakage happens, and we are here to discuss the factor behind the breakage of glass.

Nickel sulphide and thermal shock.

When the temperature causes the glass to expand and contract, and when this happens and with severity across the glass and when the centre of the glass changes in the opposite direction, the stress in the glass causes them to break.


An object that breaks spontaneously is defined as one that appears to crack or break without warning. 

Spontaneous glass breakage may appear to be easy, but the situation is actually much more complicated than it appears to be

Any time glass cools from its molten state, the amorphous nature, large coefficient of thermal expansion, and poor heat conductivity make it susceptible to freezing. 

A rock pit, as found on automobile windshields, can cause cracks to spread across heat-treated tempered glass. 

A large mass of glass will have a higher melting point than a thin sheet, since cooling will be uneven (faster on the outside than the inside).

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Types of glass

Thermally strengthened, laminated, and heated glass

Glass that is tempered is commonly used as safety glass. Quenching is a method of rapidly cooling heated pre-cut panels of glass while they are heated to 650 degrees Celsius (1200 degrees F). 

As a result of quenching, the edges and surface of the glass become compressed, causing the center to become tensed.

A tempered glass is four to five times stronger than conventionally annealed glass during the re-heating process and rapid quenching that takes place after it is tempered. The shards of broken tempered glass are therefore very small, which eliminates the possibility of human injury from sharp edges and flying shards.

Another type of safety glass is laminated glass, which is made by sandwiching a plastic material (typically polyvinyl butyral [PVB]) between two layers of glass to prevent the panel from shattering. The most common application of laminated glass is on automobile windshields, however they are increasingly being specified for storefronts, curtain walls, and windows for hurricane protection.

Pre-cut glass panels are heated to temperatures up to 650°C during heat-strengthening, but cooling is slower than with tempering. Because of its lower compression strength, heat-strengthened glass is not as strong as tempered glass, weighing between 24,130 and 51,710 kilos (about 3500-7500 pounds) as opposed to 68,950 kilos (10,000 pounds). 

Glass that has been annealed is about twice as strong as that that has been tempered. Due to its high thermal resistance and resistance to snow- and wind-loads, it is usually specified for thermal and snow load applications.

What are the causes of glass breakage?

Spontaneous glass breakage occurred exclusively with tempered glass in Chicago, Las Vegas, Austin, Texas, and Toronto. It is particularly vulnerable to these types of failures, despite its high strength and ability to meet safety glazing requirements.

By design, tempered glass has a center tension zone that is engineered through quenching. It is this center tension zone that makes tempered glass so susceptible to catastrophic breakage.

For a sliding glass door, a shower door, or a patio set, safety glazings are commonly required. In general, ‘safety glazing’ refers to any type of glass that has been engineered to reduce the risk of serious injury.

A poor quality edge

Glass that spontaneously breaks can be caused by a number of factors. There are several ways that glass edges can be damaged: during the pre-cutting process, while being shipped, or during the installation of the glass.

Despite not being readily evident, stress concentrations may occur around these imperfections as the glass expands and contracts due to changes in in-service temperatures, wind loads, building movements, and other environmental factors.

A broken glass may appear to be the result of sudden stresses when, in reality, conditions for failure have been in place for months, if not years.

Breakage of frames

Framing-related failures may also occur when members are stretched or contracted. This is another common cause of seemingly spontaneous failures. Metal window frames and curtain wall frames lack or are inadequately equipped with gaskets, setting blocks, and edge blocks that protect glass against metal contact. The glass may suffer damage to the edge and surface of the metal frame when it is in contact with the metal’s perimeter, causing stress until it eventually breaks without apparent cause.

The nickel-sulfide particles in floating glass are tiny, extremely rare and only found by chance. Inclusions of this type cannot be visually examined when this combination is used.

Stress due to the heat

There is also the possibility of spontaneous glass breaking due to thermal stress. An edge of a glass lite is hotter than the center, leading to thermally-induced stresses. This is due to a positive temperature difference between the two edges. A tensile stress is created at the edge of the glass due to the expansion of the heated glass center. Glass is broken when the edge strength of the glass is exceeded by thermally induced stress.

Considering thermal stress is especially crucial today, since current design trends and daylighting trends are urging the industry to specify larger insulating glass units (IGUs) with high-performance solar control coatings. Inherently, large IGUs have a larger glass surface area and a larger edge area. The thermal stress analysis becomes even more thorough when solar energy management coatings are applied.

Nickel sulfide stones may form in float glass, but no known technology completely prevents this. Due to the small size of nickel sulfide stones, it is impractical to check for them in float glass.

Inclusions of nickel-sulfide

Despite being far less common, nickel-sulfide inclusions (NiS) in tempered glass are often cited as a cause for spontaneous glass breakage. The formation of nickel-sulfide stones is random during float glass production. Tempered glass is not usually affected, even if they are present.

Nickel is not used in North American glass manufacturers’ batch formulations for primary glass and they take great care in avoiding nickel in their glass-melting processes.

Float glass today does not have the technology to completely prevent nickel-sulfide stones from forming, even under rigorous quality control and procedures.

It is permitted in float glass that nickel-sulfide particles are not larger than 0.5 millimeters (1/50 inch) in size (or between 1/10 inch and 1/10 centimeters in diameter), depending on the glass size and composition quality.

Despite the fact that nickel-sulfide inclusions can occur in annealed or heat-treated glass, the problems they cause with tempered glass are specific to the tempering process. An enlargement of the stone’s volume results in its breaking. When glass is annealed or strengthened at low temperatures, nickel-sulfide particles, which are present, undergo a phase change (called the ? to ? phase change) in which they fully expand to their final size and do not deform.

Installation and manufacturing issues with toughened glass

The only type of glass that can “explode” is toughened glass, such as that used in shower screens. The glass can also break or crack if it is of a different type.

A glass that spontaneously breaks (or explodes) is said to be exploding. This is a phenomenon that happens when toughened glass breaks (or explodes). There are several causes of this:

  • The presence of inner defects such as nickel sulfide inclusions in the glass
  • A nicked or chipped edge during installation develops into a larger break outside its point of origin.
  • The glazing of the frame, resulting in stresses when the glass increases and decreases in size or deflects due to wind or thermal changes
  • Glass under thermal stress
  • Insufficient thickness of glass to resist wind loads

A variety of factors, including poor manufacturing AND incorrect installation, cause toughened glass to explode, and these implications should be known to strata managers, facility managers, insurers and the general public. The corners of toughened glass are weakest points, so if they are pushed or knocked too hard, they can explode.

Glass that soaks in heat to improve performance

It lessens the effects of spontaneous fractures on toughened (tempered) glass by soaking it in hot water for long periods.

How does nickel sulphide affect glass? 

Nickel sulphide, a component of raw glass materials, is reduced in size when heated to around 1100°C during the manufacture of float (annealed)glass. In the annealing process, the nickel sulphide in the glass expands back to its original size as the glass cools slowly. There is no effect on the properties of the glass from this expansion. When toughened glass is used, however, there will be a problem. When the glass is toughened, the temperature is heated to around 600°C, which subsequently decreases the volume of nickel sulfide. When toughened safety glass is created, heat is rapidly cooled to induce stress and tension in the glass. This rapid cooling prevents nickel sulphide from transforming, unlike annealed glass that cools slowly. Eventually, the nickel sulphide will return to its original size. When this occurs in an area of tension in the toughened glass, it causes the glass to fragment.

It is rare to find nickel sulfide in raw glass: Only about one ‘stone’ of nickel sulfide is present per 8 tonnes of raw glass (although it may appear in batches). It is estimated that nickel sulphide occurs in one stone for every eight tonnes of glass to one stone for every thirteen tonnes of glass, and some suppliers have a more frequent occurrence than others. In addition to the moments following thermal treatment, nickel sulphide can lead to the fragmentation of glass even decades after it is installed. Certain types of heat strengthened glass are also susceptible to nickel sulphide.

Although heating the glass will not completely stop it from exploding, it will significantly reduce the likelihood. It is an optional process that glass manufacturers can offer if requested. It is significantly more expensive to produce Heat Soaked panels as a result of this extra processing.

What can be done to prevent spontaneous glass breakage?

There are some times when nickel sulphide can be detected in toughened glass. Glass can be removed from flat surfaces by soaking them in hot water for up to 95% of the time.

Heat soak testing involves heating toughened glass to 290°C over an extended period of time. As the nickel sulfides expand during heat treatment, the glass pane will fracture depending on where they are contained within it.

Essentially, the objective is to remove any contamination from the glass by soaking it in hot water.

How To Deal With The Situation?

Never panic if you are ever the victim of a spontaneous glass-breakage incident. It is important to keep a cool head. Make a safe stop, contact emergency services, and document the accident as soon as possible. The sooner you obtain your insurance information, the sooner you can start getting quotes from reputable auto glass shops.

What steps you should take will depend on what kind of coverage you have and how specific your policies are. Consider working with a glass shop that will help you process your claim so that you are covered appropriately. 

Choosing the right safety solution

There have been incidents of falling glass in Toronto, Chicago, Las Vegas, and elsewhere, and two major organizations recently announced plans to deal with the problem. In their opinion, it was the use of laminated tempered glass or heat-hardened glass that would give balconies and overhead glass more security.

The Ontario Ministry of Municipal Affairs and Housing (MAH) has been asked to update building codes to mandate high-performance laminated glass for guards and glazing beyond the edge of a floor or within 50 mm (2 inches) of it. In outboard glazing located over 50mm from the edge, heat-infused tempered glass or laminated heat-strengthened glass is recommended.


Heat soak artificially ages toughened glass, and even though it’s not 100% effective, it drastically reduces the risk of the glass exploding at some point later. It is an optional process that glass manufacturers can offer if requested. It is significantly more expensive to produce Heat Soaked panels as a result of this extra processing.

Toughened or tempered glass breaks into tiny pieces instead of larger, sharp ones due to the chemistry behind it. The end result is that users are kept safe.

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