Tempered Glass Furniture Shattering

Tempered glass is still safer than standard glass.

Temperature changes in your home can cause glass furniture to explode (WEST PALM BEACH, Fla. ) - With a hammer, a Window Doctor employee struck a piece of tempered glass. Blow after blow, the glass held up. Due to that strength, furniture makers prefer using it. However, some consumers have found a downside.

"I'm surprised. I'm shocked," explained Patty Velez. Velez was watching morning television when a noise upstairs startled her. "It was loud enough it scared the dogs," Velez explained. Velez ran upstairs, and couldn't believe the mess in her room. "This whole glass was shattered like it is here," Velez said as she showed us her damaged glass cabinet. "And it was bowing three or four inches out and I could tell it was just ready to go." Within seconds, "It finished exploding and all the glass fell to the floor. It continued crackling and popping almost like popcorn on the floor."

What happened here, could happen to you. "It's common in the industry," explained Gary Orman of Innovative Window Concepts . Orman said all homeowners should beware. "You never know when or if it's going to happen," Orman said. Orman said tempered glass spontaneously shatters from normal expansion and contraction from temperature changes that  might occur in your home from air conditioning and sunshine.

"Tempered glass is tempered in a heat oven and brought up to a certain degree temperature and cooled quickly to make the glass stronger. It puts the internal pieces into compression and the external pieces into tension, and gives strength to the glass," Orman said. "There are particles in there that do not melt and those particles will change as the heat changes." "It's 4 out of 1,000 pieces that do it," Orman said.

Four out of a thousand may not sound like a lot, but there are dozens of complaints with the Consumer Product Safety Commission for patio furniture, shower doors, desks, and glass cabinets. "Would you buy another piece of furniture like that?" Strathman asked Velez. "No definitely not," Velez said.

Despite the examples, furniture makers say tempered glass is actually safer. So we set up a demonstration with the Window Doctor. We used two pieces of glass that look the same, but there's a huge difference when hit. We compared annealed or standard glass with tempered glass. After just one hit, the standard glass shatters into large sharp pieces that can easily cut you. With the tempered glass, after one hit in the same spot the glass is still in tact. Even after six hits, not a chip or a crack.

"With tempered glass the edge is what takes the tension," said Orman.

So we put the hammer to the test on the edge of the tempered glass. It took 8 hits before the glass shattered into a million pieces. The size and texture of the tempered shards are much smaller and duller compared with the annealed glass. "It might be safer but it can still cut you," Velez said.

"Now that you know this happened to other people what do you want the manufacturers to do?" Strathman asked Velez. "I think they need to tell people there is a possibility this could happen with this type of glass," Velez said. Velez's furniture was built by IKEA. Their website warns customers to handle the glass with care especially the edges which in "exceptional cases can cause the glass to break suddenly." Something Velez wishes she knew before she was left cleaning up a mess.

After our calls to IKEA, they replaced the glass in the broken cabinet and another piece of furniture to make sure this doesn't happen again. It's an issue that can impact any tempered glass furniture -- no matter the manufacturer.

Also See:  

Spontaneous Shattering - Tempered Glass - A Guide For Window Cleaners

Glass Shower Doors Can Shatter Without Warning

Annealed Glass As A Health Hazard

Windows Shattering in Dubai - NiS Problems?

Glass & Imperfections - Report Those Unsafe Windows

The Cutting Edge Of Window Scrapers

The New Unger Ergotec Ninja Scraper available in 4 inch & 6 inch.

The cutting edge of window scrapers: Torsten Deutzmann of Unger Professional Worldwide reveals why professional window cleaners rely on their scrapers so much.

The word scrape has a number of different meanings, but one of the most appropriate I have found, in terms of window cleaning, is: ‘Move a hard or sharp edge across (a surface) especially to make something smooth’.

Materials used during the construction period, such as cement, grout and paint, can splatter onto glass – and scrapers are the most effective tool to help remove such debris, and other substances that can cause significant problems due to their unsightly appearance or ability to cause physical damage to the façade of a building.

Throwing eggs at buildings can seem like a good practical joke to some but egg can be a stubborn substance to remove once dried on. Scrapers can help in these circumstances, as they can with another big problem when it comes to building maintenance – bird excrement. Bird mess not only has the potential to spread disease and bacteria, its corrosive nature can also cause damage to brickwork and building facades if left for too long. Scrapers can also be useful when dealing with fly-posting or other materials such as stickers.

Toughened safety glass, also known as tempered or safety glass and as ESG in Germany, is extremely common. It is manufactured by a process of extreme heating and rapid cooling, so that the surface area cools much quicker than the inner layer. This makes it stronger than standard glass, and, if the glass does shatter, it breaks into small ‘chunks’ instead of splintering into dangerous, jagged shards.

Extra care needs to be taken when cleaning this type of glass as issues have arisen surrounding ‘fabricating debris’. This takes the form of tiny rough imperfections, sometimes referred to as ‘glass fines’ that are created in the hardening process.

Fabricating debris has been a subject of debate for years, and it prompted the International Window Cleaning Association (IWCA) to publish the IWCA Tempered Glass Informational Bulletin 2004 – Scrapers and Fabricating Debris in 2004. It offers a range of guidance and advice, including:

• Fabricating debris consists mostly of tiny glass chips and glass dust that get baked onto the surface of some tempered glass. These surface defects, also known as glass fines, may create scratches when they are dislodged and trapped by a scraper during window cleaning

• Builders should require suppliers to provide quality tempered glass that can be cleaned without scratching, the same as glass which is not tempered

• There should be a tempered glass scratch liability waiver for all construction window cleaning contracts, and for maintenance contracts when significant scraping will be done. The builder signs a tempered glass scratch liability waiver to assure they will not blame the window cleaner for scratches due to fabricating debris on tempered glass, and will not force the window cleaner to prove that fabricating debris caused scratches on tempered glass.

Check glass

Scrapers should not scratch normal, uncoated glass when used properly, but it is always advisable to check if the glass is scratch resistant before work starts, to follow the manufacturer’s instructions and to perform a test on a hidden area.

One useful way to determine whether glass is safety glass or not is to do the lighter trick. Simply hold a lit flame, from a lighter, match or candle, in front of the glass. If you see a double reflection in the pane it is safety glass. If you see just one flame reflected back at you, then it is normal glass.

When it comes to blades, the material they are made from and the way they have been sharpened are extremely important.

Scrapers are called upon to clear the most tough and stubborn dirt, debris and residue so the steel used should be hardened and corrosion resistant, ensuring that blades stay sharper, and rust-free, for longer. Carbon steel or low/high alloy stainless steels can provide these properties. Carbon steel will produce a stiffer blade, whereas those made from stainless steel are more flexible.

Carbon steel is a hard material, giving the cutting edge greater stability. The blade will stay sharp, but as water and/or cleaning chemicals are often used to lubricate the surface of the window being cleaned, this will have an effect as carbon steel rusts more quickly than stainless steel.

In contrast, stainless steel is more flexible and stays rust-free thanks to its high chrome content, which makes it a more expensive option. Being softer in terms of material means that the finely ground surface will wear down and lose its sharpness quicker than a carbon steel blade.

Dual-sided window cleaning blades made from corrosion resistant 440A grade stainless steel provide excellent edge retention, which means that the blades stay sharp for a long time. These blades benefit greatly from going through a precise honing process, which creates a cutting angle that is sharp and consistent, enhancing the speed and effectiveness of every scraper pass.

Scrapers need to be used with care, the golden rule being never to use one on dry glass. Always wet your window with the correct cleaning solution for the material you are about to remove as this helps to lubricate the blade.

It’s also important to scrape in one direction only, lift the scraper from the surface, and then reapply it. Scraping the blade back and forth across a window increases the chances of dirt being trapped under the blade and causing scratches. Clean your blade regularly in water and always apply an even pressure, holding the blade flat against the glass.

Old, worn-out or damaged blades must be changed regularly to ensure optimum results, and safety is also highly important. When not in use, caps should be placed over blades, or retracted, to minimise the risk of cuts.

The most effective and up-to-date models feature ergonomically designed handles which provide a more comfortable fit in the hand, minimising stresses and strains on hands, arms and shoulders. The latest innovation to hit the scraper market is the ability to change the angle of the scraper head from straight to 30 degrees at the touch of a button. This ensures a smooth and swift transition between manual and pole work.

Blades that are easy to change, using a slider mechanism, are preferable; and it’s also worth investing in a holster that allows you to store your scraper when not in use, but makes it easily accessible when needed. Choose one that has the ability to fit onto a range of tool belts, and has a solid back to protect your leg/body from cuts.

Scrapers have been used by the window cleaning, glass and building industries for years, and they are still the tools to go to when faced with certain types of dirt and debris. As design and technology know-how helps to improve the results they achieve, they can only retain their usefulness for many years to come.

Click to take you to the download page.

The Glass Tempering Handbook: Jonathan Barr has published 'The Glass Tempering Handbook', which "aims to explain and demystify the glass tempering process" in only 52 pages. It's packed with information and practical advice including glass fines on tempered glass surfaces and how they affect cleaning with metal blades - is one of many topics addressed by Barr. 

Glass Shower Doors Can Shatter Without Warning

Classic meandering pattern of heat-related stress crack, accompanied by evidence of edge damage. In this case, the building had both: edge damage and underspecified glass. Reflective blinds and a South exposure combined to create a high frequency of this type of breakage.

Glass Shower Doors Can Shatter Without Warning (Chicago): If your shower door is made of glass, you may endure injuries, a big clean up and thousands of dollars down the drain. CBS 2′s Dave Savini first exposed tempered-glass patio tables suddenly exploding. Now he found the same happening with shower doors. Dorothy Malinski’s shower door suddenly exploded while her mother was bathing. “I heard this big bang, this big boom,” said Malinski.  “I couldn’t enter all the way because there’s glass all over the counter, in the sink, on the floor.” Her mother was cut on her hands and face.

Even though tempered-glass shower doors are supposed to break into small pieces — to prevent injuries from larger, sharper pieces of glass — they can break in bigger shards. That is what happened to Larry Kucharik, who was injured while cleaning up the shattered glass from his shower door. “I just tapped the top of it and a chunk of it came down and hit my ankle,” said Kucharik, whose ankle is still scarred. “It started bleeding, and there was a lot of blood all over the floor.”

The U.S. Consumer Product Safety Commission reports more than 60 complaints of shower doors shattering for no reason — just suddenly exploding, causing lacerations and bleeding. People reported needing stitches and even surgery. Mark Meshulam, a glass and window consultant, reviewed the reports. “These are the types of injuries and situations that I would expect to see when something goes wrong with shower doors,” he says. He says a microscopic imperfection during the manufacturing process can grow and migrate, weakening the glass until it suddenly shatters. It can even shatter without it being touched. “I would say treat the doors gingerly,” Meshulam warns. “Do not bang them. Don’t allow children to hang on the towel bars.”

He also says look for chips near brackets, the towel bar and along the edges. Also, make sure the door only moves the way it is supposed to and is not loose on the track or hinges. In Larry Kucharik’s case, the manufacturer replaced his shower door at no cost. This has also been a problem at hotels. Meshulam says one reportedly had 50 doors shatter. He would like to see protective film on shower doors to catch breaking glass. This is a tempered glass problem, so it involves various door manufacturers and the ages of glass. If this happens to you, call the Consumer Product Safety Commission and the door manufacturer.

Also see here & here. 

Chicago Window Expert - Mark Meshulam (pictured) is a consultant for glass breakage and expert witness for personal injury due to glass breakage. When tempered glass breaks, the energy retained in the glass due to internal tension/compression releases explosively and produces a breakage pattern sometimes called “cubes’.

Seeing a cubist breakage pattern does not tell you why the glass broke, it only tells you that the glass was tempered. Generally, there are three reasons tempered glass will break: impact, edge damage or inclusions. Inclusions are tiny impurities in the glass. The most well known are nickel sulfide, however there are also silica and gaseous inclusions which look like tiny bubbles.

Normally, when tempered glass breaks, it falls down into a pile of little cubes. Only the most patient window consultants with the most generous client would ever consider piecing the cubes together to determine the cause of breakage. That being said, I have personally spent many hours picking through the rubble looking for an important clue: a pair of adjacent hexagons, known as a butterfly pattern, that borders a nickel sulfide inclusion.

If you look closely, you can see the point of impact on this tempered glass. A laminated interlayer holds the cubes in place.

However, occasionally the pieces of broken tempered glass will stay in the opening, locked to each other like blocks in a masonry arch. And just like in a masonry arch, if you remove the keystone, the arch – or glass in this case – comes tumbling down. This picture above shows broken glass which was a part of a laminated unit. The PVB (polyvinyl butyrate) interlayer held the pieces in place, giving us an opportunity to observe that impact damage is visible, even in tempered glass.

Spontaneous Breakage in Tempered Glass: Glass, and especially tempered glass, sometimes breaks all by itself. This can be quite disconcerting when, as has happened in a public place which will go unnamed here in our great city, large, thick panes of tempered glass basically blew up fairly frequently. The unusual cause in this rare instance: the glazing contractor attempted to grind the edges of the glass after it was tempered, creating a series of time bombs. It is a very bad idea to modify glass after it is tempered!

A more well-known, but also quite rare cause of spontaneous breakage is nickel sulfide inclusions. If you read the previous post, you will already be down with the fact that glass is made from melted powders. A nickel sulfide inclusion is a tiny rock of unmelted material that remains in the glass. Below see an artists graphic representation of a nickel sulfide inclusion.

Artists representation of nickel sulfide inclusion.

You can well imagine that a little rock embedded in a slab of glass which is under high tension/compression forces, could weaken the glass and eventually cause breakage. But the story gets worse. Nickel sulfide grows an additional 4% of its size over time, especially in the presence of heat. If it is located in the strata in the glass between tension and compression, and it grows, kaboom!


Exploding Glass Shower Doors: One of the scariest, yet somewhat common type of tempered glass spontaneous breakage is in glass shower doors. They are exposed to banging against bumpers, heat from the shower, wrenching action of through-mounted towel bars and of course, nickel sulfide inclusions. In hotels, multiply the risk factors by the number of rooms and the lack of care typically taken by a hotel patron. There can be a delay between impact and crack propagation in tempered glass, just like any other glass, and sometimes the time the glass finally explodes seems ironic and and Machiavellian. Quite often the perverted glass will explode while the unsuspecting victim is in the shower.
Let’s count the problems: 1. The victim is naked. 2. There are sharp cubes of glass projectiles flying around. 3. The victim is bare footed. 4. The victim must walk barefooted over a field of freshly shattered glass shards. So here’s a tip for readers who actually do take showers: If your shower door shatters, stand still for a moment and take stock of the situation. Hopefully you are not cut too badly. Without moving your feet too much, look for a towel. Try to grab it and lay it down on the glass so you can walk out. Then get the hell out and never shower again.

Stress Cracks (see head picture): A “stress crack” will usually only happen in annealed or heat strengthened glass. Stress cracks emanate from the edge of the glass and meander about apparently without purpose. But there is a purpose: to relieve stress. However, the term “stress crack” can be misleading. If annealed glass is subjected to thermal fluctuations beyond its capabilities, it will break in a way that will relieve the stresses induced by thermal changes. This type of failure is a design issue. Heat strengthened glass should have been specified for the application. However, there can be a near-identical breakage pattern which emanates from damage in the glass edge that fails as stresses, such as thermal, are applied.
To tell the difference between a true stress crack and a crack due to edge damage, look at the edge of the glass for a chip, which we window linguists call an “oyster”. You might have to look hard because the oyster could be buried in the primary seal on the #2 or #3 surface. Another clue would be the distribution of glass breakage in the building. It would be normal to find stress-like cracks on elevations with greater temperature swings. But does the breakage also coincide with the use of reflective interior blinds, especially in a partially opened position? That would be indicative of a true stress crack, rather than a crack induced by edge damage.

Spontaneous Shattering - Tempered Glass - A Guide For Window Cleaners

At some time or another whilst window cleaning tempered glass/safety glass, you may suddenly find a glass door or table just shatter on you without reason. Depending on which country you are in, most new shop glass or public area comes under the safety glass law. And they break quite frequently. This has happened twice for me & each time I was no where near the doors & luckily the business owner/home owner was present. Either way, how you decide who takes the blame, if the window in question is under guarantee or what other factors come into play will decide the outcome to who pays for the damage. So next time you get asked to clean those patio glass tables or shower doors, take heed. Think it won't happen to you? Read on.

The story below gives you the dangers & what happens when that glass shatters without warning. Safety glass is designed to shatter differently from other types of glass, to help prevent injuries from flying shards. Tempered glass is exceptionally strong and heat resistant and gets its strength from a tempering process in which the glass is heated to extremely high temperatures and cooled down quickly. Tempered glass is heat resistant, making it 4 to 5 times stronger than regular glass and harder to break. It is often referred to as "safety glass." Tempered glass is made strong by an extreme heat and then rapid cooling process.

How Tempered Glass Shatters: During the tempering process, the inner layers of a pane of glass become compressed at a higher rate than the outer layers. This process is repeated several times to create a complex web of stress lines that is invisible to the naked eye. When something causes tempered glass to shatter, it shatters along all of these stress lines. The glass breaks into many small bits that are rounded or cuboid in shape, often with relatively smooth edges. The bits are often about the size of the eraser on a pencil. Because the network of stress lines covers the entire pane of each piece of tempered glass, it will all shatter at once when it fails.



Shattered! The danger hanging in your bathroom by Bob Sullivan: I had just finished showering and turned off the water. Soaking wet, I did what millions of Americans do every day - I reached for my snazzy sliding glass shower door. Seconds later, glass was raining down on me. The door had failed somehow and exploded into a million little pieces. The sound was hideous, something between nails on a chalkboard and a torrential downpour. Only this didn't make me wet, it made me bloody. Glass shower doors are a substantial upgrade from old, mold-magnet plastic shower curtains found in many older homes. They look great. They let ambient light into the shower and make the bathroom look larger. If you have fancy tile rimming your tub, they show that off.

The aesthetics come with a cost however, as I recently learned the hard way: Glass shower and tub enclosures can shatter without warning, endangering any person or pet in the path of the raining glass. Interviews with building inspectors, glass companies and manufacturers - along with a quick Internet search for complaints - reveal that it's fairly common for bath doors to shatter, a tendency that isn’t made clear in glossy brochures with beautiful images of modern bathrooms. It's important to note, however, that the doors are made of special tempered safety glass, required by federal, state, and local building codes and designed to break into small, relatively harmless shards. A shattered shower door will produce a pile of glass chips similar to the glass left in your back seat after a criminal breaks a car window to steal a GPS. In doing research for this story, I found no reports of life-threatening injuries from a broken shower door.

In my case, I was left with about 20 cuts - not much worse than paper cuts - along the right side of my body and on my feet. I had one fairly large gash on the top of my foot that bled profusely, perhaps because a piece of the door hardware fell on it. And I had quite a scare. I had to figure out a safe way to climb out of the pile of broken glass without suffering more cuts, and then I had to shower in bath No. 2 to get broken glass shards off my body. Even so, I was picking small pieces out of my skin for the next day or so. I sent pictures of the incident to Kohler, the manufacturer of my shower door, which confirmed it was their product. "Glass doors do shatter," said Kohler spokeswoman Kristine Cristina. "We really can't give you an answer to how often because many people don't call to tell us." She said she believed the incidence was very low, however -- in the past two years, she said she knew of fewer than 10 incidents like mine. "It is very few and far between," Cristina said.

But it is not hard to find similar tales of bathroom floors covered in broken glass. In many cases, consumers report shower doors spontaneous exploding even when no one is in the bathroom.
"That's called a spontaneous blow," said Kathleen Bond, president of Sunset Glass in Bellevue, Wash., which occasionally is called on to replace broken shower doors. "Somebody is at the dinner table and they hear this crash." What would make shower doors suddenly explode? It turns out that their greatest strength – safety - is also their greatest weakness. When glass is heated in the tempering process, its tensile strength is altered. While it becomes much stronger and resistant to direct impact, it becomes much more susceptible to a side impact. As a result, tempered glass dropped on its edge will readily shatter.

"I've broken tempered glass just trying to remove it,” said Terry Love, a Seattle-area plumber. “When it pops, it's just instant. It's pretty amazing when you see it, how quickly it happens." Cristina, the Kohler spokeswoman, said that sometimes a small fracture will occur on the edge of a shower door that won't immediately cause it to shatter. Hours or days later, the door will then explode, creating the appearance of a spontaneous blow, she said. "It can happen for 100 different reasons," she said. The door could be incorrectly installed, rubber stoppers might be missing or cracked or the runner which lets the door slide is damaged. Or abusive treatment by consumers, such as rough openings and closings, could cause such a crack. Bond said many incidents of breakage she's heard about involve cleaning staff who improperly handle the doors.

I don't know why my shower doors broke; there's not enough of them left to do honest forensic work, and the Kohler company declined to inspect them. I installed the doors myself about five years ago, using one of Kohler's "EZ Install" systems, and they worked flawlessly until last week. Still, it's possible there was some kind of operator error. My memory is distorted by the surprise of the event, but I remember it this way: I grabbed for the door, felt it slip down slightly and then it exploded. I believe my door fell off the overhead runner, perhaps because a plastic wheel supporting the door broke. Slipping just an inch or so onto the bottom frame of the door could cause an explosion, according to several people interviewed for this story. Still, after expressing concern for well-being, Cristina noted that "the tempered glass did what it was supposed to do."

My still-swollen right foot doesn't necessarily agree, but in truth, my injuries are remarkably negligible given the amount of glass that showered over me, and I am lucky that the tempering worked as well as it did. I shudder to think about the injuries I might have sustained were this normal glass. It's important to note that there's nothing special about Kohler shower doors. There are scattered complaints about shower doors and tempered glass involving several manufacturers. The Consumer Product Safety Commission, the agency charged with tracking complaints and issuing voluntary product recalls, uses a variety of statistical methods to estimate the number of injuries caused by thousands of consumer products to build a database it calls the National Electronic Injury Surveillance System. The information is generated from actual consumer complaints as well as sampling of data providing by hospital emergency rooms, said agency spokeswoman Nychelle Fleming.

The system tracks and estimates injuries caused by "glass bathtub or shower enclosures," and a query showed that they were involved in an estimated 1,986 incidents during 2009. There were another estimated 4,470 injuries involving "bathtub enclosures" where the word “glass” was not used by the consumer or hospital. Reading a random sample of those reports, however, made it clear that most involved glass enclosures. But accidental shattering is not the only cause for those injuries. The supporting reports suggest that about half of the injuries were caused by a direct impact with the door, such as slipping and falling into it. For perspective, there were an estimated 86,000 injuries related to toilets during 2009 -- most involving some variation of "falling off."

There have been no recent voluntary recalls of shower door products, but Kohler voluntarily recalled 41,000 doors with swinging hinges -- different from the sliding doors on my shower – in 2001. In its press release about the recall, the Consumer Product Safety Commission said the hinges of the door could fail, "causing the shower door to fall and injure nearby consumers."

WHAT TO DO:

Glass in the home is a hazard, as any family with an aspiring athlete will tell you. Glass doors and windows are no match for thrown baseballs or footballs – or even a child who falls into one. There is no such thing as an injury-proof home. Glass shower doors are hardly the most dangerous glass in the house. Consumer Reports last year made the case that glass coffee tables pose a far greater risk, precisely because tempered glass is often not used. It said the tables cause approximately 20,000 injuries per year. “This is a serious safety hazard with a simple remedy,” wrote Donald Mays, senior director of Product Safety and Technical Policy for Consumers Union. Still, the risk posed by glass shower doors is real. Russel Ray, a San Diego-based home inspector, said he believes injuries from falling into doors – as opposed to spontaneous shattering -- are a greater concern. As a result, he thinks glass doors probably aren’t suitable for homes with elderly residents. “In assisted living facilities, you just don’t see them anymore,” he said. Parents with small children might also consider the added risks of glass shower doors. In case of a spontaneous blowout, Love, the plumber, said it’s important to have a bath towel handy and to use it to throw over broken glass on the floor to create a safe route out of the bathroom. Bond, of Sunset Glass, said she believes frosted or otherwise less transparent shower doors tend to shatter more often.

Kohler also offered this set of safety tips for long-term care of shower doors:
* Ensure moving panels are securely attached to the door system. If concerned, consult your instructions or contact the manufacturer.
* Periodically check the shower door hardware to ensure fasteners remain secure. Tighten them if needed.
* Ensure moving glass panel is not directly contacting the wall or metal during operation. That means checking the panel alignment and making sure the bumpers and seals are in good condition.
* Inspect glass regularly for any chips or cracks, paying special attention to glass edges, notches, and around holes in the glass for hardware. If there is any evidence of a crack, replace the glass panel immediately.
* Do not use the shower door towel bars as a safety grab bar or as a lift assist when getting in and out of the bath, or lowering and lifting off a toilet.

Windows Shattering in Dubai - NiS Problems?

Shattered windows spark safety fears: DUBAI: Windows in high-rise apartment blocks are spontaneously breaking because of a combination of shoddy workmanship and inadequate building regulations, construction experts say. “I came home from work and it was smashed, and I’m not quite sure how or why,” said Nina, 38, a Briton, who found a half metre-long window damaged in her one-bedroom flat on the 36th floor of a tower in New Dubai. “On the ground there were a few splinters, but it was more the window being cracked while still in the frame.” According to experts, Nina was probably the victim of building contractors who had improperly fitted window panes. Large temperature fluctuations then caused the metal frames to expand and contract, straining the glass beyond its breaking point, they believe. The problem is compounded by insufficient building regulations with regards to window installation, they say, leaving standards to be decided by contractors and developers. “There are some incredibly bad practices – contractors who don’t know what they’re doing, putting things together in ways that are completely unacceptable,” said Tom Bell-Wright, founder and owner of Thomas Bell-Wright International Consultants, which specialises in building facades. “As far as regulations are concerned about installing windows and glass, there aren’t any.”



Asked if such regulations were maintained by Dubai Municipality, Kamal Azayam, a mechanical engineer who works in the qualifications and building studies section, said: “As far as I know, nothing.” Such decisions were not overseen by the Government, he said, but instead depended “on the requirements of the consultants”. Christine Stewart (pictured) is baffled as to why a glass panel in the lounge of her apartment suddenly shattered into dozens of pieces on Saturday. “Nothing had hit it, nothing had happened,” said Ms Stewart, 46, a Briton who works in the media. “It just literally went, and people were sitting nearby. It could have hit them, but luckily it didn’t. “What worries me is what caused such a thing to happen, is it going to happen again, and how safe are our apartments.”
When Barti Makhijani returned to her 28th-floor apartment in Dubai Marina recently, she found one of the five window panes in her bedroom, which run from floor to ceiling, was cracked in numerous places, but still intact. “It looked at first glance like it was raining on just that window,” said Mrs Makhijani, 30, an Indian who lives with her two children. “It was shattered, as if a large stone had hit and some sort of ripple effect all along that centre pane. From what I understand, it was the outside pane that was shattered. “I’ve got children around, and what if somebody throws something at that window like a ball because I’m not always in to guard the window?” The cost of replacing the window, about Dh12,000 (US$3,200), was borne by Mrs Makhijani’s insurance. But the men who did the repair told her “it wasn’t the first flat in the building that experienced it”. Paul Rogers, managing director at Eminent Surveyors and Loss Adjusters, described Mrs Makhijani’s window as “frosting up”. This happens when windows are installed without the necessary “wedges”, which act as shock absorbers. This exposes them to greater amounts of thermal pressure, making them more prone to buckling. “It’s mostly the outside pane that shatters,” he said. “If the inside shatters, that’s serious because it means the glass was fitted the wrong way.”

THERMAL BREAKS
Glazing that absorbs solar radiation is liable to break due to thermal shock. Thermal shock is caused by too great a difference in thermal expansion between one section of glazing and another (see diagram below). The center of the glass exposed to the sun heats up much more rapidly than the part of the glass which is shaded or enclosed within the frame. The resulting solar-induced thermal stress can, if the critical limit is reached, cause the glass to break. Various factors can cause thermal breaks, including:
• The geographical position of the building, facade orientation, window placement (vertical or slope);
• Interior factors, such as air conditioning;
• Glass-related factors, e.g. tinted glass;
• Shading patterns.
Thermal tempering and heat strengthening increase the resistance of glass to thermal breaks.

TEMPERED SAFETY GLASS: Glass, by its very nature, is considered a fragile material because there is always a certain number of virtually invisible surface imperfections. The most common imperfection is micro-cracking. When subjected to stress, the cracks open, expand and eventually cause the glass to break. To overcome this drawback, glass is subjected to a special heat-treating process that locks the surface in a state of compression to helps and prevent cracking. Heat treating consists in heating the glass to just below the softening point (620°C / 1200°F) and then cooling it rapidly and uniformly. During the cooling process, the surface layers of the glass harden and contract, while the central core, which is still warm, stays viscous and follows the movement of the contraction. As the core cools and hardens, the rigid surface layers lock it in, compressing the surface of the glass. When the core is completely cooled, the surface of the glass is locked in a state of compression and the central core in a state of tension. As a result, surface scratches or cracks will be subjected to compression, which in turn causes them to close. The glass is therefore stronger. The mechanical strength and thermal endurance of tempered tempered glass is four to five times higher than that of annealed glass. Thermally tempered glass shatters into a multitude of small fragments when broken and, therefore, cannot be cut or edged after being tempered. Because these processes would destroy the glass, they are carried out prior to tempering.

The process of tempering float glass can cause a nickel sulfide inclusion to change from its normal state (known as a low-temperature structure) to a different high-temperature, crystalline structure. When the glass is cooled quickly (as part of the process) the NiS particle is unable to change back to its original form. Over a certain period of time NiS will slowly convert to the original low temperature structure. This means the NiS increases in size, and the mechanical stresses caused by this cause the tempered pane to shatter, for no apparent reason (hence spontaneous glass breakage).

NiS and spontaneous breakage: In various situations fully-tempered glass may break for no reason. Many factors might cause such spontaneous breakages, but the most common are nickel sulphide inclusions. Nickel sulphide inclusion, also known as NiS, occurs during the manufacturing process for float glass. In the glass batch, nickel-rich contaminants such as stainless steel might be present, and then combine with sulphur form nickel sulphide inclusions. Glass manufacturers take extraordinary steps to minimize the potential for nickel sulphide inclusions. Considering that a large furnace may produce up to 600 tons of glass per day, total elimination of contaminants is extremely difficult. When glass is heat-treated during successive stages, in order to obtain fully-tempered glass, nickel sulphide inclusions change in size from what is known as a low-temperature structure to a high-temperature, crystalline structure. When cooled quickly the NiS particle is unable to change back to its original form. Over a certain period of time NiS will slowly convert to the original form (LT) phase with an increase in volume of about 2 - 4%. Such increase of NiS will cause glass breakage.

The Achille Heel of Toughened Glass: nickel sulphide inclusions- More here.