Dear Glass Detective,
I am an importer and distributor of furniture that uses tempered glass from China. I have received increased calls over spontaneously exploding glass tabletops. What can I do to ensure, or lessen, the chance of this happening? The occurrence of this happening while someone is actually at the table scares me. So far, all reports have been when no one is in the room.
Let me begin by thanking you for making contact with the Glass Detective in regards to the problem you are encountering with exploding tempered glass tabletops. Specifically, you said that you are an importer and distributor of furniture products manufactured in China and that of late, you have been receiving an increasing number of calls about glass tops exploding spontaneously—meaning that they are exploding without any apparent reason. They are not being hit with something or having something dropped on them, rather, they are exploding “on their own”. You further stated that thus far no one has been reported as having been injured from this exploding glass problem but you did say that the situation “scares” you. And personally and professionally, I think I would be scared too!
While you did not identify the exact sizes of these exploding glass tops or their thicknesses, a piece of ½-inch tempered glass weighs approximately 6.5 pounds per square foot. This means that 48-inch by 48-inch tabletop glass would weigh over 100 pounds Even if the glass top were to break into small pieces as it breaks, the fact is that over 100 pounds of those broken pieces are going to fall onto something or someone. If this glass tabletop were loaded down with food, silverware, and dishes or perhaps even hot coffee or tea, real damage, and injury could occur. I really am not intending to be an alarmist or add to your concerns, but I do think your concerns need to be addressed and addressed soon.
I have seen this problem up close and personal. I was personally involved with the installation of over one hundred pieces of ½” tempered glass in an atrium glass railing project at a Chicago hotel a few years ago and after the project was completed, we started experiencing spontaneous glass breakage. Because the first few breaks occurred at night, the first thought was that they were being hit by something or someone such as the cleaning crew. No one was too concerned. Soon the rate of glass breakage increased and the glass was breaking during the night hours and during the day. When this tempered glass broke, it would explode out of the rail system and rain down into the lobby. Over a period of about eighteen months, over 20 pieces of ½” tempered railing glass exploded out of this railing system. I’m sure you can imagine the chaos this caused. We had applied a safety film to both sides of the glass railing pieces but the film was not totally successful in holding the glass together after it broke. There were a couple of injuries but fortunately, they were minor. Coincidently, this glass also had been imported.
After a fair amount of forensic analysis, it was determined that this breakage was occurring “spontaneously” due to imperfections in the glass (technically referred to as inclusions) that occur during the raw glass manufacturing process. Specifically, nickel sulfide inclusions may be developed or created when metal contaminants that are rich in nickel are accidentally mixed into the glass-melting furnaces during the time of glass processing. These metallic components can then combine with sulfur in the batch to create nickel sulfide inclusions which are the primary cause of what is commonly called spontaneous glass breakage. There are naturally other contaminants that will on rare occasions also make it into the mixing process but for the most part, these are not a problem. Believe it or not, there is even a standard (ASTM C 1036) that establishes maximum allowable levels for this inclusion situation.
The real trouble begins when glass is tempered. During tempering, these nickel sulfide inclusions tend to be altered into a state which allows them to expand as time and temperature impact the glass panel in which they are residing. This expansion can, over some period of time, create enough stress to cause the glass to break. Because it is tempered glass, when it breaks it will often explode all over the place into hundreds of small fragments. I have personally witnessed this and have seen some minor skin cuts and eye injuries caused by it. I have also served as an expert witness in a case involving this.
If you can somehow save the broken glass at the origin point of the break (and I have done this) you can then have the piece of glass, at the break origin point, examined under ultra-high magnification. Then you actually can see the nickel sulfide inclusion/stone in the glass. As an aside, historically, the thicker the glass, the more likely you are to have these tempered glass spontaneous breakage problems.
1. So now the question becomes, how do we prevent this? The somewhat bad news is that you probably cannot absolutely and permanently eliminate spontaneous breakage from occurring in tempered glass. But you can certainly greatly minimize it. First, you should only deal with high-quality manufacturers who have a reputation for quality and who have been in business for a reasonable period of time. The Glass Detective is a long-time believer in the old adage that “You get what you pay for.” It is as true with glass as it is with anything and everything else. Remember, all glass is not created (manufactured) equally!
2. There is a process known as glass heat soaking which takes tempered glass and reheats it to a level below the tempering point and then cools it under controlled conditions. Tempered glass with nickel sulfide inclusions in it will typically (or usually) break during this heat soaking procedure. In essence, this process causes the glass that will ultimately break, to break under controlled conditions before it is installed in a building or put into use as a glass tabletop or glass railing. Far better that it breaks during heat soaking than after it has been installed or while serving as someone’s kitchen table.
The heat soak process is not a 100% guarantee. It will reduce the possibility of spontaneous breakage but it cannot promise protection. It is also not free. So there is added cost to be considered. There are heat soak providers throughout North America that will gladly perform this work for you. If you need assistance in identifying suppliers for this, please reconnect with us and we can provide you with contact information. I wish you well with your future business endeavors and thank you again for contacting the Glass Detective with your question. I hope the information being provided is beneficial to you as you move forward.
The Glass Doctor has over 40 years of experience in the architectural glass and automotive glass industries. Got a custom glass question for the Glass Doctor? Ask him!