Safety glass: Is it doing what you think it does?
The term safety glass inspires confidence, however sometimes that confidence is not really justified. The problem lies in the difference between what safety glass is designed to do, and what you might think it does.
Since the late 1960’s, good people at such organizations as ANSI, CPSC and other groups have worked hard to develop and test safety glass standards with the goal of making the public safer. But safer from what?
Safety glass standards ANSI Z97.1 and CPSC 16 CFR 1201 are all about reducing the risk of death and laceration in the event you fall through and break the glass. Such an accident can easily happen if you were to walk through a glass door lite or slip in the shower and fall against a glass shower enclosure. In fact, thousands of these occurrences prompted the development of the safety glazing standards.
Safety glazing standards have done a very good job of substantially reducing the number and severity of broken window and door glass laceration injuries and deaths via two strategies:
- Using tempered safety glass which breaks in very small pieces when broken, and
- Using laminated safety glass which holds together even if the glass is broken
In architectural applications, tempered glass and laminated glass can be used interchangeably when the only criterion is the need for safety glazing. But they behave quite differently and because of this, they are not equally safe in all situations.
For instance, consider a 10th floor balcony glass handrail.
Let’s say the glass breaks for whatever reason (and tempered glass does have the ability to break spontaneously, even when nobody is around). If the glass is tempered, hundreds of small glass cubes will spray out onto the street with the first gust of wind. How safe is the pedestrian who is showered by a rain of glass cubes? Will they get in her eyes?
But wait, those cubes don’t always fully disengage from one another. Sometimes the cubes of the “safety glass” cling to one another in clumps like tiny puzzle pieces. How safe is the pedestrian who is hit by one of these clumps? The edges of the clumps are jagged and abrasive as a hack saw blade.
What about the child running around the balcony unaware that some of the glass handrail is missing? Eric Clapton’s 6 year old son Colin died in this type of tragedy. He ran right through an open floor-level window.
What about laminated safety glass? If it stays affixed in the railing framing, things look pretty good, right?
But what if the laminated safety glass is not affixed well and takes flight like a flying carpet? Would you take your chances as a pedestrian below that? Anna Flores lost her life in 1999 in Chicago when a large piece of glass took flight and sailed across Wabash Street, over the elevated train tracks, impacting her in the head as she walked with her daughter.
And what of people on the balcony with the full laminated lite missing? Absent the visual cues of a few shards remaining around the edges of the frame, even an adult might not notice that the railing is no longer a safety barrier.
The info-graphic above illustrates the distinctly different hazard profiles of tempered and laminated safety glass using a glass handrail as an example, even though both are considered safety glass. The conclusion is quite simple: if the glass stays together and in the frame, a very good degree of safety exists even if the glass is completely broken.
What Doesn’t Safety Glass Do?
Safety glass is not designed to prevent you from falling through the glass. It is also not designed to prevent the broken glass from falling out and injuring people who might be below a broken window or balcony railing glass.
That being said, properties of tempered glass and laminated glass will reduce such occurrences. For instance, tempered glass is considered to be 4-5 times stronger for resisting uniform loads than annealed glass. This greater strength will reduce the chance you will break, and therefore break through the glass door when you walk into it.
Laminated glass will do a better job of keeping you from falling through the glass even if it breaks, but there is no guarantee that the heavy “wet blanket” of glass will stay in the opening, because that is not part of the design of safety glass.
Conclusion: “Safety Glass” needs an expanded definition
The limited definition of “safety glass” as a product that causes fewer serious lacerations when broken has reached a point of obsolescence. We need to move in a direction where a broader concept of glass safety becomes the new definition. In this new definition, glass safety will mean protecting people from not only cuts, but also from falling through the glass, and keeping the glass in the frame so it does not fall on people below.
Mark Meshulam, Chicago Window Expert was recently featured in this TV news story from KDKA-CBS Pittsburgh. See it here: How Safe Is The Glass Used In Doors And Window? Be sure to watch the video.
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If you are interested in learning more about nickel sulfide inclusions that can spontaneously shatter temper glass, see this photo album: Nickel Sulfide Inclusion: A tiny speck that destroys tempered glass
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11 thoughts on “Safety Glass: Is It Really Safe?”
Congratulations to Susan Koeppen and the KDKA production team for an excellent piece on glass safety. See it here and be sure to watch the video:
How Safe Is The Glass Used In Doors And Window?
This article is very informative but it makes me ask – “what is the solution?”. Is the answer to stop specifying floor to ceiling glass and glass balcony guards? I have heard of a new laminated glass product that is starting to be used for guardrails. Here the lamination holds the glass in place and does not behave like a wet blanket. But how do you handle floor to ceiling glass in a window?
If you have an existing structure with this problem a 3M security / safety film with a wet glaze or mechanical attachment system would be a cost effective solution.
Typical applications for bent laminated glass include railing systems, elevator and revolving door enclosures, skylight and overhead glazing, and interior partitions. In addition to minimizing risk of injury from broken glass fragments, bent laminated glass is effective in security areas, reduces sound transmission, blocks potentially harmful ultra-violet light rays, and is available in a range of color tints.
In the event of safety laminated glass breaking, it is held in place by the interlayer of transparent plastic. These intermediate layers keeps glass bonded even when broken, and its high strength prevents the glass from breaking up into large sharp pieces.
The association just installed all glass balconies. They refuse to tell me if it is ok to actually go out on mine as of yet. They are literally avoiding my calls and messages. The originally sealed balcony door has since been opened which led me to think I could go out. I notice that there are openings between glass squares, not on all of them…just a few? They are about an inch wide. Is this normal? How can I tell if my balcony is safe and ready for use?
Gaps in the railing glass under 4″ are sometimes designed into the product but to know if your specific railings are ready for prime time requires the OK of a professional who understands these things.
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Awesome article on glass safety. A very important point that you mention, “even though the glass is laminated the glass glazing should be it properly done to avoid accidents.”
Hi, I liked your article. I have four french doors that have Low E Tempered Safety Glass. I also have an appointment to have #M security film put on the doors to help in case of attempted robberies. Do I need both? Thanks!
My wife and I have been thinking of installing tempered glass in our home. I did not know that the tempered glass was safer than the regular glass because it breaks in smaller pieces. We want to make sure our house is as safe as possible while still looking good and tempered glass helps with that.