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What is Safety Glass?

Monday June 12th, 2023
Safety glass is an important type of glass because building codes require it in certain applications. These regulations apply to both commercial and residential building codes. Because of its importance, homeowners and business owners alike will benefit from knowing what safety glass is and the different types of safety glass options available. 

4 Types of Safety Glass 
  1. Tempered Glass
  2. Laminated Glass
  3. Wire Glass
  4. Bullet-proof glass 
Not only is it important to understand each type of safety glass, but it’s also essential to know where it’s commonly used and when it’s a legal requirement to use safety glass. By learning the ins and outs of safety glass, you can avoid building code violations and ensure your family or customers are in a safe environment. 

What is Safety Glass? 

Safety glass is used in areas where human safety is a concern. It refers to a few different types of glass, including laminated glass and tempered glass. What these glass types have in common is their strength and impact resistance, which makes them much harder to break than regular glass. If they do break, they are much safer to handle, as they either break into small harmless cubes (tempered glass) or stick to a plastic layer between the glass (laminated). 

Each type of safety glass differs from the others in how it’s made and its final structure. Some safety glass is stronger and more impact resistant than others. Furthermore, certain areas specific types of safety glass, while others will require safety glass but not a specific one. In this way, it’s highly important to become familiar with each type of safety glass, which we’ll dive into more detail about below. 

Safety glass has to meet specific requirements set forth by the International Building Code (IBC) for it to be classified as safety glass, also known as safety glazing. The glass is evaluated by putting it through a performance test to evaluate its impact resistance and breakpoint. 

Other strong and break-resistant glass types, such as heat-strengthened glass, are safer glass options than regular annealed glass but don’t qualify as safety glass. This is because heat-strengthened glass still breaks into large shards with sharp edges. 

In other words, the way the glass breaks is an essential component of safety glass. Imagine a commercial building with lots of people and large picture windows. Let’s say a fire or severe storm caused the windows to shatter. In this scenario, flying shards of sharp glass would be extremely dangerous. Safety glass ensures hazardous glass isn’t an issue, and is much safer when it comes to clean up. For these reasons, safety glass is a requirement for specific areas in a home or business. 

4 Types of Safety Glass 

1. Tempered Glass 

Tempered glass is one of the most commonly used types of safety glass. It is four times stronger, more heat resistant, and breaks differently than annealed glass. Tempered glass is also called toughened glass—these names are used interchangeably. 

Rather than shattering into jagged shards, as annealed glass does, tempered safety glass breaks into many small pieces with rounded edges. This type of broken glass is much safer to clean than large shards of sharp glass, and prevents injury when the glass breaks. Because of its strength, heat resistance, and the way it breaks, it is used in a variety of items, such as glass table tops and phone screens.  

How is Tempered Glass Made? 

Tempered safety glass is made from regular annealed glass that goes through an intense heating and cooling process. It can also be made with a chemical treatment. 

With the heat method, the annealed glass is first cut to size and inspected for imperfections that could affect the tempering process. After the glass is inspected, it is ready for tempering. Using a tempering oven, the glass is exposed to extreme heat with temperatures more than 1,000 degrees Fahrenheit. Then, the glass is immediately moved to an area for rapid cooling by a machine that blows frigid temperatures at it. This second half of the process, where the glass undergoes rapid cooling, is called quenching. 

Through exposure to extreme temperatures, the glass changes its structure. The outside of the glass cools much faster than the internal glass, creating tension, which causes surface compression for the outer layer. This tension causes the glass to become ‘tempered’ making it stronger and safer than annealed glass. 

Once the glass is tempered, it can’t be cut or edged down because it will cause the glass to lose its strength or shatter. This is a critical aspect of tempered glass to keep in mind, especially when ordering custom tempered glass windows, as the window glass will need to be the correct size and can’t be cut or resized after ordering. 

Heating is the most common way tempered glass is made, but glass can also be tempered with chemicals. This is referred to as chemical tempering, and occurs when various chemicals exchange ions on the glass surface to create surface compression. However, chemical tempering is much more costly than the heat method, so it is not widely used. 

How Strong is Tempered Glass? 

Tempered glass is thoroughly tested in order for it to qualify as safety glass. According to Federal Specification DD-G-1403B, tempered glass must have a minimum surface compression of 10,000 PSI or pounds per square inch and a minimum edge compression of 9,700 PSI. 

Given tempered glass’s PSI, its general breaking point in weight is 24,000 PSI, whereas annealed glass’ breaking point is 6,000 PSI. With its increased impact resistance, tempered glass can withstand much more wind pressure, about twice the amount as ordinary glass.

When it comes to heat and thermal stress, tempered safety glass can withstand much hotter and more extreme temperature changes when compared to annealed glass. Regular glass will crack or break when exposed to temperatures around 105 degrees Fahrenheit, whereas tempered glass has a temperature difference threshold of around 500 degrees Fahrenheit. Because of its incredible resistance to heat, thermal breakage is not as much of a concern with tempered glass. 

However, on rare occasions, temperature fluctuations can cause tempered glass to shatter spontaneously. During the heating and quelching process, the glass may have tiny particles, including nickel-sulfide, which can expand during heat treatment, halt expansion when cooled, and then continue expansion when the glass is exposed to high heat temperatures. This expansion can cause the glass to shatter, but it is extremely rare. This is why manufacturers take special care to inspect the glass before beginning the heat process. 

2. Laminated Glass 

Laminated glass is perhaps the top safety glass on the market today. While tempered glass is more commonly used, laminated glass is the top safety glass because it’s even stronger and safer than laminated glass. This is due to how laminated glass breaks and how it’s made. 

How is Laminated Glass Made? 

Laminated safety glass doesn’t shatter to the ground when broken, like annealed glass or even tempered glass. Rather, the broken glass stays suspended within the door or window frame. This is due to how it’s constructed: it’s made of two or more panes of glass joined together by a layer of polyvinyl butyral (PVB), a type of plastic. When broken, the glass sticks to the plastic interlayer between the glass. The PVB makes laminated safety glass much harder to break than regular annealed glass. While laminated glass isn’t considered shatterproof glass, it’s close to it with its shatter-resistant makeup.

This plastic interlayer also increases its impact resistance; it’s able to withstand extreme force, such as bullets and bombs. Plus, if the glass is to break, there isn’t a concern for flying or falling glass. Ultimately, this greatly protects the people inside buildings with prominent windows and skylights.

The type of glass used to create laminated glass can range from regular annealed glass to toughened glass. Laminated glass made with a heat strengthened glass, such as tempered glass, makes it that much safer, stronger, and more impact resistant.

Laminated glass ranges in safety, UV protection, strength, and more, depending on the type of plastic used between the glass and how many layers of glass/plastic is used. For example, laminated glass can be bulletproof glass, depending on how thick the glass is, how many layers of glass/plastic there are, and the type of plastic used. 

The most common interlayer material is PVB, but it can also be made with Ethylene Vinyl Acetate (EVA) and Thermoplastic Polyurethane (TPU). Usually, multiple layers of PVB, EVA, or TPU are used to increase the glass’s strength and above benefits. The layers of glass and PVB is written in millimeters to describe the thickness of the finished laminated glass. The thicker the glass, the stronger, safer, and more impact resistant it is. 

Furthermore, laminated safety glass has several benefits other than its increased safety and security. For starters, laminated glass can be cut after it’s manufactured, making it useful for home projects where the glass may need to be resized. It also has the benefit of reducing UV rays and noise, increasing insulation. These advantages stem from the plastic layer between the glass, which helps reduce heat transfer and sound waves. Its insulating abilities and UV protection can be increased by using Low E glass for your laminated glass. In this way, laminated glass is quite versatile and can be used for a variety of different appliances and projects. 

3. Wire Glass 

Wire glass is an interesting type of glass because it’s technically not considered safety glass; however, it is a fired rated glass. For building codes that require safety glass in a “hazardous” location, wire glass shouldn’t be used. But, wire glass is the most common and cost-effective fire-rated glass for areas that need fire protection. 

How is Wire Glass Made? 

Wire glass isn’t considered a type of safety glazing because it’s regular annealed glass that contains a wire mesh. During glass production, the wire mesh is placed in the molten glass, which then cools and hardens around the wire. Annealed glass isn’t strong enough to handle the impact of human weight, and could shatter more easily than tempered or laminated glass. Because of this, wire glass doesn’t have the strength or impact resistance required for it to be considered safety glass. 

That said, it is still safer than ordinary glass because if shattered, the broken glass is held in place by the metal wire. Moreover, wired glass is fire resistant because the wire within the glass holds the glass together when heat from the fire causes it to crack. Then, the heat causes the glass to melt and “heal” the cracks. The wire holds the glass in place throughout the process, preventing flame, smoke, and hot gasses to pass through it. Fire rated glass must also be able to withstand water pressure from a fire hose, which wired glass can withstand.  

If you’re interested in wired glass for a commercial building, you’ll want to check out the building codes for your area to ensure that wired glass meets the safety requirements for that area. To make it a safety glass that meets safety code requirements, it needs a special coating to strengthen it. If it needs a special coating, this can be done during the production phase, and must be factory-applied. Furthermore, wire glass can’t be tempered or heat-strengthened, but unlike tempered or heat-strengthened glass, a wired glass sheet can be cut after production. 

4. Bullet-proof Glass 

When it comes to safety glazing, you can’t get much better than bullet-proof glass. This glass type is more accurately called ballistic glass or bullet-resistant glass. The term “resistant” is more realistic than “proof” because there isn’t any type of glass or clear plastic material that is completely bulletproof. However, bullet-resistant glass is highly impact resistant, and can prevent the majority of ballistic assaults from penetrating the glass. 

How is Bullet-proof Glass Made? 

Bullet-proof glass is essentially laminated glass with multiple layers of plastic and glass. The plastic used may be polyvinyl butyral (PVB) or an even stronger type of plastic, and the glass is usually thicker than ordinary glass. Bullet-resistant glass may also be tempered, making it that much stronger and more impact resistant. 

The goal with ballistic glass is to have a tough outer layer of thick glass that helps stop the projectile, while the inner plastic layers flexes and absorbs the energy of the impact. The overall strength and flexibility of the bullet resistant glass will prevent it from shattering, and the plastic interlayers will hold the window or glass structure in place. The combination of the thick heat-strengthened glass and plastic interlayers makes bullet-proof glass a high-profile security glass used in areas where human safety is a top priority. 

Where Should Safety Glass Be Used? 

Safety glazing should be used in any area that is considered a “hazardous location.” The International Building Code (IBC) distinguishes seven hazardous locations that require safety glass. The locations refer to areas with door glass, window glass, glass in wet areas, and more. There are some exceptions to these requirements, so it’s important to research your local building codes for further information. 

1. Glass Doors

Glass doors usually require safety glass. As the IBC states, “Glazing in all fixed and operable panels of swinging, sliding, and bifold doors shall be considered a hazardous location.” The reason for this is that doors are part of “high-traffic areas,” and they experience frequent use. The glass in the door should be able to withstand the force of a slammed door and external forces, such as extreme weather. Because of this, tempered glass is usually used in glass doors. Furthermore, “glass within 24 inches horizontally from a door where the bottom of the glazing is less than 60 inches above the floor is considered a hazardous location.” This would include any windows near a door with the above dimensions. 

2. Large Windows

Large windows also require safety glass when they are “greater than nine square feet, are less than 18 inches from the floor, the top is greater than 36 inches from the floor, and the window is within 36 inches of a walking surface.” Any windows near stairways and ramps might have to have safety glazing as well. Specifically, if the bottom of the window is less than 60 inches above the walking surface, it is considered a hazardous location and must have safety glass. Similarly, large glass windows near the bottom of stairs may require safety glazing. 

3. Wet Areas

Glazing in wet areas usually has to be safety glazed, with a few exceptions. Most notably, shower doors, bathtubs, and shower enclosures must be made with safety glass. Tempered glass is commonly used in these settings. 

4. Other Applications 

Other areas where safety glass is commonly used and may be required include skylights, refrigerator shelving, glass table tops, safety eyewear, overhead glazing, a glass walking surface, glass railings, glass shelving, automobile windows, and glass display cases. 

Wired glass is commonly used in buildings that require fire protection and fire-resistant glass, such as hospitals, schools, and government buildings. 

While the above locations require the use of safety glazing or fire rated glass, you can also use safety glazing in areas that don’t necessarily require it. You can use safety glass whenever you want increased safety and security for your windows and doors. For example, safety glass can be used when you want security glass to prevent break-ins, or if you live in an area that experiences frequent severe storms. 

Is Safety Glass a Legal Requirement? 

Yes, safety glass is a legal requirement for any area that is considered a hazardous location. If your building isn’t “up to code,” you can face fines or other legal penalties. If you are building a new home or flipping a home, the building will need to be inspected to ensure it meets all building codes. If it doesn’t, you will have to fix the issue, or you may not be able to sell the home. The same applies to commercial buildings. For these reasons, it’s much better to be aware of safety glass requirements before you begin your project.  

Even if you are a homeowner just needing to replace a window, it’s important that your new window is up to code. This will prevent any issues that may arise in the future if you plan to sell your home. These codes are required for a reason: safety. By complying with building requirements, you create a safer environment for everyone and (and it is less of a hassle for yourself in the long run). 

It’s essential to research your local and federal building regulations to ensure that your building project is up to code. Furthermore, there are separate building regulations for commercial and residential buildings. Commercial buildings usually have stricter requirements for the use of safety glazing, so if you’re a business owner or commercial builder, it’s extra important to be well aware of commercial building codes for glass structures, doors, and windows. 

Examples of hazardous locations that legally require safety glass are listed above. As those codes are set forth by the International Building Code, they are more general. You may find more specific requirements depending on your state building codes. 

Using Safety Glass for Your Windows and Doors

After learning the ins and outs of safety glass, it’s no wonder why it’s such an important glass type to be aware of. Not only is safety glass a high-quality option for your windows and doors, but it’s also legally required in certain areas. Plus, with knowledge of each different glass type— including laminated, tempered, wired, and bullet-proof—you can make an informed decision on which safety glass is best for your project. 

If you’re planning on designing a quality glass door or custom window, check out the incredible selection and customization options Rustica has to offer. As specialty designers of high-quality doors and windows, we’re confident we have what you’re looking for. Whether you need a strong shower door with tempered glass or a custom window with laminated glass, we’ve got you covered. Contact Rustica’s design team to start creating your custom glass door or window with safety glass today! 

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