How to Make Safety Glass

You make safety glass primarily in two ways: by tempering annealed glass with heat and rapid quenching to lock in surface compression, or by laminating two or more glass sheets with a polymer interlayer under heat and pressure. For most non‑industrial settings, only lamination (often using EVA film with vacuum bagging) is realistically achievable; tempering requires specialized furnaces and rigorous quality controls. Below, we explain both methods step by step, including tools, standards, and safety considerations.

What Counts as “Safety Glass” and Where It’s Required

Safety glass is designed to reduce the risk of injury from breakage. Tempered glass crumbles into small, relatively blunt fragments; laminated glass holds together via its interlayer even when cracked. Building codes typically require safety glass in doors, showers, railings, skylights, and other “hazardous locations.” Compliance is verified by impact tests and product markings.

The Two Primary Methods

Tempered (Toughened) Glass

Tempered glass is produced by heating cut, edge‑finished annealed glass to around 620–650°C and then rapidly quenching it with high‑velocity air. The process creates a surface compression layer that makes the glass several times stronger than annealed glass and causes it to fragment into “dice” upon failure.

Laminated Glass

Laminated glass sandwiches a polymer interlayer—commonly PVB, EVA, or ionoplast (e.g., SGP)—between glass plies. Heat and pressure bond the stack so that broken shards adhere to the interlayer, maintaining residual integrity for safety, security, and acoustic performance.

Tools, Equipment, and Materials

Whether you temper or laminate, the right equipment and materials are essential. The list below outlines what’s typically used in industrial and small‑shop settings.

• Glass: Float (annealed) sheets, sized and edged to final dimensions before any tempering; thickness commonly 3–12 mm.
• Cutting and finishing: CNC or manual cutting table, waterjet for holes/notches, seaming or polishing tools, and washing/drying line.
• Tempering: Convection tempering furnace with quench section (air knives), optional heat‑soak oven per EN 14179 to mitigate nickel sulfide inclusion breakage.
• Lamination: Cleanroom or clean area, dehumidified storage (especially for PVB), layup table, nip rollers or vacuum de‑airing, and an autoclave; or EVA vacuum‑bag oven for small‑scale work without autoclave.
• Interlayers: PVB (0.38 mm typical; 0.76 mm for higher impact), EVA (0.38–0.76 mm), ionoplast/SGP (0.89 mm+ for structural), acoustic PVB, or specialty films.
• Quality control: Polariscopes for stress, pendulum impact rig (EN 12600) or drop ball, fragmentation boxes, thickness and bow gauges, haze meter for laminated transparency.
• Safety gear: Cut‑resistant gloves, eye/face protection, respirator for fine silica dust, heat PPE near furnaces/autoclaves, and proper lifting equipment for panes.

Together, these tools and materials enable consistent, code‑compliant safety glass production; industrial tempering requires the largest capital outlay, while EVA lamination enables lower‑volume shops to produce safety glazing.

Process 1: Tempered (Toughened) Glass

Tempering is a tightly controlled thermal process; every cutout or edge detail must be completed before the heat cycle because tempered glass cannot be cut or drilled afterward.

1. Specify and cut: Select float glass thickness appropriate for load and span. Cut to net size; add all holes and notches. Keep hole centers at least 2× glass thickness from edges; hole diameter typically ≥ glass thickness; inside corner radii ideally ≥ 1.5× thickness.
2. Edge finishing: Seam or polish edges to remove micro‑cracks that can trigger failure during tempering and service.
3. Wash and dry: Use a deionized water washer and dryer; avoid fingerprints and debris that cause anisotropy marks or breakage.
4. Load furnace: Place panes on ceramic rollers. Heat to ~620–650°C until the core reaches temperature (soak time depends on thickness and furnace type).
5. Quench: Transfer immediately to the quench section; impinge high‑velocity air to rapidly cool surfaces while the core cools more slowly, forming surface compression and core tension.
6. Optional heat soak: For critical facades, perform EN 14179 heat‑soak testing (~290°C hold) to reduce spontaneous breakage risk from nickel sulfide inclusions.
7. Inspect and stamp: Check fragmentation (a 100×100 mm area should contain sufficient small particles per ANSI/EN criteria), bow/warp, roller wave, and surface defects; permanently mark with standard and manufacturer ID.

If executed correctly, tempered glass delivers high impact resistance and safe fragmentation, but all post‑tempering machining is prohibited, and visual anisotropy (strain patterns) is normal under polarized light.

Process 2: Laminated Glass

Lamination bonds two or more plies with a polymer that retains fragments after breakage and can add acoustic, UV, or structural performance. PVB typically requires humidity control and an autoclave; EVA can be processed with vacuum bagging for small batches.

1. Condition materials: Store PVB at ~20–25°C and 20–30% RH; keep glass and interlayers clean and free of dust.
2. Prepare plies: Cut and edge glass to final size. Wash and dry thoroughly; handle with gloves in a clean area.
3. Layup: Stack glass–interlayer–glass (or multi‑ply) on a clean table. Overhang interlayer slightly for later trimming. Insert alignment pins if needed.
4. De‑airing:

   • PVB/SGP line: Use heated nip rollers to tack layers and purge air; optionally employ vacuum rings.
   • EVA method: Enclose the stack in a silicone vacuum bag or vacuum membrane; pull vacuum to remove air.

5. Bonding:

   • Autoclave (PVB/SGP): Heat to ~130–145°C at ~0.8–1.3 MPa (8–13 bar) for 30–60 minutes, depending on thickness and load; then cool under pressure.
   • EVA oven: Heat to ~120–140°C for 60–120 minutes under vacuum, then cool before releasing vacuum.

6. Trim and finish: Remove interlayer squeeze‑out, clean edges, and inspect for bubbles, haze, or delamination.
7. Test and mark: Verify impact rating (e.g., EN 12600 or CPSC 16 CFR 1201 Category I/II), shear modulus needs for structural applications, and apply permanent marking.

Laminated glass remains intact when cracked, making it essential for overhead glazing, balustrades with redundancy, and security products; interlayer choice (standard PVB, acoustic PVB, EVA, or ionoplast) should match the performance required.

Process 3: Chemically Strengthened Glass (Specialized)

Chemical strengthening uses ion exchange to create a deep compressive layer, particularly valuable for very thin or complexly shaped glass. On its own, it does not usually meet impact “safety glass” requirements and is often combined with lamination.

1. Prepare glass: Clean, edge, and finish all features; typically soda‑lime or aluminosilicate compositions.
2. Ion exchange: Submerge glass in a molten potassium nitrate bath at roughly 380–450°C for several hours; larger K+ ions replace Na+ in the surface, inducing compression.
3. Rinse and tempering alternative: Rinse, cool, and test surface compression (common targets for soda‑lime are ~100–200 MPa, deeper layers for aluminosilicate).
4. Laminate if needed: Combine chemically strengthened plies with a polymer interlayer to achieve safety glazing performance and certification.

This process yields high scratch resistance and strength in thin sections (e.g., consumer electronics or specialty architectural parts), but certification as safety glazing generally requires lamination and testing.

Quality Control, Testing, and Certification

Regulatory compliance varies by region and application; testing verifies impact performance, fragmentation, and durability. The following standards are commonly referenced in 2024.

• United States: CPSC 16 CFR 1201 (Cat I/II), ANSI Z97.1; labeling is mandatory for safety glazing in hazardous locations.
• Europe/UK: EN 12150 (tempered), EN 14449 (laminated), EN 12600 (pendulum impact), EN 14179 (heat soak); UK transitioned from BS 6206 to EN standards.
• Australia/NZ: AS/NZS 2208; Canada: CAN/CGSB 12.1; other regions have comparable codes.
• Factory controls: Fragmentation counts, pendulum or drop‑ball impact tests, edge quality checks, bow/warp and roller wave tolerances, haze and bubble inspection for laminates.

Using the correct standards and documenting test results are essential for code approval and for long‑term performance in service.

Safety, Handling, and Design Notes

Glass fabrication entails high heat, heavy loads, and sharp edges; safe practices and sound design rules reduce breakage and injuries.

• Edges first: Most tempered failures originate at poor edges; ensure proper seaming/polishing and adequate hole/edge distances.
• No post‑processing: Never cut, drill, or sand tempered glass. All fabrication occurs before tempering.
• Thermal considerations: Dark frits or coatings can create thermal stress; consult furnace recipes and glass processor guidance.
• Lamination environment: Control dust and humidity; PVB is hygroscopic and requires dehumidified handling.
• Support and installation: Allow for building movement and edge clearances; use compatible sealants to avoid interlayer edge defects.
• PPE and lifting: Use glass lifters, A‑frames, and proper PPE; follow lockout/tagout on furnaces and autoclaves.

Attention to these fundamentals prevents costly failures and helps ensure consistent, safe outcomes from furnace to installation.

Common Pitfalls and How to Avoid Them

Many quality issues trace back to preparation errors, environmental control, or pushing process limits. Watch for the following.

• Nickel sulfide inclusions: Use certified raw glass, consider heat‑soak for critical facades, and design redundancy where possible.
• Bubbles/haze in laminates: Improve cleaning, de‑airing, and autoclave cycles; manage PVB moisture and layup cleanliness.
• Edge lift/delamination: Seal edges from moisture, avoid incompatible sealants, and ensure proper interlayer trimming.
• Roller wave and bow: Optimize furnace loading, temperature uniformity, and quench balance to reduce optical distortion.
• Anisotropy visibility: Adjust quench, use low‑strain recipes, and set client expectations about polarization artifacts.

Proactive process control and realistic specifications help minimize these risks and protect both safety and aesthetics.

Feasibility: DIY vs. Professional Production

Fully compliant tempered glass production is an industrial process; small shops and DIYers should not attempt it. However, small‑scale laminated safety glass is achievable with proper equipment and care.

• Not DIY: Tempering requires a certified furnace, quench, and QA testing; improper tempering is dangerous.
• Possible DIY: EVA vacuum‑bag lamination can produce small safety panels; still adhere to standards and seek testing if used in regulated applications.
• When to outsource: Any glazing in doors, railings, overhead, or code‑regulated locations should be sourced from certified processors with documented test data.

Choosing the right fabrication route and partner ensures code compliance and reduces liability in safety‑critical applications.

Costs, Lead Times, and End‑of‑Life

Budget and project timelines depend on the method and performance level.

• Cost drivers: Interlayer type and thickness, coatings, edgework, holes/notches, and heat‑soak testing add to price.
• Lead times: Tempered glass often ships in days to weeks; laminated glass may require longer due to autoclave schedules and QC.
• Recycling: Tempered glass is difficult to recycle into float; laminated glass requires delamination. Design for maintenance and replacement.

Planning for fabrication complexity and future serviceability helps manage total lifecycle costs while maintaining safety.

Key Takeaways

Making safety glass means either tempering annealed glass to induce surface compression or laminating glass plies with a robust interlayer. Tempering is industrial and cannot be done after cutting; lamination can be scaled from autoclave lines to small EVA setups. Meeting regional standards—such as ANSI Z97.1, CPSC 16 CFR 1201, EN 12150/12600/14449—is non‑negotiable for code compliance. Prioritize edge quality, cleanliness, and process control to ensure reliable, safe performance.

Summary: Tempered glass offers high strength and safe fragmentation, while laminated glass provides post‑breakage integrity and broader functionality. Choose the method based on application and regulatory demands, and use certified processes and testing to deliver truly “safety” glass.

Can you cut safety glass with a glass cutter?

All right then you just want to put some firm pressure down across the glass. Being it is safety glass you’re going to have to cut both sides of glass. So you hear that.

How to make glass shatterproof?

To make glass “shatterproof” or, more accurately, shatter-resistant, you can apply a high-performance security film, replace existing glass with tempered or laminated glass, or upgrade to polycarbonate glazing. Security films hold broken glass shards together to prevent injury, while tempered glass is strengthened through a heating and cooling process that makes it up to five times stronger and causes it to break into dull clumps instead of sharp pieces. Laminated glass, which involves sandwiching a plastic layer between two panes of glass, is even stronger and also holds shattered pieces together. 
Apply a Security Film 

1. Choose a Film: Select a high-performance security or safety film, which is a cost-effective way to improve existing glass. 
2. Apply the Film: Carefully apply the film to the surface of the glass. The film acts as an extra layer, preventing the glass from shattering into dangerous fragments. 
3. Results: The film makes the glass harder to break and ensures that any broken pieces remain held together by the film, increasing safety. 

Upgrade to Stronger Glass 

• Tempered Glass: Opens in new tabThis type of glass is treated with heat and rapid cooling to create a surface layer that is strong and resistant to external forces. 
• Laminated Glass: Opens in new tabThis involves placing a plastic interlayer, such as polyvinyl butyral (PVB), between two panes of glass. The plastic holds the pieces together if the glass breaks, resembling the structure of a sandwich. 
• Polycarbonate Glazing: Opens in new tabFor maximum impact resistance, especially in certain high-security applications, plastic-based polycarbonate can be used instead of glass. 

Consider Both Options

• Layered Security: For enhanced safety, you can combine methods, such as using laminated glass with a security film applied to its surface. 
• Professional Installation: Upgrading to tempered or laminated glass is best done by a professional. 
• DIY Option: Some DIY processes can laminate glass using plastic film, binder clips, and a toaster oven, but this is for experimental or small-scale projects. 

Can you add a film to glass to make it safety glass?

Among the most universally-applicable options for window protection film is 3M™ Scotchshield™ Safety & Security Window Films. Available for residential and commercial applications, this product line mitigates hazards from shattered glass during natural disasters, blasts, or forced entry.

How is safety glass made?

Safety glass is made using two primary methods: lamination, where two panes of glass are bonded together with a plastic interlayer, and tempering, a heat treatment that makes a single pane of glass shatter into small, blunt pieces. Laminated glass holds together on impact, while tempered glass breaks safely into granular pieces, with both processes designed to reduce the risk of injury from broken glass.
 
Laminated Glass
This type of safety glass consists of two or more sheets of ordinary glass with a plastic interlayer, often polyvinyl butyral (PVB), sandwiched between them. The layers are then bonded together under heat and pressure, forming a composite that is stronger and stiffer than a single sheet of glass. When laminated glass breaks, the plastic layer holds the shattered pieces of glass together, preventing them from flying and causing harm. 
Tempered Glass
This process uses controlled thermal or chemical treatments to increase the strength of a single piece of glass. 

• Thermal Tempering: Opens in new tabThe glass is heated to a high temperature (above its glass transition temperature) and then rapidly cooled with forced air (quenched). This process creates balanced internal stresses, making the glass five to ten times stronger than annealed glass.
• Chemical Toughening: Opens in new tabAn alternative chemical process involves immersing glass in a molten salt bath to exchange smaller sodium ions with larger potassium ions, forcing the glass surface into compression.

When tempered glass breaks, instead of shattering into large, sharp shards, it crumbles into small, blunt, cube-like pieces. This significantly reduces the risk of injury compared to regular glass. 
This video explains how tempered glass is made and its characteristics: 1mHow It’s Made ArchiveYouTube · Jul 10, 2016