ANSI Z97.1 Safety Glazing: Impact Test, Classes, and Labeling

ANSI Z97.1 is the American National Standard that sets minimum safety performance requirements for glass and plastic glazing installed in buildings. The current edition, ANSI Z97.1-2015 (R2020), tells manufacturers how safety glazing must be tested, classified, and permanently marked before it can be installed anywhere a person might walk or fall into it. If you are specifying, installing, or inspecting glass in a door, shower, railing, or low window, this is the standard the product has to meet, and the permanent mark etched into the corner of the glass is how you confirm it.¹

What the Standard Covers

Four glazing types fall under ANSI Z97.1: fully tempered glass, laminated glass, organic-coated glass, and plastic glazing. Tempered glass is heat-treated so it fractures into small granular pieces instead of jagged shards. Laminated glass bonds a tough interlayer between two lites so the assembly holds together on impact. Organic-coated glass uses an applied film to keep fragments attached to the pane, and plastic glazing swaps the glass out for a polymer sheet.¹

The standard applies when any of these products becomes part of a building’s permanent structure. Furniture glass, freestanding decorative mirrors, and similar consumer items are outside its scope because they are not building components. The dividing line is installation: glass mounted in a wall, door, guard, or enclosure has to comply, and glass sitting on a coffee table does not.

Where Building Codes Require Safety Glazing

The International Building Code and International Residential Code identify “hazardous locations” where installed glazing must meet ANSI Z97.1 or its federal counterpart, 16 CFR 1201. These are places where a person is most likely to trip, slip, or collide with glass, and a building inspector will check every one of them.

All glass in swinging, sliding, and bifold doors, with narrow exceptions for openings too small to pass a 3-inch sphere.
Panels within 24 inches of a door edge, where the bottom of the glass is less than 60 inches above the floor.
Individual panes larger than 9 square feet where the bottom edge sits below 18 inches, the top edge is above 36 inches, and a walking surface is within 36 inches.
All glazing in guards or railings, regardless of size or height.
Glass in or near showers, bathtubs, hot tubs, saunas, steam rooms, and swimming pools where the bottom edge is less than 60 inches from the standing surface.
Glazing adjacent to stair landings, or along stairways and ramps, where the bottom edge is less than 36 inches above the walking surface.

Local jurisdictions sometimes expand these lists through amendments, so treat the model code as a floor. Anyone specifying glass for a specific project should confirm what the local building department requires on top of the IBC or IRC.

How the Impact Test Works

The core test simulates a person falling into a glass surface. A 100-pound leather bag filled with lead shot is suspended above a mounted specimen, pulled back, and released to swing into the center of the pane. The drop height sets the impact energy: 48 inches for the Class A test, about 400 foot-pounds; 18 inches for the Class B test, about 150 foot-pounds.²

Four specimens are tested. Products seeking the “Unlimited” size designation are tested at 34 by 76 inches, which is the standard’s full-size panel. Anything tested smaller earns only a “Limited” designation, and the minimum specimen size in that category is 16 by 30 inches.²

What Counts as a Pass

A specimen passes if one of three things happens on impact: the glass does not break, the glass breaks but the bag does not punch through the opening, or the glass breaks into fragments that meet strict weight limits. A specimen fails if the shot bag passes completely through, or if the breakage produces large dangerous shards.²

Fragment limits depend on the glass type. For tempered glass, technicians collect the 10 largest uncracked pieces within five minutes of impact. Together those 10 pieces cannot weigh more than the equivalent of 10 square inches of the original pane at its nominal thickness. In practice this forces tempered glass to crumble into small granular pieces rather than break into plates.²

For laminated and organic-coated glass, the test measures fragments that detach within three minutes of impact. Total detached weight cannot exceed the equivalent of 15.5 square inches of the specimen, and no single detached piece can exceed the equivalent of 6.82 square inches. Particles smaller than one square inch are excluded from the count. The interlayer or coating is doing its job if virtually all the broken glass stays stuck together.²

Class A, Class B, and the Size Letter

Every certified product carries a two-part rating: a performance class and a size designation.

Class A products passed the 48-inch drop, roughly 400 foot-pounds of force. Class A is required for higher-risk locations including shower and bathtub enclosures, sliding patio doors, and any door containing glazing larger than 9 square feet. Class B products passed the 18-inch drop, roughly 150 foot-pounds, and are acceptable for storm doors and other doors where no single lite exceeds 9 square feet.²

The size letter tells you how the product was tested. “U” (Unlimited) means the specimen was tested at 34 by 76 inches, the full-size panel, so the product can be used at any size. “L” (Limited) means the manufacturer tested at a smaller dimension and the product can only be installed in openings no larger than the tested specimen.³ A “UA” mark is the strongest rating available: full-size, highest impact. “LB” is a smaller specimen that passed the lower impact test.

Durability and Weathering

Passing the impact test is not enough. Laminated glass has to survive a boil test that stresses the interlayer. Three 12-by-12-inch specimens are soaked in 150°F water for three minutes, then transferred to boiling water for two hours. Afterward, no bubbles or defects can appear more than half an inch from the edge of the specimen. If the interlayer starts separating under that heat and humidity, the product is not fit for long-term service.²

Plastic and organic-coated glazing face weathering tests that simulate years of sun exposure. For exterior applications, the standard accepts either one year of natural outdoor exposure in South Florida or 3,000 hours in a xenon-arc accelerated weathering chamber. Indoor-only products go through a similar 3,000-hour xenon-arc cycle at lower intensity with no water spray. After weathering, a Charpy impact test measures the material’s residual strength; a drop of more than 25 percent from unexposed samples fails the product, as does any visible bubbling or degradation.²

Reading the Permanent Label

Every piece of safety glazing has to carry a permanent mark, often called the “bug,” that a building inspector can read after installation. The mark has to be etched, sandblasted, fired, or otherwise permanently affixed so it cannot be peeled off or washed away. A temporary adhesive sticker does not satisfy the requirement.⁴

A compliant permanent label contains:

The manufacturer’s name or trademark.³
The standard designation, “ANSI Z97.1-2015” and/or “16 CFR 1201,” depending on which standards the product is certified to.⁴
The size and class, written as the U or L letter followed by the A or B class, such as “UA” or “LB.”⁴
The nominal thickness of the glass, though laminated products certified through SGCC are no longer required to include it.⁴
The SGCC certification number, if the product carries that certification.

Organic-coated glass that was tested from one side only for environmental exposure has extra labeling obligations. The coating side must carry a permanent “GLAZE THIS SIDE IN” instruction, and a temporary message at least a quarter-inch tall reading “SEE PERMANENT LABEL FOR IMPORTANT MOUNTING INSTRUCTIONS” has to cover the central half of the glass surface until the installer removes it.⁵

One installation trap catches fabricators making insulated glass units. When individual lites are assembled into double- or triple-pane units, the original safety mark on each lite has to stay visible after fabrication. If the framing or spacer bar covers the bug, the unit will fail inspection. Mark placement needs to be planned before assembly to avoid a costly tearout.

Third-Party Certification Through SGCC

The Safety Glazing Certification Council runs the primary third-party program for products tested to ANSI Z97.1. SGCC certification is not strictly required by the standard, but many building departments and specifiers treat it as the practical proof of compliance because it adds independent verification on top of the manufacturer’s own test results.⁶

To earn initial certification, a manufacturer submits passing test reports from an SGCC-approved laboratory for each product thickness it wants certified. Once the reports pass review and fees are paid, SGCC assigns a certification number and authorizes use of the SGCC logo on products of the same fabrication as the tested samples.⁶ SGCC inspectors then visit each plant twice a year to select production samples off the line and ship them to an approved lab for re-testing.⁷ A facility can lose certification for failing re-tests or improperly labeling its products.

How ANSI Z97.1 Relates to 16 CFR 1201

ANSI Z97.1 is a voluntary consensus standard. The federal regulation that makes safety glazing legally mandatory for consumer products is 16 CFR 1201, enforced by the Consumer Product Safety Commission. In practice the two overlap almost completely, because 16 CFR 1201 requires products to be tested “in accordance with all of the applicable test provisions of ANSI Z97.1-2015.”⁸

The main terminology difference is that 16 CFR 1201 historically used “Category” while ANSI Z97.1 uses “Class.” CPSC aligned the two in 2016, so Category I is now explicitly Class B and Category II is Class A.⁹ Under 16 CFR 1201, Category I covers storm doors, combination doors, and other doors where no single lite exceeds 9 square feet. Category II covers shower and bathtub enclosures, sliding patio doors, and any door containing a lite larger than 9 square feet.⁸ Because the test methods are now identical, a product certified to Class A automatically satisfies Category II, and labels often list both designations side by side.

Wired Glass and the End of Class C

Traditional wired glass — the kind with a visible wire mesh embedded in it — has long been used in fire-rated door assemblies. Under 16 CFR 1201, wired glass installed in fire doors required by local fire codes is explicitly exempt from impact testing requirements.⁸ The exemption exists because wired glass historically could not pass the standard impact tests; the wire mesh actually makes it more dangerous on impact, producing jagged shards held together by wire.

Older versions of ANSI Z97.1 included a Class C rating with a lower 100-foot-pound impact threshold that some wired glass could meet. The 2015 edition eliminated Class C entirely, so all safety glazing now has to pass either Class A or Class B.⁹ Modern fire-rated products, including ceramic glass and filmed glass assemblies, can satisfy both fire resistance and impact safety at the same time. Traditional wired glass remains legal in fire assemblies under the federal exemption, but it cannot carry an ANSI Z97.1 safety rating.

1
The ANSI Blog. ANSI Z97.1 and Safety Glazing Material Markings
2
City of Detroit. ANSI Z97.1-2015 Safety Performance Specifications and Methods of Test
3
Safety Glazing Certification Council. SGCC Implementation of New ANSI Z97.1 2015
4
Safety Glazing Certification Council. SGCC Label Requirements
5
eCFR. 16 CFR 1201.5 – Labeling
6
Safety Glazing Certification Council. Get SGCC Certified
7
Safety Glazing Certification Council. Notice of Changes to Certification – Coated Glass Guidelines
8
eCFR. 16 CFR Part 1201 – Safety Standard for Architectural Glazing Materials
9
Federal Register. Safety Standard for Architectural Glazing Materials