Safety glass is a stronger, safer version of ordinary glass. It is often used in locations where harm due to breakage is likely, such as in cars and low windows.
It is found in the following two forms:
- Laminated safety glass is commonly found in car windshields. It is produced by bonding a resin or a thin, transparent plastic film, known as PVB, between multiple sheets of ordinary glass. When shattered, this type of glass will adhere to the plastic sheet and be held in place.Laminated safety glass is effective in blocking most ultraviolet radiation, as well as sound, and it’s also used in cutting boards, thermometers, and bullet-resistant bank windows.
- Tempered safety glass fractures parallel to its edge rather than perpendicular, and when it shatters, it breaks into small, rounded, generally safe pieces. It is created by heating glass to a high temperature and then rapidly cooling it to produce compression stress fractures on the surface, while retaining tension in the center. The glass is several times stronger as a result of the process, and it can withstand significantly higher temperatures. Tempered safety glass is commonly found in rear and side car windows, computer monitors, and storm doors. Unlike laminated safety glass, it cannot be custom-cut once it is formed.
Where in a home might you find it?
Laminated glass may sometimes be found in shower enclosures, but it’s generally uncommon in homes. Tempered glass appears more often and can be found in storm doors, skylights, sliding glass doors, and unsafe locations. Safety glass should be found in locations considered to be, according to the 2006 version of the International Residential Code (IRC), “subject to human impact.” It describes these locations, as well as their exceptions, in “R308.4 – Hazardous locations” under “Section R308 – Glazing” as the following:
R308.4: The Following Shall Be Considered Specific Hazardous Locations for the Purposes of Glazing:
- Glazing in swinging doors except jalousies
- Glazing in fixed and sliding panels of sliding door assemblies, and panels in sliding and bifold closet door assemblies.
- Glazing in storm doors.
- Glazing in all unframed swinging doors.
- Glazing in doors and enclosures for hot tubs, whirlpools, saunas, steam rooms, bathtubs, and showers. Glazing in any part of a building wall enclosing these compartments where the bottom exposed edge of the glazing is less than 60 inches measured vertically above any standing or walking surface.
- . Glazing in an individual fixed or operable panel adjacent to a door where the nearest vertical edge is within a 24-inch arc of the door in a closed position and whose bottom edge is less than 60 inches above the floor or walking surface.
- . Glazing in an individual fixed or operable panel, other than those locations described in Items 5 and 6 above, that meets all of the following conditions:
- Exposed area of an individual pane larger than 9 square feet.
- Bottom edge less than 18 inches above the floor.
- Top edge more than 36 inches above the floor.
- One or more walking surfaces within 36 inches horizontally of the glazing
- All glazing in railings regardless of an area or height above a walking surface. Included are structural baluster panels and nonstructural infill panels.
- Glazing in walls and fences enclosing indoor and outdoor swimming pools, hot tubs, and spas where the bottom edge of the glazing is less than 60 inches above a walking surface and within 60 inches horizontally of the water’s edge. This shall apply to single glazing and all panes in multiple glazing
- Glazing adjacent to stairways, landings and ramps within 36 inches horizontally of a walking surface when the exposed surface of the glass is less than 60 inches above the plane of the adjacent walking surface.
- Glazing adjacent to stairways within 60 inches horizontally of the bottom tread of a stairway in any direction when the exposed surface of the glass is less than 60 inches above the nose of the tread.
Exception: The following products, materials and uses are exempt from the above hazardous locations:
- Openings in doors through which a 3-inch sphere is unable to pass.
- Glazing in Section R308.4, Items 1, 6, or 7, in decorative glass.
- Glazing in Section R308.4, Item 6, when there is an intervening wall or other permanent barrier between the door and the glazing.
- Glazing in Section R308.4, Item 6, in walls perpendicular to the plane of the door in a closed position, other than the wall toward which the door swings when opened, or where access through the door is to a closet or storage area 3 feet or less in depth. Glazing in these applications shall comply with Section R308.4, Item 7.
- Glazing in Section R308.4, Items 7 and 10, when a protective bar is installed on the accessible side(s) of the glazing 36 inches ± 2 inches above the floor. The bar shall be capable of withstanding a horizontal load of 50 pounds per linear foot without contacting the glass and be a minimum of 1-1/2 inches in height.
- Outboard panes in insulating glass units and other multiple glazed panels in Section R308.4, Item 7, when the bottom edge of the glass is 25 feet or more above grade, a roof, walking surface, or other horizontal surfaces within 45 degrees of a horizontal surface adjacent to the glass exterior.
- Louvered windows and jalousies complying with the requirements of Section R308.2.
- Mirrors and other glass panels mounted or hung on a surface that provides a continuous backing support.
- Safety glazing in Section R308.4, Items 10 and 11, is not required where:
- the side of a stairway, landing or ramp has a guardrail or handrail, including balusters or infill panels, complying with the provisions of the handrail and guardrail requirements; and
- the plane of the glass is more than 18 inches from the railing; or
- when a solid wall or panel extends from the plane of the adjacent walking surface to 34 inches to 36 inches above the floor and the construction at the top of that wall or panel is capable of withstanding the same horizontal load as the protective bar
- . Glass block panels complying with Section R610.
How do you identify safety glass?
If safety glass is not specifically labeled as such, there are often signs that aid in its identification. Unfortunately, it may be impossible to identify ordinary glass with certainty without breaking it.
According to the IRC, tempered glass must contain an identifying label. It states that a label must be “acid-etched, sandblasted, ceramic-fired, laser-etched, embossed, or be of a type which, once applied, cannot be removed without being destroyed.” Tempered spandrel glass, an opaque glass found in commercial curtain walls, is exempt from this rule because an etched label can cause the entire panel to fracture.
Of multipane assemblies containing safety glass, the IRC states the following:
R308.1.1 Identification of multipane assemblies. Multipane assemblies having individual panes not exceeding 1 square foot in exposed area shall have at least one pane in the assembly identified in accordance with Section R308.1. All other panes in the assembly shall be labeled "16CFR1201."
Section R308.1 details identification as follows:
R308.1 Identification. Except as indicated in Section R308.1.1, each pane of glazing installed in hazardous locations as defined in Section R308.4 shall be provided with a manufacturer's or installer’s label designating the type and thickness of glass and the safety glazing standard with which it complies, which is visible in the final installation. The label shall be acid-etched, sandblasted, ceramicfired, embossed-mark, or shall be of a type which, once applied, cannot be removed without being destroyed.
Country-specific laws similarly require a permanent label on most or all safety glass. In the UK, for instance, tempered glass must include a “T,” and laminated glass must include an “L.” New Zealand requires, according to Clause 303.7 of NZS 4223:Part3:1999, that all safety glass have a label at the bottom that includes the following information:
- the name and registered trademark or code of the manufacturer or supplier;
- the type of safety glazing material. This may be in the form of a code, such as “T” for toughened glass, or “L” for laminated glass, as indicated by the relevant test Standard (refer to AS/NZS 2208);
- the Standard to which the safety glazing material has been tested, e.g. AS/NZS 2208;
- if applicable, the classification relating to impact test behaviour, i.e., A for Grade A, B for Grade B, or C for Grade C.
Laminated safety glass is often labeled, although codes do not always require it to be. An easy way to tell if unlabeled glass is laminated is by examining the reflection of your hand or some other object. As there are two pieces of glass, you should see two different images, but you must be careful not to confuse them with the inner and outer surfaces of a single sheet of ordinary glass. Laminated glass is also slightly thicker than ordinary glass, although this difference is difficult to discern without the aid of very precise measuring instruments.
Tempered glass can also be identified through polarized glasses when viewed from an angle. Black lines, a result of the heating and cooling process, should appear as your angle from the glass surface increases and you approach the glass’s side.
When uncertain, homeowners should always assume that glass is not safety glass.