Large, clear sheets of glass are a hallmark of many public spaces today. Transparent walls in entries, facades, and interior partitions have also become headline grabbers when people mistake them for open walkways and collide with them in high profile buildings.
In this article, Architect & Premises Safety Expert, Mark Monteith shares some of the most common types of glass used in transparent walls and panels, their related hazards, and the codes and standards that apply to their use.
Transparent Glass Panels: Doors, Facades, & Partitions - Expert Overview
The National Safety Council (NSC) and the National Glazing Association (NGA) introduced standards for safety glazing in 1966, following an increase in injuries, particularly in children. Following the NSC and NGA study, state and local jurisdictions began to adopt legislation making it unlawful to install or replace any non-safety glazing in areas identified as hazardous such as bathrooms, and near doors and stairs. By 1971, The Federal Government enacted similar legislation.
Today, most model building codes are in alignment on the hazardous locations requiring safety glazing. However, local property maintenance codes vary greatly in their treatment of existing non-safety glass. Some lack requirements for identifying this potential danger, while several cities and U.S. states now require postings or markings for transparent panels of any type in hazardous commercial locations to prevent impact injuries. Where non safety glass still remains, owners have a number of options. Here are some of them listed in order of decreasing cost:
- Replace older float glass with labeled safety glazing ($$$$)
- Install a 1 ½” bar at 36” height with ability to resist 50# / Linear Foot ($$$)
- Laminate glass with full panel protective safety film ($$)
- Apply posting, marking, decals, or etchings to improve visibility ($)
In 1966, the American National Standards Institute (ANSI) introduced specifications and methods of testing for transparent safety glazing material designed to promote safety and to reduce cutting and piercing injuries from human contact. These requirements included permanent markings with labels identifying compliance. They were later revised to include Consumer Product Safety Commission (CPSC) Standards for glass under 9 square feet and over 9 square feet.
Model building codes gradually aligned their definitions of the hazardous locations where safety glass would be required over the last fifty years. The International Building Code includes doors and glass within 24” of a door and less than 60” over a walking surface, with some exceptions. A fixed or operable transparent panel may be considered a hazardous location if it meets all of the following:
- The exposed area of an individual pane is greater than 9 square feet (0.84 m2).
- The bottom edge of the glazing is less than 18 inches (457 mm) above the floor.
- The top edge of the glazing is greater than 36 inches (914 mm) above the floor.
- One or more walking surface(s) are within 36 inches (914 mm), measured horizontally and in a straight line, of the plane of the glazing
Float & Annealed Glass
Cast over a bed of molten metal, float glass produces a very flat surface, and is not safety glass. Annealed glass is float glass made more stable through a controlled cooling process. While slightly stronger, it is not designed to withstand human impacts, and breaks into large, sharp pieces, causing both impact injuries and devastating secondary lacerations when someone recoils or falls into broken shards. Many incidents have resulted in nerve damage and fatal blood loss from walking or falling into float or annealed glass. It remains the most common type of glazing used in buildings today.
Tempered Safety Glazing
Tempered glass, developed in the late 19th century, is several times stronger than float glass and not as likely to break. When it does, surface stress added during the cooling process causes it to shatter into a web of small, rounded pieces that fall loose without long shards. Walking into this kind of safety glazing is more likely to result in injuries from direct impact or the resulting fall then in lacerations. Tempered glass is the most likely type of glazing to be found in locations considered hazardous in up-to-date commercial buildings.
Laminated Safety Glazing
Invented over 100 years ago, laminated glazing consists of two or more layers of glass plus a bonding interlayer that gives it additional strength and other properties. It can be manufactured as safety glazing when meeting applicable criteria. Under impact, the tempered layers tend to form web like cracking, but the pieces are held in place by the interlayer, usually preventing them from dropping out of the frame. Its combined properties of strength, safety, acoustics, and ability to hold together after impact have found use in larger glass walls, sound controlled spaces, auto windshields, facades, and balconies, where falling pieces could present another hazard. A person colliding with a fixed laminated panel is very unlikely to break it, or to be cut by loose shards, but could experience an impact injury and/or a fall to the floor.
PREMISES LIABILITY INVESTIGATIONS INVOLVING GLASS
Glass can be a safe building component when used in compliance with recognized standards and protected from human impact, but injuries still regularly occur. Old float or wired glass still in use where modern standards require safety glazing products; improperly installed replacement glass panels and tempered or heat strengthened glass which fail during use; and inadequately marked or protected glass panels which cannot be reliably identified can all result in injury. The premises safety experts at Robson Forensic have investigated many injuries involving pedestrian collisions with glass doors, windows, and other partitions.
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Architecture, Construction & Premises Safety Expert
Mark Monteith is a registered architect with extensive experience in the design, construction, and planning of structures and landscapes. His architectural experience includes academic campuses, museums, places of worship, national historic landmarks, theaters, municipal buildings, commercial properties, and residential structures. Over 25 years, Mark’s career included new construction, renovation, and campus and urban planning. His expertise extends to sustainable design, façade and building envelopes, building and site accessibility, construction documentation and administration, project management, and owner representation. Mark earned his Bachelor of Science from Penn State University, and is a Leadership in Energy & Environmental Design accredited professional and National Council of Architectural Registration Boards mentor.