In this article, Architect and Premises Safety Expert, Anthony Shinsky, NCARB, AIA discusses the use of glass in buildings and the premises safety implications. His discussion covers the various categories of glass, the use of glass in windows, doors, and partitions, and relevant safety standards.
BUILDING GLASS AND GLAZING SAFETY
Glass is one of the most used materials in buildings and has been for the last 100 years. While commercially popular, some types of modern building glass may represent a serious danger.
Types of modern glass include:
- Annealed Glass (Float Glass) is ordinary glass that is cut into “stock sheets” for packaging and shipping. It can be cut again. It breaks into sharp shards.
- Heat Strengthened Glass (H.S. Glass) is annealed glass that goes through a heating and cooling process designed to double its strength in comparison to ordinary annealed glass.
- Laminated Glass has two separate pieces of annealed, heat strengthened or tempered glass sandwiched around a layer of clear polyvinyl butaryl (PVB). …It is a safety glazing product. One side can shatter from impact without the other side shattering, and, when the glass shatters, it does not delaminate into shards…
- Tempered Glass is created during manufacture by rapidly cooling the outer surfaces of the glass while the inner portion remains viscous. … The result is a piece of glass that is four times more resistant to impact than annealed glass. When tempered glass breaks, it fractures perpendicular to the plane of the surface, rather than parallel to it, resulting in small cubes that are less likely to cause significant injury…
Float glass was the most common type of glass used in buildings until recent times. Depending on its age, condition and thickness, float glass can break and shatter under human impact. When it shatters, float glass breaks into shards that are sharp and pointed. These shards can easily cut flesh and tendons, and the results can be severe or even deadly.
According to the National Safety Council, hundreds of people are injured each year through their encounter with broken float glass. When someone impacts float glass, the danger is twofold. The first is the likelihood of being cut during the impact; the second involves the instincts of many people to pull their body, arm, or leg away from the glass. As the injured person recoils, the pointed shards can make deep lacerations that can be life threatening.
As far back as the 1960’s there was recognition that float glass was a dangerous product when used in locations where human impact loads were foreseeable. A combined study by the National Safety Council (NSC) and the National Glazing Association (NGA) of that time period found that greater than 300,000 people a year were being injured through glass impact incidents.
Glass safety standards were developed that aimed at curbing this trend. Many states issued regulations requiring safety glazing in the 1960’s and building codes began incorporating requirements for safety glazing in certain building areas. In 1966 the ANSI Z97.1 standard for transparent safety glazing materials used in buildings was developed and adopted as a National standard. ANSI Z97.1 included test criteria for glazing that was designed to mimic human impact loads.
First produced in Europe, wired glass was introduced to the United States in or around 1890. Wired glass was one of the first products to be used as a “safety glass”. While not as strong as the later developed annealed or tempered glass, wired glass was used for over 50 years in windows in doors and along corridors, and those areas required to provide fire separation protection. Written into fire and life safety codes for much of those 50 years, wired glass can still be found in buildings today.
Wired glass is less strong than float glass. Under impact, body parts can break the glass, and the embedded wires present a significant risk of injury. The use of wired glass has faded with the introduction of ceramic and tempered glass products but it is still present in many older buildings today.
STRENGTHENED GLASS AND GLAZING
Commonly referred to as safety glazing, heat strengthened, laminated, and tempered glass, as well as ceramic, plastic and polymer products are now commonly used glazing materials in areas subject to the likelihood of human impact.
These products are less likely to break when subjected to impact and less likely to cause serious injury if broken. Heat strengthened and tempered glass break into rounded cubes which may still contain sharp edges, but do not form dagger-like shards. Laminated glass products may break, but are held together by an interlayer of plastic or polymer reducing the likelihood of exposure to sharp edges.
In the late 1970’s the ANSI Z97.1 standard was modified and required safety glass to be identified with a manufacturing label such as that seen here.
But tempered glass and other types of safety glazing are not hazard free. Depending upon where and how they are used, even these products can be hazardous.
What are hazardous locations for glass and glazing? Model codes, including the International Building Code, define these areas as those subject to human impact. Generally, they are the areas surrounding a doorway and places where it is foreseeable that a person could walk and encounter glazing, such as patios, and fully glazed storefronts. Other areas may include along stairways, ramps, and pedestrian paths where the glass is within 5’ of the walking path and closer than 18” to the floor. Shower and sauna enclosures and glass enclosures at some recreational and sports areas are also identified as impact hazard areas.
Storefronts and glazed curtainwalls may not be reliably identified by people walking nearby and they can easily be confused with an open walking path. Transparent glass walls where the glass cannot be easily distinguished from the surroundings should be made conspicuous to prevent impact injuries. Floor to ceiling storefronts, shopping malls, restaurants, office buildings, and other commercial environments often include these features. Without appropriate markings, people can unintentionally walk into these features and become injured without breaking the glass.
GLASS GUARDS, HANDRAILS AND WALKWAYS
A common feature in commercial and retail environments, Glass guards and handrails require the same safety features as non-glass guards and handrails. ASTM Standard E2358, , provides requirements for these features. Impact resistance, breakage tolerance, deflection of the system, and the free area between components are all regulated by this standard and the failure to meet any one of them can result in injury.
Glass walkways, while less common, are also required to comply with a nationally recognized standard. ASTM E2751,, provides requirements for structural performance, markings for clarity and slip resistance for the design and construction of these features.
PREVENTING INJURY AT EXISTING BUILDING GLASS INSTALLATIONS
The use of glass in windows, doors, storefronts, along stairs or ramps and similarly glazed features do not have to be dangerous if relatively simple precautionary measures are taken to assist people in identifying and avoiding these hazardous locations. Existing float glass can be covered with guards or a transparent film to prevent it from shattering and most glass can be easily removed and replaced with an appropriate safety glazing material.
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 broken glass, falling glass panels, and pedestrian collisions with doors, windows, and other partitions. Submit an inquiry or contact the author of this article to discuss your case and how we can assist.
Architect & Premises Safety Expert
Anthony is a Registered Architect with over twenty seven years of professional experience in the Architectural and Engineering Consultant industry. His expertise in facility design, construction, and architectural professional practice, along with his extensive experience in the premises safety aspects of the built environment, are applied to relevant forensic casework.
This article was developed in concert with other members of the Premises Safety practice group. For assistance determining which expert is best qualified to investigate the specific technical aspects of your case, please contact your local Robson Forensic office or submit an inquiry through our website.