Views: 27 Author: Site Editor Publish Time: 2020-04-24 Origin: Site
There are a number of different systems available for providing a fire rating while also maintaining light passage and a clear view. Fire rated rooms and stairwells do not necessarily need to be solid walled and dark – architects can specify glazing systems or glass opening protectives to keep a space filled with natural light.
It is important to note that the glazing systems and specialty glass products listed below are more expensive that standard safety glass types like laminated or tempered glass (we have another article that covers standard glass types). Architects must consider the cost of the material and their design goals before specifying vast areas of fire glass.
The first thing to consider when specifying rated glass is what you are trying to protect against. There is an important difference between fire-protective glass and fire-resistive glass and the building codes are very specific about where each are to be used. Architects should be sure they understand the difference and that they have clearly documented where they each type is required.
Fire-protective glass prevents the spread of fire and smoke. However, it will not prevent radiant heat transfer. That means that as the glass heats up from fire on one side, objects on the other side of the glass will feel the heat. Wired glass, specially tempered glass, and glass-ceramics are considered fire-protective glass and can generally be used where the building code calls for an opening protective.
Fire-resistive glass prevents the spread of fire and smoke; in addition it also stops radiant and conductive heat transfer so that objects on the protected side do not get hot enough to spontaneously combust. This is generally achieved by creating a laminated assembly that is composed of a number of layers of glass separated by heat resistant interlayers. Fire-resistive glass is used where the building code calls for a fire-resistive assembly, which also means that the temperature-rise on the protected side must be below a threshold (usually 250 degrees in rise beyond ambient).
Wire mesh glass was, for a long time, the only type of rated glazing available. It is made from a sheet of glass that has a wire grid mesh incorporated into it. The wire holds the glass in place when it is exposed to the high heat of a fire. However, the wire makes the glass less durable so it is more prone to breakage due to impact. In addition, the wire creates a more jagged breakage pattern, which is very dangerous. Due to the safety concerns, many building codes no longer allow wired glass in doors or sidelights, especially in schools and gymnasiums.
Safety wired glass has the same fire-resistant properties of normal wire glass, but it also has film that allows it to meet safety requirements so it can be used in doors and sidelights. The film holds the glass in place if it were to break so that broken pieces will not cause injury.
The biggest benefit of wire glass is the low cost compared to other types of fire glass. However, other options are starting to become more competitive.
A cost effective alternative to wired glass is tempered glass that has been tested and has a fire-rated label. However, there are two main drawbacks. First, it will usually not be able to survive the hose stream test. Second, since it can’t pass the hose test, tempered fire glass carries a maximum rating of 20-minutes so it has limited use.
Ceramic glass, usually referred to as glass-ceramic, is a glass product that resists high heat levels. Because it can handle 800-degree-F changes in temperature, glass-ceramic is used for glass cooktops and fireplace doors, but it is also suitable for fire rated glazing with a rating up to 3 hours.
Glass-ceramic is made from a normal sheet of glass. The pane gets a heat treatment that causes a crystallization process, which must be carefully controlled. The crystallization creates a stronger piece of glass that has high thermal stability.
Ceramic glass is a versatile product. It can be tinted, clear, or mirrored. It can also be included in insulated glass units (IGUs), which can contribute to energy efficiency. Due to its range of aesthetic offerings, glass-ceramic is quickly becoming a popular choice for fire rated glazing.
Intumescent fire rated glazing is a laminated product made up of alternating layers of glass and clear intumescent inner layers. The fire rating can be up to 3 hours depending on the number of inner layers used.
When exposed to a fire, the outer layer of glass shatters. The intumescent inner layer holds the broken glass in place, but it also rapidly expands to provide an insulated layer of protection that prevents the spread of fire and smoke as well as preventing thermal heat radiation.
The main benefit of intumescent glass is that it prevent thermal heat radiation so it can be used in a fire-resistive assembly as long as it has been tested and is labeled for that use.
It is important to note that both the glass and the framing system work together to provide a fire rating, which is why we use the word “assembly” regularly in this article. Both the frame and the glass should have the same rating; although, the building codes do provide exceptions where a higher rating than required is allowed (always refer to local codes when designing a system).
Where a system of different components is used, all components should be properly labeled so that the ratings are clear and can be checked in the field. Fire rated systems are critical life safety components and need to be thoroughly reviewed in both the design and construction phases to ensure they meet code requirements.