Q: I’m working on a job in a hotel that requires an exterior 20 minute fire rated door. Is there a problem with using polished wire glass on the door? Can polished wire glass be used on the interior/corridor side of the door and ¼ tempered glass be used on the exterior side of door?

A: There IS a problem using polished wire glass on EITHER side of the door. Refer back to the 2009 International Building Code section 715.4.7.4 - Safety Glazing where it says, "Fire-protection rated glazing installed in Fire doors in areas subject to human impact in hazardous locations shall comply with Chapter 24." Chapter  24 section 2406.4 states, "The following shall be considered specific hazardous locations requiring safety glazing materials, 1. Glazing in swinging doors, except jalousies."

Wire Glass IS NOT safety glass. It will not comply with the code. You should go to a supplier who can recommend alternative products, such as "Firelite".

I have seen many terrible injuries from wire glass over the last 25 years. When a body part goes thru the glass, usually a hand and arm, the person instinctively pulls the hand back. That action strips the skin and tendons and leaves the person with many years of surgical reconstruction and a lifelong injury.

Q: Is there a difference between AS 1 glass and AS 2 glass? I had forklift that needed a new windshield and I requested that AS 2 glass be used per the manufacturer’s instructions. AS 1 glass was used and the glass now has a 47 inch crack in it that no one can explain. The installer is telling me that there is no difference between AS 1 and AS 2 glass and that if he had installed AS 2 glass it would not have made a difference. There is no indication that something hit the glass; it hasn’t been stored in any extreme temperatures.

A: AS stands for American Standard. The number indicates the position in the vehicle where the glass may be used, based on its optical quality. AS1 is the clearest glass (at least 70% light transmission), is laminated, and can be used anywhere in a motor vehicle (typically just the windshield). AS2 is tempered with at least 70% light transmissions, and can be used anywhere except the windshield, and AS3 can be used in certain locations in certain vehicles (and can be laminated or tempered, and has less than 70% light transmission).

In the example you give (a forklift), this is an off-the-road vehicle where low speeds are typical. It is entirely possible that the forklift manufacturer does recommend an AS2 windshield since the “clearest glass” (AS1) may not be needed. I do not believe the Federal Government (i.e. NHTSA) regulates equipment used on such vehicles….at least I’ve never seen such regulations if they exist.

Bottom line…the difference between the two is the light transmittance or clarity. AS 1 or 2 would not have any effect on whether the glass broke or not.

Q: I'm trying to determine if there is an existing standard for weathering of common window glass, color-shift in sunlight, etc. Can you help?

A: All standards related to glass are found in the ASTM 2009 version of Annual Book of Standards, Section 15, Volume 15.02, Glass and Ceramic Whitewares. The book may be purchased at www.astm.org.

Q: I installed 8 sections of frameless glass railings, each section about 2 ft high and 7 ft long. I can see a small imperfection, a small thin line, across the top of the railing. My supplier says this is normal with tempered glass and that is not an imperfection. The client says he wants the railing to be taken out and replaced to avoid any future problems. And get this – the only way anyone can see the thin line is while they are wearing polarized sunglasses; no one can see this with the naked eye. Is this thin line normal or do you think it’s an indication of a problem?

A: The "line" in question is normal in this product when viewed through polarized lenses. Sometimes it even appears as a "wavy" line when the tempering oven was a little too hot. For your information, a line, or distortion, is also seen when the railing glass is laminated and viewed at an acute angle OR through polarized lenses. Other tempering effects when viewed through polarized lenses are: halos in the glass, dark and lite spots and, sometimes, a slight curvature. The temperature of the tempering oven and the viewing conditions are the key to this mystery.

Q: I notice the term “tonnes” is used offered in describing the size of a glass plant opening or the amount of glass produced in a year, but I do not know how to quantify what this means, can you help? For example, a “700 mn tonnes plant opening” means they will produce 700 million tones of glass a year, but can one draw a conclusion on the size of the glass from statements like this?

A: A "tonne" is a metric ton. Some Glass manufacturing facilities use this term to define their output. It has nothing to do with the size of the glass. Here’s more information.

Q: I am providing glass for fire rated doors and fire rated frames in a school in Pennsylvania. Does the glass have to be wired glass or can it just be safety glass?

A: Wire glass is permitted in locations that need a fire rating. However, if the location is also a hazardous location, safety glass must be used and wire glass is not an approved safety glass. Tempered glass, which is an approved safety glass, is not an approved fire rated glass (when it breaks it shatters into small "dice like" pieces, evacuates the opening, and the fire gets in).

Most fire rated glass used in schools today has a 20 minute to 1 hour rating. This means it must retain the fire for 20 minutes or 1 hour before it fails. There are several manufacturers who provide a product that will satisfy both the fire and safety codes.

I would direct you to Section 715, Opening Protectives, of the 2006 International Building Code ( or whatever year version of the code that is used in his area ). This section gives the guidelines for his problem.

Q: I had two large windows (about 8 ft tall and 5 ft wide) installed in my living room and tempered glass was not used as I requested. The company that completed the installation wants to come back and put a film over them instead of replacing them. Is it possible to place a film over a large piece of glass to make it “tempered?”

A: NO, NO, NO, & NO! That will not make it "tempered". Annealed glass is tempered in a tempering oven. This makes it "Safety Glass" and suitable for the hazardous locations that are referenced in the building codes. Applying a film over annealed glass does NOT make it Safety Glass.

If the window is 5'x 8' (the width is always stated first) and subject to human impact as defined in the building codes, then it must be Safety Glass. There are two kinds. Tempered and Laminated. Tempered is produced as I stated above. Laminated glass is made by putting a film layer BETWEEN two pieces of glass and then putting it in a laminating chamber under pressure and high temperature.

Q: This may sound like an unusual request, but here it is, my boss recalls hearing about an unbreakable glass. I'm an architect in the design group at the Massachusetts Bay Transportation Authority (Boston's bus, subway and commuter rail agency) and we are having vandalism problems with our glass windscreens and passenger shelters and would like to find a glass that can stand up to abuse. If you can point me in the right direction I would be eternally grateful.

A: There are several kinds of unbreakable glass that was developed in Europe. It is very expensive and will not stop vandals from trying to "etch" or break it. If you google "unbreakable glass" you will probably find a lot of references.

The Mass Bay Transit Authority is not alone in trying to fix the vandalism problem. There are many toughened glass products and several polycarbonate products that won't break, but they can still be defaced. Tough problem...with no real answer...yet.