Based on the information you have provided, we have calculated the thermal stress for both the inboard and outboard lite as a percentage of the allowable thermal stress for annealed glass.

Generally...

• A percentage below 95% should not require heat treating under normal conditions.

• A percentage of 105% or above probably requires heat treating.

• A percentage between 95% and 105% may also require heat treating if the glass has damaged edges, or if it's been improperly handled or glazed.

In all cases a conservative approach has been taken. It is assumed that light color, closed, non-ventilated, venetian blinds are installed. Thermally broken frames are assumed.

It is assumed that the glass will be properly installed with undamaged clean cut edges and with no unusual heat traps from insulating drapes, blinds or drop ceilings.

HVAC air vents should be directed to blow away from the glass.

Glazing Details...

• Glass must be adequately supported with proper size, location, and type of setting blocks.

• Adequate clearance and bite (face and edge) must be provided without creating excessive edge cover.

• Use wept or vented frames to prevent water or ice accumulation.

• No contact allowed between glass and metal (frame, fastening screws, etc.).

• Anti-walk blocks must be provided in dry glazing.

• Framing system must be plane and square to prevent glass deflection, twisting, or bowing and must be within allowable limits outlined in the Pilkington “Good Glazing Guidelines” brochure.

Handling and Installation...

• Annealed glass must have clean-cut edges without chips, spalls, or other damage. Glass must be carefully handled during unpacking and installation to avoid edge damage. The use of a rolling block during installation is highly recommended to protect corners when rotating the glass.

• Surface damage from other construction activities such as welding, sand blasting, etc. must be avoided.

• Temporary construction situations, such as sunlight shining on glass covered with polyethylene film or with construction materials stacked behind the glazings, may cause thermal stresses in excess of the maximum allowable levels. This must be avoided.

In Service Conditions...

• HVAC system start-up must be carefully controlled, particularly in cold weather, to guard against thermally shocking the glass. HVAC vents should not direct hot or cold air directly against glass.

• Any blinds, draperies or other window covering must be included in a thermal stress review. In general, it is preferable that blinds and draperies be placed 2” away from the glass, vented top and bottom, or be provided with a lock-out to prevent the blinds from turning more than 60 degrees from the horizontal position.

• Drop ceilings or blind pockets can act as heat traps and must also be included in a thermal stress review.

• Placing objects (or signs) on or against the glass, which impede natural air circulation, may cause high temporary stress which can cause glass breakage.

For additional information, see the following Pilkington ATS bulletins...

Thermal Stress	ATS-123
Guidelines for Prevention of Thermal Stress Breakage in Annealed Glass	ATS-136
Thermal Stress for Pilkington Glass Combinations	ATS-139

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This information is offered for assistance in the application of Pilkington flat glass products, but IT DOES NOT CONSTITUTE A WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE. Actual ThermalStress may vary in particular applications.

http://www.pilkington.com/nsg/disclaimer.htm