1. Evaluation of risk of breakage by thermal shock
2008
Technical Advisory Service
Thermal shock

2. Thermal shock Definition Parameters of influence Method of calculation
Example of calculation

3. Thermal shock - Definition
A breaking by thermal shock occurs when there is a too high difference of temperature between two point of a annealed glass.
Indeed, if the temperature of the glass increases, this glass expands.
Reminder : Coefficient of linear expansion : m/(m °C)
Ex: T° difference of 50°C for a 2 m glass
 m/(m °C) x 50°C x 2 m = 0,0009 m = 0,9 mm

4. Thermal shock - Definition
This phenomenon does not present a problem if the increase in temperature is uniform on all the glazing and if the movement is not blocked.
On the other hand, if the border of the glazing remains cold, it will prevent the hot part from dilating freely and it results the beginning traction constraints.
At a certain difference of temperature between two points of a same glazing, there is a risk of thermal breakage.

5. Thermal shock

6. Thermal shock
Thermal shock

7. Thermal shock

8. Thermal shock
Thermal breakage starts allways at the edge of the glass, perpendicular to the edge and the 2 faces.
The breakage can be single or multiple.

9. Thermal shock
Thermal shock

10. Thermal shock Definition Parameters of influence Method of calculation
Example of calculation

11. Thermal shock – Parameters of influence
Climatic conditions
Parameters depending of the glazing and its setting
Outside « architectural » parameters
Inside « architectural » parameters

12. Thermal shock – Parameters of influence
Climatic conditions :
Daily difference of temperature (°C)
Solar intensity (W/m²)

13. Thermal shock – Parameters of influence
Parameters depending of the glazing and its setting
Nature of glass  Energy absorption (EA)

14. Thermal shock – Parameters of influence
Parameters depending of the glazing and its setting
Type of setting and colour of the frame

15. Thermal shock – Parameters of influence
Parameters depending of the glazing and its setting
Structural glazing
VGG
Alu with thermal break
Dark alu without thermal break
Middle alu without thermal break
Wood or PVC
Clear alu without thermal break
Dark steel
Clear steel
Concrete/Masonry

16. Thermal shock – Parameters of influence
Parameters depending of the glazing and its setting
State of the glass edges : damaged edges or presenting chips increase the risk of thermal breaking, these one starting from these weak points.

17. Thermal shock – Parameters of influence
Parameters depending of the glazing and its setting
Use of TV or sliding frame with Low E
Toughened or heat strengthened glass

18. Thermal shock – Parameters of influence

19. Thermal shock – Parameters of influence
Parameters depending of the glazing and its setting
Glass in a roof
Inside temperature
Outside temperature

20. Thermal shock – Parameters of influence
Outside « architectural » parameters
Exposure of the facade (in the Northern hemisphere)

21. Thermal shock – Parameters of influence

22. Thermal shock – Parameters of influence

23. Thermal shock – Parameters of influence
Outside « architectural » parameters
Eventual shadows on the glazing (eaves of a building, blind) and letting only one part of the glazing in the shadow.

24. Thermal shock – Parameters of influence

25. Thermal shock – Parameters of influence

26. Thermal shock – Parameters of influence

27. Thermal shock – Parameters of influence

28. more and more dangerous

29. Thermal shock – Parameters of influence
Inside « architectural » parameters
Presence of blinds
Proximity of heating appliances
Proximity of the inside aeration forcing air system (hot or cold) on the glazing
Inside ceiling
Proximity of a dark object behind the glazing

30. Thermal shock – Parameters of influence

31. Thermal shock – Parameters of influence
Minimum distance 20 cm
Liquid temperature max 65°C

32. Thermal shock – Parameters of influence
Risk if L < h

33. Thermal shock Definition Parameters of influence Method of calculation
Example of calculation

34. Thermal shock – « Glass in building » method
1°) Basic calculation of Dt :
SV: Dt = I . AE + A . he
he + hi he + hi
With I = solar intensity (750 à 850 W/m²)
A = maximum daily t° range (10 à 13 °C)
DV: Dte = …
Dti = …

35. Thermal shock – « Glass in building » method
2°) Influence of the inside blinds :
Dt1 = Dt + Dt’

36. Thermal shock – « Glass in building » method
2°) Influence of the inside blinds : Values of Dt’
Simple glazing
Ventilated space
Non ventilated space
Open weave
3°C
6°C
Closed weave
4°C
7°C
Venetian blinds
5°C
8°C

37. Thermal shock – « Glass in building » method
2°) Influence of the inside blinds : Values of Dt’
Double glazing
Outside glazing
Inside glazing
Ventilated space
Non ventilated space
Open weave
2°C
4°C
8°C
Closed weave
3°C
5°C
9°C
Venetian blinds
6°C
10°C

38. Thermal shock – « Glass in building » method
3°) Influence of the frame :
Dt2 = Dt1 x f1

39. Thermal shock – « Glass in building » method
3°) Influence of the frame :
Type of frame f1
Concrete 1
Clear steel
0,9
Dark steel
0,8
Steel with thermal break
Clear alu without thermal break
Wood of PVC
0,75
Dark alu without thermal break
0,7
Alu with thermal break
Structural glazing
0,5

40. Thermal shock – « Glass in building » method
4°) Influence of the outside shadows :
Dt3 = Dt2 x f2

41. SV and outside glass of DG
Thermal shock – « Glass in building » method
4°) Influence of the outside shadows
Sort of shadow
SV and outside glass of DG
Inside glass of DG
1,2
1,1
1,5

42. Thermal shock – « Glass in building » method
Stress in the glass :
s = E . e = E . a . DT3 = 0,63 . DT3
Criteria of acceptability :
DT3 < 30°C  OK
DT3 > 30°C  a thermal treatment (toughened or heat strengthened) is necessary

43. Thermal shock – « Glass in building » method
Notes :
Thermal treatment can be toughened or heat strengthened glass
Advantage of a toughned glass : it is a safety glass against injuries too
Advantage or a heat strengthened glass : does not present a risk of spontaneous breakin and so, no heat soak treatment is needed

44. Thermal shock – « Glass in building » method
Notes :
The edge treatment is not considered as a good solution to prevent of the risk of thermal shock
The spandrels must always be tempered

45. Thermal shock Definition Parameters of influence Method of calculation
Example of calculation

47. Thermal shock – Example of calculation
Example of a calculation :
6 mm Stopsol Supersilver Dark Blue pos.2 12 mm air 6 mm Planibel clear
AEe = 55
AEi = 4

48. Thermal shock – Example of calculation
Example of a calculation :
6 mm Stopsol supersilver Dark Blue pos.2 12 mm air 6 mm Planibel clear
Setting in an aluminium frame with thermal break and outside shadow
DTe = 33,5 °C
DTi = 13,0 °C
 The glass outside must be tempered

49. Thermal shock – Example of calculation
Example of a calculation :
6 mm Stopsol supersilver Dark Blue pos.2 12 mm air 6 mm Planibel clear
Setting in Structural glazing without shadow nor blind
DTe = 17,6 °C
DTi = 8,5 °C
 A thermal treatment is not necessary

51. Thermal shock – Method « Glass in building »
Advantages:
Simple, proven and safety
Disadvantages:
Does not allow the calculation of triple glazing and double skin façades