From the history of
Since the 60's in the construction of fireproof glazing used special products - hollow glass blocks, as well as refractory sheet reinforced and tempered glass. Fire-resistant structures were made deaf in steel frames or directly in reinforced concrete or brick structures. The limit of fire resistance of such products was assessed only on the basis of signs of collapse or formation of through holes, they were not required to withstand the action of fire that did not heat up to critical temperatures.
All these products behave differently under fire.
Hollow glass blocks
Hollow glass blocks (DSTU 9272-66) under the influence of fire begin to crack after 1-2 minutes; 25 minutes after the start of the fire, the front walls are covered with cracks. But, despite this, the glass blocks do not fall apart, remain in place, and for another half an hour fire-fighting glazing made of glass blocks can withstand the effects of fire without significant damage. After 50 minutes of fire, the walls of the blocks begin to deform due to the softening of the glass. By the 80th minute, these walls melt, but the fire-resistant structure (as a whole), assembled from glass blocks, still retains its fire-resistant ability. Upon further heating, the walls of unheated glass blocks are deformed and then melted. The through openings formed at the same time characterize approach of a limit of fire resistance of a design.
Fireproof glazing of hollow glass blocks dramatically reduces the intensity of thermal radiation of the flame. Thus, after 15-20 minutes of fire, the temperature at a distance of 0.5 m from the surface of unheated glass blocks does not exceed 650 C, while the temperature of the surface reaches 1500 C. After 25 minutes, the temperature of the unheated surface reaches 3000 C.
Reinforced refractory glass
Reinforced refractory glass (DSTU 7481-55) is an ordinary silicate glass with a thickness of 5.5 - 6.0 mm in which a steel mesh of wire 0.5 mm thick is fused. The grid contributes to a more uniform temperature distribution over the volume of the glass, which reduces the temperature stress, in addition, it increases the strength of the glass from the effects of lateral forces. Therefore, during the fire, the reinforced glass, although it cracks, does not fall out immediately. Reinforced glass begins to crack in 1 minute after the start of fire. After 30-40 minutes, the glass softens, deforms and gradually begins to come out of the mounts and at a fire temperature of 8700 C, it falls out of the weave under its own weight - the limit of fire resistance of the structure. On average, the value of the limit of fire resistance of fireproof glazing with reinforced glass is 0.75 (h) for single and 1.2 (h) for double glazing.
However, fireproof glazing with reinforced glass weakly prevents the thermal radiation of the flame, so after 10 minutes after the start of fire at a distance of 0.2 m from the surface of single unheated glazing, the temperature reaches 2000 C, and after 20 minutes - already 5000 C. Thermal radiation through glass causes charring of veneer and decay of fabric at a distance of up to 1.25 m from the unheated surface, and at a distance of 0.5-0.9 m - veneer and fabric catch fire.
Tempered refractory glass
Tempered refractory glass when installed with gaps of 3-5 mm around the perimeter can withstand heat for 10-15 minutes, after which it is annealed and turns into normal and the limit of fire resistance of glass.
For longer and more reliable protection against fire, completely different design solutions for fire barriers are required.