In a fire, time is not measured in hours, but in minutes. The internal temperature can rocket to 1,000°C within 10 minutes. Plain glass breaks in the first 2-3 minutes, leaving a huge opening through which flames, hot gases and lethal smoke invade. In this scenario, seconds save lives.
Fire-Rated Glass panes are specially designed to withstand fire (without collapsing) for a defined period - long enough for occupants to evacuate and the fire brigade to intervene. They are critical in every building, from apartment blocks and hotels to hospitals.
Ordinary glass (even a double-glazed energy unit) cannot withstand the thermal stress of a fire. The rapid, near-instantaneous temperature rise creates thermal shock many times worse than what we analysed in the relevant article.
At 250°C – 300°C, plain glass cracks extensively. At 400°C – 500°C, fragments begin to fall, creating openings through which the fire advances into adjacent spaces. The fire is now fed with fresh oxygen, spreading the nightmare. Even Securit or Triplex glass, as analysed in previous articles, is entirely powerless against fire due to the extreme thermal shock.
Fire-rated glass is classified into three categories according to what exactly it blocks.
The most basic level. The glass withstands flames and smoke, does not break and does not create openings. However, heat passes through. If you stand opposite, the radiated heat is so intense it can cause burns or ignite flammable materials (e.g. papers, curtains) on the "safe" side. Used mainly in fire-rated stairwell doors, in areas where nobody is expected to stand very close.
Intermediate level. Offers everything E does, but additionally features a special metallic coating that reflects part of the heat back into the fire. It limits transmission of radiated heat on the safe side to below 15 kW/m². The temperature on the safe side drops significantly, allowing safe evacuation provided people do not linger close to the pane for too long.
The top category. The glass lets nothing through - neither flames, nor smoke, nor heat. The "safe" side must not exceed +140°C above room temperature. Critical in hospitals, care homes, schools, and any space where people cannot move quickly.
How does a transparent pane manage to keep heat out? The answer lies in a remarkable material: intumescent gel.
The gel is a clear, watery substance, trapped between the glass layers. It is completely invisible - the glass looks normal. In simpler applications (where only integrity is required, not insulation), borosilicate glass or glass-ceramic crystals are used instead. These do not contain gel but inherently possess enormous resistance to thermal shock.
As the temperature rises, the gel reacts: it evaporates the water inside, expands, hardens and becomes a dense, opaque shield (effectively "blinding" the glass). This shield acts as a thermal wall, keeping lethal heat on the fire side. The evaporation process absorbs enormous amounts of heat, buying precious minutes.
The number after the category indicates minutes of endurance: EI30 = 30 minutes, EI60 = 60 minutes, EI90 = 90 minutes, EI120 = 120 minutes. The most common in Greece are EI30 and EI60.
Don't make the same mistake we mentioned with ballistic glass: a fire-rated pane is not certified on its own. It is certified as a system together with an equally fire-rated frame.
Aluminium melts at 660°C. In a fire at 1,000°C, the frame will dissolve long before the glass's protection time expires. The hinges will melt, the door will fall and the fire will find a clear path.
Steel fire-rated frames or aluminium with a special fireproof core (intumescent material inside) are used. The gaskets are fire-rated and expand in heat, sealing every gap.
Fire-rated glass is a building's "invisible firefighter". It does not extinguish the fire, but buys the precious minutes that occupants need to reach the exit and the fire brigade to intervene. It is worth remembering that fire protection is not a luxury - it is a legal obligation in every multi-storey building, hotel, school and public building.
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