Wire is the traditional way of enhancing the fire resistance of glass. Wire mesh is laid between two plates of glass and the sandwich hot-rolled. The result is Pilkington Pyroshield™ 2, today's widely used fire-resistant product.
The mid-1970s saw the development of Pilkington Pyrostop®, an advanced glazing without wires which not only blocks the spread of fire but also remains cool on the side away from the fire. The secret is intumescence - formation of a heat-opaque barrier that develops in situ under the influence of heat. Sodium silicate (waterglass) interlayers, when heated to only 150°C in a fire, release water to form a glassy silicate foam, opaque to both heat and light.
began life as a multi-layer sandwich of glass and sodium silicate layers, batch-made and set in a steel frame. The number of layers varied depending on the fire regulation to be met. Three such intumescent layers would meet most architectural specifications. But an oil rig or tanker, or transparent protection for treasures on public view, might require many more. The technology has now been perfected to attain almost the clarity of float glass.
Pilkington Pyrostop® can provide fire protection for as long as 120 minutes, affording both radiant heat insulation and protection against smoke and flame penetration. Development continues to meet ever-tightening fire regulations.
Recent studies have led to special polymer layers that char on heating. The foamed black char has excellent fire-resistant properties and remains firmly adherent to glass. Hybrid structures incorporating both silicate and polymer layers allow thinner, lighter and more cost effective designs to meet specific fire protection requirements.