BS EN 13501-2BS 476-22Approved Document B
Fire Safety Compartmentation (E, EW & EI)
Fire safety glazing is divided into Integrity (E), Radiation Control (EW), and Thermal Insulation (EI). Glass cannot be certified in isolation — it must be tested and certified as an entire assembly (glass, framing, seals, fixings).
UK Regulatory Mandate:Approved Document B mandates EI class on protected fire stairwells and escape routes to prevent flashover ignition of escaping occupants’ clothing.
1. Classification Boundaries (E vs EW vs EI)
Class E prevents the passage of flames and hot smoke for the declared duration (30/60/90 mins), but allows radiant heat to pass through freely. Class EW restricts transmitted radiation to < 15 kW/m². Class EI restricts temperature rise on the unexposed non-fire face to ≤ 140°C mean above ambient.
2. Intumescent Chemistry & Mechanics
EI fire glass incorporates clear hydrated sodium silicate interlayers. Upon exposure to fire at ~120°C, the water chemically foams and expands into an opaque, rigid, mineral heat shield that absorbs thermal energy.
Critical Specification Pitfalls to Avoid
- •Substituting standard toughened glass for fire-resistant glass (standard toughened shatters within 3 to 5 minutes)
- •Installing fire glass into non-fire-rated standard timber or aluminium frames