Fire Engineering in Buildings

Fire Engineering in Buildings

• Fire design is crucial for protecting occupants, limiting structural damage, and preventing fire spread to adjacent buildings. Examples like the World Trade Center collapse and Australian bushfires highlight this importance.

Fire Progression

• Fire begins with ignition (sufficient fuel, oxygen, and heat).
• Fire grows as heat spreads via radiation and convection.
• A fully developed fire generates extremely high temperatures, damaging materials and structures.
• Fire cools and dies out as fuels are consumed. Hot gases collect under ceilings, rapidly raising temperatures and spreading flames.

Fire Resistance Period (FRP)

• FRP is the time a building element can withstand fire without losing function.
• Goals include occupant evacuation, property protection, and firefighter response time. For example, office building structural elements need a 90-minute FRP.

Fire Limit States

• Strength: Structural members must withstand fire-induced loads.
• Integrity: Preventing fire and smoke spread through cracks.
• Insulation: Ensuring the other side of a wall remains cool enough to prevent ignition.

Structural Fire Resistance

• Beams: Beams, exposed on various sides, need specific thickness and cover based on FRP.
• Slabs: One-way and two-way slabs require appropriate thickness and reinforcement for fire resistance. For example, hollow-core slabs may need added insulation.

Fire Protection Systems

• Passive Protection: Built-in fire-resistant walls, floors, ceilings, like concrete-encased steel beams that maintain strength during fires.
• Active Protection: Systems activated during fire, such as smoke detectors, alarms, sprinkler systems (automatically spray water), and hydrants/hose reels.

Fire Spread Mechanisms

• Conduction: Heat travels through materials (walls, floors, ceilings).
• Convection: Hot gases and smoke rise (open stairwells, shafts).
• Radiation: Heat travels in straight lines, igniting nearby combustibles (e.g., glass windows spreading fire).

Building Classifications and Fire Risks

• Building classes (e.g., residential, apartments, offices, warehouses, hospitals) have varying fire risks and required fire safety standards (as per the NCC). Hospitals (Class 9) need the highest standards due to occupant vulnerability.

Active Fire Protection - Sprinkler Systems

• Sprinkler heads burst when the temperature exceeds a set limit (releasing water).
• Benefits include reduced property damage and saving lives. Sprinklers are mandatory in Australia for high-rise buildings over 25 meters.

Increasing Fire Resistance

• Insulation: Using fire-resistant materials (like under-slab insulation).
• Thickness: Increasing the thickness of structural elements (example: 120 mm slab with insulation can achieve a 2-hour FRP).

Key Takeaways

• Fire engineering aims to protect building occupants and structures.
• Building elements must adhere to fire resistance standards based on building type.
• Active and passive fire protection systems work together to reduce fire risks.