Fire & Smoke Modelling to validate fire and life safety acceptance criteria in tunnels
As tunnels can be a complex interconnected network in underground or enclosed spaces, fire situations in the tunnels will pose highly hazardous conditions to the passengers in terms fire safety and life safety.
As such, smoke ventilation and fire engineering analysis are critical to demonstrate that all fire and life safety acceptance criteria in the tunnels can be met. Holistic fire safety engineering approaches involving extensive smoke and fire modelling are commonly adopted to validate the effectiveness of the emergency tunnel ventilation during fire situations in accordance with relevant standards such as NFPA 502 as well as any applicable AHJ’s requirements.
Multi-purpose tunnel ventilation systems in road tunnels can be designed for :
The volume of air required for the dilution of pollutants as well as other factors, such as tunnel length, location, type of traffic, environmental laws, and not least, fire and life safety criteria during a fire situation, shall be taken into consideration when designing a ventilation system for a particular tunnel.
Smoke Ventilation in Tunnels
Fire safety engineering analysis can be conducted to demonstrate that the level of safety provided by a natural smoke ventilation system for the tunnels is equal or higher than a mechanical emergency tunnel smoke ventilation system in terms of tenability limits for evacuation as stipulated in NFPA502 and the fire safety requirements by the Authority Having Jurisdiction.
In general, there are 3 types of Emergency Smoke Ventilation Systems commonly used for Tunnels:
Natural Smoke Ventilation Concept
Fire safety engineering analysis conducted to demonstrate that the natural smoke ventilation system is effective to maintain tenable conditions for evacuation as stipulated in NFPA502.
Natural smoke ventilation concept developed using CFD modelling and evacuation simulation based on the strategic natural louvre openings and the exit/entry points of tunnel to facilitate the smoke exhaust.
Fire and Smoke Modelling Simulation to assess Tenability Limits
Hot buoyant smoke and gases are released from the tunnel along the natural openings at the fire location to maintain a tenable smoke clear height of at least 2.5m above floor level for the safe evacuation of occupants.
ASET/RSET > 2 is achieved with at an acceptable level of life safety.
Longitudinal Mechanical Smoke Ventilation Concept
Localised Mechanical Smoke Extraction Concept
Smoke is extracted in the vicinity of the fire source to maintain tenable conditions along the tunnel for safe occupant evacuation.
Fire Detection Systems for the mitigation of tunnel fires
Smaller design fire sizes can be mitigated with tunnel fire detection and warning systems to activate the fire suppression systems.
Commonly used fire detection systems;
Good fire safety engineering practice involves the realization of the performance objectives of the fire codes
as well as the expectations of all stakeholders.
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