ABSTRACT
This study aims to identify the most effectivesolution for fire protection systems in a 2396m² parking facility, comparing prescriptive and performance-based methodologies. Through CFD (FDS) simulations, it is found that prescriptive mechanical ventilation allows widespread smoke, impeding evacuation and firefighting. In contrast, performance-based solutions, especially those using natural ventilation, provide better smoke control, improve visibility, and safer evacuation. The results suggest that performance-based methods are more effective and cost-efficient for fire protection in complex environments like underground parking garages.
INTRODUCTION
Parking lots and garages are among the most critical places in terms of fire risk due to the concurrence of several factors: They are generally underground facilities, which present difficulties in ventilation, smoke extraction, and evacuation tasks; they present problems for tackling fire extinguishment as the only possibility to attack the fire is from entrance or exit zones. Additionally, the use of sprinklers carries the risk of lowering the smoke layer by reducing its temperature; lastly, there is the presence of flammable liquids (classified as a Class I potentially explosive atmosphere by REBT ITC-BT 29), proximity between vehicles, etc.
Currently, there are two methodologies for designing fire protection systems:
- Traditional prescriptive solution (Application of regulations). It is usually an expensive and ineffective solution, but approved by authorities. However, 2/3 of fire victims die from smoke inhalation with this type of installation. This solution proposes two ventilation systems for fire protection: on the one hand, ducted mechanical ventilation, which is an expensive installation (ventilation ducts up to the roof) and has low efficiency in smoke extraction (blowing is always more effective than extracting). On the other hand, natural ventilation.
- Performance-based methods (adapting the fire protection solution to the particular case). For applying this methodology, FDS is essential to determine the feasibility of these systems. The ventilation systems proposed by performance-based methods are jet fan ventilation and exhaust ventilation. The first case has a lower installation cost and greater efficiency in smoke displacement (blowing), it is possible to optimize its operation through FDS analysis and it allows the creation of smoke-free corridors for firefighter access (necessary in critical installations). The second case also has a low implementation cost but involves a loss of useful parking area (there must be space on the parking roof for its use), it generally works well with natural ventilation, and its operating and maintenance cost is zero.
CASE STUDY
The installation under study is a parking facility with an area of 2396m², a maximum capacity of 60 people, and an estimated evacuation time of 120 seconds.
The different solutions that will be assessed are the following:
▪ Prescriptive solution with mechanical ventilation: Extraction flow per parking space of 150 l/space. At least one extraction and one admission opening for every 100 m². Distance between extraction openings less than 10 m (distance to the ceiling less than 0.5 m). Number of duct networks > 2 as there are more than 15 parking spaces. It does not apply to install complementary smoke curtains to this solution due to insufficient height. (DB HS-3)
▪ Performance-based solution using jet fans: Extraction flow of 10 air changes per hour. Proposed layout to leave an entrance area clear for firefighter access to ensure safe fire extinguishment.
▪ Performance-based solution with natural ventilation: Mixed openings in at least 2 opposite areas of the parking. Distance from any area of the parking to an opening less than 25 m. Since the distance between openings is greater than 30 m, another equidistant opening is placed with a tolerance of 5%. It is complemented with the installation of curtains to create smoke zones of less than 2000 m². (DB HS-3).
In all cases, it is assumed that the distance from any point in the parking to the emergency exits is less than 35 m (CTE DB SI).
OBJECTIVE
The main objective of this study is to determine which of these solutions, and fire protection systems is the most effective for this particular installation regarding safety and costs. As a result of this, it will also be possible to conclude which of the two approaches, prescriptive or performance-based, provides the best solution.
RESULTS
After conducting these simulations, with Pyrosim y FDS, the described conditions, the following results are obtained for each proposed solution:
▪ Prescriptive solution with mechanical ventilation: Smoke spreads almost throughout the entire volume of the parking. No significant effect of the ducts on smoke extraction is perceived. At 120 s, there is no visibility in the areas near the fire, but there are no detected problems for evacuation (distance < 35 m), it is the quadratic development of the fire that provides enough margin for occupant evacuation, not the extraction system. No visibility at 1.5 m height in almost the entire parking at 600 s with increasing smoke layer thickness at the fire origin, which implies impossibility for firefighters to perform extinguishment tasks inside, their response time should be 8-9 minutes.
▪ Performance-based solution using jet fans: Significant deterioration of visibility once the jet fans are operational, although by then the evacuation would have been completed (120s). Deterioration of visibility at 180 s compared to extraction by ducts. Stabilization of smoke propagation by jet fans from 180 to 300 s, with adequate visibility at the entrance near the extraction.
▪ Performance-based solution with natural ventilation: Very efficient operation of the smoke zones created by curtains. Smoke propagation stabilizes early, with the courtyards acting as an exhaust/suction system from the direction opposite to the fire origin. Temperatures above 200ºC in the smoke layer only near the fire origin, with little variation from 5 to 10 minutes in the smoke-affected areas, making it easily accessible for firefighters under safe conditions.
CONCLUSION
Thanks to fire dynamic simulation (FDS) , it has been possible to determine which of the proposed solutions is the most efficient in fire protection. This kind of CFD analyses provide in-depth knowledge of how the various solutions will perform in the same design and a technical justification for their implementation in the case of performance-based solutions.
In fact, these perfomance based solutions have proven to allow the development of safer solutions with longer evacuation times, which is essential if implemented in buildings like this, where evacuation presents significant difficulties. Additionally, the cost savings can be very significant for an installation, as well as in maintenance and operation costs.
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