In the New York City Building Code, a post-fire smoke purge system is defined as a natural or mechanical ventilation system intended to remove smoke from indoor areas once a fire has been extinguished. It is important to note that post-fire smoke purge systems are not designed to fight an active fire, but rather to help resume normal activities as quickly as possible once the fire is controlled. Therefore, post-fire smoke purging is not considered a life safety system and is not subject to the same requirements as smoke control systems.
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The New York Building Code covers post-fire smoke purge systems in detail in Chapter 9, Section 916, establishing the minimum requirements for their design and installation. The building code also lists the four cases in which these systems are mandatory:
- Tall buildings subject to Section 403 of the New York Building Code.
- Buildings where any floor has an area of more than 50,000 square feet.
- Buildings with spaces located at least 100 feet away from natural ventilation openings, which are defined as operable windows and doors with at least 5% of the total floor area.
- Locations with high stacks of inventory or rack storage containing combustible materials as defined by the New York Fire Code.
Regardless of occupancy type, all post-fire smoke purge systems must exhaust air from outside the building to a safe area and in accordance with the requirements of the New York Mechanical Code. The air extracted by post-fire smoke purge systems must not be recirculated to other areas of the building under any circumstances.
Post-Fire Smoke Purge in Multi-Family Residential Occupancies (R-2)
The New York Building Code accepts two different methods for sizing post-fire smoke purge systems that will serve R-2 occupancies: stair ventilation or corridor ventilation. You only need to deploy one of them to meet the code requirements.
If stair ventilation is used, a ventilation system must be implemented at the top of all closed exit stairways. The system must be reversible, capable of both injecting fresh air and exhausting internal air with smoke. To determine the required capacity of the ventilation system, the two values below must be calculated for the highest floor of the building. Then, the larger of the two values is used:
- 6 air changes per hour (ACH)
- 1 cubic foot per minute per square foot of floor area (CFM/ft2)
If corridor ventilation is used, each corridor must be equipped with reversible fans and ducts. The required fan system capacity is 6 ACH or 1 CFM/ft2, whichever is greater. In this case, the calculation is made based on the sum of the largest area of the apartment and the area of the hallway.
In both cases, the post-fire smoke purge system must be equipped with manual controls. If a fire command center is required under Code Section 911, it must include post-fire smoke purge control. On the other hand, if a fire command center is not mandatory, manual control must be included in the fire alarm center. The control must be equipped with a graphic display that indicates the areas of the building served by each post-fire smoke purge system.
If stair ventilation is used, Fire Department personnel control the post-fire smoke purge system by opening the doors leading from the affected floor to the stairwell. If the building utilizes corridor ventilation, each floor must be equipped with dedicated post-fire smoke purge controls.
If an R-2 building meets one of the following conditions, the post-fire smoke purge system is no longer required:
- Windows that can be opened in all living spaces: They must have a glazed area of at least 12 square meters each, and their total area must be at least 10% of the useful area served. Each window shall have an opening area of at least 6 square feet, with a total opening area equivalent to at least 5% of the floor area served. The opening area of windows must be at least 30 inches above the floor and free from any devices that limit their opening. Additionally, windows must comply with Chapter 12 of the New York Building Code.
- Smoke-Proof Enclosures: A post-fire smoke purge system is not required if all exits are constructed as smoke-tight enclosures in compliance with the New York Administrative Code.
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Post-fire smoke purging in other occupancies
Post-fire smoke purge systems for occupancies that are not rated R-2 are subject to a common set of specifications. The general design requirements are as follows:
- Post-fire smoke purging may utilize a dedicated installation, the existing HVAC system, or other openings leading to the exterior of the building, as long as it has the capacity to remove smoke from occupied spaces.
- Mechanical or natural ventilation can be used, but the system must be capable of expelling cold smoke.
- All smoke must be exhausted outdoors, in a safe location and without being recirculated to other areas of the building, meeting the requirements of the New York Mechanical Code.
Exhaust capacity
The post-fire smoke purge system for occupancies other than R-2 can be zoned and calculated based on the largest area served, where the minimum capacity is 6 ACH or 1 CFM/ft2, whichever is greater. If false ceilings are used, the volume above must be considered when calculating the ACH. Regardless of which value is greater, it is necessary to ensure that sufficient supplementary air is supplied through doors, windows, leaks or mechanical ventilation.
Control Requirements
As with R-2 occupancies, the post-fire smoke purge system must be controlled manually from the fire command center or fire alarm control unit, whichever applies to the building in question. There must be a graphic representation of the building areas served by each system, individual controls being necessary for each area in the case of zoned systems.
Manual controls of post-fire smoke purge systems shall not override the operations of the smoke control system, but shall override the shutdown signal provided by the fire alarm system.
Final Observations
Like any building system, the post-fire smoke purge system must be serviced regularly to ensure proper operation when needed. The New York Building Code requires that testing records be kept on site for inspection by the Fire Department.
If you are developing a construction project in New York City, check whether a post-fire smoke purge system is mandatory. The best way to ensure that you will comply with New York codes is to retain the services of a qualified consultant or engineering firm before proceeding with the project. Keep in mind that post-fire smoke purge systems are subject to many requirements of the New York Building Code, Administrative Code, Fire Code, and Mechanical Code.
Editor's Note: This post was originally published in May 2016 and has been reworked and updated for greater accuracy and comprehensiveness.
