When a fire occurs inside a building, there are additional risk factors besides getting burned by the fire itself. Smoke can also be very dangerous as it limits visibility and can make evacuation difficult. Additionally, smoke contains carbon monoxide (CO), which is a gas that is highly toxic to humans – at concentrations above 10,000 ppm, carbon monoxide causes unconsciousness within seconds and death within minutes.
A post-fire smoke purge system aims to extract smoke from interior spaces and make them suitable for occupancy as quickly as possible after the fire has been controlled. For this reason, it is not considered a life safety system like sprinklers by New York codes, but it is required in many occupancy classifications.
This article will provide an overview of the two post-fire smoke elimination methods accepted by the New York Building Code for multifamily residential buildings: stair ventilation and hallway ventilation. Deploying one of them is sufficient for code compliance, but they can also be used together. These systems are also required in other occupancy classifications, and the complete list of requirements and specifications can be found in Chapter 9, Section 916, of the New York Building Code.
Stair ventilation
As its name implies, a stair ventilation system uses stairs as ducts to remove smoke from indoor spaces. Openable doors connect the stairwell to all levels of the building and are manually operated by fire department personnel to service the floor requiring smoke purging.
If this type of post-fire smoke purge system is implemented, it must include all stairwells in the building. Each staircase must be equipped with a reversible fan at the top, allowing both fresh air to enter and internal air to be exhausted. The fan must have a capacity of 6 ACH or 1 CFM per square foot, whichever is greater, based on the largest floor space served by the staircase. Fan capacity is calculated based on the largest floor area to ensure it will be able to serve any other floor if affected.
The location of post-fire smoke purge controls changes depending on other fire protection requirements. In buildings where a fire command center is mandatory in accordance with article 911, manual controls for the post-fire smoke purge system must be installed. On the other hand, if the fire command center is not required for the building in question, post-fire smoke purge controls should be located on the fire alarm panel. In both cases, controls must include a chart indicating which areas of the building are served by each post-fire smoke purge system. This way, firefighters can easily find and open the stairwell doors corresponding to the level where smoke purging is required.
Corridor Ventilation
When this approach is used, smoke from each level is exhausted directly to the outside by reversible fans, without using stairs as chimneys. The required duct and fan capacity in this case is also 6 ACH or 1 CFM per square foot, whichever is greater, but based on the hallway area plus the largest apartment on the floor. The logic is similar to that for stair ventilation systems: capacity is based on the largest apartment so that the post-fire smoke purge system can serve any other apartment on the floor.
Controls must be located in the fire command center if required for the building, or in the fire alarm panel if there is no fire command center. Individual controls are required for each smoke purge system, as well as a chart indicating the portions of the building served by each system.
Comparison between the two types of systems
For a given building size, stair ventilation generally has a lower cost because fans and controls are consolidated into fewer units located above the stairs. However, the system is more complex to operate because firefighters must manually open the door connecting the affected floor to the stairwell used to purge the smoke. On the other hand, a hallway ventilation system is easier to operate but more expensive to build since there are more fans, each with its own ducts, electrical wiring and controls.
Regardless of the system configuration used, it must be maintained in optimal condition, with on-site testing records for review by the New York Fire Department.
Cases where post-fire smoke purging is not necessary
There are two cases in which the New York Building Code does not require post-fire smoke purging in high-rise multifamily buildings: when the building has a minimum window area that can be opened as described in the Building Code, or when there are smoke-proof enclosures are used for all exits. If the post-fire smoke purge system is omitted based on the minimum window opening area exception, the following conditions must be met:
- Windows that can be opened must be installed in all habitable rooms in accordance with Chapter 12 of the New York Building Code – Indoor Environment. The total window area must be at least 10% of the useful area served.
- Windows must have a glazed area of at least 12 square feet, with an opening area of at least 6 square feet, and without jambs or devices that prevent full opening. Thus, the minimum area that can be opened is at least 5% of the useful area served.
- Windows must be installed at least 30 inches above the finished floor.
If any other New York code requires window guards for the building in question, and these include stops or other limiting devices that prevent windows from fully opening, the post-fire smoke purge system is still required.
Final Observations
Post-fire smoke purging plays a very important role inside buildings, restoring adequate occupancy conditions as quickly as possible after the fire is controlled. Real estate developers can seek professional engineering services to help them decide between stair ventilation and hallway ventilation in new construction. No option can be considered better than the other, as each has advantages and disadvantages.
It is important to note that the requirements of other New York codes also apply to post-fire smoke purge systems, including the New York Fire Code and the New York Mechanical Code. Getting professional assistance is the most effective way to ensure a new project is code compliant.
