Multifamily Buildings with Post-Fire Smoke Purge Systems

When a fire breaks out in a structure, added risk factors aside from getting burned should get addressed. Smoke can be just as dangerous as fire. In fact, it can be lethal since it restricts visibility and can hinder the evacuation process. As you may already know, smoke produces carbon monoxide (CO), which is a very toxic gas for people. At concentrations of above 10,000 ppm, carbon monoxide can knock you unconscious in seconds and end your life just a few minutes later.

Post-fire smoke purge systems take on the purpose of removing smoke from indoor areas. They help make indoor areas fit for occupancy as quickly as possible after fire damage. They are not regarded as life safety systems like sprinklers are, but many occupancy classifications still require them.

This article will give you a summary of two post-fire smoke purge systems allowed by the NYC Building Code. We will focus on multifamily residential structures in regard to corridor ventilation and stair ventilation.

Having one system installed is enough to comply with city codes. However, in some cases, both systems can get used together. Two post-fire smoke purge systems are generally required in other occupancy classifications as well. You can view the complete list of specifications and requirements in Chapter 9, Section 916, of the New York City Building Code.

Stair Ventilation

Stair ventilation systems use staircases as channels to eliminate smoke from indoor areas. In stair ventilation systems, doors can open to connect the staircase with each level in the structure. They are then manually operable by fire personnel to assist the affected floors that require smoke purging.

When a post-fire smoke purge system gets deployed, they must include all staircases in the structure. Each staircase gets equipped with a reversible fan near the top. When needed, both indoor air exhaust and fresh air supply can get into the structure. The fan will need to have a capacity of 6 ACH or 1 CFM per sq ft, whichever is greater based on the floor with the most square feet served by the staircase. The fan capacity is also determined based on the largest floor area. This is to ensure that it will be capable of serving any other floor that gets affected. The location of post-fire smoke purge controls will also change. (dependent on additional fire protection requirements)

According to Section 911, in structures that require the presence of a fire command center, manual controls for post-fire smoke purge systems must be used. Then, if the fire command center is not needed for the structure, post-fire smoke purge controls can get placed in the fire alarm panel. Either way, the controls will include a sign showing which areas are services by which post-fire smoke purge system. This is to assure that firefighters can quickly locate and open the doors to the stairs matching the level that requires purging.

Corridor Ventilation

In cases where you use corridor ventilation, it’s possible to drain smoke coming from each level outside. This process takes place without utilizing staircases as smokestacks. The needed duct and fan size for corridor ventilation is 6 ACH or 1 CFM per sq ft, whichever is greater, much like stair ventilation systems. However, with corridor ventilation, the calculations get based on the size of the corridor added to the size of the largest apartment on the floor.

The structure of the system is very similar to that of stair ventilation systems. The capacity is generally based on the biggest apartment. This is so the post-fire smoke purge systems are able to serve any additional apartments on that floor.

The controls are then located in the fire command center when required by the building. (or the fire alarm panel in cases with no fire command center.) Separate controls for each smoke purge system must be present. Again, signs showing the building areas served by each individual system must be present.

Stair Ventilation vs. Corridor Ventilation

Depending on building size, stair ventilation systems are commonly more economical. This is because controls and fans are combined into fewer units and positioned at the top of staircases. But stair ventilation systems tend to be more difficult to manage. This is because fire personnel then have to manually open the door joining the appropriate floor to the staircase utilized to purge the smoke. Comparatively, corridor ventilation systems are simpler to run but take more time to construct. This is because more fans exist, each with separate ducts, wiring, and controls.

There is a requirement for optimal conditions no matter which system configuration you utilize. Testing reports are then required to be left on-site for inspection by the New York City Fire Department.

Instances In Which Post-Fire Smoke Purge is Not Required

There a couple of cases in which building codes do not mandate post-fire smoke purge in high-rise multifamily buildings. One is where the building has got a minimum openable window area as described in the Building Code. Another is when smoke-proof enclosures get used on all exits. In case the post-fire smoke purge system gets omitted completely, which is determined by the minimum openable window areas exclusion, the following conditions must get met:

The installation of openable windows in livable areas, compliant with Chapter 12 of the Building Code: The entire window area must be a minimum of 10% of floor areas served. Windows should have a glazed section of at least 12 sq. ft, with an openable section of at least 6 sq. ft. They must also be devoid of stops that prevent a full opening. Therefore, the smallest openable area is at least 5% of the floor area served. Another requirement is to install windows at least 30 inches above the finished floor. If other codes call for the installation of window guards with stops or other hindering devices present, the post-fire smoke purge system is still required.

Post-fire smoke purge plays an important role in building interiors. Ideally, you want to reestablish suitable conditions for occupancy as soon as possible after a fire takes place. Real estate property developers can obtain professional engineering services to assist them to decide between stair ventilation or corridor ventilation in new constructions. No option is generally seen as better than the other because each has benefits and drawbacks.

It is essential to know the requirements of other codes related to post-fire smoke purge systems, including the NYC Fire Code and any Mechanical Codes. Getting qualified assistance is always the most effective way to ensure a new project is code-compliant.

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