The recently updated NFPA 88A (2023) introduces several critical new requirements for parking structure ventilation systems, particularly the addition of mixing fans and post-fire smoke control operations, which were previously only covered by standards like BS-7346-7.

NFPA 88A (2023) updates include the mandatory installation of mixing fans in large or open parking structures, airflow velocity requirements to prevent stagnant air zones, and integration of the ventilation system with fire suppression and alarm systems to ensure safety during a fire. Additionally, the new post-fire override requirement allows local fire departments to control ventilation for effective smoke removal once the automatic fire suppression system is deactivated. All of which were not included in the 2019 and earlier editions.

While the International Mechanical Code (IMC) does not yet enforce these provisions, professionals working in jurisdictions using the International Code Council (ICC) standards can still adopt these updates as good practice design guidelines to enhance safety and operational performance. These updates make it crucial for all mechanical engineers, fire and life safety engineers, and architects to understand and implement these new provisions to improve fire safety and operational efficiency in parking structures, even in jurisdictions where NFPA 88A is not strictly enforced.

The Importance of Post-Fire Smoke Control

The inclusion of post-fire smoke control operations is a critical advancement. While this functionality has been standard in other regions, such as the UK with BS-7346-7, it is now a part of NFPA 88A, making it applicable in jurisdictions where this standard is enforced. This addition ensures that local fire departments can clear smoke effectively after a fire event, improving post-fire recovery efforts and overall safety for occupants and first responders.

Refer to the below detailed summary of each new section and table comparing the 2023 vs 2019 editions of NFPA 88A.

Details on the Major Parking Garage (Car Park) Ventilation Additions in 2023 Edition of NFPA 88A

1. Mixing Fans Requirement (New Section 6.3.5)

In the 2023 edition, mixing fans are now required in parking structures where specific conditions are met:

• If the distance between the supply air point and the nearest exhaust air point exceeds 300 ft (91 m).
• For open parking structures where opposing openings are greater than 300 ft (91 m).
• In cases where the modeled average air velocity is less than 1.3 ft/s (0.4 m/s).

These mixing fans help distribute air effectively to maintain safety and ventilation performance.

2. Airflow Velocity Control (New Section 6.3.5.1)

A new requirement mandates that no more than 10% of the parking structure’s volume should have air velocities below 1.3 ft/s (0.4 m/s). This provision ensures that stagnant air pockets, which can pose safety risks, are minimized, enhancing overall air movement within the structure.

3. Distribution of Supply Air (New Section 6.3.5.2)

Supply points, mixing fans, and exhaust fans must now be strategically arranged to ensure that supply air is distributed uniformly throughout the parking structure. This avoids ventilation dead zones and enhances the structure’s safety during regular operation and emergencies.

4. Registered Design Professional Documentation (New Section 6.3.5.3)

Design documentation must now include details on the arrangement and air velocities of the mixing fans, provided by a registered design professional. This addition is significant because it emphasizes the need for rigorous design and calculations to validate the ventilation strategy.

5. Fire System Integration (New Sections 6.3.5.4 & 6.3.5.5)

The mixing fans must be controlled via an electronic interface linked to the fire suppression and fire alarm systems. Upon activation of the automatic fire suppression system, the fans must be shut off to avoid disrupting the fire suppression system and discharge patterns.

An additional benefit of shutting off the fans is that it prevent the high air velocities from disrupting the smoke layer and pushing smoke down towards evacuating occupants (as shown in the figure 1 below). If the smoke layer remains undisturbed, occupants have more time to escape underneath the smoke layer that is developing at the ceiling level (as shown in the figure 2 below).

6. Post-Fire Smoke Control (New Section 6.3.5.6)

A significant new requirement is the post-fire override operation for mixing fans, which allows local fire departments to take control of the ventilation system after a fire. This operation enables effective smoke removal once the fire suppression system is deactivated, a feature previously covered only by standards such as BS-7346-7.

2019 vs 2023 Editions of NFPA 88A for Parking Garage (Car Park) Ventilation

2019 NFPA 88A	2023 NFPA 88A	Difference
6.3.1 All enclosed parking structures shall be ventilated by a mechanical system capable of providing a minimum of 300 L/min per m2 of floor area (1 ft3/min per ft2 of floor area) during hours of normal operation.	6.3.1 All enclosed parking structures shall be ventilated by a mechanical system capable of providing a minimum of 1 ft3/min per ft2 of floor area(300 L/min per m2 of floor area) during hours of normal operation.	No Change. Just Reworded.
6.3.2 A mechanical ventilation system shall not be required in an open parking structure.	6.3.2 A mechanical ventilation system shall not be required in an open parking structure.	No Change.
6.3.3 Mechanical ventilating systems shall be installed in accordance with NFPA 90A. Ductwork shall be constructed of noncombustible material.	6.3.3 Mechanical ventilating systems shall be installed in accordance with NFPA 90A.	No Change. Just Renumbered.
Section does not exist in 2019 and earlier.	6.3.4 Ductwork shall be constructed of noncombustible material.	No Change. Just Renumbered.
Section does not exist in 2019 and earlier.	6.3.5 Mixing fans shall be installed in parking structures where any of the following conditions apply: (1) The shortest distance between any point of the supply air to the closest point of exhaust air is greater than 300 ft (91 m). (2) Open parking structures where the opposing openings are greater than 300 ft (91 m). (3) Where supply or exhaust fans are installed and the average air velocity within the parking structure is modeled at less than 1.3 ft/s (0.4 m/s).	New Section as of 2023.
Section does not exist in 2019 and earlier.	6.3.5.1 Mixing fans shall provide a condition where no more than 10 percent of the volume of the space has air velocities below 1.3 ft/s (0.4 m/s).	New Section as of 2023.
Section does not exist in 2019 and earlier.	6.3.5.2 Supply points, mixing fans, and exhaust fans shall be arranged to distribute supply air throughout the parking structure.	New Section as of 2023.
Section does not exist in 2019 and earlier.	6.3.5.3 A registered design professional shall furnish documentation on the construction documents about the arrangement and velocities of the mixing fans.	New Section as of 2023.
Section does not exist in 2019 and earlier.	6.3.5.4 Mixing fans shall be controlled with an electronic interface to the automatic fire suppression system and the fire detection and alarm system.	New Section as of 2023.
Section does not exist in 2019 and earlier.	6.3.5.5 Mixing fan control systems shall turn off the mixing fans when the automatic fire suppression system is activated.	New Section as of 2023.
Section does not exist in 2019 and earlier.	6.3.5.6 Mixing fan control systems shall provide a post-fire override operation to allow fire stop and fire run operations by local fire departments to clear smoke once the automatic fire suppression system is deactivated.	New Section as of 2023.

Citations

1. NFPA 88A (2023 Edition): National Fire Protection Association. (2023). NFPA 88A: Standard for parking structures. National Fire Protection Association.
2. NFPA 88A (2019 Edition): National Fire Protection Association. (2019). NFPA 88A: Standard for parking structures. National Fire Protection Association.
3. ASHRAE Handbook of Smoke Control Engineering: Klote, J. H., Milke, J. A., Turnbull, P. G., Kashef, A., & Ferreira, M. J. (2012). Handbook of smoke control engineering. American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).
4. International Mechanical Code (2024 Edition): International Code Council. (2023). 2024 International mechanical code. International Code Council.