Case study: Super-tall building smoke control system

The Wilshire Grand Center project includes best practices in smoke control

By Nathan B. Wittasek, PE, CFEI, LEED AP, CASp May 18, 2020

The Wilshire Grand Center owned by Hanjin Corp. and designed by AC Martin Partners is the tallest building west of the Mississippi River. The tower comprises 890 hotel rooms with related amenities and 18 office levels above a retail and parking podium.

At the base of the 73-story tower, there is an atrium that extends from the first floor to the seventh floor. Ten pressurized stairs with pressurized vestibules serve negatively pressurized corridors in the hotel and negatively pressurized floors on the office levels. The subterranean parking garage is provided with an air change system that is integrated with the carbon monoxide ventilation and methane systems.

Figure 3 shows the atrium, highlighting combustible fuel loads, balcony conditions and modeling outputs as well as construction photos of stair and floor pressurization components.

The project embodies many of the best practices in smoke control that start with the analyses of smoke containment systems using the networked airflow model CONTAM from NIST to track air movement through the entire building, as well as fire dynamics simulator to analyze the requirements for smoke management within the atrium. Tenability criteria and evacuation times were calculated in the context of available safe egress time versus required safe egress time. Specific design fires were quantified from a possible roster of design fire scenarios and ultimately vetted by the authorities having jurisdiction.

Smoke containment and smoke management modeling approaches were compared to the NFPA 92: Standard for Smoke Control Systems algebraic equations and capacities were ultimately verified through a yearlong commissioning process.

The smoke containment systems were designed using complimentary pressurization approaches. The stair pressurization system pressurizes the stair shaft, which cascades into the vestibules on each floor via cracks under and around the doors or via transfer grills where larger quantities of air are required to achieve the required pressure gradients.

In turn, portions of the first smoke zone in which smoke is detected are depressurized such that the positive pressure gradient across the stair and vestibule doors in such a way that the requirements for the individual systems is minimized. In this way, in the unlikely event that any one fan were to fail, there would still be systems capable of generating a pressure gradient to resist smoke movement into the means of egress. To provide maximum flexibility for future tenants of the office, each floor was provided with an independent smoke exhaust fan that can be separately controlled and balanced.

The firefighters’ smoke control station is housed in the fire command center — a protected and conditioned space. A mechanical test and inspection panel — a requirement of the City of Los Angeles intended to facilitate detailed inspection and troubleshooting of smoke control components — provides control over each actively managed damper and fan in the building. The smoke control panel is designed with responding firefighters in mind, providing an intuitive interface that allows for control over a single smoke zone and all stairwell pressurization fans simultaneously.

While the system is entirely automatic based on the activation of a sprinkler waterflow or smoke detector, the manual mode allows for zoned control over each of the 10 podium and subterranean smoke zones and any of the office or hotel smoke zones. As per the system configuration, the smoke control panel will not allow the system to execute conflicting commands that could cause damage to the system or result in other failures to contain smoke or maintain tenability.

The system operation, inclusive of the configuration of automatic closing doors throughout, works the same way under emergency/standby power as is it does when on normal power. In this way, there can be a seamless transition if the building were to lose normal power and outcomes for system commands would be the same, thereby reducing the likelihood of unintended outcomes.

Author Bio: Nathan B. Wittasek is a principal and vice president at Simpson Gumpertz & Heger. Wittasek is a fire protection engineer who specializes in tall building fire life safety design with more than 20 years of experience in North America, Asia and the Middle East.