NFPA Journal: Fire protection challenges for A CITY WITHIN A CITY

The Mandalay Bay Hotel and Casino

THE MANDALAY BAY HOTEL AND CASINO is one of the largest hotels in the world. With more than 4,900 hotel rooms in a single complex, it dwarfs the major hotels in most U.S. cities. However, thinking of the property as a hotel misses the bigger part of the fire protection story. The complex includes a large casino, one of the biggest convention centers in the world, a theater, an arena, a shopping mall, and an aquarium.

In early 1996, Klai Juba Architects began designing the original 43-story building, which had about 3,800 guest rooms and suites. Below the hotel tower is a low-rise podium of about 1.4 million square feet (130,060 square meters) that contains a 125,000-square-foot (9,90-square-meter) casino, a 1,800-seat show theater, a separate performance theater for the House of Blues, and a shopping and restaurant arcade. It also includes a registration desk and service areas for Mandalay Bay and The Four Seasons hotel, both of which are in the same building but have separate entrances, as well as several restaurants, meeting rooms in The Four Seasons, and back-of-house areas.

Built at the same time were a five-story open garage with about 400,000 square feet (18,580 square meters) of parking per level, a convention center of about 300,000 square feet (27,870 square meters), an arena that can hold 12,000 people, and a connector to the Luxor hotel and Casino, which was originally intended to be used as a retail mall. The complex opened in 1999 and was an immediate success.

Following the opening, an aquarium was added, also in 2000. Next came a new three-level convention center covering 1.8 million square feet (167,221square meters) and, more recently, a 1,120-room suite hotel called The hotel at Maiidalay and a 125,000-squarc-foot (11,613-square-meter) retail mall in the Luxor connector (see Figure 1).

When considered with the Luxor and Excalibur Resort and Casino, which are also owned by Mandalay and physically connected by walkways or malls, there are more than 13,000 guest rooms and nearly 300,000 square feet (27,870 square meters) of casino area.

Fire protection issues

A complex such as the Mandalay Bay presents several key fire protection issues. First and foremost are moving and evacuating large numbers of people and providing discharge and holding areas for them. Other major issues involve compartmentation; separation of buildings and occupancies; designing and installing proper sprinkler protection, particularly in high-ceiling areas; smoke control; and the development of a logical, cohesive approach to fire alarm and notification.

Along with these major fire protection decisions, there were several more mundane but still important fire protection and code issues to resolve. These included fire-stopping beneath the raised floor of the stage of the "Mamma Mia!" musical; evacuation and security for cage areas where the money is handled; construction and protection for the Wall of Fire, the front entrance of a restaurant; and interior finishes and furnishings needed to make the project a vibrant, inviting location.

Another key feature of this and many other Las Vegas projects was the speed and pace of design and construction. From first design until The Hotel opened eight years later, more than 12 million square feet (743,203 square meters) of space was built. The original project was designed and constructed in less than three years, and the convention center expansion was completed in less than two years. Nowhere else in the country, or perhaps the world, are major projects designed and built so quickly.

In order to design and build at this pace, the owner, designer, contractor, and the authority having jurisdiction (AHJ) must cooperate closely and work as a team. Mandalay Development kept its team intact from start to finish, creating a sense of accomplishment and teamwork that is often missing in major projects. That, and the cooperation of the Clark County Building and Fire Departments in responding rapidly to issues, reviewing plans, inspecting systems and buildings, and acceptance testing final installations, is what allowed this complex to be built so quickly with such a high quality of construction.

The overall complex

The original complex contains much of the infrastructure for the future additions to the property. Because the same design team was involved throughout the process, decisions made in the first phase were reinforced, rather than compromised, by subsequent phases.

The complex has an integrated, coordinated fire protection program, the key to which is the automatic sprinkler protection installed throughout. The sprinkler, standpipe, and water supply systems are designed in accordance with NFPA Standards. The sprinkler system is supplied by fire pumps in a central plant, which is a separate, stand-alone structure. The sprinkler and standpipe systems for the entire site are interconnected, with a number of fire department connections. There are also redundant annunciators at some of the remote fire department response points.

Another important feature in a project this large is compartmentation. The entire complex is of fire-resistive construction, so building-stability and floor-to-floor separations were provided. Horizontal compartmentation, by means of 4-hour fire walls and 2-hour fire barriers, was also provided to limit the potential of very large losses (see Figure 2).

The complex is served by a single fire alarm and notification system, with automatic voice communication throughout, designed in accordance with NFPA 72. Audible zones are coordinated with sprinkler, alarm, smoke control, and compartmentation zones. On the hotel floors, alarms sound on the floor of origin, the floor above, and the floor below. On lower floors, the designer, the fire alarm contractor, and the Clark County Fire Department worked together to balance the number of people relocated and the hazard to which they may be exposed. This limits initial evacuation to those who need it first, then relies on the fire department to make subsequent evacuation decisions. This approach is typical for Las Vegas properties and is essential to controlling crowd movement.

A single fire command center (FCC) in the central plant portion of the original complex serves the entire project. The FCC is permanently staffed.

The site also has several emergency generators near the buildings they serve to support all key fire protection components.

Most of the facility, including the hotel buildings, the mall, the low-rise podium, and the convention center expansion, is designed and constructed as a high-rise building. The original convention center and the arena are separated from other buildings by 4-hour firewalls and were not treated as a high-rise. However, the primary difference is only that no smoke control was provided in the convention center.

In Nevada, buildings are considered to be high-rises when they are more than 55 feet (17 meters) high. Although the new convention center is only three stories high, the third floor is more than 55 feet above grade, so the building was constructed as a high-rise.

Specific building issues

Because of their many uses, each building at the site had some unique features that had to be considered. This article cannot address all of these features, so it concentrates instead on some of the key issues in the major building components.

The primary fire protection issue for the casino was evacuating large numbers of people. Occupant load calculations for the first floor of the building projected about 14,000 people on this floor. While the first floor is at grade level at the front end of the building, it is above grade on the other three sides. To exacerbate the problem, the five-story parking garage abuts the building on the west; the theatre and mall cover much of the north face and the House of Blues blocks another large portion; the convention center is to the southwest; and the Four Seasons lobby is to the southeast.

Although the fire alarm system does not automatically sound to the entire floor, the egress calculations assumed that all areas open to the casino or separated by less than 2-hour construction would simultaneously evacuate. To solve the exiting issues for this floor, a combination of exits direct to grade, horizontal exits to other parts of the building or to other buildings, and stairs was used.

The horizontal exits lead to the west into the garage through large sliding doors with man doors and panic hardware into the convention center, into the theater lobby on the northwest, and into the Four Seasons lobby on the southeast. Stairs discharge beneath the mall building into basement exit passageways and down to the pool area. Paths and walkways in the pool area were sized to accommodate the occupant loads of people exiting into the area.

The exit discharges beneath the mall were of particular concern. Clear areas for discharge were designated until access to Hacienda Boulevard was reached. Since the mall also covers Hacienda, analyses of smoke movement and exposures were performed to ensure that occupants would not be exposed and able to exit safely.

The arena

The arena is designed to hold up to 12,000 people in convention or concert mode and about 8,500 people in sporting-event mode. It may also be used as an extension of exhibit space on the floor of the bowl and in concourses. Therefore, the fire protection design had to be flexible while providing adequate protection for each type of event.

The smoke-protected assembly seating provisions of NFPA 101®, Life Safety Code®, were used to maximize seating. These provisions require a smoke-control system designed to keep the level of smoke above the highest occupants in the facility. This, in turn, demands that a fire size be developed.

Because the floor of the arena could be used for exhibit space, the fire size is quite large. The arena is about 80 feet (24 meters) high, so a combination of the DETACT fire model (a model developed by NIST to determine thermal detector response) and the results of U.S. Navy tests in aircraft hangars was used to estimate fire size upon sprinkler actuation. Once sprinklers actuate, the models assume the fire size, which is assumed to be 20 megawatts (MW), will remain constant.

In reality, it is very unlikely that the seats in the arena would be full when the floor is being used for exhibits. For the sake of conservatism, however, the designers assumed that the bowl seating area was completely occupied by people while the floor contained exhibits.

Above the top row of seating is a press area that will have a very small occupant load. Using the exhaust method as a means of calculating smoke-layer height and keeping it above the press area resulted in needing very-high-capacity exhaust fans, as well as the need to get supply to the floor. Rather than maintaining the smoke layer above the press level, it was allowed to descend gradually to 10 feet (3 meters) above the top public level. For the press level, a timed exiting study was performed to determine how long it would take to evacuate. This was compared to the time it would take the smoke layer to drop to that level. Using a safety factor of two, the model showed that the occupants of the press level had more than enough time to evacuate before the smoke layer reached them. Using this approach, the designers reduced the exhaust capacity and the related supply at the base by about 200,000 cubic feet per minute (5,663 cubic meters per minute).

The convention center expansion

The new convention center presented the greatest challenges for the fire protection engineering team. It is one of the largest convention centers in the world and, as such, attracts huge crowds in the range of 75,000 people. Halls A through D on the first floor alone can be combined to give 600,000 square feet (55,70 square meters) of exhibit space with an occupant load of 40,000 people.

The size of the building and the halls created two significant challenges. First, the code permitted a maximum travel distance of 250 feet (76 meters). In some exhibit configurations, travel distance to the exit doors from the halls could be as great as 450 feet (137 meters). And second, there is a need for truck access to two levels because there are large exhibit halls on two levels. This means that exiting and truck traffic need the same space.

To address the travel distance issue, a smoke study and egress analysis was performed. Although the halls are massive, the exiting was rather simple, so timed egress was manually calculated rather than computerized. This resulted in a required safe egress time (RSET).

To calculate the available safe egress time (ASET), the fire protection engineering team used computer modeling to determine when the smoke layer descended to unsafe levels. As with any similar model, a fire size had to be developed before smoke layer height could be calculated. With a ceiling height of 35 feet (11 meters), a DETACT model could be run to determine the fire size at time of sprinkler actuation. However, some shows in convention centers have large shielded areas, such as display booths or yachts, manufactured homes or trucks. The Clark County Fire Department requires sprinkler protection in large covered exhibits, so the covered display booths will not form the most challenging fire. To facilitate this protection, drop risers were provided at several columns. Thus, the remaining challenge is enclosed vehicles.

Although fully loaded trucks may be on the floor during setup and takedown, they are unlikely to be present when a show is in session. Therefore, the design team evaluated anticipated fires in yachts and mobile manufactured homes. Since yachts are typically more compartmented than manufactured homes, which may be open from end to end, the designers developed the peak heat release rate before ceiling burn-through by estimating the peak rate for a series of "rooms" in a mobile manufactured home, and combined them to assume simultaneous burning. This resulted in an estimated fire size of about 16 MW. A fast-growing fire was assumed.

The fire model CFAST was used. CFAST is an acronym for Consolidated Fire and Smoke Transport, and is a zone fire model developed at NIST. This model and other zone fire models are not normally well suited for direct application to large-volume spaces such as convention centers and warehouses. One limiting assumption the model makes is that all products of combustion rise instantaneously to the ceiling of the specified room and form a uniformly thick layer across the ceiling. If one were to observe an actual fire in the middle of a convention center, however, one would probably notice a significant variation in layer height depending on how far one was standing from the fire. For example, no upper layer will have formed initially at a distance of 200 feet (61 meters) from the fire. As the fire progresses, one would notice that, far from the fire, smoke had cooled and the layer had dropped. The smoke would also be less dense in these far-field areas. Near the fire, where the plume and ceiling jet are very hot, the layer would most likely be higher, hotter, and more hazardous. Current zone models don't readily account for this variable phenomenon.

To refine the fire modeling and more appropriately depict the fire physics in large spaces, we used the concept of "pseudo-rooms," subdividing the large halls into 18 different compartments. We chose the number of compartments based on the size of the room and degree of accuracy desired.

One may think of these compartments as individual boxes that are all open to each other by very large "door" openings. Between each compartment, the soffits of the "doors" are 33 feet (10 meters) high, as opposed to the ceiling height of 35 feet (11 meters), and the width of the "doors" is 95 percent of the length of the "compartment." Generally, these openings reduce the compartment-to-compartment flow by 2 to 5 percent. This approach provides a means of accounting for the friction, thermal and otherwise, experienced by the "flowing" products of combustion. As in a real fire, it would take appreciable amounts of combustion gases longer to collect far from the fire. In addition, combustion products farther from the fire would be cooler. Using pseudo-compartments in zone fire models better reflects this phenomenon by predicting a lower smoke layer further from the fire. The number of pseudo-compartments and size of the compartments is related to the size of the space and engineering judgment. The results are a more realistic representation of a fire in an exhibition hall.

Safe egress

Using this approach, the required safe egress time in the halls ranged from 8 minutes for the smaller halls to 15 minutes for the larger halls. The available safe egress time ranged from 10 minutes for the small halls to 20 minutes for the larger ones. In all cases, the available time exceeded the required time. Safety factors were also incorporated into the design. The ASET times were based only on the size of the hall and the smoke reservoir. In actuality, smoke control is provided in each of the halls, calculated to maintain the smoke layer at 10 feet (3 meters), so a further significant safety factor is provided. Furthermore, the times to exit were doubled before comparing the RSET and ASET The times shown above are those which include the double evacuation time factor.

The Mandalay Bay is one of the largest connected buildings in the world, with a calculated occupant load of more than 100,000 people. Developing a fire program for such a project requires a comprehensive, thoughtful approach, and the close cooperation of the entire ownership, design, and construction team. Fortunately, this type of teamwork existed during the eight years it took to construct this complex.

By James R. Quiter, P.E.

JAMES R QUITER, PE, is a principal of Arup, an international engineering firm, and head of ArupFire in the Americas. He served as Arup's project manager and principal in charge for the convention center, mall, and hotel expansion projects, and as RJA's principal in charge during the earlier phases. Quiter is also chair of the NFPA Safety to Life Correlating Committee and of the newly formed NFPA High-Rise Building Safety Advisory Committee.