The Las Vegas Fire Department was handed one of its greatest challenges ever how to fight a fire and provide evacuation at a structure well over 100 stories high. The Stratosphere is an architectural wonder. The tower stands 1,149 feet high, making it the tallest building west of the Mississippi River. It is also the tallest free-standing observation tower in the nation.
Approved by the City Council in April 1990, the Stratosphere was completed and opened on April 29, 1996. The tower is only the crown jewel of the $550 million Stratosphere complex, which includes a 120,000-square-foot shopping mall, 97,000-square-foot casino and 1,500-room hotel. By mid-1997, construction should be completed on an 80,000-square-foot aquarium and an additional 1,000-room hotel. There are also plans for additional hotel rooms for a total of 4,000.
The highest area that can be occupied on Stratosphere is 921 feet high, with a mast rising up to 1,149 feet. The tower is a 13-story building ("The Pod") sitting atop concrete support legs ("The Shaft") 775 feet high. The Pod is considered a mixed-use occupancy for assembly and retail use. It does not contain any sleeping areas. A gross floor area of 112,321 square feet contains a 360-degree revolving restaurant which makes a complete revolution in one hour; meeting and conference rooms; wedding chapels; shops; indoor and outdoor observation areas; rides at the top level; and an area of refuge on the bottom two levels. The total occupant load, including employees, of the Stratosphere is 2,650 people. The Shaft is made of all non-combustible material, and contains only minor mechanical equipment. It is the shaft for elevators, one stairway and utilities.
On Level 12, at 909 feet in the air, is the "Let it Ride High Roller" the world's highest roller coaster, careening on an 865-foot track, reaching speeds of 35 mph and dipping sharply at 32-degree angles.
At the 921-foot level is the world's highest thrill ride, the "Big Shot." Passengers sit in the 16 seats with restraints on an air cylinder device that is attached to the mast on top of the tower. They are shot 160 feet up the mast within two to three seconds reaching about 45 mph and a gravitational force of four Gs. Immediately, they are thrust down at a force less than one negative G but faster than a free fall. The Big Shot is operated with compressed air that reaches between 30,000 and 40,000 pounds of thrust.
Those are just part of what will keep guests coming to this "one of a kind" attraction. The design engineering and cooperative collaboration that make this building so fire safe were also one of a kind. In an effort to ensure this kind of safety, the Las Vegas Fire Department attended numerous design and construction meetings to provide input on how all of the life safety systems would function and be installed.
The pre-planning began the moment the concept was introduced. The department dedicated four fire inspectors to the project. Several suppression personnel were available on an as-needed basis to ensure all was going according to the approved designs. What made this project work was the cooperation between the building department, the fire department and the contractors. They conducted joint inspections and attended numerous meetings together to keep up to date on every aspect.
All of the life safety systems testing was coordinated by a consultant who specializes in that area. All of this testing was done with teams from the fire department and building department, engineers, and contractors from fire sprinkler, fire alarm and plumbing companies. This way, if any question or problem came up during a life safety system test, the answers were provided or solutions were worked out on the spot, without delay.
One of the most intriguing aspects of the tower was how to provide evacuation of the 2,650 people in the event of a major fire. The fire department's fire protection engineering staff, with the help of a fire protection engineering consultant, was involved with all designs for the tower. After much research into buildings of this type, the team decided that no codes existed that would cover all of the needs of this unprecedented building, so it wrote or rewrote some of the codes for the unique aspects of the Stratosphere.
Sound engineering practices were applied to all concepts used on the tower. The building would only have room for one exit stairway with 1,644 steps and four elevators down the center of the shaft, unheard of in many model codes. The steps would prove to be a trying experience for any person with health problems, children, or anyone with disabilities. However, the Shaft stair could still be used by the people who prefer that means of evacuation. There are two enlarged landing rest areas at the 264-foot and 532-foot levels of the Shaft stairs. Emergency phones are located at 100-foot intervals if a problem occurs.
For Safety Of Visitors
The team decided to use the concept of building an area of refuge on the first two floors of the Pod a concrete bunker void of any combustibles with a two-hour fire rating and equipped throughout with sprinklers. Since heat and smoke from a fire in the Pod would tend to rise up, locating the areas of refuge at the lowest two levels provides a safe area. The area has open ventilation to the outside air providing smoke control and ventilation. In the event of a fire, people will exit down to this area and await evacuation. This will provide protection for the occupants from any fire problems that may occur above, in the pod, for a long period of time. This area will hold the entire occupant load of the Pod.
To evacuate all of those people safely and quickly, it was determined that the elevators would need to be used unprecedented in established practices.
The team began work on how to make this concept succeed. The four elevators are a special double deck elevator. One car is attached on top of another car. These elevators can evacuate two floors at one time. (One elevator is dedicated to service use and firefighter use.) These elevators travel at 1,800 feet per minute, making them some of the fastest in the world. There are two separate two-hour rated shafts with two elevators in each shaft. The motors are in rooms protected by a two-hour rating. This insures that there will always have a set of elevators operating in the event one set fails.
Because the express elevators are the primary evacuation means from the areas of refuge, locating the refuge areas at the bottom eliminates the problem of the elevators traveling through the fire floors. If any one elevator is out of service, the occupant load of the Pod is reduced by 25 percent. The occupant load is monitored electronically by turnstiles at the bottom of the tower.
To ensure that all of the life safety systems, including the elevators, will function the building was designed with three emergency power generators providing a redundant backup. The emergency power for the building goes up one side of the shaft in a rated enclosure and the primary building power goes up another rated enclosure. This design provides for an additional backup, ensuring that power will not fail due to an electrical fire in a power shaft. The tower has an automatic fire sprinkler and standpipe systems throughout. The design of the system is unique in that it has a higher density of water than required for this type of building.
The three stairs serving the Pod between the areas of refuge at the 775-foot level and the top at the 921-foot level are provided with Class I standpipes equipped with 21/2-inch hose valves. Hose cabinets with Class II standpipe and 100 feet of 11/2-inch hose and variable fog nozzles are located throughout the different floor levels of the pod. One Class I standpipe equipped with 21/2-inch hose valve is provided at the enlarged landings (at 264-foot and 532-foot elevations) within the shaft in the core structure.
The water supply system for the fire protection consists of two diesel fire pumps rated for 1,000 gpm with a high-pressure rating of 405 psi at ground level. Pumps take suction from two separate municipal connections feeding four water storage tanks with the capacity of 7,500 gallons each. A total of 30,000 gallons of fire protection water is located at the top of the tower on the 11th floor at the 896-foot elevation. Two electric fire pumps take suction from the water tanks on floor 11 of the Pod. The pumps are rated for 1,000 gpm at 100 psi and located on the 10th floor of the tower at the 882-foot elevation, providing supply for the sprinkler and standpipe systems.
The second diesel fire pump at the ground level is only for backup, in case of a failure of the primary pump. The four 7,500-gallon tanks on the top have individual supply lines and float valves. These tanks are the secondary water supply and could provide suppression water if the pumps at the bottom fail to provide the makeup water. The redundancy in having four tanks is comforting, since failure in one, two or even three tanks would leave sufficient water for the automatic fire sprinkler systems. The electric fire pumps at the top draw water from the tanks and supplies the automatic sprinkler and the standpipe systems. Once again, the second electric fire pump at the top is for the purpose of redundancy.
The redundancies built into the water supply system mean that only multiple catastrophes could render the automatic fire sprinkler and standpipe systems without a water supply. To provide yet another backup, high-pressure hoses were purchased for engine crews to let them provide the needed supply to the building. In order to take over the system in the Stratosphere, a minimum pressure of 454 psi is required by an engine company, a task that one engine company cannot produce without having special pumping equipment. The Las Vegas Fire Department, after investigating how to pump this much pressure without having to buy trucks with specialized equipment, did a significant amount of research to develop a procedure. This research included working with the Los Angeles City, CA, Fire Department and local fire protection system companies.
Finally, a plan was developed. A series pump operation would be needed to develop the 454-psi-plus required pressures. Series pumping is nothing more than a short relay pump operation in which the pumper takes water from the fire hydrant, and pumps into the intake of the second pumper. The second pumper boosts the pressure even higher. This method is used when pressures higher than the capabilities of a single pumper are required.
Series pumping is based on the principle that allows the centrifugal pump in the fire department pumper to take advantage of incoming pressure. This actually boosts the pressure and capacity of the pump itself without requiring an increase in horsepower by the engine turning the pump. When two or more pumpers are pumping in series, they divide the overall required pressure to supply the system between them.
This type of operation lets the pumpers operate at a safe rpm range and also allows for an increase in flow. The department had to develop special operating procedures to utilize this unusual approach of pumping, and training was then provided to all personnel involved. While conducting the practice drills, pressures in excess of 600 psi were achieved at the discharge of the second pumper. This provided pressures in excess of 100 psi on the 12th level of the Pod at the 909-feet elevation. During another practice drill, the series pump operation was able to produce a flow of 1,100 gpm via two 21/2-inch open butt lines on the simulated fire floor 850 feet up. The residual pressure at the standpipe was 35 psi, indicating that more water was available.
The Stratosphere is provided with a fully automatic and a manual fire alarm system. The addressable emergency voice/alarm communication system performs typical control functions, as do other high-rise building fire alarm systems. These functions include automatic release of hold-open doors, shutting down HVAC systems, activating smoke management systems and recalling elevator. The alarm system also shuts down the thrill rides and stops the restaurant turntable from rotating in the event of an emergency.
Automatic smoke detection is provided throughout the Pod, except for the kitchens, which are provided with combination rate-of-rise heat detectors, and the areas of refuge, which are open to the outside. Manual pull stations are located within each stair at each floor level of the Pod. Speakers and strobes are located throughout the pod.
Three identical, fire alarm control panels are located in each of the three fire command centers. The main fire command center at the ground floor is located by the Las Vegas Boulevard entrance. Fire command center 2 is located at the base of the tower at the Shaft stair discharge, and center 3 is located at the lower area of refuge level at the 775-foot elevation. Redundancy is the reason for having three command centers. These rooms have identical fire alarm panels, smoke management graphic panels, and elevator control and monitoring systems. These rooms are designed for the storage of fire department equipment such as hose, nozzles, air bottles, turnouts and gurneys.
Upon activation of the fire alarm system, the occupants of the floor of origin and the floors above and below are directed to the area of refuge for the purpose of evacuation, if deemed necessary. The area of refuge has adequate capacity to handle the entire occupant load of the Pod, if total evacuation is required.
The pressure sandwich concept is applied in the design of the smoke management system for the Pod. Upon activation of the smoke management system, the floor of origin will be in exhaust mode, and the floors above and below will be in pressurization mode. Dedicated exhaust fans are provided for the smoke management system. The normal HVAC system will provide 100 percent outside air in the smoke management mode. All stairways and elevator lobbies in the Pod also become pressurized. The Pod is located high above the base building, the Shaft stair is pressurized and has two-hour-rated enclosures, so the probability that the products of combustion will affect the Pod's occupants is minimized.
In a fire scenario involving the base building, the Pod is not required to be evacuated, unless determined by the fire department as necessary. Because of the very limited fuel load, a fire in the Shaft stair should not impact the Pod's occupants. Automatic evacuation will only be conducted if the fire is located in the Pod. In this scenario since the areas of refuge are at the lowest level of the Pod and the products of combustion tend to spread upward, the occupants will not be exposed to heat or smoke. The express elevator traveling from the areas of refuge to the base building would not be impacted by such a fire.
The Las Vegas Fire Department conducted several drills with Stratosphere Corp. personnel. All alarm and evacuation procedures have been worked out. The training of Stratosphere personnel is ongoing and the they will be attending a "High Rise Life Safety Program" designed and taught by fire department personnel.
This program has been in place in Las Vegas for many years and has proven to be effective in preventing or minimizing fire loss in high-rise buildings. Such training teaches personnel how to work with the fire department during an emergency. The employees learn how a fire starts, how to fight a fire with extinguishers and hoselines, and how to handle bomb threats and bomb recognition. Participants do live-fire training and learn how to minimize water damage from flowing sprinkler heads. The most important item that is taught is how to prevent fires from occurring by following fire safety practices.
The fire department plans to conduct monthly drills with personnel at the Stratosphere and will continue to update its pre-plan.
Numerous man hours have gone into this project, and this time commitment will continue since Stratosphere Corp. is building phases two and three for the additions to the mall, casino and hotel. This building will be a landmark for many years to come. This entire process has made the fire department smarter ... and the community safer. Considering the unique ride attractions, it is one small step for the adventurous thrill seekers and one giant leap for fire-safe buildings.
Darrol Mosley is a senior fire inspector with the Las Vegas, NV, Fire Department.
