The Building

9 - 1 1 R e s e a r c h

an attempt to uncover the truth about September 11th 2001

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M.I.T., Rotch Visual Collections

Visual Communications in Building Technology Project

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3.7 LIFE SAFETY SYSTEMS

All of the physical systems thus far described have played a unique role in creating the office space within Sixty State Street. The last physical system to be described is not really a unique system, but rather a collection of many smaller systems and sub-systems whose composite role is to ensure the safety of the tenants using the building. These systems are concerned with problems that stem from the ever present danger of fire. The necessity for such life safety construction in highrise structures has been highlighted by many serious fires outside of the United States. [60, 61] Partially due to our stricter fire regulations, no disasters have befallen major highrise structures in the United States. This good record must be interpreted as a continuing signal that life safety must be a primary design consideration in highrise buildings.

The life safety systems used in Sixty State Street are most easily understood in terms of the different design strategies they represent rather than the specific hardware from which they are constructed. Figure 3.26 attempts to show all the major components of the various life safety systems. Associated with all of the active life safety systems are detection devices and alarms, monitored through one central location on the plaza level. This monitoring location also serves as the building's communication and security center and the control room for both the HVAC and elevator systems. It is from this room that authorized personnel may control the building in the case of a fire or any other emergency.

Figure 3.26 PERSPECTIVE OF LIFE SAFETY SYSTEMS

What are the life safety strategies that are implicitly or explicitly present in Sixty State Street? The first strategy is potentially the most important and often the least obvious -- prevention. The basic concept of prevention is to limit the possible sources of the ignition and to minimize the material available that might respond to possible ignition sources. The electrical system is designed to the National Electrical Code [62] promulgated by the National Fire Protection Association as a minimum standard to prevent ignition from electrical system malfunction. In addition to this built-in attempt to limit ignition sources, certain portions of the building will be declared no smoking zones to further limit potential fire sources. Most building materials found in Sixty State Street are non-combustible, representing another attempt to prevent fire ignition.

Since the working spaces in Sixty State Street cannot in themselves be regulated as to content and potential ignition sources, it is reasonable to expect fires to start. Given a fire ignition, the next life safety strategy employed is to control the fire through suppression. Each floor of the building is fully sprinklered with fusible link sprinkler heads. These sprinklers are fed from a sprinkler loop (see Figure 3.26) branching from a 6-inch standpipe (see Figure 3.27) located in one of the stairwells. In turn, this 6-inch standpipe and the additional standpipe located in the second stairvell are supplied water by an emergency diesel driven upfeed pump located on the second lower level. Once water begins to flow through any sprinkler, a flow meter alarm is triggered sending a signal to the central control room. Manual fire extinguishers are available on each floor at distances never greater than 50 feet from any work station.

Figure 3.27 LIFE SAFETY SYSTEMS

1. .....2.
1. Applying fireproofing to steel.
2. Fireproofing of structural steel.

3. .....4.
3. Sprinkler supply pipes (red elbows).
4. Pumps for the sprinkler system.

5. .....6.
5. Sprinkler system flow control.
6. Four fire safety features.

7. .....8.
7. Three safety features, one tamper alarm.
8. Complete fire protected stairwell.

9. .....10.
9. Building systems with sprinkler pipe showing.
10. Sprinkler pipe awaiting fixture.

At each floor level, in both stairwells, the standpipes have 2-1/2 inch fire hose outlets (see Figure 3.27). If a fire is not totally suppressed by the sprinkler system or hand extinguishers, firemen can move to adjacent floors by manually controlling the elevators, driven by emergency electrical power. From these adjacent floors they can move within the stairvell to the hose outlets and commence to fight out from the stairwell to suppress the fire.

As the fire is fought it is essential to minimize its potential spread and to maintain habitable environments on the non-fire floors. The third life-safety strategy is to physically control the fire's movement. To accomplish this, Sixty State Street is vertically compartmented by fire rated floor systems and fire rated walls surrounding all vertical shafts. To maintain this compartmentation and avoid gross failures of the structure, it is necessary to provide fire resistance in the form of sprayed on cementitious fireproofing on all major structural elements (see Figure 3.27).

In addition to the compartmentation of the structure, the HVAC system is also utilized to minimize fire spread. A smoke detector in the return air plenum activates the fire sub-systems of the HVAC system. The main fresh air supply shaft is reversed and becomes a smoke exhaust shaft with the opening of fire dampers on the fire floor (see Figure 3.27), the closing of fresh air dampers, (see Figure 3.27) on all other floors and the starting of an exhaust fan on the 38th floor. On the service level, fans are activated to pressurize all stairwells and elevator shafts and to supply fresh air to non-fire floors through what had been the relief air shaft. The overall effect of this reversal is to create a negative pressure on the fire floor such that smoke cannot spread through shafts and other openings to non-fire areas.

As the fire is being fought, alarms are sounded and one-way speakers on each floor guide the tenants to safe areas within the building. The fourth life-safety strategy is provided by moving those endangered by the fire. Movement off the fire floor is normally accomplished through either of the two positively pressurized stairwells to adjacent safe floors. The manually controlled elevators can also be used for movement, but are usually reserved for fire fighting personnel.

Figure 3.27 LIFE SAFETY SYSTEMS

11. .....12.
11. Sprinkler head installed.
12. Alarm light and stand pipe.

13. .....14.
13. Three safety features.
14. Fire alarm control center.

15. .....16.
15. Remote controlled smoke damper.
16. Remote controlled smoke damper.

17. .....18.
17. Smoke damper at open position.
18. Fresh air inlet for stairwell.

19. .....20.
19. Smoke damper in elevator shaft.
20. Elevator shaft exhaust fan.

21. .....22.
21. Damper control in duct.
22. ?

23. .....24.
23. Fire exit with four safety features.
24. Emergency generator.

Life safety considerations are responded to by all of the systems and subsystems mentioned above. The key, however, to understanding the concept behind Sixty State Street's life safety systems are the key strategies: prevention, suppression, containment and egress.

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