National Institute of Standards and Techno

Technology Administration

U.S. Department of Commerce

NIST Response to the World Trade Center Di

Federal Building and Fire Safety Investiga

of 

the World Trade Center Disaster

Part IV – Life Safety

April 5, 2005
Analysis of Life Safety Analysis of Life Safety 

• Nearly 1,200 first person interviews of occupants and emergency 

plus 700 published media accounts

• Review of emergency communication records (radio communica

calls, 500 plus post-9/11 FDNY interviews)

• Evacuation and occupant behavior:

• Building population demographics; analysis of decedents• Evacuation rates; roof evacuation; communications to occup

impaired occupants; building damage observations

• Emergency response:

• First responder roles; situational awareness; access; high-ris

radio communications; command and control

• Active fire protection systems:

• Significant pre-9/11 fires; sprinkler and standpipe system; fire 

system; smoke management system
First-Person Interviews Person Interviews

• 1,056 Interviews involving building occupants

• 225 face-to-face interviews• 803 telephone interviews• 28 participants in 6 focus groups

• 116 Interviews with emergency responders

• 68 FDNY interviews• 25 NYPD interviews• 15 PANYNJ interviews• 8 other interviews

• Over 700 published media interviews• Over 500 interviews conducted by FDNY soon after September 
Communications Sources Communications Sources

• The PANYNJ provided radio and telephone communications reco

related to the emergency response.

• NYPD provided radio communications recordings for the Special 

Units frequencies and Division 1 frequency that were used in opethe WTC and the Division 1 citywide frequency.

• New York City provided NIST with opportunity to listen to recordin

telephone calls made to 9-1-1 Emergency Operators and FDNY FDispatchers. The FDNY Manhattan dispatch communications tapsupplied to NIST.

• PANYNJ also supplied a recording from the FDNY high-rise chan

Authority Police Dept. (PAPD) channel 30 repeater located at the 

Note: The FDNY Field Communications truck was not in service a

recordings of FDNY radio communications at the site were not m
Evacuation and Emergency Response Evacuation and Emergency Response

Based on 1,056 interviews of surviving WTC occupants and 116 intemergency responders.

• It is estimated that 17,400 occupants (± 1,200) were present in the WTC tower

morning of September 11, 2001. The initial population of each tower was similar

in WTC 1 and 8,500 (± 900) in WTC 2. Of those present on September 11, 2001, 

also present during the 1993 bombing. 

• About 6 percent of the surviving occupants reported a pre-existing limi

mobility. These limitations included obesity, heart condition, needing assist

pregnancy, asthma, being elderly, chronic condition, recent surgery or injury

• About 7 percent of the surviving occupants reported having special kno

the building. These included fire safety staff, floor wardens, searchers, buil

maintenance, and security staff. Searchers assist the floor wardens in facilit

• Approximately 87 percent of the WTC tower occupants, including more than 9

those below the floors of impact, were able to evacuate successfully. 

• Rough estimates indicate that about 20 percent or more of the 2,567 building oc

emergency responders who were in the WTC towers and lost their lives may 

in the buildings just prior to their collapse. This estimate includes 118 occupan

floors of impact who died but not the large but unknown number of occupants abov

impact who may have been alive prior to collapse.
Decedent Analysis Decedent Analysis

September11Victims.com: This site is dedicated to 

the victims of September 11, 2001 tragedy.

Portraits: 9/11/01: Published by the New York Times 

in 2003, this book includes short interviews with family members of many decedents.

CNN.com In-Depth Special 

(http://www.cnn.com/SPECIALS/2001/memorial/index.html): Tribute site for people to write remembrances of decedents.

Badge List maintained by Port Authority of New York 

and New Jersey: Includes name, employer, building, and floor for all occupants with badgeaccess to WTC 1 or WTC 2.

Numerous memorial sites maintained by companies 

which lost employees: Includes names and remembrances of decedents. Examples include the Port Authority, Fire and Police Departments, Marsh & McLennan Companies, EuroBrokers, Fiduciary Trust, and others.

Newsday.com: Includes short stories written about 

specific decedents.

NIST Interviews with occupants and family members* Where possible, eyewitness accounts were used to place individuals. 

Where no specific accounts existed, employer and floor information was used to place individuals.

Total No Information United Flight 175 American Flight 11 Bystander/Nearby Building Occupant 

Volunteer Responders 

Federal 

Hospital/Paramedic 

PAPD 

NYPD FDNY 

First Responders (Total) Unknown Location Inside WTC 1 or WTC 2Confirmed Below Impact in WTC 1 or WTC 2

Below Impact 

At or Above Impact 

World Trade Center 2 Occupants 

Below Impact 

At or Above Impact 

World Trade Center 1 Occupants 

Likely Location at Time of Impact* 
Evacuation Rates in the WTC Towers Evacuation Rates in the WTC Towers

• The overall evacuation rate in WTC 2 (108 survivors per min) was about 50 pe

than that in WTC 1 (73 survivors per min). Overall, about 7,900 survivors evacu

73 min (i.e., from the instant the WTC 1 was struck by aircraft until WTC 2 collapse

7,500 survivors evacuated WTC 1 in 103 min.

• After the first airplane struck WTC 1 and before the second airplane struck W

survivors in WTC 2 were twice as likely as those in WTC 1 to have already exited t

percent versus 21 percent). The rate of evacuation completion in WTC 2 was tWTC 1 during that same period.

• Approximately 75 percent of WTC 2 occupants above the 78th floor at 8:46 am 

descended below the 78th floor prior to the aircraft strike at 9:03 am.

• Functioning elevators allowed many (roughly 3,000) survivors to self-ev

during the 16 minutes prior to aircraft impact. All but one of the 99 elevat

were not functioning, and survivors could only use the stairways.

• Soon after WTC 2 was struck by the airplane until about 20 min before each buildi

survivors in WTC 2 and WTC 1 exited at about the same rate (the prior evacuation 

• During the last 20 min before each building collapsed, the evacuation rate in both b

to about one-fifth the immediately prior evacuation rate. This suggests that for tho

able to reach and use undamaged exits and stairways, the egress capacity (nwidth of exits and stairways) was adequate to accommodate survivors.
Evacuation Rates in the WTC Towers (2

Evacuation Rates in the WTC Towers (2

• Even though a percentage of evacuees reported that they perceived counterflow (

ingress) to be problem, it was found not to be a significant factor in the total ev

occupants in WTC 1 when compared to other factors, including evacuation initia

evacuation interruption, and encountering obstacles in the evacuation path (environsuch as smoke, water, or debris.

• Based on use of existing egress models and actual evacuation time on September 

estimated that a full capacity evacuation of each WTC tower with 25,000 peoplethe number present on September 11, 2001—would have required about 4 houbuildings been full, it is possible that as many as 14,000 people may have lost based on rough estimates using existing models. To achieve a significantly fas

evacuation at full capacity would have required increases in egress capacity (numb

exits and stairways). The egress capacity required by current building codes an

based on a “phased” evacuation strategy, not “full” evacuation. 

• The average surviving occupants moved slower down stairs and through stai

previously reported for non-emergency evacuations.

• In WTC 1, the average surviving occupant spent 48 seconds per floor descend

This translates to approximately 0.2 m/s (0.65 ft/s), which is about 50% of the 

measurement presented in the SFPE Handbook of Fire Protection Engineering 

emergency evacuations.

• In WTC 1, each stairwell door exited approximately 37 people per minute, ave

minutes, which is comparable to the slowest measurement presented in the SFFire Protection Engineering for non-emergency evacuations.
Condition of Stairwells Condition of Stairwells

• The stairwells, with partition wall enclosures that provided a 2 h fire-rating but little s

integrity, were damaged in the region of the aircraft impacted floors. 

• One of the stairwells in WTC 2 (Stairwell A on the Northwest side) was passab

of aircraft impact for some period of time after WTC 2 was attacked.

• All three stairwells in WTC 1 and the two other stairwells in WTC 2 were rendered im

the region of aircraft impact.
Stairwell Remoteness Requirements Stairwell Remoteness Requirements

• The 1968 NYC Building Code required stairwells to be as 

as practicable.’

• New York City Local Law 16 (1984) amended the 1968 NY

Code to require the minimum distance between exit door oall buildings to be 30 feet or one-third the maximum travel the floor, whichever is greater.

• IBC 2003, NFPA 5000, & the NFPA Life Safety Code requ

least two stairwells on any floor shall be located at least:

• One-third of the diagonal of the area served, if fully spr• One-half of the diagonal of the area served, if not fullysprinklered,

measured from door edge to door edge along a straight lin

the walking path between the doors, if the corridors have ware rated for at least one hour.
• Tenant floors in WTC 1 and WTC 2 had a diagonal distance of 294 ft. Therefore, one

diagonal distance would have been 98 ft and one-half of the diagonal distance would 

The corridor walls in the WTC Towers were two hour rated; the 1996 due diligence rethat some of the corridor separation walls did not run slab-to-slab and would have bee

unrated since they terminated at the suspended ceiling.

• Stairwell separation in WTC 1 and WTC 2 ranged from 70 ft (Floors 83 and abov

impact region in WTC 1) to 200 ft (Floors 79 – 82, including the impact region in demonstrating that large stairwell separations in the WTC towers were practica

• On some WTC floors (e.g., the floors of impact in WTC 2), the separation of stai

exceeded the typical model code requirement (98 ft sprinklered; 147 ft unsprink

floors (e.g., the floors of impact in WTC 1), the stair separation was not consiste

model code criteria.

• The maximum travel distance for the WTC towers was about 180 ft. The stairwell se

consistent with the 2001 NYC building code requirement of one-third the travel 

• The advantages of moving stairwell locations on the floor plan include reclamation of 

occupant use above terminated elevator shafts and overcoming obstructions posed b

installed on mechanical floors.

• A walking path measurement may allow two stairwells to be physically proximate, yet 

walking path distance between doors (i.e., scissor stairs), although the IBC credits sci

single stairwell.

Findings on Stairwell Remoteness Findings on Stairwell Remoteness
Egress Provisions: Windows on the Wor

Egress Provisions: Windows on the Wor

• The 106th and 107th floors of WTC 1 contained a restaurant, bar, function room

support areas, and offices from which the operation was run. 

• The design number of occupants for a typical “office use” floor in the WTC tow

the design number of occupants for the “assembly use” floors was over 1,130 for floor 106 and 1,013 for floor 107 (Fasullo 1995).

• The 1968 NYC Building Code required a minimum of four stairwells servin

occupant loads greater than 1,000.

• Locating assembly space high in a building poses additional challenges since 

Building Code does not permit the capacity of an egress component to be decdirection of travel.

• NIST found no evidence indicating that the Building Code requirements f

spaces (floors 106 and 107 of WTC 1; floor 107 of WTC 2) were considereoriginal design of the WTC towers.

• Since the September 11, 2001 attack took place at breakfast time, there were 

(guests and staff) in the Windows on the World floors who lost their lives. If th

occurred when floors 106 and 107 were loaded near their capacity, as maoccupants could have lost their lives, since there were no survivors abovimpact in WTC 1.
Egress Provisions: Windows on the Wo

Egress Provisions: Windows on the Wo

• The egress provisions for the Windows on the World floors were not consisten

Building Code requirements. The PANYNJ and NYC Department of Buildings r

agreement in December 1994, and a solution was implemented in 1995.

• The solution implemented in 1995 created areas of refuge on those floors where occ

wait to get into the stairs that did not have adequate capacity for the numbers of peo

• Each floor was divided into 3 areas of refuge; each area of refuge containing a st

areas of refuge were delineated by 2-hour fire-rated separation walls that snaked 

floors (they were not aligned on the two floors of WTC 1).

• In the NYC Building Code, the allowable stairwell capacity is doubled when 2 are

provided on a floor and tripled when there are 3 or more areas of refuge. Each a

must contain a stairwell and must be totally enclosed in 2-hour fire rated construccurrent national model codes allow a doubling but not a tripling of allowable capa

• There is no evidence that the solution implemented in 1995 considered the NYC 

Code requirement for a minimum of four stairwells serving areas with occupanthan 1,000.

• The Code intent could have been met with four 44-inch stairways; a total of 176 i

there been four stairwells, overall capacity would have increased by about 20 per

towers had two 44-inch stairwells and one 56-inch stairway for a total of 144 inchtheir remoteness and survivability on September 11, 2001 would not necessarily 

• It remains unclear how often 1,000 persons occupied a single floor at one time; re

fourth stairwell would have been difficult and expensive.
Egress Provisions: Top of the World Egress Provisions: Top of the World

• The 107th floor of WTC 2 contained a public observation deck called Top of th

operated by the lessee of the space. The facilities included several shops, fo

small theater, exhibits, and a perimeter viewing area. Visitors could also asceescalators to an open, roof-top deck which was raised to provide unobstructed 

• The design number of occupants for this “assembly use” floor was 1,751, abo

the maximum number of occupants permitted under the NYC Building Code. 

load of the roof-top deck was not included in this estimate, even though deck could exit the facility only from the 107th floor.

• The proposed solution included subdivision of the area into 3 areas of refuge

• A 5,610 ft

2 area with Stairwell A and an occupant load of 935 people

• A 2,430 ft

2 area with Stairwell B and an occupant load of 343 people

• A 2,940 ft

2 area with Stairwell C and an occupant load of 473 people

• The stairway capacity after subdivision was 360 each for Stairways A and C a

Stairway B. The total capacity for all three stairways was 1,170.

• The occupant load of the perimeter gallery alone was 1,267 people which 

the stairway capacity of 1,170 after subdivision into areas of refuge. Onrefuge with Stairwell B had an occupant load less than the maximum capstairway. Stairwell A had an occupant load more than 2-1/2 times the sta
Egress Provisions: Top of the World (2) Egress Provisions: Top of the World (2)

• Taking advantage of a New York City building code provision w

a lower basis for occupant load, the PANYNJ permitted a maxim

occupant load of 1,170 on the floor, which was to be enforced b

of the space with periodic oversight by the PANYNJ.

• The PANYNJ provided NIST with the following response with regard to th

used to limit the number of visitors to the observation deck:“For controlling the number of occupants on the observation level in WTC turnstiles on the mezzanine before the entrance to the elevators that wercount the number of people going up, but since the patrons exited via a d& location, there was no way to count the number of people leaving - and 

calculate the number actually on the deck. Since the turnstiles were not vtheir use was discontinued later and the number of ticket sales was used 

the number of occupants. The length of the line waiting for the elevators down were constantly observed by staff. If the crowds grew too large, tichalted until the crowd size was reduced.”

• Less than ten people who were present on the observation level at the tim

impact perished on September 11th. The number of people who were prmanaged to evacuate is unknown.
Termination of Stairways Termination of Stairways

• The termination of stairways A and C at the mezzanine level was 

repeated discussion between the PANYNJ and the NYC DepartmBuildings over the years.

• The NYC Building Code required that egress stairs only terminate 

opening to a “public way.”

• The mezzanine opened at the Plaza level and to the concourse, 

below via escalators, which do not meet the typical definition of a 

• The PANYNJ contended that the NYC DOB agreed in the 1960s t

was a public way and that the concourse was an underground strnot find any correspondence or citations detailing these agreemen

• The PANYNJ commissioned a due diligence study in 1996 which 

issue and identified it as one for which there were no plans to addPANYNJ made significant improvements at the concourse level in shopping mall area after the 1993 bombing via new corridors that travel distance to exits.
Stairwell Improvements After the 1993 Bo

Stairwell Improvements After the 1993 Bo

• The PANYNJ made improvements to the stairwells of the 

Towers in light of the 4 hours needed to evacuate WTC 1 the 1993 bombing.

• Specific improvements made were:

• Battery operated emergency lighting in stairwells (an

elevators).

• Photoluminescent paint on handrails, stair treads, a

centerline indicating the path to be followed.

• Explicit LED signs on each doorway to indicate whe
Occupant Preparedness Occupant Preparedness

• Two-thirds of surviving occupants reported having participated in a fire dr

12 months prior to September 11, 2001, while 17 percent reported that they training during that same period.

• Of those participating in fire drills, 93 percent were instructed about the lo

nearest stairwell.

• Overall, slightly over half of the survivors, however, had never used a s

WTC prior to September 11, 2001 (NYC Local Law 5 prohibits requiring o

practice stairwell evacuation.)

• Occupants were often unprepared for the physical challenge of full buildin

Numerous occupants required one or more periods of rest during stairwell descelevators after finding the stairwells strenuous.

• Occupants were often unprepared to encounter transfer hallways during t

descent. Groups of evacuees occasionally hesitated or debated a course of ac

encountering a transfer hallway. 

• Mobility challenged occupants were not universally identified or prepared 

building evacuation. One occupant, for example, reported being ‘left’ on their fcolleagues, called authorities for assistance, and was eventually assisted by str(occupants). 
Roof Evacuation Roof Evacuation

• The PANYNJ’s standard occupant evacuation procedures and drills requ

stairways to exit at the bottom of the WTC towers. The standard procedu

keep the doors to the roof locked. The PANYNJ reports that it never adto evacuate upward. Roof access required use of an electronic swipe c

through the first two doors and a security officer watching a closed-circui

22nd floor of WTC 1 to open the third door via a buzzer. 

• The 1968 BCNYC required access to roofs with slopes less than 20 degr

least one stair in buildings greater than 3 stories (or 40 ft) in height. 

• The Code does not state the purpose of this access but, since it is in the sectio

Construction and not Means of Egress it does not necessarily imply roof rescu

providing fire department access to flat roofs.

• The current code (2003) permits such access from a stair, ladder or scuttle, ev

not intended for rescue. There is no prohibition of locking this access, which is 

fire department use since they have the means to open locked doors.

• There were at least two decedents who had tried to get to the roof and fo

access locked to both the WTC towers. In addition, a PANYNJ employee Floor 105 of WTC 2 was unable to walk down the stairs, or go to the roof on radio by another PANYNJ employee (PANYNJ Channel Y).
Roof Evacuation (2) Roof Evacuation (2)

• The NYPD and FDNY policies for roof operations were focused 

on providing emergency responders with access into the buildthe fire floors for firefighting, conventional rescue, and comfooccupants. Roof rescue was considered a measure of last resused, for example, to assist occupants with medical emergenc

• The NYPD aviation unit arrived at the WTC site soon after WTC 1 w

attacked. Despite repeated attempts to examine the possibility of raccess/rescue, smoke and heat conditions at the top of the WTC to

prevented the conduct of safe roof operations. 

• Due to the limited capacity of a typical helicopter and travel tim

rescue was never considered as a viable strategy for general 

evacuation; even if it had been possible for a helicopter to gai

to the roof, possibly only a very small fraction of the large numpeople trapped above the impact zone could have been rescue

September 11, 2001.
Public Address System Announcements Public Address System Announcements 

• Damage to the 22nd floor communication closet likely disabled the building-

announcement capability in WTC 1. The closet was located in a hallway aelevator shaft in the core of the building. Many announcement attempts wthe lobby command station.

• Announcements in WTC 2 were heard by occupants building-wide before t

aircraft struck at 9:03 am. Announcements were also heard in at least the (including above the impact area) after the second aircraft struck at 9.03 am

• At 9:00 am an announcement stated “There is a fire condition in WTC 1

secure. Please return to your offices.”

• At 9:02 am an announcement stated “May I have your attention please. 

is in Building 1. However, if conditions on your floor warrant, you may w

an orderly evacuation.”

• At 9:20 am an announcement was made updating occupants on the con

building and progress of the evacuation and informing occupants that if 

to leave, they could then use the concourse.

• Prior to 9:37 am an announcement instructed occupants to “go down” t
Emergency Communications to WTC Occ

Emergency Communications to WTC Oc

• Occupants called 9-1-1 and the Port Authority seeking 

assistance and advice.

• Opportunities to improve occupant’s situational aw

were often lost. Specific knowledge about location and impact damage was only occasionally commun

occupants who requested the information and was wapparent coordination.

• Some operators advised sheltering (e.g., many 9-1-1 op

while others advised evacuation (e.g., many PA Police operators); some permitted window breaking while otheinstructed occupants not to break windows.
Observations of Building Damage, WTC 

Observations of Building Damage, WTC 

Observations from interviews, emergency calls, or published accounts.‘?’ indicates a floor where no observer was found after impact, a blank indicates that an observer did not report that condition. Additional analysis pending.

Smoke

Sprinklers / water

Fatally injured people

Power outage

Jet fuel

Fallen ceiling tiles

Fire alarms

Collapsed walls

Extreme heat

Fire

Fireballs

–– 110

?????????????????????????????????????????????????????????????????????????????? ? ? ? ? ? ? ? ? ? ? –– 100????????????????????????????????????????????????????????????????????????????????????????

–– 90–– 80

Smoke

Sprinklers / water

Fatally injured people

Power outage

Jet fuel

Fallen ceiling tiles

Fire alarms

Collapsed walls

Extreme heat

Fire

Fireballs

–– 70–– 60–– 50

Smoke

Sprinklers / water

Fatally injured people

Power outage

Jet fuel

Fallen ceil

Fi

??????????????????????????????????????????

MER
Observations of Building Damage, WTC 

Observations of Building Damage, WTC 

Smoke

Sprinklers / water

Fatally injured people

Power outage

Jet fuel

Fallen ceiling tiles

Fire alarms

Collapsed walls

Extreme heat

Fire

Fireballs

??????????? –– 110???????????????????????????????????????????????????????????????????????????????????????? –– 100?????????????????????????????????????????????????????????????????????????????????????????????????????????????? –– 90???????????????????????????????????????????????????????

–– 80

???????????

Smoke

Sprinklers / water

Fatally injured people

Power outage

Jet fuel

Fallen ceiling tiles

Fire alarms

Collapsed walls

Extreme heat

Fire

Fireballs

???????????

–– 70

???????????

–– 60

??????????????????????????????????????????????????????? –– 50???????????????????????????????????????????????????????

Smoke

Sprinklers / water

Fatally injured people

Power outage

Jet fuel

Fallen ceiling ti

Fire al

????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????

MER

Observations from interviews, emergency calls, or published accounts.‘?’ indicates a floor where no observer was found after impact, a blank indicates that an observer did not report that condition. Additional analysis pending.
Evacuation of WTC 7 Evacuation of WTC 7

• The decision to evacuate WTC 7 was made by building officials a

a.m., although some occupants self-evacuated prior to that time.

• Occupants used both stairwells and elevators to evacuate. • Full evacuation was completed by about 9:30 a.m., although a sm

of individuals (with emergency responsibilities) became entrappebuilding beyond 10:30 a.m. 

• Many of the occupants evacuated North through the loading doc

far from WTC 1 and WTC 2 as possible. 

• There were no significant injuries reported from the evacuation o

in, WTC 7. 

• Additional findings, if any, will be provided in the final WTC 7 inve

report.
Role of Emergency Responders Role of Emergency Responders

FDNY - Established operational control and the Incident Co

Post for the WTC operations, conducted evacuation and operations, and fought fires at the disaster.

PAPD - Established security at the WTC and conducted ev

and rescue operations.

NYPD - Established traffic control, perimeter security at the 

security for command posts, and conducted evacuation arescue operations inside the WTC. The aviation units su

observation capabilities and assessed the potential for rorescue.

OEM - Functioned as a multi-agency command resource c

provided support for all agencies and departments workin

disaster.
Changes After the 1993 Bombing Changes After the 1993 Bombing

• FDNY worked with the PANYNJ to upgrade WTC fire prot

• FDNY high-rise radio repeater was installed• Fire Command Desks installed in WTC 1 and 2• Elevator intercom system was upgraded• New Operations Control Center was added to the co

the B1 level of WTC 2

• Multiple power sources installed for emergency lighti

• New decentralized fire alarm system was installed at • Various fire drills were conducted at the WTC and so

included FDNY participation
FDNY’s Initial “Size-up” of WTC Conditions

• A large aircraft had hit the WTC 1 building. • Large fires were burning on multiple floors at and above the im• The elevators were not working and people were trapped insid

the elevators.

• The sprinkler system and standpipe systems were likely comp• It was likely that no water supply was available to fight the fires 

above the impact zone.

• It was likely that many of the occupants trapped at and above t

zone were already dead or would die before help could get to t

Emergency Responder Operations Emergency Responder Operations 
FDNY Units Dispatch to the WTC FDNY Units Dispatch to the WTC

3

26 35

66

121

171

0 0

6

23 30

74

0

50

100150200250

8:46 8:48 8:50 9:00 9:15 9:59 

time (h:m)

Number of Units 

Dispatched Signal Arrival

Dispatch and Arrival of FDNY Units 
FDNY Operations at the WTC FDNY Operations at the WTC

Three operational strategies:Outside Command Posts & Inside Command Communicating with thCommand Post - Fires in the buildings were too large and were located the buildings to accomplish fire fighting activities that could save the lives above the fires. The objective was to evacuate and rescue all below the fCommand Officers for Inside Operations - The fires were too large to The objective was to get enough personnel and equipment upstairs to cut through the fire to rescue occupants above the fires, and also evacuate abelow the fires.Company Level Command - They saw this as a conventional but large fire. The objective was to get up to the fire floors and extinguish the fires. 

cases, firefighters were persuaded by higher ranking officers to switch frofire fighting to evacuation and rescue operations. 

No first responder interviewed by NIST 

the WTC towers wou
Situational Awareness:

• Emergency responders working outside the WTC buildings who 

building conditions and communicate over radios had adequate awareness.

• Situational awareness for personnel who observed the building d

fires from outside the buildings before entering experienced diffi

maintaining their awareness after entering the buildings.

• Emergency responders working inside of the WTC buildings, wh

see what was happening outside and had poor radio communicapoor situational awareness. 

• Emergency responders working inside of the WTC buildings, wh

see what was happening outside and had good radio communicbetter situational awareness than those with poor radio commun

Emergency Responder Operations Emergency Responder Operations 
• After aircraft impact, only two elevators out of 198 w

operating inside the two WTC towers. WTC 1, from t

lobby to the 16th floor. WTC 2, from the lobby to the 40t

• The stairways were filled with occupants evacuating the 

buildings. FDNY personnel and other emergency responders reported difficulty attempting to climb thstairs due to this counterflow.

• Counter flow in the staircases made it difficult for emerg

responders to carry equipment up the stairways.

• Counter flow in the staircases caused teams of emerge

responders to become separated, causing delays and disrupting team operations.

FDNY Access to the WTC Towers FDNY Access to the WTC Towers
Emergency Responders & High Emergency Responders & High

-Rise Buildin

Rise Buildin

• First responding FDNY units took from 4 to 10 minutes to get to 

complex. They then got their equipment and received assignmeanother 3 to 5 minutes. Time to begin operations 7 to 15 minute

• Of the 27 emergency responders interviewed that were inside W

maximum floor height achieved before WTC 2 collapsed, a time hour 13 minutes.

1 – A police officer carrying no extra equipment and in a patrolman’s 

uniform climbed to the 44th floor.

8 – Emergency responders (FDNY, PAPD, NYPD) climbed to the 30’s

Two FDNY took an elevator to the 16th floor.

16 – Emergency responders (mostly FDNY) climbed to the 20’s.2 – Emergency responders (NYPD) climbed to the teens.

• Estimated climbing rate based on a 60 minute climbing perio

maximum height: 1.4 to 2 minutes/floor
High-Rise Buildings & Emergency Resp

Rise Buildings & Emergency Resp

Example: Fire department response to a 60 story high-rise building

trapped above fires on the 58th floor and no operating eleva

Lobby

Firefighters begin to climb 10 minutes

Fire department arrival 4 minutes 

Firefighters carrying equipment and

wearing PPE ~ 70 minutes

Firefighters carrying no equipment and not

wearing PPE ~ 50 minutes

Fires Firefighters carrying equipment and wearing PPE ~ 125 minutes

Firefighters carrying no equipment and not

wearing PPE ~ 90 minutes
• All three of the responding departments, FDNY, NY

PAPD experienced difficulties with radio communic

• Each of the departments was aware of the shortfall

associated with their radio communications systemthey related to operations in high-rise buildings.

• Two basic issues with radio communications:

1. Normal function of the radio equipment in high-

environments. (Radio signal attenuation in stee

concrete buildings)

2. The volume of radio traffic

Radio Communications Radio Communications
Emergency Communication Recordings Emergency Communication Recordings 

• NIST reviewed audio communications tapes recorded by the PANYNJ, i

recording of the FDNY’s city-wide high-rise Channel 7 (Port Authority PoDepartment’s [PAPD] Channel 30) radio repeater that was located at the 

• NIST reviewed audio tapes copied from original NYPD communications 

including NYPD internal department operations.

• FDNY communications recordings from the WTC location on Septe

2001, are not available because the primary field communication trthe shop for repairs. A back-up field-communications van used in which did not have a recording capability—was destroyed when thtowers collapsed.

• The best record of radio communications reflecting fire departmen

at the WTC site came from the FDNY Channel 7/PAPD Channel 30 aperson accounts provided by FDNY personnel during their intervieaddition, FDNY provided the Manhattan Dispatch communication ta

• The PANYNJ installed the radio repeater system for use by FDNY after 

bombing.
Analysis of Emergency Communication

Analysis of Emergency Communication

• After the first aircraft struck WTC 1, there was an approximate factor o

increase in traffic level over the normal level of emergency responcommunications, followed by an approximate factor of 3 steady increa

level of subsequent traffic.

• A surge in communications traffic volume made it more difficult to 

the flow of communications and delivery of information.

• Roughly a third to a half of the radio messages transmitted during these 

traffic surge conditions were not complete messages nor understand

• FDNY’s city-wide high-rise Channel 7 (PAPD Channel 30) radio rep

the WTC site was operating, although communications problems wperceived in WTC 1.

• NYPD aviation unit personnel reported critical information about the im

collapse of the WTC towers several minutes prior to their collapse. No has been found to suggest that the information was further commall emergency responders at the scene.
Radio Communications in High Radio Communications in High

-Rise Bu

Rise Bu

• Challenging radio-f

propagation enviroand reinforced conbuildings.

• Large scale operat

• Number of first • Communication

and protocols.

• Surge in traffic; 

• Interoperability of r

communication tecamong different emresponder organiza

• Identification, locat

Schematic of WTC Radio Repeater System first responders.
• Analysis of the FDNY City-wide, high-rise, channel 7 (PAPD channe

repeater recording indicates that the World Trade Center high-rise was operating.

• At approximately 9:05 a.m. the repeater’s recording system recorded the 

Lobby Command Post attempts to check repeater operations. Handset talkie radio communications were recorded.

• It is possible that one or both of the following conditions complicated the 

that took place at the WTC 1 Lobby Command Post:

• The radio repeater handset earpiece was broken.• The radio repeater handset volume was not turned up.

• It is unlikely that the repeater’s antenna was broken or misdirected 

since radio signals were received during the radio check from insidand the communications that followed from inside WTC 2. Even if was functioning, it is possible the quality of communications was i

• The repeater’s system recorded radio communications that took place b

several different firefighters and several different FDNY officers as they inside WTC 2.

WTC High WTC High-Rise Radio Repeater System Rise Radio Repeater System
Command and Control Command and Control

• Emergency responders— including key incident commanders—di

adequate information (voice, video, and data) on, nor an overall peof, the conditions in the WTC buildings and what was happening eat the WTC site. Interagency information sharing was inadequate.

• FDNY command and control was seriously affected by the lack of 

communications.

• A preponderance of evidence indicates that lack of timely informa

sharing and inadequate communication capabilities likely contribuloss of emergency responder lives. Statement extracted from an emresponder interview: If communications were better, more firefightehave been saved.

• Large numbers of fire fighters were dispatched to the WTC site be

adequate command posts and staff could be assembled to manag

• Self-dispatch complicated command and control at the site. FDNY 

command and control was affected by many self-dispatched private anambulance units that contributed to clogging the streets so that other re

assigned to the WTC had difficulty getting through.

• FDNY apparatus had to be moved to allow some ambulances to get thr

exit the site with victims.
• FDNY’s system for maintaining records of unit assignments at each command 

capable of managing the numbers of units and personnel assigned to the incid

• FDNY, NYPD, and PAPD: there was no means to back-up the unit assignment r

generated at the command posts.

• Interagency operations were detrimentally affected with the loss of the OEM co

that was located inside WTC 7 due to the decision made to evacuate the buildi

am before WTC 2 collapsed. First person interview data and photographic data sh

functions became dispersed, the computer systems and other supporting systems w

unified operations structure was diminished. OEM personnel were working with diffe

responder departments and were located at the various department command posts

• A significant amount of evidence (first person interviews, reports, and photographic d

• In general, all departments attempted to work together to save as many liv

and protect the citizens of New York City on the morning of September 11

• At times some issues related to a given department’s operational responsibility 

competitive nature of departments did exist during the WTC operations; some o

experienced were due to personnel not understanding the operating practices o

• Emergency responder interviews suggest that inter-agency competition had m

operations at the WTC complex before the towers collapsed.

Command and Control (2) Command and Control (2)
Mobility Impaired Occupants Mobility Impaired Occupants

• As the emergency responders started evacuating WTC 1 after th

of WTC 2, they found mobility impaired occupants still in the stairdown.

• Ambulatory mobility impaired occupants typically walked down th

one hand on each hand rail and took one step at a time going doaddition, they were typically accompanied by one person, anotheor an emergency responder. This blocked others behind them frmore rapidly down the stairs.

• FDNY and PAPD personnel found 40 to 60 mobility impaired 

on the 12th floor of WTC 1 as they went down and attempted 

each floor on their way out. These impaired individuals had be

on this floor in an attempt to clear the stairways.

• Emergency responders were assisting approximately 20 of t

mobility impaired people down the staircase just prior to the of WTC 1. It is unknown how many fatalities occurred with this g
Significant Fires Prior to September 11, 

Significant Fires Prior to September 11, 

• FDNY provided information from 397 operations fire reports from 1970 to 2001 and 

investigation records from 1977 to 2001; PANYNJ records destroyed during collap

• Most significant incidents:

• Major 1975 fire in WTC 1 prior to installation of sprinklers.• 1993 bombing in B-1 level below south face of WTC 1.

• 47 other substantial fires; activated a sprinkler or required hoses to suppress:

• 16 exercised multiple sprinklers or standpipe connected hoses (with or withou

sprinkler activation); 

• 12 in WTC 1, 3 in WTC 2, and 1 in WTC 7. • 12 fires occurred between 6 pm and 4 am; remainder included 2 dumpster fires, 1 ki

overheating of fan motor bearing.

• 5 unlisted/unclassified, 6 suspicious/incendiary, 2 discarded material, 3 electrical/me• Only two fires extended to as much as 15% of the space on the floor.

• 31 fires involved use of one standpipe hose or one hose and discharge of one 

• 23 in WTC 1, 7 in WTC 2

• Available evidence suggests that no fire activated more than 3 sprinklers in areas 

automatic sprinklers.

• There is no known loss of life as a result of any of these fires (not including the 199

incident and the September 11, 2001 terrorist attacks)
Noteworthy Significant Fires Noteworthy Significant Fires

• February 14, 1975:

• Fire started on the 11th floor of WTC 1.

• Fire damage occurred on the 10th through the 19th floors.• Approximately 9,000 ft

2 of 11th floor contents in the southea

was destroyed or damaged.

• Sprinklers had not been installed in the office spaces.• Fire barriers divided the floor into quadrants.

• April 19, 1980:

• Fire started on the 106th floor of WTC1.

• Approximately 300 occupants from Windows of the World r

the 107th floor were evacuated.

• April 17, 1981:

• Fire started on the 7th floor of WTC 1.

• Approximately 1,500 occupants were evacuated from floors 
Sprinkler and Standpipe Systems Sprinkler and Standpipe Systems

• Sprinklers had been installed throughout WTC 1, 2, and 7 by Sep

2001, except for areas that were exempted from required sprinkle

• Storage tanks with direct connections to the NYC water distributi

supplied water to the WTC towers and to floors 21 to 47 of WTC to 20 of WTC 7 were supplied via the NYC system and an autpump with no secondary supply.

• The supply piping from the 100th floor of the WTC towers resulted 

water supply to several floors; this installation was not consistent best practices, although this inconsistency had no impact on the September 11, 2001.

• Manual initiation of the electrical fire pumps was required to prov

supplemental water in all three buildings, while automatic initiatioby NFPA 14, it is unlikely to have made a difference on Septembthe sprinkler systems were automatic from the water tanks.

• The water supply risers were configured to provide redundancy; 

floor level controls were vulnerable to single point failures since tonly one connection to the sprinkler water riser.
Sprinkler and Standpipe Systems (2) Sprinkler and Standpipe Systems (2)

• Analysis indicated that the sprinkler systems were capable of con

typical fire with a coverage area up to 4,500 ft2 which is three tim

design area specified, but represents less than 15% of the area ofloor.

• The 5th floor generator room in WTC 7 was not equipped with a s

system; nor was it required by the NYCBC.

• No evidence was found that the generator/fuel day-tank enclosur

elsewhere in WTC 7 were protected by a fire suppression system

• Primary and backup power were provided in all three buildings; s

operability could have been affected by the lack of redundancy olines to the emergency fire pumps once power was lost.

• Due to the magnitude of the initial fires and the likely aircraft impa

the suppression systems in the WTC towers could not have been control the fires on September 11, 2001.
Fire Alarm Systems Fire Alarm Systems

• The fire alarm systems in WTC 1 and 2 provided for automatic fire detect

required manual activation of notification devices. The fire alarm system in provided automatic detection and notification.

• The fire alarm systems in WTC 1, 2, and 7 were only capable of determinin

displaying (1) areas that had at some time reached alarm point conditions, 

that had not.

• The fire alarm systems collected information that is valuable for understand

and smoke development in a building:

• The system in WTC 1 and 2 had extensive back-up command capabilities and har

provided multiple places where some alarm history data were stored; up to 13 sto

were identified.

• The system in WTC 7 recorded information at 1 location, the fire command station 

floor lobby; the system was monitored offsite, but provided only one piece of informalarm was triggered in the building.”

• The fire alarm systems in WTC 1 and WTC 2 were monitored by the PANY

an overwhelming number of alarms registered and displayed at the Ffire and other automatic alarm information at the FCS was not used to evacuation; there was no means at the FCS to determine whether or not a

reached or could be heard on intended floors.
Fire Alarm Systems Fire Alarm Systems

• The fire alarm signal was delayed until 12 minutes after impact of WT

manual activation of the system was required in the WTC towers to nooccupants.

• The notification appliance circuit (which provided the voice message o

the speakers) and the warden/standpipe telephone circuit were not rethe higher performance of the signaling line circuits (that monitored th

and supervisory devices and could turn on the notification appliance circu

• The firefighter telephone systems in the WTC towers were not used on Se

2001; this is not uncommon since firefighters are trained to use their radiopreferred means of communications.

• Although the fire alarm systems in the WTC towers used multiple commun

risers, the systems experienced performance degradation, especially in Wnotification and communication functions appeared to have been lost abovfloors.

• The fire alarm system in WTC 7 sent only one signal (at 10:00:52 a.m

WTC 2 collapsed) to the monitoring company indicating a fire conditsignal did not contain any specific information about the location of 

the building. Since the system was in a test condition that morning (a rouwhen building maintenance is underway), the signal was recorded and did the operator’s screen at the monitoring company.
Smoke Management Systems Smoke Management Systems

• Smoke purge systems were installed in WTC 1, 2, and 7; these sys

used the components of the main HVAC (heating, ventilation, and aiconditioning) systems, were intended to remove smoke and other gacombustion products from the fire area after a fire was extinguished. systems were to be activated manually at the direction FDNY.

• The smoke management systems in the WTC towers, which provide

capability for a manual smoke purge within an individual HVAC zone quadrant-by-quadrant basis, were not initiated on September 11, 2

determined that the likelihood of these systems being functional was to the damage inflicted by the aircraft impacts.

• Analysis indicates that the disruption of the HVAC system, particula

aircraft impact rupture of large return air shafts and related duccreated a major path for vertical smoke spread in the buildings.

• If the smoke purge sequence had been initiated in the WTC towe

unlikely that the system would have functioned as designed due 

electrical power and/or damage to the HVAC shafts and other struct

in the impact zone that were an integral part of the smoke purge sys
Example of Vertical Smoke Spread Example of Vertical Smoke Spread
Smoke Management System (2) Smoke Management System (2)

• The 1968 NYCBC, or retroactive provisions in the various 

laws enacted after the WTC towers were built, did not reqbuildings like the WTC towers to have active smoke mansystems and/or combination fire/smoke dampers if they cautomatic sprinklers throughout.

• The PANYNJ commissioned a due diligence study in 199

cited the lack of vents in the stairs that were required in lipressurization by Local Law 5 (1973). The PANYNJ cites that, due to the height of the stair shafts, the required venbe ineffective. As an alternative, the PANYNJ pressurizecorridors with outside air (which was not required).
Smoke Management Systems (3) Smoke Management Systems (3)

• None of the potential alternative smoke management systems evaluated 

prevented smoke spread for the postulated aircraft impact damage scenariosystems were capable of operation after the buildings sustained damage from Design fire scenarios evaluated were: sprinklered fire; full-floor burnout; two-ffire scenario without shaft damage; and 9/11 with shaft damage. Systems ev

• Smoke purge (exhaust fans in the core; entire ventilation zone, not floor-by-flo

detectors at exhaust duct inlets; sequence in WTC instruction manual)

• Core pressurization (supply fans rather than exhaust fans pressurize the core)

• Building pressurization (supply fan in entire building; exhaust fans only in vent

fire origin)

• Sandwich pressurization (concept involves exhausting floor of fire origin and p

floors above and below; sandwich achieved by ventilation zones)

• Zoned smoke control with stair pressurization (hypothetical approach based on 

stair pressurization; capable of exhausting on a floor-by-floor basis; normal opventilation zones; fire/smoke dampers in all supply/exhaust ducts; dampers clofire origin)

• Stair pressurization would have been ineffective in improving conditions fo

trying to exit the buildings during the events of September 11, 2001.

• Installation of combination fire/smoke dampers in HVAC ductwork, which 

required by the NYC Building Code, would have acted to slow the developmhazardous conditions on the uppermost floors of the building, but would had a significant effect on the ability of occupants to egress the buildings due impassability of the exit stairways.
Factors that Enhanced Life Safety on Factors that Enhanced Life Safety on 

September 11, 2001 September 11, 2001

• Since the buildings were occupied by only about 1/3 of the building’s full 

25,000 occupants, the egress capacity (number and width of exits and stadequate for those survivors seeking and able to reach and use undama

stairways.

• Functioning elevators in WTC 2 enabled nearly 3,000 occupants to self-e

to aircraft impact.

• Greater remoteness of stairwells in the impact areas of WTC 2 that enab

stairwells to remain marginally passable after aircraft impact.

• Participation of a large number (two-thirds) of surviving occupants in 

the prior 12 months, with almost all of those (93 percent) instructed alocation of the nearest stairwell. 

• Upgrades made to the life safety system components after the 1993 bom• Evacuation assistance provided by emergency responders to building oc

• As a result of the above factors, approximately 87 percent of the WT

occupants, including more than 99 percent of those below the floorwere able to evacuate successfully.
Future Practices and Technologies that Future Practices and Technologies that 

Potentially Could Have Improved Life Sa

Potentially Could Have Improved Life Sa

on September 11, 2001 (Requires Analys

on September 11, 2001 (Requires Analy

• Improved performance to delay or prevent building collapse.• Improved stairwell integrity via increased remoteness of stairwells and/or 

structural integrity of stairwell enclosures.

• Better communications to occupants and among first responders via imp

systems and timely information sharing.

• Better command and control for large-scale incident management (e.g., l

command posts and physical assets; interagency coordination).

• Better evacuation training (e.g., practice stairwell evacuation, roof rescue 

feasible as a standard option, existence of transfer hallways).

• Other life safety features (e.g., fire protected and structurally hardened e

available for occupant use during emergencies; vibration protected elevathose used in seismic regions; self-evacuation capability for mobility impaoccupants; operational smoke and fire control systems).
Uncertainties and Limitations Associate

Uncertainties and Limitations Associate

Evacuation and Emergency Response Evacuation and Emergency Response

• NIST recognized the inherent limitations and uncertainties in its 

of the evacuation and emergency response:

• Human factors associated with building occupants (training; situational awar

evacuation initiation time)

• Human factors associated with emergency response (situational awareness; 

communications; command and control; interagency coordination)

• Effect of building design on evacuation and emergency response (collapse t

elevators; sprinkler and standpipe systems; self-evacuation systems for mobemergency communication systems)

• In developing its findings and results, NIST carefully consi

these uncertainties within the context of available factual efrom documents, recordings, first-person interviews, analyvisual data.
Web site Web site http:// http://wtc.nist.gov wtc.nist.gov

Email to Email to wtc@nist.gov wtc@nist.gov

Facsimile to (301) 975 Facsimile to (301) 975-6122

Regular mail: Regular mail:

WTC Technical Information Repository, Stop 8

Technical Information Repository, Stop 8

100 Bureau Drive, Gaithersburg, MD 20899 Bureau Drive, Gaithersburg, MD 20899-86