FEMA 426 / December 2003

Risk Management Series
Reference Manual 
to Mitigate Potential Terrorist Attacks Against 
Buildings
December 200


FEM


Reference Manual to 
Mitigate Potential 
Terrorist
Attacks Against Buildings
PROVIDING PROTECTION TO PEOPLE AND BUILDING


www.fema.go


Any opinions, findings, conclusions, or recommendations expressed in this 
publication do not necessarily reflect the views of FEMA. Additionally, neither FEMA 
or any of its employees makes any warrantee, expressed or implied, or assumes any 
legal liability or responsibility for the accuracy, completeness, or usefulness of any 
information, product, or process included in this publication. Users of information 
from this publication assume all liability arising from such use




The creation of the Department of Homeland Security (DHS) is one of the most 
significant transformations in the Federal Government in decades, establishing a 
department whose first priority is to protect the nation against terrorist attacks. 
Within the DHS, the Directorate of Emergency Preparedness and Response (EP&R) is 
focused on ensuring that our nation is prepared for catastrophes, including both 
natural disasters and terrorist assaults.
Central to this mission is the protection of people and the critical infrastructure of 
the built environment. This Reference Manual to Mitigate Potential Terrorist Attacks 
Against Buildings provides guidance to the building science community of architects 
and engineers, to reduce physical damage to buildings, related infrastructure, and 
people caused by terrorist assaults.  
The comprehensive approach to understanding how to improve security in high 
occupancy buildings will better protect the nation from potential threats by 
identifying key actions and design criteria to strengthen our buildings from the 
forces that might be anticipated in a terrorist assault. It is important to note that 
many of the methodologies in this publication have been adapted from other 
government sources and modified to meet the mission of the DHS. This allows for 
the effective transfer of decades of federal and Department of Defense research and 
experience to the broader building science community.
This document was prepared by the Building Sciences and Technology Branch of the 
Mitigation Division, part of EP&R. The DHS would like to thank the following 
agencies for their contribution and input to this publication:
_	General Services Administration
_	Naval Facilities Engineering Service Center
_	Naval Facilities Command (NAVFAC) Criteria Office
_	USACE Protective Design Center
_	Department of Veterans Affairs
_	Centers for Disease Control and Prevention/National Institute for 
Occupational Safety and Health
_	Department of Justice, Office of Domestic Preparedness (DHS - Border and 
Transportation Security)
_	United States Air Force - Civil Engineer Support Agency


Michael D. Brown
Under Secretary
Emergency Preparedness
and Response Directorate
Anthony S. Lowe
Director
Mitigation Division
Emergency Preparedness and Response Directorate




FOREWORD AND ACKNOWLEDGMENT



BACKGROUND
The Federal Emergency Management Agency (FEMA) developed this Reference Manual 
to Mitigate Potential Terrorist Attacks Against Buildings to provide needed information on 
how to mitigate the effects of potential terrorist attacks. The intended audience in-
cludes the building sciences community of architects and engineers working for 
private institutions, and state and local government ofÞcials working in the building 
sciences community. The manual supports FEMAÕs Mission (Lead America to 
prepare for, prevent, respond to, and recover from disasters) and the Strategic PlanÕs 
Goal 3 (Prepare the Nation to address the consequences of terrorism), all of which 
will be done within the all-hazards framework and the needs of Homeland Security.
The building science community, as a result of FEMAÕs efforts, has incorporated 
extensive building science into designing and constructing buildings against natural 
hazards (earthquake, Þre, ßood, and wind). To date, the same level of understanding 
has not been applied to manmade hazards (terrorism/intentional acts) and tech-
nological hazards (accidental events). Since September 11, 2001, terrorism has 
become a dominant domestic concern. Security can no longer be viewed as a 
standalone capability that can be purchased as an afterthought and then put in place. 
Life, safety, and security issues must become a design goal from the beginning. 
OBJECTIVE AND SCOPE 
The objective of this manual is to reduce physical damage to structural and non-
structural components of buildings and related infrastructure, and also to reduce 
resultant casualties during conventional bomb attacks, as well as attacks using 
chemical, biological, and radiological (CBR) agents. Although the process is general 
in nature and applies to most building uses, this manual is most applicable for six 
speciÞc types of facilities:
_   Commercial ofÞce facilities
_   Retail commercial facilities
_   Light industrial and manufacturing facilities
_   Health care facilities
_   Local schools (K-12), and
_   Higher education (university) facilities
The processes and measures may not generally be economical or applicable to lighter 
density occupancies, such as single-family homes. More intense occupancies (e.g., 
industrial facilities) have already been addressed in most cases.
This is one of a series of publications that address security issues in high-population, 
private sector buildings. This document is the foundation of the Building Vulnerability 
Design Against Terrorist Attacks Training Course (FEMA 438).
The purpose of this manual is to provide guidance to the building sciences 
community working for private institutions. It presents tools to help decision-makers 
assess the performance of their buildings against terrorist threats and to rank 
recommendations. It is up to the decision-makers to decide which types of threats 
they wish to protect against and to determine their level of risk to each threat. Those 
decision-makers who consider their buildings to be at high risk can use this 
guidance as necessary.
The information contained in this document is:
_  not mandatory
_  not applicable to all buildings
_  not applicable when it interferes with other hazards such as Þre
This manual presents incremental approaches that can be implemented over time to 
decrease the vulnerability of buildings to terrorist threats. Many of the 
recommendations can be implemented quickly and cost-effectively.
ASSUMPTIONS
The information provided herein builds upon the synergies between the mitigation 
measures for natural hazards and manmade hazards. For example, seismic standards 
for non-structural building components are beneÞcial against the explosive blast of 
conventional bombs. Hurricane window design, especially against ßying debris, 
applies also to explosive blast. Landscaping for mitigation against wildÞres improves 
detection of placed devices. Ventilation system design against airborne biological, 
chemical, and radiological agents also works for similar hazardous material releases, 
whether intentional or accidental. Assessing threat, vulnerability, and risk may be 
complicated when comparing natural against manmade hazards. A natural hazard 
refers to a natural event such as a ßood, wind, or seismic disaster. Historical data have 
been used by FEMA and other agencies/organizations to economically quantify the 
risk for natural hazards. Manmade hazards include technological hazards and 
terrorism and they are distinct from natural hazards primarily in that they originate 
from human activity. Technological hazards are assumed to be accidental and that 
their consequences are unintended. There is limited discussion of technological 
hazards in this document. For manmade hazards, the threat and likelihood of 
occurrence are less well deÞned and the associated vulnerabilities have many con-
siderations that impact making good risk management decisions.
ORGANIZATION AND CONTENT OF THE MANUAL
This manual contains many how-to aspects based upon current information 
contained in FEMA, Department of Commerce, Department of Defense (including 
Army, Navy, and Air Force), Department of Justice, General Services Administration, 
Department of Veterans Affairs, Centers for Disease Control and Prevention/National 
Institute for Occupational Safety and Health, and other publications. It is intended to 
provide an understanding of the current methodologies for assessing threat/hazard, 
vulnerability, and risk, and the design considerations needed to improve protection 
of new and existing buildings and the people occupying them. As needed, this 
manual should be supplemented with more extensive technical resources, as well as 
the use of experts when necessary.
_  Chapter 1 presents selected methodologies to integrate threat/hazard, asset value, 
and vulnerability assessment information. This information becomes the input 
for determining relative levels of risk. Higher risk hazards require mitigation 
measures to reduce risk. The chapter also provides an assessment checklist that 
compiles many best practices (based upon current technologies and scientiÞc 
research) to consider during the design of a new building or renovation of an 
existing building. The checklist can also be used to assess the vulnerability of 
existing buildings within the context of the deÞned threats.
_  Chapter 2 discusses architectural and engineering design considerations 
(mitigation measures), starting at the perimeter of the property line, and includes 
the orientation of the building on the site. Therefore, this chapter covers issues 
outside the building envelope.  
_  Chapter 3 provides the same considerations for the building Ð its envelope, systems, 
and interior layout. 
_  Chapter 4 provides a discussion of blast theory to understand the dynamics of the 
blast pressure wave, the response of building components, and a consistent 
approach to deÞne levels of protection.
_  Chapter 5 presents CBR measures that can be taken to mitigate vulnerabilities and 
reduce associated risks for these terrorist tactics or technological hazards.
_  Appendices A, B, and C contain acronyms, general deÞnitions, and CBR 
deÞnitions, respectively.  
_  Appendix D describes electronic security systems and design considerations. 
_  Appendices E and F present a comprehensive bibliography of publications, and the 
associations and organizations capturing the building security guidance needed 
by the building sciences community, respectively.
ACKNOWLEDGMENTS
Principal Authors:
Michael Chipley, UTD, Inc.
Michael Kaminskas, UTD, Inc.
Wesley Lyon, UTD, Inc.
David Beshlin, UTD, Inc.
Mark Hester, UTD, Inc.
Contributors:
Milagros Kennett, FEMA, Project OfÞcer, Risk Management Series Publications
Eric Letvin, Greenhorne & OÕMara, Inc., Consultant 
Project Manager
Eve Hinman, ATC/Hinman Consulting Engineers, Inc.
G. Scott Earnest, CDC/NIOSH
Michael Gressel, CDC/NIOSH
Kenneth Mead, CDC/NIOSH
D. Shawn Fenn, FEMA
Randall Hoffman, UTD, Inc.
Damian Kolbay, UTD, Inc.
Mark Hankewycz, Gage-Babcock, Inc.
Christopher Arnold, Building Systems Development, Inc.
Deb Daly, Greenhorne & OÕMara, Inc.
Wanda Rizer, Greenhorne & OÕMara, Inc.
Julie Liptak, Greenhorne & OÕMara, Inc.
Bob Pendley, Greenhorne & OÕMara, Inc.
Bill Modzeleski, Department of Education
Project Advisory Panel:
Wade Belcher, General Services Administration
Curt Betts, U.S. Army Corps of Engineers
Jim Caulder, U.S. Air Force Ð Civil Engineer Support Agency
Marcelle Habibion, Department of Veterans Affairs
Joseph Hartman, U.S. Army Corps of Engineers
David Hattis, Building TechnoIogy, Inc.
Rick Jones, Naval Facilities Engineering Service Center
Kurt Knight, Department of Veterans Affairs
Frederick Krimgold, Virginia Tech
John Lynch, Naval Facilities Command (NAVFAC) Criteria OfÞce
Terry Pruitt, Department of Homeland Security
Chris Rojahn, Applied Technology Council
Lloyd Siegel, Department of Veterans Affairs
William Whiddon, Building Technology, Inc. 
This manual was prepared under contract to FEMA. It will be revised periodically, and 
comments and feedback to improve future editions are welcome. Please send 
comments and feedback by e-mail to riskmanagementseriespubs@dhs.go 




TABLE OF CONTENT



FOREWORD AND ACKNOWLEDGMENTSi
Backgroundi
Objective and Scopei
Assumptionsiii
Organization and Content of the Manualiii
Acknowledgmentsv
CHAPTER 1 Ð ASSET VALUE, THREAT/HAZARD, VULNERABILITY, AND RISK1-
1
1.1  Asset Value Assessment1-10
1.1.1  Identifying Building Core Functions1-11
1.1.2  Identifying Building Infrastructure1-11
1.1.3  Quantifying Asset Value1-12
1.2 Threat/Hazard Assessment1-14
1.2.1  Threat/Hazard Identification1-14
1.2.2  Threat Definition of Physical Attack  on a Building1-21
1.3 Vulnerability Assessment1-24
1.4  Risk Assessment1-35
1.5  Risk Management1-42
1.6  Building Vulnerabilty Assessment Checklist 1-45
CHAPTER 2 Ð SITE AND LAYOUT DESIGN GUIDANCE2-1
2.1  Land Use Considerations2-2
2.2  Site Planning2-6
2.2.1  Site Design2-6
2.2.2  Layout and Form2-6
2.2.3  Vehicular and Pedestrian Circulation2-11
2.2.4  Infrastructures and Lifelines2-13
2.2.5  Landscape and Urban Design2-14
2.3  Stand-off Distance2-22
2.4  Controlled Access Zones2-25
2.4.1  Physical Protective Barriers2-27
2.4.2  Other Perimeter Barriers2-30
2.4.3  Anti-ram Vehicle Barriers2-32
2.5  Entry Control and Vehicular Access2-36
2.6  Signage2-40
2.7  Parking2-42
2.8  Loading Docks and Service Access2-44
2.9  Physical Security Lighting2-45
2.10  Site Utilities2-47
2.11  Summary of Site Mitigation Measures2-51
2.12  Crime Prevention Through Environmental  Design (CPTED)2-59
CHAPTER 3 Ð BUILDING DESIGN GUIDANCE3-1
3.1  Architectural3-3
3.1.1  Building Configuration3-3
3.1.2  Space Design3-6
3.1.3  Other Design Considerations3-8
3.2  Building Structural and Nonstructural Systems3-10
3.2.1  Building Design to Achieve a Desired  Protection Level3-10
3.2.2  Progressive Collapse3-10
3.2.3  Loads and Stresses3-13
3.2.4 Good Engineering Practice Guidelines3-14
3.2.5  Building Materials3-16
3.2.6  Methods and References3-16
3.3  Building Envelope3-17
3.3.1  Building Exterior3-17
3.3.2  Exterior Wall Design3-18
3.3.3  Window Design3-20
3.3.4  Doors3-31
3.3.5  Roof System Design3-32
3.4  Mechanical Systems3-33
3.5  Electrical Systems3-44
3.6  Fire Protection Systems3-45
3.7  Communications Systems3-45
3.8  Electronic Security Systems3-46
3.9 Entry-control Stations3-48
3.10 Physical Security Systems3-50
3.11  Summary of Building Envelope Mitigation Measures3-50
CHAPTER 4 Ð EXPLOSIVE BLAST4-1
4.1  Blast Effects4-1
4.1.1  Building Damage4-6
4.1.2  Injuries4-8
4.1.3  Levels of Protection4-8
4.2  Stand-off Distance and the Effects of Blast4-13
4.3  Predicting Blast Effects4-16
4.3.1  Blast Load Predictions4-16
4.3.2  Blast Effects Predictions4-18
CHAPTER 5 Ð CHEMICAL, BIOLOGICAL, AND RADIOLOGICAL MEASURES5-1
5.1  Evacuation5-2
5.2  Sheltering in Place5-2
5.3  Personal Protective Equipment5-5
5.4  Air Filtration and Pressurization5-7
5.4.1  Air Filtration and Cleaning Principles5-8
5.4.2  Applying External Filtration5-20
5.4.3  Applying Internal Filtration  (Recirculation Filter Units)5-24
5.4.4  Radiological Hazards5-25
5.5  Exhausting and Purging5-26
5.6  CBR Detection5-26
5.7  Indications of CBR Contamination5-31
APPENDIX A Ð  Acronyms
APPENDIX B Ð  General Glossary 
APPENDIX C Ð  Chemical, Biological, and Radiological  Terms Glossary 
APPENDIX D Ð  Electronic Security Systems
APPENDIX E Ð  Bibliography
APPENDIX F Ð Associations and Organization


TABLES
Chapter 1
Table 1-1  Asset Value Scale1-13
Table 1-2  Nominal Building Asset Value Assessment1-14
Table 1-3  Event Profiles for Terrorism and  Technological Hazards1-17
Table 1-4  Homeland Security Threat Conditions1-24
Table 1-5  Site/Building Inherent Vulnerability  Assessment Matrix (Partial Risk 
Assessment)1-25
Table 1-6  Classification Table Extracts1-26
Table 1-7  Selected Extracts -- Recommended  Standards Chart1-27
Table 1-8  Level of Visibility1-29
Table 1-9  Criticality of Target Site1-30
Table 1-10  Target Value to Potential Threat Element1-30
Table 1-11  Aggressor Access to Target1-31
Table 1-12  Target Threat of Hazard (WMD Materials)1-31
Table 1-13  Site Population Capacity1-32
Table 1-14  Potential for Collateral Damage  (Mass Casualties)1-32
Table 1-15  Building Summary Sheet1-33
Table 1-16  Building Ranking1-33
Table 1-17  Simplified Building Ranking Matrix1-34
Table 1-18  Risk Factors Definitions1-38
Table 1-19  Total Risk Color Code1-38
Table 1-20  Site Functional Pre-Assessment  Screening Matrix1-38
Table 1-21  Site Infrastructure Systems  Pre-Assessment Screening Matrix1-39
Table 1-22 Building Vulnerablilty Assessment  Checklist1-46
Chapter 2
Table 2-1 Correlation of Mitigation Measures  to Threats2-54
Chapter 3
Table 3-1 Glazing Protection Levels Based on  Fragment Impact Locations3-21
Table 3-2  Correlation of GSA Glazing Performance  Conditions and DoD Levels of 
Protection  for New Buildings3-22
Chapter 4
Table 4-1 DoD Minimum Antiterrorism (AT)  Standards for New Buildings4-9
Table 4-2  Correlation of DoD Level of Protection  to Incident Pressure4-10
Table 4-3  Damage Approximations4-19
Chapter 5
Table 5-1 Comparison of ASHRAE Standards  52.1 and 52.25-12
Table 5-2  Indicators of a Possible Chemical  Incident5-34
Table 5-3  Indicators of a Possible Biological  Incident5-35
Table 5-4  Indicators of a Possible Radiological  Incident5-36

FIGURES
Chapter 1
Figure 1-1    Recent acts of terrorism1-2
Figure 1-2   Total facilities struck by international  terrorist attacks in 1997-2002 and  
total facilities attacked in 20021-3
Figure 1-3 The assessment process model1-5
Figure 1-4  Satellite imagery/GIS tool1-7
Figure 1-5  Satellite imagery/GIS tool1-8
Figure 1-6 Aggressor weapons1-15
Figure 1-7  Estimated plume from a 1-ton chlorine  spill in Washington, DC1-16
Figure 1-8  Facility system interactions1-23
Figure 1-9  Common system vulnerabilities1-35
Figure 1-10  Non-redundant critical functions  collocated near loading dock1-41
Figure 1-11  Vulnerability examples1-42
Figure 1-12  Typical building design and  construction process1-43
Figure 1-13  Risk management choices1-44
Chapter 2
Figure 2-1 An example of using GIS to identify  adjacent hazards2-5
Figure 2-2 Clustered versus dispersed site layouts2-8
Figure 2-3  Clustering to enhance surveillance opportunities while minimizing views 
into the buildings2-8
Figure 2-4 Streetscape security elements2-17
Figure 2-5 Blocking of sight lines2-20
Figure 2-6 Improper building siting and view  relationships2-21
Figure 2-7 Clear zone with unobstructed views2-21
Figure 2-8 Concept of stand-off distance2-22
Figure 2-9 Stand-off distance and building separation2-23
Figure 2-10 Exclusive and non-exclusive zones2-26
Figure 2-11 Application of perimeter barrier elements2-28
Figure 2-12  Using street closing to create a controlled  access area2-31
Figure 2-13 Sample bollard applications2-33
Figure 2-14 Examples of active and passive vehicle barriers2-35
Figure 2-15 Combined multi-user gate2-37
Figure 2-16 Summary of site mitigation measures2-53
Chapter 3
Figure 3-1 Glazed areas perpendicularly oriented  away from streets3-5
Figure 3-2 Re-entrant corners in a floor plan3-6
Figure 3-3 Offset doors through foyer3-7
Figure 3-4 Side view of a test structure illustrating  performance conditions of Table 3-
23-22
Figure 3-5 An unprotected window subject to a  large explosion3-23
Figure 3-6 Narrow and recessed windows  with sloped sills3-29
Figure 3-7 Sacrificial roof3-33
Figure 3-8 Example of protecting outdoor air intakes3-36
Figure 3-9 Example of elevated air intake3-36
Figure 3-10 Another example of protecting outdoor  air intakes3-37
Figure 3-11 Example of enclosing an existing  vulnerable air intake3-38
Figure 3-12 Physical security devices3-48
Chapter 4
Figure 4-1 Typical pressure-time history4-2
Figure 4-2 Reflected pressure coefficient vs. angle  of incidence4-3
Figure 4-3 Typical impulse waveform4-4
Figure 4-4 Blast pressure effects on a structure4-7
Figure 4-5 Explosives environments - blast range  to effects4-11
Figure 4- 6 Blast analysis of a building for a typical car  bomb detonated in the 
buildingÕs parking lot4-12
Figure 4-7 Blast analysis of a building for a typical  large truck bomb detonated in the  
buildingÕs parking lot4-12
Figure 4-8 Relationship of cost to stand-off distance4-13
Figure 4-9 Stand-off distance and its relationship  to blast impact as modeled on the  
Khobar Towers site4-15
Figure 4-10 Incident overpressure measured in  pounds per square inch, as a function 
of  stand-off distance and net explosive weight  (pounds-TNT)4-17
Chapter 5
Figure 5-1 Universal-fit escape hood5-6
Figure 5-2 Scanning electron microscope image of  a polyester-glass fiber filter5-8
Figure 5-3 Four primary filter collection mechanisms5-9
Figure 5-4 Classic collection efficiency curve5-10
Figure 5-5   A bag filter and HEPA filter5-12
Figure 5-6 Comparison of filter collection efficiency  based on particle size5-13
Figure 5-7 Typical performance of a HEPA 99.97%5-14
Figure 5-8 Scanning electron microscope image of  activated carbon pores5-14
Figure 5-9  Charcoal filter beds5-17
Figure 5-10 UVGI array used for air disinfection with  reflective surfaces5-19
Figure 5-11 A military FFA 580 air filtration system  containing both a HEPA filter and 
an  ASZM-TEDA carbon adsorber as part of  an overpressure system5-21
Figure 5-12 A commercial air filtration unit5-22
Figure 5-13  An IMS chemical detector designed for  installation in HVAC systems  5-
29
Figure 5-14 Placards associated with chemical  incidents5-35
Figure 5-15 Placards associated with biological  incidents5-36
Figure 5-16 Placards associated with radiological  incidents5-36