April 2004

Federal Guidelines

for Dam Safety

Hazard Potential Classification System for Dams 
FEDERAL GUIDELINES FOR DAM SAFETY: 

HAZARD POTENTIAL CLASSIFICATION 

SYSTEM FOR DAMS 

prepared by the 

INTERAGENCY COMMITTEE ON DAM SAFETY 

U.S. DEPARTMENT OF HOMELAND SECURITY 

FEDERAL EMERGENCY MANAGEMENT AGENCY 

OCTOBER 1998 

Reprinted January 2004 
PREFACE

In April 1977, President Carter issued a memorandum directing the review of federal dam safety activities by an 

ad hoc panel of recognized experts. In June 1979, the ad hoc interagency committee on dam safety (ICODS) 

issued its report, which contained the first guidelines for federal agency dam owners. The Federal Guidelines for 

Dam Safety (Guidelines) encourage strict safety standards in the practices and procedures employed by federal 

agencies or required of dam owners regulated by the federal agencies. The Guidelines address management 

practices and procedures but do not attempt to establish technical standards. They provide the most complete and 

authoritative statement available of the desired management practices for promoting dam safety and the welfare 

of the public. 

To supplement the Guidelines, ICODS prepared and approved federal guidelines in the areas of emergency 

action planning; earthquake analysis and design of dams; and selecting and accommodating inflow design floods 

for dams. These publications, based on the most current knowledge and experience available, provided 

authoritative statements on the state of the art for three important technical areas involving dam safety. In 1994, 

the ICODS Subcommittee to Review/Update the Federal Guidelines began an update to these guidelines to meet 

new dam safety challenges and to ensure consistency across agencies and users. In addition, the ICODS 

Subcommittee on Federal/Non-Federal Dam Safety Coordination developed a new guideline, Hazard Potential 

Classification System for Dams. 

With the passage of the National Dam Safety Program Act of 1996, Public Law 104-303, ICODS and its 

Subcommittees were reorganized to reflect the objectives and requirements of Public Law 104-303. In 1998, the 

newly convened Guidelines Development Subcommittee completed work on the update of all of the following 

guidelines: 

• Federal Guidelines for Dam Safety: Emergency Action Planning 

for Dam Owners 

• Federal Guidelines for Dam Safety: Hazard Potential Classification 

System for Dams

• Federal Guidelines for Dam Safety: Earthquake Analyses and Design of Dams 

• Federal Guidelines for Dam Safety: Selecting and Accommodating Inflow Design 

Floods for Dams 

• Federal Guidelines for Dam Safety: Glossary of Terms 

The publication of these guidelines marks the final step in the review and update process. In recognition of the 

continuing need to enhance dam safety through coordination and information exchange among federal and state 

agencies, the Guidelines Development Subcommittee will be responsible for maintaining these documents and 

establishing additional guidelines that will help achieve the objectives of the National Dam Safety Program. 

The members of all of the Task Groups responsible for the update of the guidelines are to be commended for 

their diligent and highly professional efforts. 

Harold W. Andress, Jr. 

Chairman, Interagency Committee on Dam Safety 
HAZARD POTENTIAL CLASSIFICATION SYSTEM FOR DAMS 

TASK GROUP 

Alton P. Davis Jr.** 

GEI Consultants, Inc. 

David G. Achterberg* 

DOI, Bureau of Reclamation 

Harold (Bud) W. Andress, Jr.* 

Federal Emergency Management Agency 

Jerrold W. Gotzmer* 

Federal Energy Regulatory Commission 

William Irwin* 

USDA, Natural Resources Conservation Service 

George Mills* 

Ohio Department of Natural Resources 

James Simons* 

North Carolina Department of Environmental 

Health and Natural Resources 

Constantine G. Tjoumas* 

Federal Energy Regulatory Commission 

David Bowles 

Utah State University 

Darian E. Ingram

DOI, Bureau of Reclamation 

Charles Karpowicz 

DOI, National Park Service 

Martin W. McCann, Jr. 

Stanford University 

Mark A. Riebau 

Association of State Flood Plain Managers 

Charles Sullivan 

U. S. Army Corps of Engineers 

**Chair of Task Group that completed final document 

 *Members of Task Group that completed final document 
TABLE OF CONTENTS 

I. PURPOSE..........................................................................................................................1 

II. DEFINITIONS ..................................................................................................................3 

III. CLASSIFICATION SYSTEM ........................................................................................5 

IV. DISCUSSION ....................................................................................................................7 

APPENDIX A ............................................................................................................................ A-1

APPENDIX B .............................................................................................................................B-1 
I. PURPOSE

Common practice among federal and state dam safety offices is to classify a dam according to 

the potential impact a dam failure (breach) or mis-operation (unscheduled release) would have 

on upstream and/or downstream areas or at locations remote from the dam. The existing 

classification systems are numerous and vary within and between both the federal and state 

sectors. Although differences in classification systems exist, they share a common thread: each 

system attempts to classify dams according to the potential impacts from a dam failure or misoperation, should it occur. The most significant problem with these various systems is the use of 

terms that lack clear definition. In addition, the various systems use different terminology to 

define similar concepts. This precludes consistency between the various federal and state 

agencies and understanding by the public. 

This document sets forth a hazard potential classification system for dams that is simple, clear, 

concise, and adaptable to any agency's current system. The intent is to provide straightforward 

definitions that can be applied uniformly by all federal and state dam safety agencies and can be 

readily understood by the public. It does not establish how the system will be used, such as 

prescribing specific design criteria or prioritizing inspections. Those responsibilities belong to 

the responsible regulatory authority. 

1 
II. DEFINITIONS 

For the purpose of this system, the following terms are defined: 

HAZARD POTENTIAL: The possible adverse incremental consequences that result from the 

release of water or stored contents due to failure of the dam or mis-operation of the dam or 

appurtenances. 

ADVERSE CONSEQUENCES: Negative impacts that may result from the failure of a dam. 

The primary concerns are loss of human life, economic loss (including property damage), lifeline 

disruption, and environmental impact. 

INCREMENTAL: Under the same conditions (e.g., flood, earthquake, or other event), the 

difference in impacts that would occur due to failure or mis-operation of the dam over those that 

would have occurred without failure or mis-operation of the dam and appurtenances. 

PROBABLE: Likely to occur; reasonably expected; realistic. 

HAZARD POTENTIAL CLASSIFICATION: A system that categorizes dams according to 

the degree of adverse incremental consequences of a failure or mis-operation of a dam. The 

hazard potential classification does not reflect in any way on the current condition of the dam 

(e.g., safety, structural integrity, flood routing capacity). 

3 
III. CLASSIFICATION SYSTEM

Three classification levels are adopted as follows: LOW, SIGNIFICANT, and HIGH, listed in 

order of increasing adverse incremental consequences. The classification levels build on each 

other, i.e., the higher order classification levels add to the list of consequences for the lower 

classification levels, as noted in the table on the following page. 

This hazard potential classification system should be utilized with the understanding that the 

failure of any dam or water-retaining structure, no matter how small, could represent a danger to 

downstream life and property. Whenever there is an uncontrolled release of stored water, there 

is the possibility of someone, regardless of how unexpected, being in its path. 

A primary purpose of any classification system is to select appropriate design criteria. In other 

words, design criteria will become more conservative as the potential for loss of life and/or 

property damage increases. However, postulating every conceivable circumstance that might 

remotely place a person in the inundation zone whenever a failure may occur should not be the 

basis for determining the conservatism in dam design criteria. 

This hazard potential classification system categorizes dams based on the probable loss of 

human life and the impacts on economic, environmental, and lifeline interests. Improbable loss 

of life exists where persons are only temporarily in the potential inundation area. For instance, 

this hazard potential classification system does not contemplate the improbable loss of life of the 

occasional recreational user of the river and downstream lands, passer-by, or non-overnight 

outdoor user of downstream lands. It should be understood that in any classification system, all 

possibilities cannot be defined. High usage areas of any type should be considered 

appropriately. Judgment and common sense must ultimately be a part of any decision on 

classification. Further, no allowances for evacuation or other emergency actions by the 

population should be considered because emergency procedures should not be a substitute for 

appropriate design, construction, and maintenance of dam structures. 

1. LOW HAZARD POTENTIAL 

Dams assigned the low hazard potential classification are those where failure or misoperation 

results in no probable loss of human life and low economic and/or environmental losses. Losses 

are principally limited to the owner’s property. 

2. SIGNIFICANT HAZARD POTENTIAL 

Dams assigned the significant hazard potential classification are those dams where failure or 

mis-operation results in no probable loss of human life but can cause economic loss, 

environmental damage, disruption of lifeline facilities, or can impact other concerns. Significant 

hazard potential classification dams are often located in predominantly rural or agricultural areas 

but could be located in areas with population and significant infrastructure. 

5 
3. HIGH HAZARD POTENTIAL 

Dams assigned the high hazard potential classification are those where failure or mis-operation 

will probably cause loss of human life. 

Hazard Potential Loss of Human Life Economic, Environmental, Lifeline 

Classification Losses 

Low None expected Low and generally limited to owner 

Significant None expected Yes 

High Probable. One or more Yes (but not necessary for this 

expected classification) 

6 
IV. DISCUSSION

This Hazard Potential Classification System for Dams is based on the probable loss of human 

life and the potential for economic losses, environmental damage, and/or disruption to lifelines 

caused by failure of mis-operation of a dam or its appurtenances. This Hazard Potential 

Classification System for Dams recognizes that the failure or mis-operation of any dam or waterretaining structure, no matter how small, represents a potential danger to downstream life and 

property. Whenever there is an uncontrolled release of stored water, there is always the 

possibility, regardless of how unexpected, of someone being in the path of the discharge. 

However, postulating every conceivable circumstance that might remotely place a person in the 

potential inundation zone should not be the basis for determining the appropriate classification 

level. This system considers improbable loss of life to exist where persons are only temporarily 

in the potential inundation area. 

The difference between the significant and high hazard potential classification levels is that a 

high hazard potential dam includes the probable loss of human life. The failure of a dam that is 

classified as a high hazard potential structure may or may not include adverse incremental 

consequences that would otherwise justify a significant hazard potential classification. 

The hazard potential classification assigned to a dam is based on consideration of the effects of a 

failure or mis-operation during both normal and flood flow conditions. The classification 

assigned should be based on the worst-case probable scenario of failure or mis-operation of the 

dam, i.e., the assigned classification should be based on failure consequences that will result in 

the assignment of the highest hazard potential classification of all probable failure and misoperation scenarios. Each element of a project must be evaluated to determine the proper hazard 

potential classification for the project. However, there is only one hazard potential classification 

assigned to the entire project. Individual elements are not assigned separate classifications. 

The probable scenarios considered should be reasonable, justifiable, and consistent with the 

Federal Guidelines for Dam Safety: Selecting and Accommodating Inflow Design Floods for 

Dams (FEMA). For example, assuming reasonable breach parameters and a failure during 

normal operating conditions (“sunny day” failure) may result in the released water being 

confined to the river channel and no probable loss of human life, indicating a low hazard 

potential classification. However, if the dam were assumed to fail in a similar manner during a 

flood condition, and the result would be probable loss of human life (excluding the occasional 

passer-by or recreationist) but minor economic losses, a high hazard potential classification 

would be appropriate. Once a project is placed in the high hazard potential classification, 

additional probable failure or mis-operation scenarios need only be considered if there is a need 

to determine if they would likely induce higher adverse incremental impacts. 

In most situations, the investigation of the impact of failure or mis-operation of a dam on 

downstream human life, property damage, lifeline disruption, and environmental concerns is 

sufficient to determine the appropriate hazard potential classification. However, if failure or 

mis-operation of a dam contributes to failure of a downstream dam(s), the hazard potential 

7 
classification of the dam should be at least as high as the classification of the downstream dam(s) 

and should consider the adverse incremental consequences of the domino failures. 

8 
APPENDIX A - BACKGROUND 

CHARTER 

On September 12, 1994, a Task Group was chartered to review existing hazard potential 

classification systems, identify ambiguous terminology, and propose a modified or new system 

for the hazard potential classification of dams. 

METHOD 

The Task Group met on five occasions. Minutes of each meeting were recorded. The Task 

Group assembled copies of various Federal agency hazard potential classification systems, a 

copy of the Canadian Dam Safety Association Classification System, and a summary of state 

dam safety agency classification systems. Copies of these documents are included in Appendix 

B. The Task Group reviewed these documents, considered several options, and developed the 

Hazard Potential Classification System for Dams. The draft Hazard Potential Classification 

System for Dams was submitted to the ICODS for review and comment. Comments were 

received in April 1996 and incorporated in the final Task Group report. 

DISCUSSION 

An early decision of the Task Group was to limit the work to the classification system and 

associated definitions. The Task Group would not consider issues related to future 

uses of the classification system, such as to establish design criteria, remediation schedules, 

inspection schedules, emergency action plan requirements, and/or spillway inflow design flood 

criteria. The work would be aimed at developing simple, unambiguous definitions for the 

proposed classification system. 

The Task Group reviewed existing classification systems and the history of their development. 

The existing systems generally evolved from the U.S. Army Corps of Engineers' Appendix D, 

"Recommended Guidelines for Safety Inspections of Dams" (ER 1110-2-106), dated September 

26, 1979. Although the original 1979 classification system was intended for limited use, i.e., 

primarily to prioritize inspections for the 1979-1982 inspection program, it had evolved into 

multiple systems with various nomenclatures and specific design criteria. The resulting 

hodgepodge of systems has led to confusion in the dam safety community when dealing with 

multiple agencies and across state boundaries. 

The confusion begins with the names of the major classification categories that include: HighSignificant-Low Hazard Potential, A-B-C, C-B-A, 1-2-3, and 3-2-1 for the corresponding names. 

 In addition, various High Hazard Potential definitions contain an allowance for zero, few, 1 or 

more, or up to 10 human lives lost. This variety of terms, systems, and criteria leads to confusion 

in the dam safety community and, more importantly, to a lack of understanding by the general 

public. 

The Task Group reviewed existing systems for a number of categories. Although a few have up 

to nine categories, the great majority have three, as in the original 1979 system. In view of the 

long history of the basic 1979 three-category system, the associated regulatory base, and the 

Α−1 
various associated data bases, the Task Group decided to retain the existing three-category 

system. It was further decided that the original category titles of High, Significant, and Low 

Hazard Potential would be retained so that the resulting system would be applied uniformly by all 

regulatory agencies. 

The next issue was to discuss the factors to be considered in each category. The Task Group 

decided that the four key risk factors are loss of human life; economic losses; environmental 

damage; and lifeline disruption. 

Hazard potential categories would consider increasing levels of loss. However, probable loss of 

human life would designate a High Hazard Potential Structure regardless of the magnitude of 

other losses. If no loss of life is probable as the result of dam failure or mis-operation, the dam 

would be classified as Low or Significant Hazard Potential. This is a major change from prior 

systems. In an effort to clarify ambiguities in prior classification systems, the probable loss of 

human life is defined to signify one or more lives lost. The term "probable" is specifically 

included to indicate that the scenario used to predict the loss of human life must be reasonable 

and realistic, not contrived. In the definition for High Hazard Potential, the probable loss of 

human life is further clarified to exclude the casual user of the downstream or upstream area in 

determining the potential for loss of human life. It is also stated that potential public response to 

the emergency should not be used to reduce the calculated probable loss of human life. 

The terms failure and mis-operation of a project are used by the Task Group to define the causes 

of the hazard to upstream and downstream interests. Failure of a dam is meant to include any 

cause that breaches the structure to release the stored contents (water, hazardous liquid wastes, 

slurries, or tailings). Mis-operation is meant to include any cause related to accidental or 

deliberate unscheduled release of the stored contents, such as a gate being opened more than 

planned but which does not result in full release of the reservoir contents. 

It is the intent of the Task Group that each project would be periodically re-evaluated and 

reclassified as appropriate. The frequency of review should be each time the project is scheduled 

for inspection, or at least once each 5 years. This allows for periodic changes in the assigned 

hazard potential category based on changed reservoir or downstream development. 

The Task Group considers it important that the term "Potential" be incorporated in each 

classification system name. This term helps the public understand the significant difference 

between hazards that "may" become real and any current actual safety concerns for the dam. 

It is the Task Group's conclusion that the classification system should be a universal system for 

all regulatory agencies. The classification system category names should be adopted in lieu of 

any existing numerical or alphabetical system for consistency in the dam safety community and 

to properly educate the public on the need to properly maintain this component of the Nation's 

infrastructure. 

Α−2 
TASK GROUP CONCLUSIONS 

1. The proposed Hazard Potential Classification System for Dams provides a clear, simple, 

concise, and adaptable system to classify the hazard potential for dams. 

2. The hazard potential rating does not reflect in any way on the current safety, structural 

integrity, or flood routing capability of the project water retaining structures. 

3. The proposed classification system should be submitted to ICODS with a 

recommendation for peer review by ASDSO, USCOLD, ASCE, and the Canadian Dam 

Safety Association. 

4. Future task groups should be established to consider design criteria associated with the 

various hazard classification systems. 

5. The proposed Hazard Potential Classification System should be adopted in lieu of 

existing numerical and alphabetical systems. This is necessary to eliminate confusion in 

the dam safety community and to educate the public on the importance of dam safety. 

Α−3 
APPENDIX B - EXISTING CLASSIFICATION SYSTEM INFORMATION* 

Federal Energy Regulatory Commission 

USDA, Natural Resources Conservation Service (formerly Soil Conservation Service) 

DOI, Bureau of Reclamation 

U. S. Army Corps of Engineers 

Canadian Dam Safety Association 

Summary of State Systems (compiled April 1995) 

*Note: These appendices are available only in the print publication of FEMA 333, which can be 

ordered through: FEMA Distribution Center, P.O. Box 2012, 8231 Stayton Drive, Jessup, 

Maryland 20794-2012, Phone Number 1-800-480-2520 

Β−1 
FEDERAL ENERGY REGULATORY COMMISSION 
USDA, NATURAL RESOURCES CONSERVATION SERVICE 

(FORMERLY SOIL CONSERVATION SERVICE) 
DOI, BUREAU OF RECLAMATION
U. S. ARMY CORPS OF ENGINEERS
CANADIAN DAM SAFETY ASSOCIATION
SUMMARY OF STATE SYSTEMS (COMPILED APRIL 1995)