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= Canonical External Hazard Taxonomy =

== Purpose ==
This page defines the '''authoritative canonical hazard taxonomy''' for external hazards applicable to nuclear power plants. It establishes a '''single, stable set of canonical hazard identifiers (IDs)''', their scope boundaries, and their relationships.

These canonical IDs are used consistently across:
* the External Hazards wiki
* the document index and RAG database
* future member‑facing LLM/chat tools

The taxonomy normalizes terminology used across EPRI, the NRC, ASME/ANS, and international guidance. It does '''not''' replace regulatory language and does '''not''' remove technical or site‑specific nuance.

== Core principles ==
The following principles govern how this taxonomy is used:

* '''Canonical hazard IDs are immutable.'''
** Once published, an ID must '''never''' be renamed, edited, or deleted.
** Changes in understanding are handled through descriptions, hierarchy updates, aliases, or deprecation (see below).

* '''Canonical IDs are labels, not filters.'''
** They improve grouping, traceability, and explainability.
** They must '''never''' be used to gate retrieval or render content inaccessible.

* '''Free text remains authoritative content.'''
** Canonical IDs complement semantic search and embeddings; they do not replace them.

== How to use this taxonomy ==
* Each ''hazard overview'' wiki page must reference '''exactly one canonical hazard ID'''.
* Sub‑mechanisms or refinements reference both the child and parent IDs.
* Documents and index records '''may''' map to one or more canonical hazard IDs.
** Mapping improves consistency and long‑term usability.
** Lack of a mapping does '''not''' make content invisible or invalid.
* Initiating events (for example, LOOP, LUHS) are '''not hazards''' and are excluded.

== Governance and change control ==
This taxonomy is designed to evolve '''without breaking downstream systems'''.

=== Allowed changes ===
The following may change at any time:
* Preferred hazard names
* Descriptions and scope notes
* Parent–child relationships
* Aliases and explanatory notes

=== Prohibited changes ===
* Canonical hazard IDs must '''never''' be renamed, reused, or removed.

=== Deprecation policy ===
When a hazard definition changes materially:
* The existing ID is marked '''deprecated'''.
* One or more replacement IDs are identified.
* Existing documents and index records remain valid and unchanged.

This approach preserves historical consistency while allowing the taxonomy to evolve.

== Relationship to other structures ==
* Canonical hazard IDs define '''what''' external phenomenon is being referenced.
* [[Concepts|Canonical concepts]] (defined elsewhere) describe '''how''' reasoning is performed.
* Terminology and prose remain flexible and human‑readable.

Together, these elements form a stable semantic backbone that supports long‑term knowledge retention, analysis, and AI‑assisted use.

== Top-Level Classes ==
{| class="wikitable sortable"
! Canonical ID !! Preferred Name !! Scope
|-
| EH-HYD || Hydrological Hazards || Water-related natural hazards including flooding, precipitation, and coastal events
|-
| EH-ATM || Atmospheric Hazards || Wind, storm, and weather-related hazards including tornados, hurricanes, and extreme temperatures
|-
| EH-GEO || Geological Hazards || Earth-related natural hazards including seismic, volcanic, and ground instability events
|-
| EH-BIO || Biological & Environmental Hazards || Hazards from biological organisms, drought, wildfire, and ecological phenomena
|-
| EH-ANT || Anthropogenic Hazards || Human-caused external hazards including industrial accidents, transportation, and nearby facility events
|-
| EH-ELE || Electrical & Electromagnetic Hazards || Hazards affecting electrical systems including lightning, electromagnetic interference, and grid disturbances
|-
| EH-CMB || Combined & Correlated Hazards || Multi-hazard scenarios and hazard combinations
|-
| EH-EVL || Hazard Evaluation & PRA Methods || Methodologies for identifying, screening, and assessing external hazards
|}

== Hydrological Hazards ==
{| class="wikitable sortable"
! Canonical ID !! Preferred Name !! Parent
|-
| EH-HYD-RIV || Riverine Flooding || EH-HYD
|-
| EH-HYD-PLV || Pluvial Flooding (Local Intense Precipitation) || EH-HYD
|-
| EH-HYD-CST || Coastal Flooding & Storm Surge || EH-HYD
|-
| EH-HYD-TSU || Tsunami || EH-HYD
|-
| EH-HYD-SEI || Seiche || EH-HYD
|-
| EH-HYD-DAM || Dam & Levee Failure || EH-HYD
|-
| EH-HYD-ICE || Ice-Induced Flooding (Ice Jam / Frazil Ice) || EH-HYD
|-
| EH-HYD-SLR || Sea Level Rise || EH-HYD
|-
| EH-HYD-GW || Groundwater Ingress || EH-HYD
|-
| EH-HYD-WDR || Wind-Driven Rain Intrusion || EH-HYD
|}

== Atmospheric Hazards ==
{| class="wikitable sortable"
! Canonical ID !! Preferred Name !! Parent
|-
| EH-ATM-TOR || Tornado || EH-ATM
|-
| EH-ATM-HUR || Hurricane / Tropical Cyclone || EH-ATM
|-
| EH-ATM-STW || Straight-Line / High Wind || EH-ATM
|-
| EH-ATM-DRT || Derecho / Thunderstorm Wind || EH-ATM
|-
| EH-ATM-HAL || Hail || EH-ATM
|-
| EH-ATM-SNW || Extreme Snow / Ice Storm || EH-ATM
|-
| EH-ATM-EHT || Extreme Heat || EH-ATM
|-
| EH-ATM-ECL || Extreme Cold / Freeze || EH-ATM
|-
| EH-ATM-MSL || Wind-Borne Missiles (Tornado / Hurricane Debris) || EH-ATM
|-
| EH-ATM-SND || Sandstorm / Dust Storm || EH-ATM
|}

== Geological Hazards ==
{| class="wikitable sortable"
! Canonical ID !! Preferred Name !! Parent
|-
| EH-GEO-SEI || Seismic (Vibratory Ground Motion) || EH-GEO
|-
| EH-GEO-FLT || Surface Faulting & Tectonic Deformation || EH-GEO
|-
| EH-GEO-VOL || Volcanic Activity (Ash, Lava, Lahar) || EH-GEO
|-
| EH-GEO-LND || Landslide / Slope Instability || EH-GEO
|-
| EH-GEO-SUB || Subsidence / Sinkhole / Karst Collapse || EH-GEO
|-
| EH-GEO-LIQ || Soil Liquefaction || EH-GEO
|-
| EH-GEO-ERO || Erosion & Sedimentation || EH-GEO
|}

== Biological & Environmental Hazards ==
{| class="wikitable sortable"
! Canonical ID !! Preferred Name !! Parent
|-
| EH-BIO-DRT || Drought / Low Water || EH-BIO
|-
| EH-BIO-WFR || Wildfire / Forest Fire || EH-BIO
|-
| EH-BIO-FOL || Biological Fouling (Mussels, Jellyfish, Algae) || EH-BIO
|-
| EH-BIO-VEG || Vegetation Encroachment || EH-BIO
|-
| EH-BIO-INF || Infestation (Insects, Rodents) || EH-BIO
|-
| EH-BIO-CLM || Climate Change Effects (Long-Term Trends) || EH-BIO
|}

== Anthropogenic Hazards ==
{| class="wikitable sortable"
! Canonical ID !! Preferred Name !! Parent
|-
| EH-ANT-IND || Nearby Industrial Facility Accident || EH-ANT
|-
| EH-ANT-TRN || Transportation Accident (Rail, Road, Pipeline) || EH-ANT
|-
| EH-ANT-AIR || Aircraft Impact || EH-ANT
|-
| EH-ANT-TMI || Turbine Missile (Internally Generated External Hazard) || EH-ANT
|-
| EH-ANT-EXP || External Explosion / Blast Wave || EH-ANT
|-
| EH-ANT-TOX || Toxic Gas / Chemical Release || EH-ANT
|-
| EH-ANT-FIR || External Fire (Non-Wildfire, for example, Fuel Storage) || EH-ANT
|-
| EH-ANT-SAB || Sabotage / Security Threat || EH-ANT
|}

== Electrical & Electromagnetic Hazards ==
{| class="wikitable sortable"
! Canonical ID !! Preferred Name !! Parent
|-
| EH-ELE-LTN || Lightning Strike || EH-ELE
|-
| EH-ELE-GRD || Grid Disturbance / Loss of Offsite Power (LOOP) || EH-ELE
|-
| EH-ELE-EMP || Electromagnetic Pulse (EMP) / Geomagnetic Disturbance || EH-ELE
|-
| EH-ELE-EMI || Electromagnetic Interference (EMI) || EH-ELE
|}

== Combined & Correlated Hazards ==
{| class="wikitable sortable"
! Canonical ID !! Preferred Name !! Parent
|-
| EH-CMB-SEF || Seismic + Flooding (Seismically-Induced Flooding) || EH-CMB
|-
| EH-CMB-HWF || High Wind + Flooding (Hurricane Multi-Hazard) || EH-CMB
|-
| EH-CMB-SLP || Seismic + LOOP || EH-CMB
|-
| EH-CMB-WLP || Wind + LOOP || EH-CMB
|-
| EH-CMB-CAS || Cascading / Sequential Hazard Events || EH-CMB
|-
| EH-CMB-COR || Correlated Hazard Groups || EH-CMB
|}

== Hazard Evaluation & PRA Methods ==
{| class="wikitable sortable"
! Canonical ID !! Preferred Name !! Parent
|-
| EH-EVL-SCR || Hazard Screening & Identification || EH-EVL
|-
| EH-EVL-PRA || External Events PRA (Probabilistic Risk Assessment) || EH-EVL
|-
| EH-EVL-FRG || Fragility Analysis || EH-EVL
|-
| EH-EVL-MAR || Margins Assessment || EH-EVL
|-
| EH-EVL-SMA || Seismic Margins Assessment (SMA) || EH-EVL
|-
| EH-EVL-WDN || Walkdown & Inspection Procedures || EH-EVL
|-
| EH-EVL-OPX || Operating Experience (OpE) Review || EH-EVL
|-
| EH-EVL-CLR || Climate Resilience Assessment || EH-EVL
|}

----
''EPRI technical point of contact: Chris Rochon ([mailto:CRochon@epri.com CRochon@epri.com])''

''Date last reviewed: 2026-03-23''

Taxonomy - Revision history

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