Glossary

Accident Unintended and unforeseen event or series of events and circumstances that results in one or more undesirable consequences.

Accident scenario Sequence of events leading to adverse consequences.

Atmospheric tank Vessel with a fixed or a floating roof in which hazardous substances are contained at atmospheric pressure. Atmospheric tanks are commonly used for the storage of large quantities of liquid hydrocarbons.

BLEVE Boiling liquid expanding vapor explosion. This is an explosion that is caused by the rupture of a vessel that contains a pressurized toxic or flammable liquid that is heated above its boiling point. If the liquid is flammable, a BLEVE is associated with a fireball in case of immediate ignition, or with a flash fire or a VCE if ignition is delayed.

Cascading event Chain of events in which a primary event triggers a secondary event, which in turn can cause a tertiary event, etc. During Natech accidents the risk of cascading events is generally higher than during conventional technological accidents.

Consequence Outcome of an event which can be positive or negative. An event can have more than one outcome.

Damage state Category of equipment damage as a function of natural-hazard severity.

Disaster Natural or man-made event resulting in widespread human, environmental, economic, or material losses. The adverse consequences of a disaster can exceed the ability of the affected community or society to cope using its own resources.

Domino event See Cascading event.

EC European Commission. The EC is the executive body of the European Union. As such, it is in charge of proposing legislation, implementing decisions, upholding the EU treaties, and managing the day-to-day business of the EU.

EU European Union. The EU is a supranational political and economic union which includes 28 independent and democratic Member States in the European continent.

Event tree Inductive analytical diagram in which Boolean logic is used to analyze the progression and final outcomes of an event. Event Tree Analysis is a process that traces forward in time or through a chain of causes (see also Fault Tree Analysis).

Explosion Sudden and violent release of energy accompanied by pressure and/or heat.

Fault Tree Analysis Deductive process using Boolean logic that aims to understand the causes or combinations of causes that lead to an undesired top event, usually loss of containment (see LOC). Fault Tree Analysis traces backward in time or through a causal chain.

Fireball Fire event originating from the immediate ignition of a flammable vapor or gas cloud caused by a prior catastrophic loss of containment (see BLEVE).

Flash Fire Sudden combustion of a mixture of flammable substance and air. Flash fires are characterized by high temperature, short duration, and a rapidly moving flame front. Flash fires do not cause blast waves (see BLEVE).

F–N curve Plot of the cumulative frequency (F) of different accident scenarios against the number of potential casualties (N) associated with these scenarios.

Fragility curve Probability of failure or damage as a function of the degree of natural-event loading experienced.

Frequency (relative) Likelihood of an event over a specific time interval, usually expressed as year⁻¹.

Hazard Source of danger. A hazard does not necessarily lead to harm but represents only a potential to result in harm.

Hazardous substance/material Biological, chemical, radiological, or nuclear agent which poses a threat to health, animals, or the environment.

Hazmat Hazardous material.

HAZOP Hazard and Operability Study. HAZOP is a structured and systematic process to analyze potential hazards to personnel or equipment by reviewing the design of a planned or existing process or operation to identify potential issues of concern. The advantage of HAZOP is that in addition to hazards it also addresses operability problems.

Individual risk Probability for an individual to suffer ill effects at a specific point around a hazardous installation per given time period.

Isorisk curve Level of equal individual risk around a hazardous installation.

Jet fire Fire resulting from the release of pressurized flammable materials from an aperture with significant momentum.

Lesson learned Knowledge gained from investigation, study, or other activities in regard to the technical, behavioral, cultural, management, or other factors, which led, could have led, or contributed to the occurrence of an accident or a natural disaster.

LNG Liquefied Natural Gas. LNG is a natural gas that for ease of transport and storage has been converted to liquid form, thereby significantly reducing its volume.

LOC Loss of containment. Event in which hazardous materials are released from the equipment they were contained in.

LPG Liquefied Petroleum Gas. LPG is a flammable hydrocarbon mixture and is also referred to as propane or butane.

LUP Land use planning. LUP helps ensure that hazardous installations are separated by appropriate distances from other installations and developments, thereby preventing negative consequences.

Major accident Major toxic release, fire, or explosion whose impacts on human health and the natural environment exceed specific severity thresholds.

Missile Projection of a fragment in the wake of equipment rupture. Missiles can cause damage to other equipment on- or off-site, thereby increasing the risk of cascading events.

Mitigation Actions or measures taken to reduce the impact of hazardous-materials releases if they occur. Risk mitigation, on the other hand, aims to lower the risk of an accident (see also Risk reduction).

MMI Modified Mercalli Intensity scale. This scale is used to measure the intensity of an earthquake. It is based on observed effects and ranges from a scale of I (not felt) to XII (total destruction).

Natech Technological accident involving the release of hazardous materials caused by a natural hazard. The releases can be chemical, biological, or radiological in nature.

NOAA National Oceanic and Atmospheric Administration (NOAA) of the US Department of Commerce. NOAA’s mission is to understand and predict changes in climate, weather, oceans, and coasts, and conserve and manage coastal and marine ecosystems and resources.

OECD Organisation for Economic Co-operation and Development. The OECD promotes policies that will improve the economic and social well-being of people around the world.

Organizational measure Any measure not involving physical construction that uses knowledge, practice, or agreement to reduce risks and impacts, in particular through policies and laws, awareness raising, training, and education (see also Structural measure).

PDF Probability Density Function. A PDF of a continuous random variable is a function that describes the relative likelihood for this random variable to take on a given value.

PGA Peak ground acceleration. PGA is the maximum acceleration of the ground during earthquake shaking at a specific location. It is commonly expressed in percentage of the acceleration of free fall, g, or in m/s² (where 1 g = 9.81 m/s²).

PGV Peak ground velocity. PGV is the maximum velocity of the ground subjected to an earthquake. It is measured in m/s.

Pool fire Burning pool of liquid, more specifically a fire burning above a pool of evaporating liquid.

Preparedness Measures taken before an adverse event in order to be prepared to adequately respond when the event occurs.

Pressurized tank Vessel in which hazardous substances are stored or processed at pressures higher than atmospheric pressure.

Prevention Actions or measures taken to reduce the likelihood of damage and occurrence of a hazardous-materials release.

Probability Measure for the likelihood of a random event expressed as a number between 0 and 1.

Probit method Probability unit method. It relates the magnitude of an effect (dose) to the extent of damage caused (response). The probit variable can be easily converted into a probability or percentage.

PSHA Probabilistic Seismic Hazard Analysis. PSHA aims to quantify the exceedance rate of different ground-motion levels at a specific location considering all possible earthquakes.

PTHA Probabilistic Tsunami Hazard Analysis.

QRA Quantitative Risk Analysis or Assessment. Process to estimate the risk of an event quantitatively. The outcome of a QRA is usually expressed in terms of fatalities or economic losses.

Return period Recurrence interval of a natural event, that is, an estimate of the likelihood for a flood, earthquake, etc. to occur.

Risk Combination of the frequency, or probability, of occurrence and the consequence of a hazardous event. Risk therefore includes the likelihood of conversion of a hazard into actual delivery of injury, damage, or harm. Risk is always subject to uncertainty related to the occurrence of the event.

Risk analysis Process that identifies hazard sources and estimates the associated risk.

Risk assessment Risk analysis and risk evaluation.

Risk evaluation Process in which the estimated risk is compared to given risk acceptability criteria.

Risk management Process that includes risk assessment, risk treatment, risk acceptance, and risk communication.

Risk reduction Actions that aim at lowering the probability of an adverse event, limiting its consequences, or both. The associated measures can be structural and organizational.

Risk state Category for the intensity of loss of containment.

Risk treatment Selection and implementation of measures to modify the estimated risk.

Societal risk Risk to the community from identified risk sources. Societal risk is usually expressed as F–N curves.

Structural measure Any physical construction to reduce or avoid possible impacts of hazards, or application of engineering techniques to achieve hazard-resistance and resilience in structures or systems (see also Organizational measure).

VCE Vapor cloud explosion. A VCE results from the ignition of a large cloud of flammable vapor, gas, or mist in which significant overpressure is produced.

WGCA Working Group on Chemical Accidents of the OECD.