ATEXpedy
A
Ambient temperature
The temperature of the environment in which a piece of equipment or installation operates. It influences the behaviour of flammable substances and the selection and certification of equipment for explosive atmospheres.
Area classification
The process by which the zones where an explosive atmosphere may be present are identified and delimited, taking into account the characteristics of the flammable substances, the sources of release and the existing ventilation and dispersion conditions.
ATEX
An acronym derived from the French term ATmosphères EXplosibles (explosive atmospheres). A set of European directives intended to regulate the safety of equipment, protective systems and workplaces in which potentially explosive atmospheres may be present.
ATEX certification
The process by which it is verified and documented that a piece of equipment or a protective system complies with the requirements established by Directive 2014/34/EU for use in potentially explosive atmospheres.
ATEX Directive 1999/92/EC
European regulation that establishes the minimum requirements for the protection of workers from the risks arising from explosive atmospheres in the workplace.
ATEX Directive 2014/34/EU
European regulation that establishes the requirements for the design, manufacture and marketing of equipment and protective systems intended for use in potentially explosive atmospheres.
ATEX equipment (for explosive atmospheres)
Equipment designed and certified for use in areas where explosive atmospheres may be present, complying with the safety requirements established to prevent it from becoming an ignition source.
ATEX equipment category
A classification established by Directive 2014/34/EU that defines the level of protection required for equipment intended for use in potentially explosive atmospheres, based on the probability of the presence of such an atmosphere.
- Category 1: very high level of protection, suitable for areas in which an explosive atmosphere is present continuously, frequently or for long periods.
- Category 2: high level of protection, suitable for areas in which an explosive atmosphere may occur occasionally during normal operation.
- Category 3: normal level of protection, suitable for areas in which an explosive atmosphere is unlikely during normal operation or occurs only for short periods.
ATEX equipment group
The category of equipment according to the type of explosive atmosphere in which it can be used:
- Group I: equipment for mines.
- Group II: equipment for general industry.
ATEX gas group
The classification of a gas according to its flammability properties and ignition temperature:
- IIA: propane.
- IIB: ethylene.
- IIC: hydrogen or acetylene.
ATEX risk management
The process of identifying, assessing and controlling the risks related to explosions in an industrial setting.
ATEX zone
A classified area in which an explosive atmosphere of gases, vapours or combustible dusts may exist, whose categorisation is established based on the probability of formation and the duration of the presence of such an atmosphere.
ATEX zones for combustible dust
The classification of areas where an explosive atmosphere in the form of a combustible dust cloud may be present, carried out based on the expected frequency and duration of such an atmosphere.
- Zone 20: an area in which an explosive atmosphere in the form of a combustible dust cloud is present continuously, for long periods or frequently.
- Zone 21: an area in which the occasional formation of an explosive atmosphere in the form of a combustible dust cloud is likely during normal operation.
- Zone 22: an area in which the formation of an explosive atmosphere in the form of a combustible dust cloud is not likely during normal operation and, if it does occur, will persist only for a short period of time.
ATEX zones for gases and vapours
The classification of areas where an explosive atmosphere of flammable gases or vapours may be present, carried out based on the expected frequency and duration of such an atmosphere.
- Zone 0: an area in which an explosive atmosphere is present continuously, for long periods or frequently.
- Zone 1: an area in which the occasional formation of an explosive atmosphere is likely during the normal operation of the installation.
- Zone 2: an area in which the formation of an explosive atmosphere is not likely during normal operation and, if it does occur, will persist only for a short period of time.
Autoignition temperature
The minimum temperature at which a substance ignites without the need for an external energy source.
B
Background concentration
The average concentration of a flammable substance present in a given space, excluding the direct influence of the source of release. It represents the residual concentration level generated by the accumulation and dispersion of the substance in the environment.
Batch
A quantity of non-reusable retention elements manufactured as a single group with the same requirements of type, size, materials and specific static activation pressure when the non-reusable retention elements are manufactured from the same material batch (according to standard UNE 14797:2007 “Explosion venting devices”).
Boiling point
The temperature at which a liquid boils (passes to the vapour state) under ambient pressure conditions (101.3 kPa ≈ 1,013 mbar).
C
Catastrophic defect
A failure event not considered within the normal operating conditions or the foreseeable failures of a piece of equipment, capable of generating a significant release of flammable substance due to the loss of containment of the system.
Catastrophic failure
An incident that exceeds the design parameters of the process plant and the control system.
Chain reaction
A sequence of self-sustaining chemical reactions in which the intermediate products of one reaction generate new reactions, allowing the continuous propagation of combustion.
Chemical explosion suppression
A protection technique that detects an explosion in its early stages and extinguishes it by releasing, in a controlled manner, a chemical agent that stops the development and propagation of the explosion, minimising its damage.
Classification of combustible dust
A classification system used to group combustible solid materials according to their physical and electrical characteristics, in order to determine the requirements applicable to equipment intended for explosive atmospheres containing dust.
- Group IIIA: relatively large combustible particles that do not remain suspended in the air for long periods.
- Group IIIB: non-conductive combustible dusts capable of forming explosive atmospheres when dispersed in air.
- Group IIIC: conductive combustible dusts that present additional risks associated with the accumulation and discharge of electrical charges.
Classification of combustible dust (group III)
According to their electrical and physical properties, the following groups are distinguished:
- IIIA: fibres.
- IIIB: non-conductive dust: dust with an electrical resistivity greater than 10³ Ω·m.
- IIIC: conductive dust: dust with an electrical resistivity less than or equal to 10³ Ω·m.
Classification of combustible gases
A classification system used to group flammable gases and vapours according to their ability to propagate an explosion and the ease with which it can be transmitted through joints or gaps. This classification is used for the selection of equipment intended for explosive atmospheres.
- Group IIA: gases and vapours of lower relative severity within this classification, such as propane.
- Group IIB: gases and vapours with a greater ability to propagate the explosion than those in group IIA, such as ethylene.
- Group IIC: gases and vapours with the greatest ability to propagate the explosion and the most demanding protection requirements, such as hydrogen and acetylene.
Classified area
An area identified through an area classification process in which an explosive atmosphere may be present and for which specific requirements are established for the design, installation, operation and selection of equipment.
Combustible (fuel)
Any substance that can undergo combustion in the presence of oxygen, releasing carbon dioxide and water as reaction products.
Combustible dust
Dust that, once dispersed in air and mixed with the oxygen in it at a suitable concentration, can form an explosive atmosphere in the presence of an ignition source.
Combustible dust handling
A set of procedures used to minimise the risk of dust explosions in industry. It includes ventilation, cleaning, extraction, equipment maintenance and the use of explosion prevention and protection systems.
Combustion
A rapid chemical reaction between a combustible substance and oxygen, releasing heat and light and generating combustion products such as carbon dioxide (CO₂) and water (H₂O) under normal conditions. This reaction occurs when a material reaches a temperature sufficient to start the combustion process, known as the “ignition point”.
Combustion index (CI)
A parameter that measures the ability of a substance to burn. It is evaluated based on the combustion rate and the amount of energy released during the combustion process. A high combustion index indicates that the substance has a high potential to contribute to a fire or a rapid explosion.
Critical explosion mass
The minimum quantity of flammable substance that, when in suspension, can generate an explosion if it is ignited by an ignition source.
Critical layer
An accumulation of deposited dust that, by its thickness or quantity, can increase the risk of fire or explosion if it is dispersed and comes into contact with an ignition source.
D
Declassified zone
An area previously classified or liable to classification that, as a result of prevention or control measures, ceases to require classification as an area with a risk of explosive atmosphere.
Deflagration
A type of explosion characterised by the subsonic propagation of a combustion reaction through a flammable mixture. In a deflagration, the flame front advances by heat and mass transfer to the unreacted mixture, generating a pressure rise that propagates ahead of the flame. It is the most common type of explosion in explosive atmospheres of gases, vapours and combustible dusts in industrial installations.
Delimitation of an explosion-risk zone
The determination of the spatial limits of the classified areas in which an explosive atmosphere may exist, carried out from the assessment of the sources of release, the frequency and duration of the presence of the flammable substance, as well as the ventilation and dispersion conditions. This process makes it possible to establish the extent of the applicable ATEX zones.
Detonation
A type of explosion characterised by the supersonic propagation of the combustion reaction, driven by a shock wave coupled to the reaction front. This phenomenon generates extremely rapid and high pressure increases, producing mechanical effects considerably more severe and destructive than those associated with a deflagration.
Dilution
The mixing of a substance with another in the same phase (for example, a gas with another gas) to reduce its concentration. In the ATEX field it is carried out to reduce the concentration of combustible substances and the possibility of forming an explosive atmosphere. Inert substances such as nitrogen or fresh/uncontaminated air can be used for dilution.
Dilution volume
The volume around a source of release within which the concentration of a flammable substance may be sufficient to form an explosive atmosphere before ventilation achieves its dispersion and dilution.
Dust
A finely divided solid with a particle size of less than 500 µm.
Dust explosion constant, KSt
A parameter that characterises the severity of a combustible dust explosion based on the maximum rate of pressure rise developed during the explosion. The higher the KSt value, the faster and more violent the deflagration can be.
E
Effective vent area, Ae
The actual pressure-relief area provided by a venting device, taking into account the efficiency losses associated with its design and operation.
EN standard
A set of technical standards developed and adopted at European level, with the aim of harmonising the specifications and requirements for products, services or processes in the European Union (EU). They are prepared by European standardisation organisations, such as the European Committee for Standardization (CEN), the European Committee for Electrotechnical Standardization (CENELEC) and the European Telecommunications Standards Institute (ETSI).
Equipotential bonding
A condition in which two or more conductive elements maintain the same electrical potential through their interconnection, avoiding potential differences capable of generating dangerous electrical discharges. It is a fundamental measure for controlling the risks associated with static electricity in explosive atmospheres.
Ex installation
Installations or equipment designed to be used in areas classified as ATEX, where the risk of the presence of explosive atmospheres requires additional protective measures and compliance with the regulations.
Explosibility
The ability of a substance or mixture to generate an explosion under certain conditions of concentration, dispersion and ignition. Explosibility depends on the physicochemical characteristics of the substance and the conditions of the environment in which it is found.
Explosibility index
A measure of the ability of a material to explode or form an explosive atmosphere.
Explosible dust
Dust that has the potential to form an explosive mixture when suspended in air and reaches suitable concentrations, in addition to being susceptible to ignition due to sources such as sparks or heat.
Explosion
A phenomenon characterised by a sudden release of energy that causes a rapid increase in pressure and temperature, generating a pressure wave capable of causing damage to people, equipment or structures. Depending on their characteristics and propagation mechanism, explosions can be classified into different categories, including deflagrations and detonations.
Explosion containment
A set of protective measures adopted to limit the impact and destructive effects of an explosion within a closed or partially closed space, without allowing it to propagate outside a controlled area. The main objective of containment is to protect people, equipment and installations by minimising the damage caused by overpressure, the shock wave and flame propagation.
Explosion isolation
A technique used to prevent an explosion from propagating beyond its point of origin to other parts of an installation. It can be of two types:
- Mechanical: a physical barrier that blocks the propagation of the explosion from one area to another. These are typically isolation valves and/or sealing devices applied to ducts that connect different areas of an installation.
- Chemical: the use of a substance that suppresses the explosion in its early stages, preventing it from developing.
Explosion isolation system
A set of devices intended to prevent the propagation of an explosion from a piece of equipment to other parts of the installation.
Explosion isolation valve
A protective device designed to prevent the propagation of a deflagration and its associated effects, such as flames, hot gases and overpressure, through ducts or pipes connected to a piece of equipment or an industrial process.
Explosion isolation valves can be passive, acting automatically by the effect of the explosion itself, or active, by detecting the explosive event and triggering a closing mechanism.
Explosion overpressure
The pressure increase generated during an explosion relative to the initial atmospheric pressure. It is one of the main destructive effects of an explosion.
Explosion pentagon
A model used to explain the requirements necessary for a combustible dust explosion to occur. In addition to the three elements of the fire triangle (fuel, oxidiser and ignition source), it incorporates two additional conditions: the dispersion of the fuel in the form of a cloud and the partial or total confinement of the mixture, which favours the development of dangerous pressures during combustion.
Explosion prevention and protection
Measures for safety in working environments with a risk of explosions. It includes the use of technical and organisational measures.
Explosion protection
A set of measures to be implemented in an area with ATEX risk to protect it from the consequences of an explosion (once it has occurred) in order to mitigate its effects and/or prevent it from propagating to other areas.
Related regulations: ATEX 2014/34/EU, Directive 2009/104/EC (safety at work), IEC 60079-10-1 and 2, NFPA 68 (pressure relief), ISO 21827 (explosion suppression).
Explosion protection methods act through one or more of the following functions: explosion venting, chemical suppression or isolation, mechanical isolation and/or containment.
- Explosion venting systems: devices that release the overpressure and flames created in the explosion inside a vessel, discharging them in a controlled manner towards a safe area, without the emission of fragments. In this way, structural damage to the equipment where the explosion takes place, as well as material and personal damage, is avoided.
- These pressure-relief devices can be vent panels, valves or rupture discs. In essence, they are designed to open during an explosion within a closed volume, release the overpressure and prevent the design strength of the vessel from being exceeded.
- Chemical suppression and/or isolation systems. These consist of monitoring a process variable whose value indicates the early formation of an explosion, in order to release a chemical extinguishing agent that suppresses the explosion and prevents it from developing.
- Mechanical isolation: devices that physically block the propagation of the explosion to other parts of the installation. These are typically isolation valves, which can be active or passive depending on whether or not they incorporate a detection and actuation system.
- Containment: the design of structures that withstand the effects of the explosion.
According to whether or not they act directly on the explosion, two types of protection systems can be distinguished:
- Passive protection: protection strategies that do not require active intervention in the event of an explosion. It includes explosion venting devices, flame barriers or reinforced structures that limit the propagation of the explosion.
- Active protection: strategies using systems that intervene directly in an explosion. These are chemical suppression systems or automatic extinguishing systems whose purpose is to mitigate the effects of the explosion or extinguish it.
Explosion protection barrier
A device or system intended to prevent or limit the propagation of a deflagration, its flames and its pressure effects towards connected equipment or areas, by mechanical, chemical or automatic-control methods.
Explosion protection barriers can be mechanical, using physical isolation elements, or active, by detecting the explosion and automatically injecting a suppressant agent to stop its propagation.
Explosion protection equipment
Systems designed to protect people, equipment and installations from the destructive effects of an explosion. In general terms, these systems act through one or more of the following functions: explosion venting, chemical suppression or isolation, and mechanical isolation.
Explosion protection system
A set of measures, equipment and devices intended to prevent explosions or limit their effects on people, installations and the environment.
Explosion resistance
The ability of a piece of equipment, structure or enclosure to withstand the pressures and stresses generated during an explosion without losing its structural integrity.
Explosion risk
The combination of the probability of an explosion occurring and the severity of its possible consequences for people, equipment and installations.
Explosion risk assessment
A systematic process by which the hazards associated with explosive atmospheres are identified, the probability of occurrence and the severity of their possible consequences are assessed, and the necessary measures are established to prevent explosions or limit their effects.
Explosion severity
The magnitude of the effects generated by an explosion, usually assessed by parameters such as the maximum explosion pressure and the rate of pressure rise.
Explosion suppressant
A chemical agent used to neutralise an explosion in its early stages, reducing or preventing its propagation.
Explosion suppression system
A set of detectors, control units and suppressant-agent vessels designed to detect and extinguish an explosion in its early stages.
Explosion vent panel
A device designed to allow the controlled release of the pressure generated during an explosion in an enclosure, protecting equipment and installations from structural damage.
Explosion venting
An explosion protection measure intended to limit the pressure generated during a deflagration by the controlled release of the combustion gases through a venting device, preventing structural damage to the protected equipment.
Explosive atmosphere
A mixture with air, under atmospheric conditions, of flammable substances in the form of gas, vapour, mist or combustible dust whose concentration lies within its flammability or explosibility range and which, in the presence of an effective ignition source, can give rise to an explosion.
Explosive concentration
The ratio of the concentrations of a fuel and oxygen that can cause an explosion reaction. In the case of dusts, this concentration is related to the amount of dust suspended in the air.
Explosive limits
The range of concentrations of a combustible substance in air within which an explosion can be generated.
- Lower explosive limit (LEL): the minimum concentration of a combustible substance in air that is capable of forming an explosive mixture if it meets an ignition source. Below this value, the mixture will not be rich enough to cause an explosion.
- Upper explosive limit (UEL): the maximum concentration of a combustible substance in air that can generate an explosive mixture. Above this limit, the mixture is too rich in fuel and does not contain enough oxidiser to sustain the explosion.
Extent of the classified zone
The distance or volume around a source of release within which an explosive atmosphere may exist under certain conditions of operation, ventilation and dispersion.
F
Fibre
A solid particle with an elongated shape, with a diameter of less than 500 µm and a length of less than 3000 µm.
Fire
Uncontrolled combustion that can generate heat, flames and gases. In the context of industrial safety, a fire can be a precursor to an explosion if it occurs in an environment containing flammable substances.
Fire triangle
A model used to describe the conditions necessary for the combustion of a substance, based on the simultaneous presence of a fuel, an oxidiser and an ignition source. It is the basis for developing fire and explosion prevention measures.
Fireball
A rapidly expanding mass of burning gases and combustion products produced after the release and subsequent ignition of a flammable substance.
Flame deflector
A protective device used together with explosion relief systems to modify the trajectory of the flame, hot gases and pressure wave released during a deflagration, directing them towards a controlled discharge area and reducing the risk to the surrounding areas.
Flameless vent panel (Flameless Vent)
An explosion protection device that combines a venting membrane and a flame-extinguishing element to relieve the overpressure generated by a deflagration inside a piece of equipment, preventing the propagation of flames to the outside and reducing the emission of incandescent particles.
The device consists of a metal housing resistant to explosion loads and an internal heat-dissipating element, generally made of multiple layers of metallic material with high thermal conductivity. During activation, this element absorbs and dissipates the heat of the gases and flame, allowing pressure relief while containing the flames.
Flammability limits
The range of concentrations of a fuel within which combustion can be generated. Outside this range, the mixture is too rich or too lean in fuel to be flammable.
- Lower flammability limit (LFL): the concentration of flammable gas, vapour or mist in air below which an explosive gas atmosphere will not form.
- Upper flammability limit (UFL): the concentration of flammable gas, vapour or mist in air above which an explosive gas atmosphere will not form.
Flammability range
The range of concentrations of a flammable substance in air between the lower explosive limit (LEL) and the upper explosive limit (UEL), within which ignition and propagation of combustion can occur.
Flammable liquid
A liquid that emits flammable vapours which, when mixed with air, can form an explosive atmosphere.
Flammable or combustible gas
A gaseous substance capable of burning or exploding when mixed with air or another oxidiser in suitable proportions and if there is a sufficient ignition source.
Flammable or combustible mist
A suspension of small droplets of flammable liquid in air. These mists can form a potentially explosive atmosphere if the concentration of vapour or flammable liquid particles is high enough and comes into contact with an ignition source. Common examples include oil mist in certain industries or mist from flammable solvents.
Flash point
The minimum temperature of a liquid at which, under certain standardised conditions, it gives off vapours in such an amount that it can form a flammable mixture with air.
Flash point temperature
The minimum temperature at which a liquid releases vapours in a sufficient quantity to form, with air, a flammable mixture capable of igniting in the presence of an ignition source. This parameter applies to substances that, under normal atmospheric conditions, are in a liquid state.
G
Gas
A substance that, under normal conditions of temperature and pressure, is in a gaseous state and tends to expand to occupy the entire available volume. Some gases can form explosive atmospheres when mixed with air in concentrations within their flammability limits.
Gas explosion constant, KG
A normalised parameter derived from the maximum rate of pressure rise during a combustible dust explosion, used to assess the severity of the deflagration and to design explosion protection systems.
Gas or vapour leak
The uncontrolled escape of flammable gas that can form an explosive atmosphere if not handled correctly.
H
Hot surface
A surface whose temperature is sufficient to cause the ignition of an explosive atmosphere or of a layer of combustible dust in contact with it.
Hybrid mixture
A mixture of a flammable gas or vapour with combustible dust.
I
Ignition
The process by which a substance (fuel) reaches a sufficiently high temperature to start a combustion reaction. It is the moment at which the material begins to burn; that is, when a fuel ignites in the presence of oxygen, producing a flame.
Types of ignition:
- Spontaneous, automatic or self-ignition: occurs when a flammable substance reaches its ignition temperature without a direct external source. It can arise from internal heating, decomposition, oxidation or heat accumulation.
- Caused by an external source: occurs when an external ignition source provides enough energy to start the combustion of the substance.
Ignition sensitivity
The ease with which a substance or explosive atmosphere can ignite when exposed to an ignition source.
Ignition source
A source that provides the energy necessary for a combustion reaction to occur between a combustible substance and oxygen.
Ignition temperature
The minimum temperature required for a material to ignite in the presence of a heat source.
Inert gas
A gaseous substance that does not participate in combustion reactions under the operating conditions considered.
Inerting
The addition of inert substances to another substance or mixture of substances to prevent the formation of an explosive atmosphere.
K
KG index (of a combustible gas)
The explosibility index of the air–gas mixture. A parameter used to measure the violence of the explosion of a mixture of flammable gas and air in a closed system. It is an important indicator for assessing the potential risk in environments where combustible gases are handled and for designing explosion protection systems. It is determined from explosion tests in a closed vessel, measuring the maximum pressure generated during the explosion and the time taken to reach that pressure.
Kst index
A parameter used to quantify the severity of a combustible dust explosion. It represents the maximum rate of pressure rise generated during a dust explosion and is expressed in units of bar·m/s. The higher the Kst value, the greater the potential violence of the explosion.
Regarding the classification of combustible dusts based on their Kst index, it is used to assess the potential severity of an explosion and to design explosion protection measures.
- St 0: Kst = 0 bar·m/s (non-explosive dust).
- St 1: 0 < Kst ≤ 200 bar·m/s.
- St 2: 200 < Kst ≤ 300 bar·m/s.
- St 3: Kst > 300 bar·m/s.
L
Location
A space or area in which an explosive atmosphere may be present or in which there is a possibility that one may form under certain operating conditions.
According to the probability and duration of the presence of an explosive atmosphere, locations are classified into:
- Hazardous location: an area in which an explosive atmosphere is present or may be present in such quantities that special measures are required for the selection, installation and use of equipment and systems.
- Non-hazardous location: an area in which an explosive atmosphere is not expected to be present in quantities sufficient to require special measures for the selection, installation and use of equipment and systems.
M
Maintenance
Actions to be carried out to preserve the proper performance of the materials and equipment of an installation.
It can be of two types:
- Preventive: scheduled activities to inspect, maintain or repair industrial equipment and installations with the aim of preventing failures or accidents related to explosions.
- Corrective: actions carried out to repair equipment or installations after a failure has occurred. In the context of explosions, corrective maintenance may involve the repair of safety or explosion protection systems.
Maximum Experimental Safe Gap (MESG)
The maximum opening of a standardised joint that prevents the ignition of an explosive mixture inside a piece of equipment from propagating to an external explosive mixture during a test carried out under specified conditions. The MESG is a characteristic property of each flammable gas or vapour and is one of the parameters used to classify them into explosion groups.
Maximum explosion pressure (Pmax)
The highest pressure that can be generated during an explosion in a closed volume when a combustible substance ignites. It is a key indicator of the violence of an explosion and an essential parameter for sizing explosion protection systems in areas with ATEX risk.
Maximum surface temperature
The maximum temperature that the external surface of a piece of equipment can reach during its normal operation or under foreseeable fault conditions. It is a fundamental parameter for the selection of equipment intended for explosive atmospheres.
Minimum ignition energy, MIE
The lowest energy value that initiates the combustion of a gas or dust mixture in air.
Minimum ignition temperature of a dust cloud (MITC)
The lowest temperature of a hot surface capable of causing the ignition of a cloud of combustible dust under standardised test conditions.
Minimum ignition temperature of a dust layer (MITL)
The lowest temperature of a hot surface capable of causing the ignition of a layer of combustible dust of a specified thickness under standardised test conditions.
Mist
A suspension of small droplets of liquid in air. For example, water mist in the air, which forms when the air cools to its saturation point, causing the water vapour in the air to condense into small droplets. This phenomenon is common in conditions of high humidity and low temperatures.
N
NFPA
National Fire Protection Association. An organisation founded in the United States in 1896, responsible for creating and maintaining the standards and minimum requirements for fire prevention, training, installation and use of fire protection means used both by firefighters and by personnel in charge of safety. Its standards, the “National Fire Codes”, recommend safe practices developed by experts in fire control.
Normal operation
A condition in which equipment operates in accordance with its electrical and mechanical specifications and is used within the limits indicated by the manufacturer.
O
Overheating
A condition in which a piece of equipment, component or process reaches a temperature higher than expected during its normal operation, potentially generating damage, degradation or a potential ignition source.
P
Particle size or granulometry
A parameter that describes the characteristic dimensions of the particles that make up a solid. In combustible dusts, the granulometry influences the dispersibility, flammability and ability to form an explosive atmosphere.
Pressure wave reflection
A phenomenon by which a pressure wave generated during an explosion changes direction when it impacts a surface, which can locally increase the overpressures and the associated mechanical effects.
Pressurization
A protection technique for electrical equipment by which an overpressure of a protective gas is maintained inside an enclosure, preventing the ingress of an explosive atmosphere from the surroundings.
Protection flanges
A mechanical connecting element used in explosion protection systems to secure the connection between equipment, ducts and safety devices. It is designed to withstand the mechanical loads and foreseeable overpressures during a deflagration, ensuring the integrity of the installation and the correct operation of the associated protective devices.
Purging
A technique used to clear an installation of flammable or contaminant gases. In the context of explosions, it is used to ensure that there is no explosive atmosphere before starting a process.
R
Rate of pressure rise (dP/dt)
The maximum rate of pressure rise developed during an explosion, used to characterise the violence of the deflagration and to design explosion protection measures.
Relative density (of a gas or vapour)
The density of a gas or vapour relative to the density of air at the same pressure and temperature (the relative density of air is taken as 1.0).
- Gas heavier than air: a gas with a relative density to air greater than 1.0.
- Gas lighter than air: a gas with a relative density to air lower than 1.0.
Relative humidity
The percentage of water vapour present in the air relative to the maximum amount the air can hold at a given temperature. In the presence of combustible dusts, higher humidity can reduce the accumulation of electrostatic charges, although it does not by itself eliminate the risk of explosion.
Release
The emission or leakage of a flammable substance from its point of containment into the environment, with the potential to form an explosive atmosphere. According to their expected frequency and duration, releases can be classified as continuous, primary or secondary.
Release rate
The amount of flammable substance emitted into the environment per unit of time from a source of release. It can be expressed as a mass or volumetric flow rate and is one of the parameters used for the classification of areas with a risk of explosive atmosphere.
Residual risk
The level of risk that remains after the implementation of prevention and protection measures intended to reduce the probability or consequences of an explosion.
Response time
The interval elapsed between the detection of an event and the effective actuation of an explosion prevention or protection system.
Risk reduction
A set of technical, organisational or procedural measures intended to reduce the probability of an explosion occurring or the severity of its consequences.
S
Source of release
A point in an installation, equipment or process from which a flammable substance can be emitted, leaked or discharged into the environment, with the potential to generate an explosive atmosphere under certain operating conditions.
Spark
An incandescent particle generated by a rapid release of thermal energy, visible as light and heat. In an environment containing combustible substances, a spark can act as an ignition source if the energy released is sufficient and if the combustible mixture is within its flammability or explosibility range.
Spark generator
A device that can produce sparks and act as an ignition source in hazardous environments.
Spontaneous combustion
A process by which a material internally generates and accumulates heat as a result of chemical or biological reactions, potentially igniting without the intervention of an external ignition source.
Static electricity
The accumulation of electrical charges on the surface of materials or equipment as a result of contact, friction, separation or material-flow phenomena. When the accumulated charge is discharged suddenly, it can generate a spark with enough energy to act as an ignition source in an explosive atmosphere.
T
Thermal insulator
A material used to reduce heat flow between two areas. In the ATEX context, it prevents a heat source from initiating an explosion in a potentially hazardous area.
Thermal radiation
The transfer of energy in the form of electromagnetic waves emitted by a body due to its temperature, without the need for physical contact or a material medium to propagate.
Thermodynamic instability
A condition in which a system is susceptible to undergoing combustion or explosion reactions as a result of variations in temperature and pressure conditions, affecting the stability of flammable mixtures.
Turbulence
The irregular and chaotic movement of a fluid that favours the mixing of fuel and oxidiser, potentially increasing the combustion rate and the severity of an explosion.
U
Unclassified zone
An area in which the presence of an explosive atmosphere is not foreseen in quantities or for periods that justify its classification as a hazardous area.
UNE standards
A set of technical standards prepared and published by the Spanish Association for Standardization (UNE), which is the body responsible for standardisation in Spain. These standards are very similar to the EN (European) standards, but are specifically designed for the Spanish context and are aimed at regulating, harmonising and ensuring the quality, safety, efficiency and sustainability of products, services and processes within Spain.
Unusual malfunction
A type of malfunction that can occur in exceptional cases.
V
Vapour
The gaseous phase of a substance that, under normal conditions, is usually in a liquid or solid state and that can condense by cooling or by an increase in pressure.
Vapour pressure
The pressure exerted when a solid or liquid is in equilibrium with its own vapour at a given temperature.
Vent area, Ad
The area available for discharging the pressure generated during an explosion through a venting device. It is the effective geometric opening area of the device.
Ventilation
A natural or artificial mechanism that favours the dispersion and dilution of flammable substances present in the air, reducing the probability, extent and duration of an explosive atmosphere.
Ventilation can be natural, through air currents or thermal gradients, or forced, through mechanical supply or extraction equipment.
Venting efficiency
An indicator of the performance of an explosion venting device in reducing the pressure developed during a deflagration.
Z
Zone declassification
A set of technical and organisational actions intended to control or eliminate the conditions that favour the formation of explosive atmospheres, such as reducing emissions, improving ventilation or modifying the process. As a result, a classified zone can be reassessed and reclassified to a lower-hazard category or cease to require ATEX classification.
