Key definitions
Key definitions in connection with ATEX
Explosive atmosphere
Mixture with air, under atmospheric conditions, of combustible substances in the form of gases, vapours, mists or dusts in which, after ignition has occurred, combustion spreads to the entire unburned mixture.
Potentially explosive atmosphere
An atmosphere which could become explosive due to local and operational conditions.
Maximum surface temperature
The highest temperature which is reached under normal operating conditions by a part or by the surface of devices, protective systems and components and does not cause ignition of the ambient explosive atmosphere.
Maximum service temperature
The maximum temperature which can be reached when devices and protective systems are operated under the expected operating conditions.
Temperature class
Classification of devices, protective systems and components in explosive atmospheres on the basis of maximum surface temperature.
Normal operation
Situation which occurs when the equipment, protective systems and components fulfil their intended purpose within the scope of their design parameters.
Flammable substance
Substance in the form of gas, vapour, liquid, solids or other mixtures which, together with air, can undergo an exothermic reaction after ignition.
Conductive dust
A dust with an electrical resistance which is equal to or less than 104 ohms/m.
Hybrid mixture
Mixture of air and flammable substances in various physical states.
Ignition temperature of an explosive atmosphere
Lowest temperature of a heated surface at which a flammable substance is excited to combustion with the appearance of a flame.
Maximum explosion pressure (Pmax)
Maximum pressure which is measured in a closed container during explosion of an explosive mixture under defined test conditions.
Maximum rate of pressure rise ((dp/dt)max)
The lowest temperature of a heated surface at which a flammable substance is excited to combustion with the appearance of a flame.
Reduced explosion pressure
The pressure created by the explosion of an explosive atmosphere in a container, which is either protected by a pressure relief valve or an explosion suppression device.
Inertisation
Addition of inert substances in order to prevent the formation of an explosive atmosphere.
