ATEX is the name commonly given to the framework for controlling explosive atmospheres and the standards of equipment and protective systems used in them. It is based on the requirements of two European Directives:

Also known as 'ATEX 137' or the 'ATEX Workplace Directive'. Minimum requirements for improving the health and safety protection of workers potentially at risk from explosive atmospheres. The text of the Directive and the supporting EU produced guidelines are available on the EUwebsite. For more information on how the requirements of the Directive have been put into effect in Great Britain see the information in the section on Equipment and protective systems intended for use in explosive atmospheres.

Also known as 'ATEX 95' or the 'ATEX Equipment Directive'. ATEX 94/9/EC was removed and replaced by a new Directive 2014/34/EU from April-2016.
Equipment and protective systems intended for use in potentially explosive atmospheres. The aim of this directive is to allow the free trade of 'ATEX' equipment and protective systems within the EU by removing the need for separate testing and documentation for each member state.
The regulations apply to all equipment intended for use in explosive atmospheres, whether electrical or mechanical, including protective systems. The text of the Directive and EU produced supporting guidelines are available on the EU website. For more information on how the requirements of the Directive have been put into effect in Great Britain see the section on Selection of equipment and protective systems.

The objective of Directive 2014/34/EU is to ensure free movement for the products to which it applies in the EU territory. Therefore the directive, based on Article 95 of the EC Treaty, provides for harmonised requirements and procedures to establish compliance. The directive notes that to remove barriers to trade via the New Approach, provided for in the Council Resolution of 7 May 1985, essential requirements regarding safety and other relevant attributes need to be defined by which a high level of protection will be ensured. These Essential Health and Safety Requirements (EHSRs) are listed in Annex II to Directive 2014/34/EU.

• Potential ignition sources of equipment intended for use in potentially explosive atmospheres ;
• Autonomous protective systems intended to come into operation following an explosion with the prime objective to halt the explosion immediately and/or limit the effects of explosion flames and pressures;
• Safety devices intended to contribute to the safe functioning of such equipment with respect to ignition source and to the safe functioning of autonomous protective systems;
• Components with no autonomous function essential to the safe functioning of such equipment or autonomous protective system(s) Since 1􀇥􀇦 July 2003 relevant products could only be placed on the market in the EU territory7, freely moved and operated as designed and intended in the expected environment if they comply with directive 94/9/EC (and other relevant legislation).

Directive 2014/34/EU provides for the first time harmonised requirements for non-electrical equipment, equipment intended for use in environments which are potentially explosive due to dust hazards and protective systems. Safety devices intended for use outside explosive atmospheres which are required for or contribute to the safe functioning of equipment or protective systems with respect to risks of explosion are also included. This is an increase in scope compared to former national regulations for equipment and systems intended for use in potentially explosive atmospheres.

In Great Britain the requirements of Directive 99/92/EC were put into effect through regulations 7 and 11 of the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR).
The requirements in DSEAR apply to most workplaces where a potentially explosive atmosphere may occur. Some industry sectors and work activities are exempted because there is other legislation that fulfils the requirements. These exemptions are listed in regulation 3 of DSEAR In DSEAR, an explosive atmosphere is defined as a mixture of dangerous substances with air, under atmospheric conditions, in the form of gases, vapours, mist or dust in which, after ignition has occurred, combustion spreads to the entire unburned mixture.
Atmospheric conditions are commonly referred to as ambient temperatures and pressures. That is to say temperatures of -20°C to 40°C and pressures of 0.8 to 1.1 bar.
Many workplaces may contain, or have activities that produce, explosive or potentially explosive atmospheres. Examples include places where work activities create or release flammable gases or vapours, such as vehicle paint spraying, or in workplaces handling fine organic dusts such as grain flour or wood.
Explosive atmospheres can be caused by flammable gases, mists or vapours or by combustible dusts. If there is enough of the substance, mixed with air, then all it needs is a source of ignition to cause an explosion.
Explosions can cause loss of life and serious injuries as well as significant damage. Preventing releases of dangerous substances, which can create explosive atmospheres, and preventing sources of ignition are two widely used ways of reducing the risk. Using the correct equipment can help greatly in this.
The Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) place duties on employers to eliminate or control the risks from explosive atmospheres in the workplace. A summary of those requirements can be found below.

Many workplaces may contain, or have activities that produce, explosive or potentially explosive atmospheres. Examples include places where work activities create or release flammable gases or vapours, such as vehicle paint spraying, or in workplaces handling fine organic dusts such as grain flour or wood.

DSEAR requires employers to eliminate or control the risks from dangerous substances - further information on these requirements can be found on the DSEAR web page[6]. In addition to the general requirements, the Regulations place the following specific duties on employers with workplaces where explosive atmospheres may occur.

Employers must classify areas where hazardous explosive atmospheres may occur into zones. The classification given to a particular zone, and its size and location, depends on the likelihood of an explosive atmosphere occurring and its persistence if it does. Schedule 2 of DSEAR contains descriptions of the various classifications of zones for gases and vapours and for dusts.

Areas classified into zones must be protected from sources of ignition. Equipment and protective systems intended to be used in zoned areas should be selected to meet the requirements of the Equipment and Protective Systems Intended for use in Potentially Explosive Atmospheres Regulations 1996. Equipment already in use before July 2003 can continue to be used indefinitely provided a risk assessment shows it is safe to do so.

A “hazardous area” is defined as an area in which the atmosphere contains, or may contain in sufficient quantities, flammable or explosive gases, dusts or vapours. In such an atmosphere a fire or explosion is possible when three basic conditions are met. This is often referred to as the “hazardous area” or “combustion” triangle. • When electrical equipment is used in, around, or near an atmosphere that has flammable gases or vapours, flammable liquids, combustible dusts, ignitable fibers or flyings, there is always a possibility or risk that a fire or explosion might occur. Those areas where the possibility or risk of fire or explosion might occur due to an explosive atmosphere and/or mixture is often called a hazardous (or classified) location/area. Currently there are two systems used to classify these hazardous areas; the Class/Division system and the Zone system. The Class/Division system is used predominately in the United States and Canada, whereas the rest of the world generally uses the Zone system.

Hazardous locations as per the Zone system are classified according to its Zone which can be gas or dust. For gas atmospheres electrical equipment is further divided into Groups and Subgroups.

The Zone defines the probability of the hazardous material, gas or dust, being present in sufficient quantities to produce explosive or ignitable mixtures.

The table below shows the relationship between the category and the expected zone of use.

The Type of Hazard
The type of hazard will be in the form of either a gas or vapours or a dust or fiber. The classification of these hazardous is primarily divided into two groups depending on whether it is in a mining or above surface industry. These are defined below:
Group I: Electrical equipment for use in mines and underground installations susceptible to firedamp.
Group II and Group III: Electrical equipment for use in surface installations.
Group II: Gases are grouped together based upon the amount of energy required to ignite the most explosive mixture of the gas with air.
Group III: Dusts are subdivided according to the nature of the explosive atmosphere for which it is intended.
Groups II & III are further sub-divided depending upon the hazard.

Group IIA Atmosphere containing propane, or gases and vapours of equivalent hazard.
Group IIB Atmosphere containing ethylene, or gases and vapours of equivalent hazard.
Group IIC Atmosphere containing acetylene or hydrogen, or gases and vapours of equivalent hazard.

Protection Type
To ensure safety in a given situation, equipment is placed into protection level categories according to manufacture method and suitability for different situations. Category 1 is the highest safety level and Category 3 the lowest. Although there are many types of protection, a few are detailed.

The Type of Hazard
EPL Ga: Equipment for explosive gas atmospheres, having a 'very high' level of protection, which is not a source of ignition in normal operation, expected faults or when subject to rare faults.
EPL Gb: Equipment for explosive gas atmospheres, having a 'high' level of protection, which is not a source of ignition in normal operation or when subject to faults that may be expected, though not necessarily on a regular basis.
NOTE: The majority of the standard Ex-protection concepts bring equipment within this equipment protection level.
EPL Gc: Equipment for explosive gas atmospheres, having a 'enhanced' level of protection, which is not a source of ignition in normal operation and which may have some additional protection to ensure that it remains inactive as an ignition source in the case of regular expected occurrences (for example failure of a lamp).
NOTE: Typically this will be Ex n equipment.
EPL Da: Equipment for combustible dust atmospheres, having a 'very high' level of protection, which is not a source of ignition in normal operation or when subject to rare faults.
EPL Db: Equipment for combustible dust atmospheres, having a 'high' level of protection, which is not a source of ignition in normal operation or when subject to faults that may be expected, though not necessarily on a regular basis.
EPL Dc: Equipment for combustible dust atmospheres, having an 'enhanced' level of protection, which is not a source of ignition in normal operation and which may have some additional protection to ensure that it remains inactive as an ignition source in the case of regular expected occurrences.

Ingress Protection (IP) rating are developed by the European Committee for Electro Technical Standardization (CENELEC) (NEMA IEC 60529 Degree of Protection Provided by Enclosure -IP Code), specifying the environmental protection the enclosure provides.
The IP Rating is an accepted engineering standard for defining the protection of electrical equipment from dust and moisture ingress.
For pressure sensors and associated instrumentation the 2 digit version of the IP rating is used to indicate how well the design will prevent dust and water getting into the electronic enclosure.
The IP rating normally has two digits :
1st Digit :Protection from solid objects or materials 2nd Digit :Protection from liquids (water)
IP First digit - Protect against solid objects or materials
The higher the first digit of IP rating, the better the ingress protection from dust, sand or dirt particles penetrating the outer enclosure and damaging the internal components.

IP Second digit - Protect against liquid (water)
The higher the second digit of IP rating, the better the ingress protection from water moisture leaking inside and corroding components or shorting out electrical & electronic circuits

Example: IP rating
IP 65: First Numeral 6 describes totally protected against dust, Second Numeral 5 describes protected against low pressure water jet from all direction

Another important consideration is the temperature classification of the electrical equipment. The surface temperature or any parts of the electrical equipment that may be exposed to the hazardous atmosphere should be tested that it does not exceeds 80% of the auto-ignition temperature of the specific gas or vapours in the area where the equipment is intended to be used.
The temperature classification on the electrical equipment label will be one of the following (in degree Celsius):