Oil refinery

Fundamentals of explosion protection

Operations in many different industries can create explosive atmospheres that present a great danger to both life and equipment. In the chemical and petrochemical industries these are caused primarily by flammable gases, vapors or mists. In mining, mills and other areas, dust can combine with the air to become highly explosive. Unsafe equipment can ignite these mixtures, resulting in explosions.
Products and systems for use in potentially explosive atmospheres

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Background to the ATEX Directive

 

In order to ensure safety, various organizations around the world issue directives, standards and statutes on explosion protection. Directive 94/9/EC was passed by the EU in 1994 as the basis for standardized, pan-European regulation for equipment and protective systems. The new and currently applicable Directive 2014/34/EU was adopted in 2014 and has been in force since April 2016. Directive 1999/92/EC, which defines the minimum regulations for improving the health protection and safety of employees that could be endangered by potentially explosive atmospheres, exists in parallel to this. These mandatory provisions are known as ATEX directives (French: ATmosphères EXplosives). 

 

In order to avoid dangers, certain measures must be implemented in a prescribed order. Primary explosion protection prevents the formation of an explosive atmosphere. Secondary explosion protection prevents the ignition of hazardous, potentially explosive atmospheres, e.g. through the use of special equipment and protective systems. As part of this, various hazardous areas – known as Ex zones – are defined for potentially explosive gases, vapors and dusts. Tertiary explosion protection restricts the impact of any explosion to a safe level.


For this purpose, various characteristics such as the flash point of the gases, vapors or dusts and their explosion limits are included in the equation.

Industrial controls in hazardous areas

 

Industries in which hazardous areas occur therefore require switching equipment that is capable of switching, protecting and controlling in potentially explosive atmospheres. The devices themselves may be located either inside or outside the hazardous area.

 

An ATEX certification is necessary for the use of such devices. In its SIRIUS portfolio, Siemens offers a host of devices that are certified in accordance with the current ATEX Directive. 

SIRIUS Control

SIRIUS Control

These devices are not located in the hazardous area themselves, but can switch and protect motors that are specially designed for use in hazardous areas. There are no specific requirements imposed on the switching device (e.g. contactor); special attention is paid here to motor overload protection, which must satisfy specific ATEX requirements and is to be certified accordingly.

SIRIUS Hybrid

SIRIUS Hybrid

These devices are not located in the hazardous area themselves, but can switch and protect motors that are specially designed for use in hazardous areas. The attention here is on motor overload protection, which must satisfy specific ATEX requirements and is to be certified accordingly.

SIRIUS Command

SIRIUS Command

In the case of Sirius ACT 3SU1 pushbuttons and indicator lights there are versions that are specially tested and approved for use in potentially explosive areas. Support is provided here by special LED modules that cannot overheat, as well as by devices operated in intrinsically safe circuits that cannot generate any dangerous sparks in the hazardous area.

SIRIUS Monitor

SIRIUS Monitor

Simocode and monitoring relays, such as the 3RN2 thermistor motor protection relay, either measure the temperature directly by means of sensors in the motor or transformer windings or calculate the motor temperature on the basis of the measured currents in order to detect at an early stage any overheating caused by an overload. In addition to thermistor motor protection and overload motor protection, Simocode also offers dry-running protection for centrifugal pumps based on active power monitoring of the pump motor.