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Equipment Surface Temperature Classification

Classification of the maximum surface temperature of equipment has been established internationally to create a uniform reference table (unless otherwise specified on equipment selected, the maximum ambient temperature is taken as being 40°C, in line with IEC 60079 Standards). The purpose of the temperature classification is to place equipment into an appropriate category according to its specific thermal properties when exposed to the worst case conditions.

Equipment Protection Levels (EPLs)

Explosive Atmospheres According to IEC

The following information is intended as a basic guide to explosive atmosphere equipment concepts and practice. National or international guidelines and Codes of Practice for explosive atmosphere installations should always be referred to in order to comply with specific local requirements.

Risk Assessment Process

In addressing the factors of risk in the explosive atmosphere, a process of risk assessment and risk control should be undertaken to ensure a safe working environment. This process will involve identifying who and what is likely to be at risk of harm, and will include an evaluation of these risks.

Area Classification Plan

A set of documents providing information on the explosive atmospheres of the plant as a minimum should comprise of: - Area classification drawings - A set of drawings showing to scale the complete layout of the facility, marking the extensions of the explosive atmospheres defined based on the - specific data associated with the flammable substances, sources of release and areas of risk for all elevations - Details of the flammable substances being stored, handled, or processed - Details of the sources of release - Information on the areas of risk - Information relating to the ventilation and air conditioning design in enclosed spaces, which affects the classification and extent of explosive atmospheres.

Cable Gland for Cables Entering Ex e & Ex i Equipment

Although the minimum requirements for Ex e and Ex i enclosures could be met by cable glands with a single outer seal, the majority of users prefer to standardise on a double seal cable gland, to maintain a site standard, and ensure that cable gland types are not inadvertently mixed between different types of equipment protection.

Certification

Before products, equipment, or protective systems can be selected for installation in explosive atmospheres they should first be certified as being suitable for that application. A Certificate of Conformity for equipment intended for use in Explosive Atmospheres is evidence that the product, equipment or protective system conforms and has been tested to a relevant standard.

Gas Groups

The categorisation of Gas Groups to enable the safe selection of equipment intended for use in explosive atmospheres, which includes all potentially explosive gas, vapour, or chemical, would normally be found in the appropriate National or International Code of Practice related to the project or plant location.

Form of Protection Ex ‘n’

Enclosures with protection Type ‘n’ (e.g. IEC 60079-15): Permitted only in areas where the likelihood of a flammable atmosphere is remote (i.e. Zone 2 Explosive Atmospheres), EPL Gc, Type ‘n’ Equipment was historically divided into a number of different sub-forms.

Form of Protection Ex ‘m’

Encapsulation Type ‘m’ (e.g. IEC 60079-5): Encapsulation of arcing and sparking components or equipment in a fashion which ensures that there is no exposure to explosive mixtures which may be present, and the surface temperature is controlled under normal and fault conditions, thus preventing ignition from occurring.

Form of Protection Ex ‘i’

Intrinsically Safe Enclosure / System Type ‘i’ (e.g. IEC 60079-11): Intrinsically Safe Equipment (Sub grouped into Ex ‘ia’, Ex ‘ib’, and Ex ‘ic’) incorporates circuits which, due to their low spark energy potential, are not capable of igniting an explosive mixture. Ex ‘ib’ equipment is designed to be safe under one fault condition and can be used in Zone 1 explosive atmospheres. Ex ‘ia’ equipment is designed to be safe under two fault conditions and can be used in Zone 0 explosive atmospheres. Ex ‘ic’ equipment is designed to be safe in normal operation, without any faults, and can be used only in Zone 2 explosive atmospheres. The recent introduction of Ex ‘ic’, according to IEC 60079-11, for Zone 2 applications co-incides with the removal of protection method ‘nL’ from IEC 60079-15.

Form of Protection Ex ‘de’

Combined Flameproof Enclosure Type ‘d’ & Increased Safety Enclosure Type ‘e’ (e.g. IEC 60079-1 & IEC 60079-7): Primary Flameproof Type ‘d’ Enclosure with Secondary Increased Safety Type ‘e’ Protection, allowing reduced frequency of periodic maintenance and inspection cycle because of the ‘e’ philosophy strategically employed. In the case of Flameproof Type ‘d’ Enclosures having an Increased Safety Type ‘e’ Terminal Chamber, ‘line barriers’ would normally be utilised between the Type ‘d’ and Type ‘e’ compartments creating an indirect cable entry interface.

Form of Protection Ex ‘e’

Increased Safety Enclosure Type ‘e’ (e.g. IEC 60079-7): Whilst explosive mixtures may enter the equipment, the enclosure is not designed to withstand an internal explosion. Instead, the likelihood of a fault condition, which could result in ignition of explosive mixtures, is significantly reduced by the following measures. The (non-incendive) components used in the equipment shall not produce arcs or sparks or dangerous temperatures in normal working conditions.

Form of Protection Ex ‘o’

Oil Immersion with Enclosure Protection Type ‘o’ (e.g. IEC 60079-18): Although not very common, oil immersed equipment, for example early forms of switchgear or transformers, are normally marked Ex 'o' but if the equipment was certified more recently it may also be marked as being Ex 'ob' or Ex 'oc', which includes the EPL code Gb or Gc in this abbreviated marking. The general principal of the form of protection Ex 'o' remains the same.

ATEX Overview

ATEX is the name given to a set of European Directives relating to explosive atmospheres that takes its name from the French translation ‘Atmosphères Explosibles’, and spells out a set of Essential Health & Safety Requirements (EHSR’s) and conformity assessment procedures which when followed should enable the industry to operate safely avoiding accident or incident.

Relationships between EPLs & Types of Protection

Relationship between EPLs & Types of Protection The recognised types of protection according to IEC standards have been allocated default EPLs according to Table 2 of IEC 60079-14.