Explosion Protection Methods
Hot surfaces, sparks, arcs and electrostatic discharges are all potentially incendive sources. Electrical equipment for hazardous area operation is designed to exclude, suppress or contain the effect of these sources. This is achieved by a variety of established, approved methods to render the equipment explosionproof. These include immersing the electrical equipment in oil, filling the equipment enclosure with an inert powder, and encapsulation of the fittings to ensure that the flammable mixture is excluded and cannot interface with the incendive components.
The different methods of protection, their coding and the standards against which they are approved are included in the table below.
IEC 60079 series documents have been released. These are referred to in BS EN 60079 part 0, Electrical Apparatus for Explosive Atmospheres, General requirements. Parts of this IEC series will be based on, and equivalent to, the BS EN 50 series documents. The foreword to BS EN 60079 notes that it is based on the text of BS EN 50014.
Methods of Protection, Coding & Standards
| Protection method and standard | Symbol | Details |
| Oil immersion protection EN 50015 IEC 60079 – 6 BS EN 5501 | EEx 'o' | This is an old method mainly used with switchgear. Any spark generated by the operation of the switchgear is formed under oil and the venting is controlled. |
| Pressurised protection EN 50016 IEC 60079 – 2 BS EN 50016 | EEx 'p' | There are two protection methods. One maintains a positive static pressure inside the equipment. The other involves a continuous flow of air or inert gas to neutralise or carry away any flammable mixture entering or being formed within the enclosure. Essential to both methods are monitoring systems and purging schedules. |
| Powder Filling Protection EN 50017 IEC 60079 – 5 BS EN 50017 | EEx 'q' | This method involves the mounting of potentially incendive components in an enclosure filled with an inert powder. The enclosure is also vented. The method is primarily of use where the incendive action is the abnormal release of electrical energy by the rupture of fuses or failure of components such as capacitors. The method is commonly used for components inside Ex ‘e’ or Ex ‘N’ apparatus and for heavy-duty traction batteries. |
| Flameproof Enclosure Protection EN 50018 IEC 60079–1 BS EN 50018 | EEx 'd' | In this method the potential incendive components are contained within an enclosure. Although the flammable atmosphere can enter the enclosure, any resulting explosion is contained and its transmission outside the enclosure prevented. |
| Increased Safety Protection EN 50019 IEC 60079 – 7 BS EN 50019 | EEx 'e' | In this method any components that produce sparks as part of their normal operation are excluded from the equipment. Components are designed to reduce substantially the likelihood of the occurrence of fault conditions that could cause ignition. This is done by reducing and controlling working temperatures, ensuring the electrical connections are reliable, increasing insulation effectiveness, and reducing the probability of contamination by dirt and moisture ingress. |
| Intrinsic Safety Protection EN 50020 IEC 60079 – 11 BS EN 50020 | EEx 'i' | In this method the circuit parameters are reliably controlled to reduce potential spark energy to below that which will ignite the ambient gas-air mixture. This includes the occurrence faults in one 'ib' or two of the 'ia' of the components in the equipment. The coding ‘ia’ denotes that the unit will not cause ignition of explosive atmosphere under normal operation and with two faults present in the circuitry. The coding ‘ib’ denotes that the unit will not cause ignition of explosive atmosphere under normal operation and with one fault present in the circuitry. You should note that this method does not protect entirely against the local over-heating of damaged connections or conductors and these should be kept sound and suitably protected against damage. |
| Encapsulation Protection EN 50028 IEC 60079 – 18 | EEx 'm' | In this method the potentially incendive components are encapsulated so that the flammable atmosphere is excluded. The method also involves the control of the surface temperature under normal and fault conditions. |
| "Special" Protection" BASEEFA SFA 3009 | EEx 's' | This method, being special, has no exact specification. It is any method which is shown to be safe in use. The ‘s’ coding is used when equipment has been evaluated against one of the individual parts of the CENELEC series but does not comply exactly with it. Because the ‘s’ method does not have a set of rules it is not part of the harmonised series of standards. |
| Non Sparking Protection BS 4533 Section 102.51 (Luminaires) | EEx 'nA' | BS 4683 Part 3 (Control Gear) has now been superseded by BS 6941. In this method normally sparking components are excluded. Precautions are taken with connections and wiring to increase reliability, though not to as high a degree as for EEx‘e’. Where internal surfaces are hotter than the desired T rating they can be tightly enclosed to prevent the ready access of a flammable atmosphere into the internal parts. This is the "restricted breathing enclosure" method. The use of this method also means that high ingress protection ratings of IP65 and above are built into the design. |