Dynamic elaboration on the Art & Science of Hazardous Area Protection
Its a Concept. This is a part of risk assessment method It has been introduced to enable an alternate approach to current methods of selecting Ex equipments. The current method of selection of equipment is based upon the classification of Hazardous area into Zones (Ref: IEC 60079-10-1 for Explosive Gas Atmosphere & IEC 60079-10-2 for Combustible Dust Atmospheres) Different protection concepts ( incorporated in the electrical equipments ) and Area Classification (in Zones ) are traditionally related as:
Protection Concept incorporated in the equipment
Mostly used Zones
May be used in
|Intrinsic Safety ‘ia||Zone 0||Zone1 & Zone2|
|Intrinsic Safety ‘ ib||Zone 1||Zone 2|
|Intrinsic Safety ‘ic||Zone 2|
|Flame Proof ‘d||Zone 1||Zone2|
|Increased Safety ‘e||Zone1||Zone2|
|Encapsulation ‘ma||Zone0||Zone1 & Zone 2|
|Encapsulation ‘mb||Zone1||Zone 2|
|Power (Quartz) filling||Zone1||Zone2|
In the years BEPL ( before the Equipment Protection Level Era ), the Ex equipment selection process was based entirely upon the ( built-in) type of protection.
EPL was introduced through IEC 60079-14 (2007) . The idea is to elaborate the information about the inherent ignition risk of the equipment during normal operation , expected faults and during rare faults. It is logical that any equipment having VERY HIGH LEVEL OF Protection during NORMAL Operation, during EXPECTED FAULTS and during RARE FAULTS , have a LOWER Probability of becoming an ignition source . By virtue of this property this equipment is definitely FIT for use in an area having a HIGH Probability of becoming HAZARDOUS. The area having a HIGH Probability of becoming HAZARDOUS is ZONE 0 , so only the equipments with the highest EPL should go (installed ) in Zone 0. Following this course of reasoning we end up in following the following table:
Now we easily relate the ZONES and traditional protection techniques and in turn Equipment protection levels.
The (traditional )Relation between ELP (Levels) and protection Techniques
ref: IEC 60079-14-2007 & IEC 60079-14-2013
Reference : IEC 60079-0 2014 . Additional Information about FLAMEPROOF ENCLOSURE MARKING
Flameproof enclosures “d” shall be marked in accordance with IEC 60079-0 , with the following additional marking for the type of protection “d” :-
1. da For level of protection “da” , complying with the requirements of section 4.2, the marking shall include “da”
2. db “db” should comply with the requirements of section 4.3
3. dc “dc” should comply with the requirements of section 4.4
IEC 60079-0 2014th edition , introduces an additional EPL for FLAMEPROOF enclosures ,namely “da”. (in addition to the previously implemented EPLs “db’ & “dc” .
Section 4.3 gives us the area of use/application of EPL “da” , which is : ONLY, THE CATALYTIC SENSORS OF PORTABLE COMBUSTIBLE GAS DETECTORS
Equipped, with the Knowledge of :-
The Protection built in the equipment by the manufacturer and indicated by the EPL (Equipment Protection Level)
The Magnitude of the Hazard present on a particular site or an area (Indicated by the Class & Zone)
The type and ‘personality’ of the chemical involved (As indicated by the GAS GROUPS , IEC Grouping NOT ATEX)
It would (logically) be easier to make a proper selection of the Electrical equipment most suited for the protection job.
For a particular (IEC-allowed combination ) the overall cost will be fixed. The fixed scale is at the bottom . We can clearly see the inherent error in safety if the starting scale is COST(The fixed scale).
It is obvious that an economic solution may not be safe.
An interesting remark about the marking.
Ex d+e IIB T4 Ga
This marking is of an electrical equipment protected by two Types of Protection which is intended to be completely installed inside the area requiring EPL Ga.
Apparently Ga and Ex d + Ex e seems to be mismatched but in reality it means that the manufacturer is using two types of protections to achieve the Ga level of EPL.
This is one way of achieving the required EPL & it is in accordance with the objectives of the concept of EPL. The manufacturer is to clearly indicate the inherent ignition risk of the equipment through its EPL, no matter what type of protection is used.
(Follow the following Simple Rule of Thumb)