Equipment Protection Levels (EPL)
Equipment Protection Level (EPL) indicates the likelihood that a piece of equipment will become a source of ignition. Defined in IEC/EN 60079-0, EPL provides a bridge between zone classification (the hazard) and protection methods (the solution).
EPL Definitions
Gas Atmospheres
| EPL | Protection Level | Definition | Suitable for |
|---|---|---|---|
| Ga | Very high | Equipment remains safe even with two independent faults | Zone 0, 1, 2 |
| Gb | High | Equipment remains safe with a single fault | Zone 1, 2 |
| Gc | Enhanced | Equipment remains safe under normal operation; may have additional measures for fault conditions | Zone 2 |
Dust Atmospheres
| EPL | Protection Level | Definition | Suitable for |
|---|---|---|---|
| Da | Very high | Equipment remains safe even with two independent faults | Zone 20, 21, 22 |
| Db | High | Equipment remains safe with a single fault | Zone 21, 22 |
| Dc | Enhanced | Equipment remains safe under normal operation | Zone 22 |
Mining
| EPL | Protection Level | Definition |
|---|---|---|
| Ma | Very high | Equipment can be left energized in an explosive atmosphere; safe with two faults |
| Mb | High | Equipment must be de-energized when explosive atmosphere is detected; safe with one fault |
EPL to Zone Mapping
The fundamental rule: the EPL of installed equipment must match or exceed the zone requirement.
| Zone | Minimum EPL Required |
|---|---|
| Zone 0 | Ga |
| Zone 1 | Gb (or Ga) |
| Zone 2 | Gc (or Gb, or Ga) |
| Zone 20 | Da |
| Zone 21 | Db (or Da) |
| Zone 22 | Dc (or Db, or Da) |
Equipment with a higher EPL can always be used in a less hazardous zone (Ga equipment in Zone 2 is acceptable, though often unnecessarily expensive).
EPL to Protection Method Mapping
| EPL | Available Protection Methods |
|---|---|
| Ga | Ex ia, Ex ma |
| Gb | Ex db, Ex eb, Ex ib, Ex mb, Ex px, Ex py, Ex o, Ex q, [Ex Op pr, Ex Op sh] |
| Gc | Ex dc, Ex ec, Ex ic, Ex mc, Ex pz, Ex nA, Ex nC, Ex nR, Ex nL |
| Da | Ex ia, Ex ma, Ex ta |
| Db | Ex ib, Ex mb, Ex tb, Ex pd |
| Dc | Ex ic, Ex mc, Ex tc |
EPL vs ATEX Categories
ATEX Directive 2014/34/EU uses categories rather than EPL. The mapping is:
| ATEX Category | EPL Equivalent | Zoner |
|---|---|---|
| 1G | Ga | Zone 0, 1, 2 |
| 2G | Gb | Zone 1, 2 |
| 3G | Gc | Zone 2 |
| 1D | Da | Zone 20, 21, 22 |
| 2D | Db | Zone 21, 22 |
| 3D | Dc | Zone 22 |
| M1 | Ma | Mines (energized in Ex atm) |
| M2 | Mb | Mines (de-energized in Ex atm) |
In ATEX marking, the category appears as the number+letter: II 2G means Group II, Category 2G (= EPL Gb).
Fault Tolerance
The EPL letter suffix (a, b, c) directly relates to fault tolerance:
EPL "a" (Very High — Ga/Da/Ma)
- Equipment must remain safe during normal operation AND with two independent faults
- Must apply a safety factor of 1.5× to all protection parameters
- Only Ex ia and Ex ma meet this requirement
- Most rigorous testing and documentation
EPL "b" (High — Gb/Db/Mb)
- Equipment must remain safe during normal operation AND with one fault
- Safety factor of 1.5×
- Covers most common industrial protection methods (Ex d, Ex e, Ex ib, Ex p, etc.)
- Majority of installed Ex equipment worldwide is EPL Gb/Db
EPL "c" (Enhanced — Gc/Dc)
- Equipment must remain safe during normal operation
- May include measures to reduce ignition probability during fault conditions
- Equipment may simply shut down or alarm on fault detection
- Lower cost, suitable for Zone 2/22 where explosive atmosphere is unlikely
Practical Considerations
Over-specifying EPL
Installing Ga/Da equipment in Zone 2/22 is technically acceptable but:
- Significantly more expensive
- May be harder to maintain (Ex ia restrictions on modifications)
- The zone classification should be reviewed first — the area may qualify as Zone 1
Under-specifying EPL
Installing Gc equipment in Zone 1 is a violation. This is a common compliance error discovered during inspections. Always verify:
- Zone classification drawing is current
- Equipment EPL matches or exceeds the zone
- Gas group and temperature class are also correct
Mixed Installations
A single piece of equipment can have multiple EPLs for different parts:
Ex db [ib Ga] IIC T4 Gb
This means the main enclosure is EPL Gb (flameproof), but it contains intrinsically safe circuits rated EPL Ga.
Related Files
- Zone Classification — how zones determine required EPL
- Protection Methods — available methods per EPL
- Ex Markings — how EPL appears in equipment marking
- Standarder — IEC 60079-0 defines EPL framework
- Certification — how EPL is verified and certified