1. The single protection method accepted in Zone 0 is intrinsic safety
This one question used to be a fairly simple one to answer before the EPL (Equipment
Protection Level) concept was introduced in 2007. Back then, the answer was yes, the single
approved protection method for use in Zone 0 was the intrinsically safe method.
Before the EPL concept incorporation into the standards, equipment selection was done by a
relationship between the type of Zone assigned to the hazardous area and the Device
Category assigned to the equipment being considered.
So, for hazardous areas created by gasses and vapours, you followed this table:
Zone
Zone 0
Zone 1
Zone 2
Zone 20
Zone 21
Zone 22
Device Category
1G
2G
3G
1D
2D
3D
The letter G of the Device Category indicates gasses. It can be also D, for hazardous areas
due to the presence of flammable dusts. Or can also be G/D, meaning that the equipment
can be used both in gas and dust explosive atmospheres.
This table was simple and straightforward, but from my personal point of view, created a
possible issue: the Zone number is not the same as the Device Category number.
This means that for Zone 0 you must use 1G rated equipment, for Zone 1 you must use 2G
rated equipment and for Zone 2, 3G rated equipment was required.
This inconsistency in the labeling and markings is a possible source of errors. I never
understood, nor I could find a suitable explanation about this inconsistency.
Wouldn’t it be easier and safer to correlate the Device Category with the Zone numbers?
Why not use Device Category 0 for Zone 0, Device Category 1 for Zone 1, and device
category 2 for Zone 2?
Go figure…
But, with the introduction of the ATEX Directive 94/9EC equipment selection criteria shifted
from the technical requirements of the equipment to the installation area.
By doing this, three levels of protection for gases and another three levels of protection
were defined:
ATEX Category
1G
2G
3G
1D
2D
3D
Type of substance
Gas
Gas
Gas
Dusts
Dusts
Dusts
Protection Level Required
Very High
High
Normal
Very High
High
Normal
Zone
Zone 0
Zone 1
Zone 2
Zone 20
Zone 21
Zone 22
which initially associated the adequate level of protection to the corresponding Device
Category.
If you translate this table according to the adequate protection methods, the result is the
following table of equivalence:
Zone
Zone 0
Zone 1
Zone 2
Device Category
1G
1G - 2G
3G - 2G -3G
Zone 20
Zone 21
Zone 22
1D
1D - 2D
1D -2D-3D
Adequate method of protection
Ex ia – Ex ma
Ex d – Ex e – Ex i – Ex m – Ex p – Ex o – Ex q
Ex d – Ex e – Ex i – Ex m – Ex p – Ex o – Ex q – Ex
n
pD – mD – tD – iaD – ibD
pD – mD – tD – iaD – ibD
pD – mD – tD – iaD – ibD
If, at this point, you have become confused, you are not alone. I spent some time reading the
standards before starting to figure out the implications of these tables.
Finally, in 2010, the EN 60079-14 standard introduced a method for risk assessment that is
based on the Equipment Protection Level or EPL.
The EPL approach is an alternative to the traditional method based in the Device Category.
The traditional method assigns types of protection using statistical data about the likelihood
or frequency of presence of an explosive atmosphere.
EPL indicates the risk ignition that is intrinsic to the equipment, independently from the
method of protection employed.
This new approach has the advantage of additional flexibility and easier equipment
selection. And is an alternative way that does not replace the Device Category method.
The final equipment selection table is this one:
Zone
Zone 0
Zone 1
ATEX Category
1G
2G
Zone 2
3G
Zone 20
Zone 21
Zone 22
1D
2D
3D
Adequate method of protection
Ex ia – Ex ma
Ex d – Ex e – Ex i – Ex m – Ex p – Ex
o – Ex q
Ex d – Ex e – Ex i – Ex m – Ex p – Ex
o – Ex q – Ex n
pD – mD – tD – iaD – ibD
pD – mD – tD – iaD – ibD
pD – mD – tD – iaD – ibD
EPL
Ga
Gb
Gc
Da
Db
Dc
The corresponding EPL meanings are the following:
•
•
EPL Ga: Equipment for explosive atmospheres due to the presence of flammable gas,
with a level of protection 'very high', which is not a source of ignition in normal
operation, or in case of expected failure or when subjected to a rare failure.
EPL Gb: Equipment for use in explosive atmospheres due to the presence of
flammable gas, with a 'high' level of protection that is not the source of ignition in
•
•
•
•
normal operation or when subject to expected malfunctions, although not on a
regular basis.
EPL Gc: Equipment for use in explosive atmospheres due to the presence of gas, with
a level of protection „increased‟ that is not a source of ignition in normal operation.
It has some additional security measures in order to ensure that it remains a source
of ignition not active in case of expected events on a regular basis (for example, the
failure of a lamp).
EPL Da: Equipment for explosive atmospheres due to the presence of combustible
dust, which has a level of protection 'very high’ and does not constitute a source of
ignition in normal operation or when subject to rare failures.
EPL Db: Equipment for explosive atmospheres due to the presence of combustible
dust, which has a level of protection 'high'. It does not constitute a source of ignition
in normal operation or when subject to expected failures, although not on a regular
basis.
EPL Dc: Equipment for explosive atmospheres due to the presence of dust, with a
level of protection 'increased', which is not a source of ignition in normal operation.
It may have additional protections in order to ensure that it remains inactive as a
source of ignition in the case of regular and waited failure.
If you have experience with intrinsic safety, you will surely be able to relate the a, b and c
letters to the intrinsic safety levels of safety against faults:
•
•
•
“ia” means that the system is intrinsically safe even in the event of two simultaneous
faults.
“ib” means that the system is intrinsically safe even in the event of a single fault.
“ic” means that the system is intrinsically safe in normal operation with no fault
tolerance.
By using the EPL method, it is possible to specify the required equipment protection levels
by identifying the correct zones in the area classification documentation:
Zone
Zone 0
Zone 1
Zone 2
Zone 20
Zone 21
Zone 22
Acceptable Equipment Protection Levels
Ga
Ga or Gb
Ga, Gb or Gc
Da
Da or Db
Da, Db or Dc
And the eventual answer to the original question comes now in the following table:
EPL
Ga
Type of protection
Intrinsically safe
encapsulation
Code
ia
ma
Relevant standard
IEC 60079-11
IEC 60079-18
Two distinct types of
protection each
meetimg EPL Gb
Protection of
equipment and
transmission systems
using optical
radiation
Special protection
IEC 60079-26
op is
IEC 60079-28
sa
IEC 6079-33
This table shows that, in addition to the intrinsically safe method, by using the EPL
equipment selection methodology you can also use the encapsulation method, the
combined protection method, the inherently safe optical system method and any certified
method that might be developed in the future.