What is a Hazardous Area?

- A hazardous area is a location which either has or may have an explosive concentration of gas, vapour or dust.
- The more often the flammable substance is present, the more hazardous the area is.
- An area that has the presence of flammable gas. Hazardous areas are divided into the following:-
Zone 0: > 1000 hours /year
Zone 1: 10 to 1000 hours/year
Zone 2: < 10 hours/year
Dust explosion pentagon

Example of hazardous area zones

Building a Certificate Label
- Marking and meaning for Electro-Technical Equipment/ Apparatus
- Certified according to CENELEC Standard
Gas protection
Dust protection

European Conformity Mark

EN Certifying Body ID Code

Mark for Explosion Protection
Means that apparatus is design Tested in accordance with ATEX Directive 94/9/EC.

Equipment Group
- Group I – firedamp (mining only)
- Group II – Surface industry only

Equipment Category
ATEX does not allow for the possibility of zone variances in apparatus. The category system means that the manufacturer must demonstrate the ATEX H&S essential requirements by testing.
- Cat 1: zone 0, 20 = 1G or 1D : very high safety protection by 2 protective measures/ faults
- Cat 2: zone 1, 21 = 2G or 2D: sufficient safety by 1 protective measure/ fault
- Cat 3: zone 2, 22 = or 3G or 3D: sufficient safety during normal operation- manufacturers declaration

Explosion Proof

Type of Protection
Intrinsic safety | Ex ia | Zone 0 |
Intrinsic safety | Ex ib | Zone 1 |
Flameproof | Ex d | Zone 1 & 2 |
Increased safety | Ex e | Zone 1 & 2 |
Purging | Ex p | Zone 1 & 2 |
Encapsulation | Ex m | Zone 1 & 2 |
Oil filled | Ex o | Zone 1 & 2 |
Powder filled | Ex q | Zone 1 & 2 |
For Zone 2 applications there are some alternatives
- Ex nA – non-sparking
- Ex nR – restricted breathing
- Ex nL – energy limited
- Ex nC – encapsulated, enclosed break, hermetically sealed, non-incendive sealed device

Gas / Equipment Sub Group
Gases are subdivided according to their MESG or the Maximum Experimental Safe Gap (derived from flameproof tests)
- Group IIA – MESG > 0.9 mm
- Group IIB – 0.5 mm ≤ MESG ≤ 0.9 mm
- Group IIC – MESG < 0.5 mm
- Group IIIC- Dust protected
CENELEC Marking | Typical Gas |
I | Methane (Firedamp) |
IIA | Propane |
IIB | Ethylene |
IIC | Hydrogen |
IIIC | Dust only |

Temperature Classes
- Referred to as the “T” rating
- The T Class of equipment relates to the maximum surface temperature of the equipment and the Auto Ignition Temperature or AIT of the hazardous material
- A high AIT does not make the hazardous material less dangerous. It can actually make them more dangerous as they will burn much hotter
- T1 – ignition temp. > 450°C
- T2 – ignition temp. > 300°C
- T3 – ignition temp. > 200°C
- T4 – ignition temp. > 135°C
- T5 – ignition temp. > 100°C
- T6 – ignition temp. > 85°C
- T6 rating is appropriate for ALL hazardous areas
- As T-max does not exceed 85°C so it will not ignite ANY hazardous material
NB. Group II apparatus is divided into T classes according to its maximum surface temperature. In the same manner, gases are classified on the basis of different ignition energies of the different gases but still using these T - ratings

Equipment Protection Levels (EPL)
IEC 60079 standards now include provision for equipment on the basis of risk. If the consequences of an explosion are deemed particularly severe, then to decrease the risk, the category/zone relationship can be changed to give a lower possibility of ignition. So category 2 apparatus could be selected for use in a zone 2 for instance
Group | EPL | Intended for Equipment Group | Giving Protection... |
Group I | Ma | Equipment for mining | High level of protection against becoming an ignition source |
Mb | Level of protection which can be electrically isolated if hazardous atmosphere is known to exist | ||
Goup II | Ga | Equipment for explosive gas atmospheres | Very High level of protection against becoming an ignition source |
Gb | High level of protection against becoming an ignition source | ||
Gc | Assured level of protection against becoming an ignition source in normal operation | ||
Goup III | Da | Equipment for explosive dust atmospheres | Very High level of protection against becoming an ignition source |
Db | High level of protection against becoming an ignition source | ||
Dc | Assured level of protection against becoming an ignition source in normal operation |

Ambient Temperature
- The T class indicates the maximum temperature of surfaces which could ignite an external explosive atmosphere
- Unless indicated, the ambient temperature range for which the equipment is intended is -20C to + 40C
- If the T amb range is other than standard, the T-Class will be followed by the applicable ambient for example:
T4 (65C Amb)
(would mean that the equipment would not exceed its T4 rating (135C) EVEN IF the ambient temperature gets as hot as 65C)

Dust Protection
Dust is every bit as dangerous as gas and as such it has now become essential to hazardous area certification. Every enclosure now must be tested in a dust chamber and at indEx we have the most up to date certification tests.
Basically the same principles apply as with the gas label.
However there are differences:
- II 2 D = Surface industry, equipment category, dust
- tb = Protection by enclosure (IEC 60079-31)
ta = Zone 20
tb = Zone 21
tc = Zone 22 - IIIC = Equipment Sub Group (Dust)
- T85°C = Maximum surface temperature of enclosure
- Db = Equipment protection level – this is a zone 1 for instance
- IP66 = Ingress protection – IP6X means complete protection from dust
ATEX Zone 0, 20, 1, 21 Protection Types
Ex Marking Code | Protection principle | Definition | Application | Standard | Possible use | Equipment protection level (EPL) |
|
Flame Proof | Prevents transmission of explosion to surroundings |
|
|
Luminaries, rotating machines, Switchgear |
|
|
Increased Safety | Prevents arcing, sparking and hot surfaces |
|
|
Terminal and junction boxes, lighting, rotating machines |
|
|
Intrinsic Safety | Prevents arcing, sparking and hot surfaces by energy limitation |
|
|
Measuring and instrumentation, fieldbus |
|
|
Pressurised | Hazardous material isolated from ignition capable parts |
|
|
Control panels, analysers, engines |
|
|
Simple Pressurisation |
|
|
|
||
|
Encapsulation | Hazardous material isolated from ignition capable parts, generally by use of a potting compound |
|
|
Relays, low cost & non reparable items, engine coils/solenoids |
|
|
Oil Immersion | Hazardous material isolated from ignition capable parts, generally by use of mineral oil |
|
|
DCS, Transformers, relays, start up |
|
|
Powder Filling | Prevents transmission of explosion to surroundings, generally by use of a quartz powder |
|
|
Relays, condensers, power supplies and similar apparatus |
|
ATEX Zone 2, 22 Protection Types
Ex Marking Code | Protection principle | Definintion | Application | ATEX/CENELEC /IEC | Possible use | Equipment protection level (EPL) |
|
Non incendive | Not capable of causing ignition in normal operation |
|
|
Luminaries, low power equipment, rotating machines, fuses |
|
|
Restricted Breathing | Keep out hazardous material by means of adequate sealing (IP66) |
|
|
Arcing sparking and hot surfaces, inverters, control & inst components, actuators, relays, PLC's |
|
|
Non Sparking | Not capable of causing ignition in normal operation |
|
|
Fuses, Shunts, restistors, low power equipment, transformers, batteries |
|
|
Energy Limited | Power insufficient to cause ignition |
|
|
Lower power PCB, PLC’s |
|
|
Enclosed break | No transmisson to surroundings. |
|
|
Switch gear (closed), reduced spec Ex d, reduced encapsulation “m” for circuits |
|
Non Incendive | As above. | |||||
Hermetically sealed | Primary sparking device is fusion sealed. | |||||
Simple encapsulation | Potting compound used. | |||||
|
Pressurised | Keep out hazardous material by positive internal pressure and adequate sealing |
|
|
Renders internal Ignition capable components (high grade industrial or Zone 2 ATEX EC type quality) suitable for non-hazardous area |
|
|
Simple Pressurisation | As above |
|
|
|
Comparison of IEC and North American Terminology
Although USA & Canada are IEC members, NA terminology relating to hazardous atmospheres may still be encountered. A comparison of the 2 systems are as such
IEC Zone | NA Division |
0 | 1 |
1 | |
2 | 2 |
Class | Group | Gas/Vapour |
I | A | Acetylene |
B | Hydrogen | |
C | Ethylene | |
D | Propane | |
II | Dusts | |
E | Metal | |
F | Carbonaceous | |
G | Non conductive | |
III | Fibres | Linters |
No sub groups |
Certification Labels
Component “U” certificate

Apparatus “X” Certificate

Ingress protection
- IP ratings give protection from solid objects (IP6X) and water (IPX6)
- The minimum IP rating for Ex e is IP54
- indEx enclosures are IP66 as standard
- IP66 most onerous test – dust tight and protection from powerful water jets
- IP67 and IP68 on request
Questions, enquiries?
Call us on +44 (0)1233 801890 or email sales@indexenclosures.com