Explosion-Proof Equipment Marking: Reading the Code
Under GOST 31441.1-2011, non-electrical equipment for potentially explosive atmospheres must carry a durable marking in a visible place on the main part of the equipment. The marking encodes six things: who made it, what it is, when it was made, its group and protection level, its protection type, and, for Groups II and III, its temperature class or maximum surface temperature.
Where does the marking go?
GOST 31441.1-2011, Non-electrical equipment for potentially explosive atmospheres, requires the marking to be applied in a visible place on the main part of the equipment. It must be clear and durable enough to survive possible chemical corrosion, a plate that is unreadable after two years in service has failed its purpose.
What must the marking contain?
| Field | Content |
|---|---|
| a | Manufacturer’s name and address |
| b | Equipment type designation |
| c | Year of manufacture |
| d | Group and explosion protection level |
| e | Type or types of explosion protection |
| f | Equipment group and subgroup |
| g | Temperature class or maximum surface temperature |
Groups and protection levels
Group I, for underground mines and their surface structures, where firedamp and combustible dust are the hazards. Protection levels Ma and Mb.
Group II, for hazardous areas in premises and outdoor installations other than mines, where the hazard is a gas atmosphere. Protection levels Ga, Gb, Gc.
Group III, the equivalent for dust atmospheres. Protection levels Da, Db, Dc.
Types of explosion protection
| Symbol | Protection type |
|---|---|
| fr | Enclosure with limited gas passage |
| d | Flameproof enclosure |
| c | Constructional safety |
| b | Control of the ignition source |
| p | Pressurised enclosure |
| k | Liquid immersion |
| g | Inherent safety |
Equipment may comply with more than one, in which case each is shown.
Subgroups
I, equipment for underground mines and their surface structures.
II, or IIA, IIB, IIC, equipment for potentially explosive gas atmospheres outside mines. The letters are used where the standard for the particular protection type requires them.
III, or IIIA, IIIB, IIIC, the same for potentially explosive dust atmospheres.
The subgroups nest upward: IIB equipment is suitable where IIA is called for, and IIC equipment where IIA or IIB is called for. IIIB and IIIC behave the same way.
Where equipment is intended for one specific gas only, the designation II is followed by the chemical formula or the name of that gas.
Temperature
For Group II, the marking carries the temperature class, the maximum surface temperature in °C, or both. Where both appear, the temperature class comes last, in parentheses:
T1 or 350 °C or 350 °C (T1)Two exceptions. Group II equipment with a maximum surface temperature above 450 °C shows only the temperature value, for example 600 °C. Group II equipment intended for a specific gas need not be marked with a surface temperature at all.
For Group III, the marking shows the maximum surface temperature preceded by T, together with the degree of protection provided by the enclosure:
T110 °C IP54Fittings are not marked with a temperature class or maximum surface temperature.
What if the surface temperature depends on the process?
Sometimes the maximum surface temperature is not a property of the equipment but of what it is handling, the heated liquid passing through a pump being the standard example. In that case the temperature class or surface temperature may be left off the marking, provided the marking reflects that this is what has been done and the operation manual explains it. Silence on the plate with nothing in the manual is not compliance.
Frequently asked questions
What is the difference between Group I, II and III?
Group I is equipment for underground mines and their surface structures, where firedamp or combustible dust is the hazard, and carries protection levels Ma or Mb. Group II covers potentially explosive gas atmospheres outside mines, with levels Ga, Gb or Gc. Group III covers potentially explosive dust atmospheres outside mines, with levels Da, Db or Dc.
Is IIC equipment acceptable where IIA is required?
Yes. The subgroups are cumulative upward. Equipment marked IIB is suitable wherever IIA is required, and equipment marked IIC is suitable wherever IIA or IIB is required. The same relationship holds for the dust subgroups IIIA, IIIB and IIIC.
What if the surface temperature depends on the process rather than the equipment?
Where the actual maximum surface temperature depends mainly on operating conditions and not on the equipment itself, the temperature of the liquid in a pump, for example, the temperature class or surface temperature may be omitted from the marking. That omission has to be reflected in the marking and explained in the operation manual.
Not sure which of these applies to your product? Send it and we will tell you
Related articles
Certifying Explosion-Proof Equipment for Brazil
INMETRO certification for Ex equipment: the three product categories, the document list, and when IECEx gives presumption of conformity and ATEX does not.
TR CU 017 Testing: Why Clothes Cannot Use Foreign Reports
Adult clothing must be tested in the EAEU, one failed test fails the product, and a composition that does not match the declaration fails by construction.
TR CU 032 vs the PED Directive: Two Philosophies
Both regulate pressure equipment safety, but one puts risk analysis on the manufacturer and the other prescribes the requirements. What that means in practice.
