Equipment approved for explosive atmospheres carries a short code on its nameplate, the Ex marking, stating exactly where the device may be used. It is routinely mistaken for a product number. Here is how to read it.
See the infographic: How to read an Ex marking
Two systems sit behind that code. Within the EU, the ATEX Directive requires equipment intended for explosive atmospheres to be assessed and marked before it can be placed on the market. Internationally, the IECEx scheme certifies the same equipment against the same technical standards, the IEC 60079 series. Because both rest on those standards, the marking reads identically under either, which is why it is known simply as the Ex marking, Ex being the long-standing abbreviation for explosion protection.
It matters most in powder handling. Lactose, starch or an active ingredient sits harmlessly in a drum but behaves differently once dispersed in air. Areas where a dust cloud can form, or where a settled layer can be disturbed, are classified as hazardous, and equipment taken into them must be certified not to act as an ignition source. Every character of the marking is doing work in that judgement.
Take two real examples. A Bartec terminal box is marked Ex eb IIC T6 Gb and Ex tb IIIC T85°C Db, under certificate IECEx BAS 07.0034X. An Armadex digital camera is marked Ex ic IIC T4 Gc and Ex ic IIIB T135°C Dc, under IECEx OBAC 25.0008X. Both are current. Read them left to right and you can place either device without asking anyone.
After the Ex prefix comes the type of protection, which tells you how ignition is prevented. The box uses eb, increased safety, for gas and tb, protection by enclosure, for dust. The camera uses ic, intrinsic safety, for both, meaning its circuits cannot store enough energy to ignite anything. Then comes the group: IIC covers the gases that ignite most readily, while IIIA, IIIB and IIIC refer to combustible flyings, non-conductive dust and conductive dust. Most pharmaceutical powders are non-conductive, so IIIB.
Temperature follows, and the two halves handle it differently. Gas uses a class, so T6 means a maximum surface temperature of 85°C and T4 means 135°C. Dust uses no class; the number is written out, which is why the box shows T85°C and the camera T135°C. Once seen, it stops you hunting for a T class that was never going to be there.
What the last two letters tell you
The final pair matters most and gets read least. This is the equipment protection level, and it sets the zone. Gb and Db allow Zone 1 and Zone 21, where an explosive atmosphere is expected in normal operation. Gc and Dc allow Zone 2 and Zone 22 only, where it is not. So the terminal box may be installed in a room the camera may not enter.
One asymmetry is worth memorising. IIIC equipment is fine for non-conductive dust as well as conductive, but IIIB must not be used where conductive dust is present. Manufacturers certify to the broadest group they can, which is why more than eight in ten dust-rated certificates on the IECEx system are IIIC. Seeing IIIC is normal. It is IIIB that deserves a second look against the material you actually handle.
Finally, a marking is printed by the manufacturer, while the certificate behind it is issued by a certification body and can be amended, restricted or withdrawn. Both examples here can be checked free on the IECEx on-line certificate system at iecex-certs.com, which shows current status, standards applied and any specific conditions of use. It takes a minute, and it is the only way to be sure.
