Ex d vs Ex tD: How to Read the Marking on a Hazardous-Area Camera

The string on the housing

Every camera in the range carries the same published marking: Ex d IIC T6 Gb for gas and Ex tD A21 for dust. It reads like one code but it is really two certifications in one line, and each part answers a different question.

Ex d: the enclosure contains the ignition

The "d" stands for flameproof enclosure. The design assumption is that gas can get inside the housing and ignite; the enclosure is built to survive that internal explosion and to cool the escaping gases below the ignition temperature of the surrounding atmosphere. It is a pressure vessel with a very specific job.

What follows from that: the joints and the cable entry are part of the protection. A flameproof camera with a wrongly sized gland, a damaged joint face or a missing bolt is no longer flameproof, no matter what is stamped on the plate.

IIC and T6: how demanding the atmosphere is

Group IIC is the most demanding gas group — it includes hydrogen and acetylene — so equipment rated for IIC covers the less demanding groups as well. T6 is the temperature class: the hottest surface the equipment can reach stays within the limit for the gas present. T6 is the strictest of the six classes, which is why it appears on equipment intended for a wide range of cargoes rather than a specific one.

Gb is the equipment protection level: suitable for Zone 1, the area where an explosive atmosphere is likely during normal operation. None of these letters is decorative — each one narrows where the unit may be installed.

Ex tD: the dust half

The second half of the string covers combustible dust rather than gas: protection by enclosure, category A21, for a Zone 21 area where dust is likely in normal operation. A camera marked for gas is not automatically suitable for dust — the two are separate assessments, and a cargo hold or a coal-handling area is a dust question.

What the marking does not tell you

It does not tell you whether the certificate is accepted by your flag state or your class society, and it does not tell you whether the certificate covers the specific variant you are ordering. Those are paperwork questions, and they are the ones that stop a project at the surveyor's desk.

The practical instruction is simple: quote the marking to confirm the technical class, then ask for the certificate itself for the model, the variant and the authority that matters to your vessel. That is also what we say on the camera pages — the string is a specification, the certificate is the permission.