Explosion-proof cameras: zones, markings and what to specify

The zone decides the equipment, not the other way round

Hazardous areas are classified by how often a flammable atmosphere is present. The classification belongs to the site, drawn up by the operator or a consultant. A supplier cannot choose it for you, and a camera cannot upgrade a zone. Get the zone in writing before you ask for a model.

Dust areas use 20, 21 and 22 instead, and they are a different equipment family. A camera certified for gas is not automatically right for a flour silo, and the marking tells you which.

Gas group and temperature class are the second half

The gas group describes how easily the gas ignites: IIA (propane), IIB (ethylene), IIC (hydrogen, acetylene). Equipment rated IIC is suitable for IIA and IIB as well, so a higher group covers lower ones, never the reverse. The temperature class is the hottest surface the equipment may reach: T1 is 450 C, T6 is 85 C. A lower number is a hotter surface, so T6 is the most conservative.

What an ordinary camera gets wrong

The failures are physical, not electronic. An antenna drilled through the housing breaks the flame path. A gland that is not Ex-rated becomes the weakest point in the enclosure. An unused cable entry left open, or closed with a plain plug, removes the protection the label promises. A camera opened on site while the circuit is energised is a hazard regardless of its certificate.

• Every cable entry needs an Ex-rated gland or a certified blanking plug.
• The flame path is a machined joint: scratches, corrosion or paint destroy it.
• Earthing is not optional; the certificate lists the conductor size.
• An external Wi-Fi antenna on a flameproof housing usually means it is not flameproof.

The PTZ question on a tank farm

Fixed cameras cover the gate and the pump row. A PTZ earns its place where the interesting thing is far away and changes: a flare stack, a loading gantry, the far side of a tank bund. Optical zoom is what buys distance, so a 33X explosion-proof PTZ sees a detail at 200 m that a fixed camera renders as a smudge. The mechanism, not just the housing, has to be certified, because pan and tilt motors and slip rings sit inside the protected volume.

What to put in the enquiry

Give the zone, the gas group and the temperature class as written in the site classification. Add the ambient temperature range, because a camera rated for -40 to +60 C is a different product from one rated for -10 to +50 C, and the certificate states it. Then the distance to the farthest object, whether the camera must pan, and how the cable will enter the enclosure. With those six items a model can be quoted that will pass the operator review instead of being sent back.

Certificate numbers are per model, per marking and often per factory. Ask for the certificate, not a photo of a label, and check the marking on the certificate matches the marking on the housing you receive.