Start with the drawing, not the datasheet
Every hazardous-area purchase that goes wrong starts the same way: someone shortlists devices, compares them, picks one, and then discovers that the site's area classification drawing does not match what was bought. The drawing is the only document in the process that is not negotiable. It states the zone, the gas group and the temperature class, and the equipment has to satisfy all three.
A datasheet cannot be checked against a drawing, because a datasheet is written by the seller. A certificate can, because a certificate is issued by a body that has no interest in whether you buy the device. That asymmetry is the whole reason this category is procured differently from every other category of rugged hardware.
The three variables that decide everything
Zone. Zone 1 is an area in which a flammable atmosphere is likely to occur during normal operation. Zone 2 is an area in which it is not likely to occur in normal operation and, if it does, will exist only for a short time. Zone 0 is continuous or long-duration, and handheld electronics are not the answer there. The protection level required falls as you move from Zone 1 to Zone 2, and so does the cost per unit.
Gas group. Group IIA covers propane and similar, IIB covers ethylene, IIC covers hydrogen and acetylene. IIC is the strictest, and a device marked IIC is also accepted in IIA and IIB areas. The reverse is not true, which is why a device marked only IIB is a narrower product than a buyer often assumes.
Temperature class. T1 through T6, indicating the maximum surface temperature the device is permitted to reach. T4 means 135 °C, T5 means 100 °C, T6 means 85 °C. The class has to be lower — that is, cooler — than the ignition temperature of the atmosphere present. This is the variable most often overlooked, because it is the one least likely to appear in a product photo.
These three appear together in the Ex marking on the device: a protection concept,
a gas group, a temperature class, and an equipment protection level. Something of the
shape Ex ib IIC T4 Gb is telling you it is intrinsic safety, acceptable in IIC
atmospheres, capped at 135 °C, and suitable for Zone 1. Read it as four separate
statements, each of which can independently disqualify the device.
Why IP68 is the wrong answer, asked the right number of times
The confusion is not stupid, it is structural. Ingress protection and explosion protection are both printed on the box, both expressed as short codes, and both testified by the same word "rugged". But they answer unrelated questions.
IP68 says that dust cannot enter and that water cannot enter at a stated depth for a stated duration. It is a statement about the housing. It says nothing about whether the circuitry can produce a spark, nothing about how hot the surface gets under load, and nothing about whether the battery can release energy into a fault.
A device can be perfectly sealed and still be an ignition source. This matters in practice because of who catches it: not the buyer, but the site's safety engineer, at the gate, on the day the crew was told the equipment would arrive.
The certificate is issued to a build, not to a family
This is the part that catches experienced buyers. Certification attaches to a specific manufacturer, a specific model, and often a specific configuration. Two devices that look identical in a photograph can sit on different sides of the line, because one went through the assessment and the other did not.
Options make this sharper. A scanner module, a thermal camera, or a radio that is available on the standard build is frequently not covered by the certified build. Adding it afterwards can void the basis on which the certificate was issued, and the resulting device is no longer the device that was assessed — even though the marking plate still says it is.
The practical rule: configure the certified build, and buy anything outside it as a separate unit that stays outside the classified area. That is more devices, and it is the correct answer.
What to demand before the purchase order
Ask for the certificate document, not a claim about the certificate. Then check four things on it:
- The Ex marking matches the zone, gas group and temperature class on the drawing.
- The model designation matches the exact unit being quoted, including options.
- The issuing body is one your jurisdiction recognises — a notified body for ATEX, an accepted certification body for IECEx.
- The document has a number and a date, and has not expired.
If a supplier gives you an Ex marking with no document behind it, that is not a shortcut, it is the failure mode. Markings are easy to copy. Certificates are not.
For equipment going into the European Union, the ATEX route and the IECEx route are related but not interchangeable, and national authorities outside the EU may accept IECEx while requiring local registration on top. Confirm which applies to the destination country, not to the country the supplier is in.
When the certified device is not the right device anyway
Certification costs money and constrains configuration, and plenty of work on a hazardous site is done outside the classified area: the gatehouse, the workshop, the stores, the office, the vehicle. Putting a certified handset in a role that never enters a classified area spends the premium twice, because certified builds are also usually behind the general-purpose models on processor and camera.
The better shape for most sites is a split fleet: certified units for the classified area, general-purpose rugged units for everywhere else, and one radio system that both join. That last part is the one that goes wrong most often, and it has nothing to do with certification.
The radio problem, which is separate
A site's radio fleet is rarely homogeneous. Analogue UHF, DMR digital and PoC over cellular often run side by side for years during a migration, and a handset that only speaks one of them leaves part of the crew off the talkgroup. On a hazardous site this is worse than inconvenient, because the workaround is people walking to find each other.
So specify the radio separately from the certification, and confirm three things: the band the existing fleet uses, whether it is digital or analogue, and whether the certified build you need actually carries that radio. Those three constraints are set by three different teams, and the certified handset you want may not satisfy all of them at once.
A short checklist
Before the quote:
- Zone, gas group and temperature class, read off the drawing
- National approval route: ATEX, IECEx, or IECEx plus local registration
- Radio: band, digital or analogue, and PoC if cellular coverage exists
- Which work is inside the classified area and which is not
Before the order:
- Certificate document received, and the four checks above passed
- Model designation on the certificate matches the quoted configuration
- Options confirmed as covered by the certified build, or split onto a second unit
- Marking plate photograph on file, because the next inspection will ask for it
After delivery:
- Marking plate checked against the certificate, on the actual units, before issue
- Spares path agreed — a certificate does not help a crew waiting three weeks
