# ia or ib? What Intrinsic Safety Protection Levels Actually Mean
Two letters apart. Thousands of pounds apart across a fleet.
Ex ia and Ex ib are both intrinsic safety. Both work on the same principle. The difference is how much has to go wrong before the protection stops working.
## The principle first
Intrinsic safety is not armour. There is no thick casing keeping the explosion in.
It is the opposite approach. The circuit is designed so that it can never release enough energy to ignite the atmosphere in the first place — not as a spark, and not as a hot surface.
That means limiting voltage, limiting current, and limiting the energy stored in capacitors and inductors, so that even a short circuit or a broken wire cannot produce an ignition source.
You will see manufacturers describe how they do it. Hytera use silicone encapsulation around the internal circuits. Motorola and Entel use current-limited accessory connectors. All of them limit the battery.
## The fault tolerance
Here is where ia and ib separate.
**Ex ia** must remain safe with **two** independent faults present, plus the safety factors required by the standard.
**Ex ib** must remain safe with **one** fault.
There is also **Ex ic**, which must remain safe in normal operation but is not required to tolerate faults in the same way.
Think of it as layers of redundancy. Two failures, one failure, none.
## Which zone each is allowed in
This maps directly.
| Protection | Faults tolerated | Zone | Category | EPL |
|---|---|---|---|---|
| ia | 2 | 0, 1, 2 | 1G | Ga |
| ib | 1 | 1, 2 | 2G | Gb |
| ic | 0 | 2 | 3G | Gc |
The logic is straightforward. Zone 0 has a dangerous atmosphere present continuously, so the equipment must never be an ignition source even after multiple failures. Zone 1 has it occasionally, so single-fault tolerance is proportionate.
For mining, the equivalents are **Ma** and **Mb**. An **M1 Ex ia** device is allowed to keep operating during a gas outbreak underground. An **M2 Ex ib** device must be de-energised when gas is detected. That is a real operational difference, not a paperwork one.
## What you can actually buy
Most ATEX handhelds are **ib**.
The Motorola R7Ex, the whole Entel DTEx range, the Hytera HP715Ex and HP795Ex. All Ex ib, category 2, Zone 1.
**ia** radios are a smaller field. The Hytera PD715IS and PD795IS are the obvious examples, marked II 1G Ex ia IIC T3 for gas and I M1 Ex ia for mining.
Notice something in that PD795IS marking. It is **T3**, not T4.
## The trade-off nobody mentions
Achieving ia means limiting energy harder. Something has to give, and it usually shows up in the specification.
Compare the Hytera PD795IS with the newer HP715Ex:
| | PD795IS (ia) | HP715Ex (ib) |
|---|---|---|
| Protection | Ex ia IIC T3 | Ex ib IIC T4 |
| Zone | 0, 1, 2 | 1, 2 |
| Transmit power | 1 W | 2 W |
| Weight | 495 g | 390 g |
| Battery | 1800 mAh | 2150 mAh |
The ia radio gives you Zone 0. It costs you half the transmit power, an extra 105 grams on the belt, a shorter shift, and a temperature class of T3 rather than T4.
None of that is a criticism of the product. It is physics. You cannot have maximum energy limitation and maximum RF output at the same time.
## When ia is worth it
Ask one question. **Does a person, carrying a radio, physically stand in a Zone 0?**
Most of the time the honest answer is no.
Zone 0 is normally the inside of something. The vapour space above liquid in a storage tank. The interior of a mixing vessel. Places entered under confined space procedures, with the atmosphere purged and gas-tested first — at which point it is not a Zone 0 during the entry.
If people work routinely in a genuine Zone 0, or you operate underground where M1 matters, buy ia. It is the right call and the cost is justified.
If they do not, ib is not a compromise. It is the correct specification, and you keep the power, the weight and the battery life.
## A warning about mixed fleets
If you buy both, label them clearly and control them properly.
An ib radio in a Zone 0 is a non-compliant ignition source in the most dangerous place on your site. "It looks the same as the other one" is how that happens.
Different colour bodies, different asset tags, and a documented issue procedure. Not optional.
## The short version
ia means two faults. ib means one fault. ia gets you Zone 0 and costs you performance.
Buy the level your hazardous area classification requires. Not the highest number on the page.