Ex Knowledge · Fundamentals
What is intrinsic safety?
Intrinsic safety is a way of designing electrical equipment so that it can’t release enough energy, as a spark or as heat, to ignite the gas or dust around it.
How it works
An explosion needs three things: a flammable gas or dust, oxygen, and a source of ignition. In a hazardous area the first two are a fact of the site. Intrinsic safety removes the third, by limiting the voltage, current and stored energy in the circuit so that even when a fault occurs the device stays below the ignition energy of the atmosphere.
That is why an intrinsically safe phone can be carried, charged elsewhere and used normally, rather than sealed in a heavy enclosure.
Protection levels: ia, ib and ic
The letters after “Ex i” say how many faults the design tolerates, and so which zones it may enter.
| ia | Safe with two faults · Zone 0, 1, 2 |
|---|---|
| ib | Safe with one fault · Zone 1, 2 |
| ic | Safe in normal operation · Zone 2 |
Zones and equipment protection levels
Sites are classified by how often an explosive atmosphere is present. Each zone accepts equipment of a matching protection level (EPL).
| Zone 0 | Present continuously · EPL Ga |
|---|---|
| Zone 1 | Likely in normal operation · EPL Gb |
| Zone 2 | Unlikely, short periods · EPL Gc |
| Zone 20 | Present continuously · EPL Da |
|---|---|
| Zone 21 | Likely in normal operation · EPL Db |
| Zone 22 | Unlikely, short periods · EPL Dc |
Reading an Ex marking
Here is a typical marking for a handheld device certified for Zone 1 gas, decoded segment by segment.
Choosing a device
Start from your site’s area classification drawing. Match the zone, gas group and temperature class to the device, and ask for the certificate evidence before purchase.
This guide is a summary
It doesn’t replace EN IEC 60079 or your site’s DSEAR / ATEX assessment. Always follow your competent person’s area classification.