EN 60079-26 covers equipment at the highest protection level, EPL Ga. Ga means the equipment remains safe even when an explosive atmosphere is continuously present and two independent faults occur at the same time.
Straddling two zones
The standard's particular role is for equipment straddling a boundary — a sensor mounted in a tank wall, say, with one end in Zone 0 (inside the tank) and the other in Zone 1 (outside). Such equipment requires a double barrier so that a fault cannot propagate ignition from one zone into the other.
In practice, level Ga is most often achieved with intrinsic safety "ia", frequently with an additional mechanical barrier. Work in Zone 0 correspondingly demands the greatest care in PPE selection: antistatic clothing, gloves and footwear are mandatory.