Enclave Hellfire troopers are easily identified by their unique armor and heavy incinerators. They are tough opponents and are normally accompanied by 2-3 Enclave soldiers around Enclave camps and Adams Air Force Base. Normally they will continuously fire at you causing temporary blindness until you move, they are encountered at higher levels.
Their heavy armor, combined with their significantly higher-than-average health (which is on par with most companions), allows them to survive noticeably more damage than any other humanoid combatant, with the exception of certain special characters (such as General Jingwei).
The Broken Steel add-on also adds a new rank of standard Enclave soldier wearing Enclave Hellfire armor and equipped with plasma rifles. These new Enclave soldiers have the same stats as Enclave Hellfire troopers, but are labeled as "Enclave soldier" rather than "Enclave Hellfire trooper".
They bear the Hellfire title only when using their signature heavy incinerators, though the ones armed with plasma rifles are still a large threat.
Sometimes they will appear before the player has started Broken Steel if the player has it loaded.
They are the Enclave's special forces and veteran troopers and appear in less frequency than regular troops but are more of a threat.