This level is thankfully very short and can completely be finished with stealth. Sneak to the first guard and hit the switch behind him despite his warning not to do so; this will fry him. Get his pistol if you so wish, then backtrack to the junction and use the RTL to cross the burning path. Watch out for the top flames! Drop to the ground on the opposite section and use your taser to open the vent. Crawl inside and zoom in on the switch with your sniper rifle. Fire once to shut off the burning pipe and use your NV goggles to traverse this area. Drop into the next room and use the wall vent.