Remain in the maintenance room and go towards the Southern elevator shaft. Select the Cryptographic Sequencer from the inventory and use it on the control panel to start a more demanding hacking mini-game, and to determine the correct password from among several available combinations (the screenshot).
Since there is no elevator here, you will have to do with Batman's gadgets and skills. Start by using the hook to reach the ledge above. Shimmy to the ledge's other end, and select from the inventory the claw. You need to use it to rip off the grate of the ventilation shaft. Walk through the tunnel, take the ladder and approach the generator, which you need to activate, using the shock gloves.
Turn to face the elevator shaft and start using the glue grenades, which will result in sealing the three pipes that you can see in the distance and which leak steam. After you are done with that, jump onto the ledge with the sealed pipes and go right. Use the hook to make it onto the balcony above, run up and jump. Grab onto the interactive ledge and shimmy to the right.
Climb only after you are next to the next ledge. Look up and aim the hook at another interactive point. After you make it onto the next platform, locate the ladder, thanks to which you will be able to get to the very top of this location. You can now wake the door to the Boiler Room Maintenance Corridor. Use the hook to walk past the locked gate and then use the claw to unlock the venting shaft. The corridor will take you to the Boiler Room, Where you find the first one of the Firefly's four bombs.
As you have probably figured out, before you can focus on disarming the bomb, it will turn out to be necessary to eliminate all of the bandits gathered around it. The most convenient way of moving around are the vantage points but, you need to watch out for the statues around the main furnace because they are mounted with explosives (example in the screenshot).
You can, of course avoid the statues with bombs and it is especially recommendable, while playing the initial part of this scene, i.e. when the enemies do not yet realize Batman's presence and aren't yet trying to locate him. It is also worth reminding at this point that a good way to avoid the threat connected with the statues, is to extend ropes using the grapple. This is so, because attaching a rope to the statue with the C4 on it, prevents premature detonation of the charge.
When it comes to the enemies, I recommend that you, in the first place, get the one with the disrupting device. This may, however, prove to be very difficult, because the enemy with the antenna on his back, should be patrolling the boiler room's lower level, which means that you will have to break a serious sweat to eliminate him. You should also watch your step around the enemies with heat detectors and escape from the statues that they are currently scanning, or remain motionless if you come equipped with an appropriate upgrade.
You can eliminate successive bandits in any order you wish. The easiest way, of course, is to perform the inverted takedowns or hoist them using the grapple. You can also focus on quiet takedowns, using the explosive gel on the weakened surfaces or executing quiet surprise attacks from venting shafts. Continue eliminating enemies until there is only one enemy left in the boiler room. He should give up automatically and you need to interrogate him.