Try not to kill the Cleaners
Marcus was a cleaner.
Now most cleaners when describing their job tended to use works like repetitive, messy, dreary or exhausting. Generally there wasn't anything particularly noteworthy about there work, just long hours cleaning spills, mopping floors and scrubbing tables. Sure they might occasionally come home with a strange story about the latest bizarre accident that some hapless employee caused that made there job that day/night that much harder. Something to tell the family during dinner, laugh about a couple of times and them forget about it.
Marcus wasn't most cleaners.
When asked to describe his job the first he usually uses is DANGEROUS.
Instead of first telling his funny stories to the kids over dinner Marcus got to practice his stories by explaining what happened to whichever onsite doctor happened to be treating him this time.
For other cleaners an emergency meant someone dropped their coffee in the staff-room and it was staining the cheap carpet. For Marcus it meant meant missing walls, smoke damaged ceilings and strange mutagenic chemicals all over the floor.
Why was Marcus' job so different from other cleaners? The answer is rather simple. He worked for Paragon Industries.
Initially his job was fairly normal (if you discount cleaning up after the occasional explosion) but it rapidly got worse as the scientists increased in both numbers and creativity. He's dealt with power-armored footprints dented into the floors, cleaned laser burns of the walls, dodged micro-missiles that escaped into hallways and aired out rooms full of orange glowing smoke. He eventually gave up on trying to clean the pipes and left that to the sentient slime that now called them home.
He's dealt with the staff room after its been victim to mini-robot fighting to the death, super-coffee that melted the mugs if not drunk fast enough and been attacked by things in the fridge that the Krogan claims to have brought in for lunch.
In fact he's pretty sure he should have been awarded an honorary degree in chemistry because of the number and diversity of chemical spills he's had to figure out how clean up (sand works for the green ones but the purple ones set it on fire and as for the blue ones its just easier to let it melt through the floor and fix the hole afterwards).
Most would have quit after the first week but Marcus was stubborn. He took pride in his work and at the end of a long shift the relief he took in seeing the now pristine white hallway before him and the satisfaction of a job well done was enough. The knowledge that he was a part of something, no matter how underappreciated it was helped to...
Feeling the whole building shake Marcus quickly removed his heavy duty sound cancelling headphones (borrowed from the explosives lab to block out the singing coming from the salarian's lab near the corner) just in time to identify the alarms ringing before a heavily armed figure comes bursting through the wall.
"What the hell are you doing, i just finish cleaning that" he shouted. The armored figure just stood there stunned, the blue biotic wisps that surrounded it beginning to slowly dissipate because of its distraction.
"That's it, I've had enough, I QUIT!" Marcus turned around and stormed away from the now ruined hallway, shouting angrily at the secuity camera on the ceiling
"AND YOU STILL OWE ME HAZARD PAY FOR DEALING WITH ALL OF THIS"