I work with machines attached to liquid nitrogen tanks. If there is a leakage from the tank, the amount of oxygen in the room reduces drastically – that’s very dangerous, because it’s asphyxiant (you can’t breathe), especially in small, closed spaces. Since it has no colour or smell, you wouldn’t be able to tell that the leakage occurred – that’s why most labs that operate machines using liquid nitrogen have oxygen sensors. Although liquid nitrogen is not dangerous if handled carefully, it can also cause cold burns. I burned myself a few times with the splashes from the liquid, but nothing serious. However, I heard horror stories from other labs!
Our labs in general are very safe which is a bit of a boring answer! There are loads of regulations to control everything you do. In saying that I often have to work with chemicals which can kill you such as cyanide or phosgene. There are also many pyrophoric chemicals which are chemicals which catch fire if they are exposed to air.
In microbiology, we use Bunsen burners to keep clean air moving up and away from our experiments—think of like a candle, but with gas instead of wax. We also use alcohol to clean our lab benches before we start work, because it kills bacteria. Once, I accidentally lit my whole bench on fire! But luckily, the fire went out once all the alcohol burned away.
I have worked with sulfuric acid, also with the French Press used to smash bacteria to get what they have inside. This press is very dangerous because if you accidentally leave your hand inside it will smash your hand. I have also worked with liquid nitrogen (it burns by contact) and with hydrochloric acid that generates gas chloride and is very irritant for the eyes and the respiratory track
In one of my previous jobs, we used hydrofluoric acid. It’s like HCl but loads more acidic. If you get it on your skin it goes though your skin and attaches to your bones. Apparently it feels like your bones are on fire! We were super careful with it and never had any problems. There is a cool video on it!