Health Indicators
Indicators will pop up immediately to the left of your general health status during certain conditions. This is a bad thing, so you should probably try to avoid it.
Radiation
There is no longer a symbol that pops up if you have radiation, so you may want to keep a medical scanner on hand to see if you have any radiation if you see your health dropping for unknown reasons. If you seem to be gaining radiation rapidly, get to Medbay ASAP. Radiation causes toxic damage, radiation sickness, and can cause good or bad (Mostly bad) mutations.
Temperature
File:Indicator freezing.gif
It's too cold! You move at a crawl while at this temperature. If you're standing on a space tile, you'll take burn damage. This status takes awhile to go away, even if you move into a room with normal temp. Space Heaters, certain exosuits, and hot beverages will help you heat up.
File:Indicator hot.gif
It's too hot! Usually an indicator that you're ON FIRE!!! If you can't find a fire extinguisher, stop drop & roll.
To stop drop & roll, click on the "STAND" button, so that it switches over to "REST", then when you are laying down, mash the fuck out of the "RESIST" button until you are no longer on fire.
Atmosphere
File:Oxylossold.png
You are suffocating, generally because you're in space or a part of the station exposed to space. Put on some internals or move to a safer area. If you have a gas tank on and this pops up, make sure it's not empty, or that you haven't set the pressure too low. The lowest an emergency oxygen tank may go is around twenty, and the lowest a jetpack may go is seventeen.
The biohazard symbol indicates that you're breathing plasma, or possibly really bad farts. If it is the former, you'll take toxin damage as long as you do, so get some internals on and get out of there before some idiot sets the air on fire.
This indicates that the air you are breathing is too hot and is literally burning your lungs. You will take burn damage very quickly as long as you breathe this atmosphere. Generally a sign of an Engineer fucking around. Quickly get your internals on and get out of there.