You should follow some basic safety precautions when dealing with 3D printers, and there are more advanced ones for further risk reduction that is particularly important if you aren’t going to monitor your prints closely.  I must note that most of my experience and the related reading I’ve done are related to Fused Deposition Modelling (FDM), which are the printers that use an extruded plastic filament, so there are probably other safety precautions I am ignorant of for other printing methods.  If you use something other than an FDM printer, I highly recommend doing your own research to find the to safeguard yourself and your printing area.

I must also note that these are aimed at safety, and will not guarantee you don’t have spectacularly failed prints, but will reduce the risk of property damage, injury, or death (before you get scared and put off 3D printing, I’m not sure that last one has ever happened, but it’s technically possible).

Monitor your printer:

You should watch or at least check on your 3D printer periodically while it’s printing.  This helps with keeping your prints from failing spectacularly, and helps you recover for a new attempt at a print faster after a fail, but this is also important for safety reasons.  Monitoring your print ensures that you are more likely to catch any potential fire or other safety hazards before they can cause a problem.  How frequently you need to check on it depends on the quality of your printer, your experience, and the environment you are printing in.  A quality printer in a safety-conscious workspace may not require as much monitoring as a DIY kit in a household with children and pets.

Keep Clear of Hot Nozzles:

FDM printers run by forcing plastic through a hot metal nozzle to make it melt and build up structures.  Keep anything you don’t want burned away from the nozzle.  These have to be hot to melt the plastic (190 degrees Celsius/374 degrees Fahrenheit or higher), so make sure you keep body parts away from the nozzle when it is hot, and make sure kids and pets can’t get too close to the nozzle either.

Take Precautions for Fire Safety:

Related to the above, keep flammable materials away from your 3D printer as much as possible.  You don’t want a flammable item to fall onto the printer to cause obstructions or catch fire.

DO NOT build a wooden support structure OR enclosure for your 3D printer.  This include particle board.  Adding such flammable materials to close proximity with your printer increases your fire risk.

Here are some good fire safety tips in general, brought to you by a person who learned from experience:

Don’t burn your house down 3D Printing. A Cautionary Tale

I recommend reading that article in it’s entirety, but the main things I’ve taken away from it and plan on implementing are: 1) keep an electrical fire rated fire extinguisher near the printer and 2) put a smoke detector above the printer.  That way you have as much advance warning as possible and the capability to put out any fire before it can endanger your home.

Here’s another article I’ve seen on fireproofing your 3D printer.  His involves some rather extreme checking and modifications, but I can see how they could help, particularly for homemade 3D printers.

Everything you need to know to make your 3D printer fireproof!

If you use a heat gun for post-processing, don’t be an idiot.  Get a trivet to put it down on after using so it doesn’t ignite anything.

Don’t Breathe Microparticles and Fumes:

Keep your printer in a well-ventilated area to prevent buildup of microparticles in the air that you can breath in.  I know the science is not definitive on whether they are harmful, but if you don’t want to take unnecessary risks this is one way to reduce them.  If a print is going to go on a long time, it is recommended that you don’t stay in the same room for an extended period of time.  Wait a few minutes after the printer finishes to let the microparticles settle.  Apparently they settle out quickly.  Then go retrieve your print.

If you use materials other than PLA, I recommend getting a fume exhaust system of some kind, as they can put off toxic gases.

Use Common Sense when Post-Processing:

I know this seems basic common sense, but general knife/blade safety is very important.  Cut away from yourself, not towards yourself.  If I were still in the Boy Scouts I’d have to have a corner cut off of my whittling chip.  I recently gave myself a jagged cut when using one of my post-processing chisels because I was careless and trying to cut late at night.  My hands weren’t as steady as I thought they were, and I foolishly cut towards myself.  Anyway, make sure you either clamp or have the piece you are working on held securely in such a way that the force you are putting into the chisel goes straight down into the cutting board.  That way if it slips or goes through easily it goes into the board and not your hand!

Comment below if you have any more safety tips you recommend to people for keeping their hobby (or possible workplace) safe.