If you’ve been storing petrol (hopefully not in plastic bags or other random containers), it’s important to know that it can go bad, and after a while you won’t want to put it in your car or lawnmower. But you shouldn’t dump it in the street, either. Here’s what you need to know about safe disposal of old or expired gasoline.

How long does petrol take to go bad?

Petrol is volatile, meaning that it’s only just barely a liquid. Its molecules all harbour dreams of escaping and floating free in the air, and if the cap on the container is not tight enough, they will. Petrol also oxidizes easily, meaning its molecules break apart when they contact certain other chemicals, including oxygen. This property is what makes it so flammable, and so good in engines. When you oxidize fuel very rapidly, you get a fire — or, when inside a car engine, a series of very tiny explosions that move the pistons.

When gas oxidizes slowly — whether in a gas can in your garden shed — you end up with a bunch of molecules that are not quite the same as normal gasoline. They may not power your engine as well as they’re supposed to, and in some cases can gum up fuel lines.

For these reasons, you really can’t expect stored gasoline to last forever. Three to six months is about the best you can hope for when it’s stored properly; if it’s in a can with a loose cap or it has been exposed to heat, it may last even less time than that.

What happens if you dump old petrol just anywhere?

You probably know, intuitively, that neither your town’s sewer system nor the local ecosystem will be very happy about swallowing up a whole tank’s worth of petrol. Petrol is corrosive, toxic, and flammable and just plain does not belong in those places.

Dumping gasoline is illegal just about everywhere — check your local laws — and the fines involved can be substantial. Also, if you’re already trying to think of places you can dump your petrol without getting caught, you’re an arsehole.

How to safely dump old petrol

Your town, city, or council should have some kind of procedure for this, which you can look up on their website. You can also google “hazardous waste disposal [your area]” to find further options.

Follow their instructions, but typically you’ll have to do something like this:

  1. Make sure the petrol is in an approved container (again, that does not include plastic bags or random buckets).
  2. Call ahead to the waste disposal site to check hours, rules, and what else they take — you may be about to get rid of old cans of paint or car batteries at the same time.
  3. Drop it off in the right place via the approved methods, and enjoy the peace of mind that comes from getting a flammable liquid off your hands without poisoning the environment.

Extracted in full from: How to Safely Dispose of Old Petrol (lifehacker.com.au)