Does Propane Go Bad And What Happens If You Use An Old Tank?

Considering that Fox's hit 1997 animated sitcom "King of the Hill" has managed to stick in the public consciousness for over a decade after its original finale, it's hard not to talk about propane and propane accessories without hearing it all in the voice of Mike Judge's Hank Hill. What actually is propane, though, and does it have an expiration date? 

To answer the first point, propane is a colorless, odorless liquified petroleum gas (LPG) that's produced as a byproduct of processing natural gas and crude oil, and it accounts for 2% of U.S. energy usage. Much of this use is in the home, for things like heating and cooking (as, you know, imparted by Hank Hill), but it is also considered a more environmentally friendly fuel for vehicles that's cheaper, if slightly less efficient, but ultimately safer to use and store. 

As for if it goes bad? Actually, no. Whether you're using liquid or gaseous propane, the chemical itself does not appear to expire. However, it's understandable why you might believe it does; propane tanks are stamped with requalification dates to be retested, but this is to ensure the container itself is safe to store propane for household use. You can apply for a visual requalification through the Pipeline and Hazardous Materials Safety Administration, during which a tank is checked for damage like dents or cracks, rust or corrosion, missing pieces, and leaking valves — the most common risk that can be assessed via a proof-pressure hydrostatic test. This recertification date is typically five or 10 years, and one should assume a 10-year deadline from the date of manufacturing if one is otherwise unstated.

Unless your propane tank is sitting unused in the garage, it's unlikely you're going to hit its recertification date with leftover stock. A 100-pound propane tank used exclusively for your fireplace might last three weeks with regular activity. However, even if you do hit the listed date, as mentioned, the actual propane within should still be safe for cooking — don't be concerned that you've poisoned everyone if you don't notice the tank's use-by date in time.

Still, any ignitable, compressed gas such as propane or butane needs to be treated as a chemical hazardous waste risk with its own unique disposal process (you can't just leave a propane tank by your recycling bin to be picked up with the weekly garbage). The danger factor that those dates are there to prevent is because a damaged propane tank can result in a dangerous gas leak. 

To be clear, while propane is considered safer than gasoline due to its higher autoignition temperature, any combustible gas is a source of carbon monoxide, and both gas and propane are potential sources of respiratory issues when overused for daily tasks such as cooking (range stoves use about 35 gallons of propane every year). So if your tank is getting up there in years or have noticeable dents and dings, it is best to check your local county or state guidelines for best practices on how to dispose or recycle your propane tanks.