Plastic Gas Can Swelling

Plastic Gas Can Swelling

Almost everyone does it—storing gasoline at home to use it for fueling most of the internal combustion engines such as lawnmowers, chainsaws, tillers, well pumps, and weed eaters among others. It’s also stored in companies to fuel automatic generators to help out when there’s a power outage. Now, when it comes to storage, most people will obviously use the 5-gallon red containers. If you can remember, the first time you inspected the container, I believe you were nervous to find the plastic gas can swelling, and looking like a gentle touch was enough to burst it.

Although gasoline does a great job of fueling internal combustion engines, it’s a highly volatile liquid making its vapor highly flammable and easy to ignite by just a small spark. So, due to its high flammability, storing gasoline will require you to use lab-tested containers that are approved by Underwriters Laboratories (UL) or Factory Mutual (FM).

So, with that in mind, let’s get to our main topic of the day where we’ll discuss everything you need to know about plastic gas cans swelling and whether they’re safe for storing gasoline.


Plastic Gas Can Swelling: What You Should Know

Is it Normal for Plastic Gas Cans to Swell?

Just to cut the long story short, yes, it’s normal. Although you’ll generally feel nervous the first time you notice it, the good news is that it’s completely normal for gas containers to swell or shrink. You see, unlike other liquids, gasoline is more volatile and tends to vaporize much faster (at room temperature) due to its weak intermolecular attraction. Following constant temperature fluctuations, the gasoline vapor inside the plastic can will either expand or contract causing the container to swell or shrink.

Since 2009, all plastic gas containers have been forced to adhere to the EPA guidelines regarding their design. These guidelines state that gasoline cans are permitted to only vent no more than 5 psi of hydrocarbon emissions per day.

Due to these regulations, gas cans are now designed with spring-loaded caps that provide a tight seal when closed. Although they allow a limited amount of gasoline vapor to vent off, the spring tension is so tight to prevent explosions caused by excess heat from the surrounding.

Now, when it comes to filling gas in these containers, from the filling station, it’s recommended that you fill them to about 95%. This will leave a small empty gap at the top of the container to allow pressure buildup that will cause swelling and shrinking when gas vapor expands or contracts following temperature fluctuations.


What Makes These Plastic Gas Cans so Superior?


Before I even proceed, I will agree that most readers will have different opinions followed by mixed criticism here. That’s because the new plastic gas containers have had their fine share of problems when compared to the previous gas containers. Although they swell and shrink perfectly to prevent explosions, they’re susceptible to regular spillage when refueling any of your appliances that use internal combustion engines.

The spouts and the handles of these new gas cans are extremely difficult to handle causing you to spill a lot of fuel enough, to create a mess. This alone can result in emitting too many hydrocarbons to the atmosphere more than what the previous cans could.

Although the old gas cans will take the credit here, the new cans have a lot to be celebrated especially in the safety department. So, here are some of the factors that have made the new gas container to stand out.

  • Extended Shelf Life: One of the major selling points of the new plastic gas containers is their virtually airtight spring-loaded caps. With such a design, these containers can self-seal thus preventing air and oxygen from penetrating. Since exposure to air/oxygen is one of the major culprits that cause stored gasoline to degrade, your gas can last for a longer time up to about 2 years.
  • Safe: If you have kids around, then there’s no reason to worry as these gas cans are strong enough to resist rough abuse. First, the body has passed several UL tests while the spout and carrying handle has too passed FM tests for strength and resistance. About the FM tests, these plastic cans have endured heavy impacts on concrete floors from a height of 3 ft. without leaking.
  • Safe to Store in the Garage: Unlike the previous cans that allowed too much gasoline vapor to escape, the new cans are tightly sealed to prevent the constant emission of hydrocarbons. Since most garages have several electric types of equipment all around them, there will be no risks of fire caused by sparks and excess gas vapor.


How Can I Prevent My Plastic Gas Can From Swelling?


Now, if you’re worried about the swelling of your new plastic gas can, then the only remedy is to vent it. This is done by poking a small hole right behind the handle to balance the pressure from the vapor with that of the atmosphere.

Another way is to leave the spring-loaded cap not entirely tight around the nozzle. This way, it will not form a tight seal meaning there will be high hydrocarbon emissions throughout the storage period. The final method is to seal the cap tightly but release the high pressure caused by the expanding vapors more often especially when the can begins to swell.

Now, we’ve mentioned three ways you can prevent your plastic gas can from swelling. What we didn’t mention is that each of the processes is more of a tradeoff that comes with a price. First, venting plastic gas cans that have been stored in an attached garage is quite risky as small sparks or flames can easily ignite the escaping vapor.

Secondly, if you’re a prepper storing gas for long-term use, venting your gas cans will end up ruining the integrity of your gasoline. Remember, when gasoline is vented, what is released is the light-ends which are the combustible components of gasoline when it’s mixed with air.



So, there you have it. The next time you see your plastic gas can swelling, I believe you now know what it means and what you can do to release the inside pressure. Before I conclude, some people have been asking whether it’s safe to refuel an internal combustion engine with a swollen plastic gas can. Since it’s already swollen, you’ll need to either poke a hole to vent it or loosen the collar around the spout to release the excess pressure. Once the excess pressure has bled off, tighten the collar and start pouring your gasoline.

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top