A swollen gas can is under pressure, and opening it carelessly can spray gasoline vapor or liquid fuel in your face. You can release the pressure safely, but you need to do it the right way: slowly, outdoors, away from any ignition source, and with the nozzle pointed away from your body.
Why Gas Cans Swell in the First Place
Gasoline constantly releases vapors, and those vapors expand as temperature rises. A can left in a hot garage, truck bed, or direct sunlight on a summer day can build significant internal pressure in just a few hours. The hotter it gets, the more vapor pressure builds inside the sealed container.
Modern gas cans are a big part of the problem. In 2007, the EPA required manufacturers to seal in gasoline vapors to reduce emissions. The intent was to add compliant vents, but widespread confusion led many manufacturers to stop installing vents altogether. Older gas cans had a small vent cap on the back that let pressure equalize naturally. Most cans sold today don’t have that, so pressure has nowhere to go except into the walls of the container. That’s why you see the can bulging outward like an inflated balloon.
The Real Dangers of a Pressurized Can
The pressure itself won’t cause the can to explode like a bomb. Plastic gas cans are designed to flex, and the walls will stretch well before they rupture. The dangers are more practical than dramatic, but they’re still serious.
First, when you crack the seal on a pressurized can, fuel and vapor can spray outward with force. If the nozzle is pointed at you, gasoline can hit your eyes, mouth, or skin. Gasoline on skin causes irritation and chemical burns with prolonged contact. In the eyes, it causes immediate pain and can damage tissue if not flushed quickly. The CDC recommends flushing affected eyes with plain water for a full 15 minutes and rinsing exposed skin with water for two to three minutes, then washing with mild soap.
Second, the burst of vapor that escapes a pressurized can is highly flammable. Gasoline vapor ignites at concentrations as low as 1.4% in air, and a sudden release creates a rich cloud of it right at the opening. Any nearby spark, flame, cigarette, or even a running engine can ignite that cloud instantly.
Third, static electricity is a less obvious but real risk. Plastic gas cans can accumulate static charge, especially when sitting on plastic truck bed liners or other insulating surfaces. A static spark between your hand and the can, or between the can and a metal surface, is enough to ignite gasoline fumes. This is the same mechanism that causes gas station fires when people slide across car seats and touch the pump nozzle.
How to Open a Swollen Can Safely
You can depressurize a swollen gas can yourself if you follow a few rules.
- Move it outdoors first. Never open a pressurized gas can in a garage, shed, or any enclosed space. You need open air so vapors disperse rather than pooling at ground level where they can reach a pilot light, water heater, or electrical outlet.
- Set the can on bare ground. Place it directly on dirt, concrete, or gravel, not on a plastic surface. Contact with the ground dissipates any static charge that has built up on the container.
- Point the opening away from you. Before loosening the cap or nozzle, angle it so any spray goes away from your face and body.
- Open it slowly. Turn the cap or nozzle just enough to hear a hiss of escaping gas. Let the pressure bleed off gradually over 10 to 15 seconds before opening it further. Think of it like cracking a shaken soda bottle. A slow release prevents the sudden spray that a quick twist would cause.
- Touch a metal object first. Before handling the can, touch a grounded metal surface (a metal fence post, a car frame while your feet are on the ground) to discharge any static on your body.
- Keep all ignition sources far away. No smoking, no running engines, no power tools, no phones you might drop. Give yourself at least 20 feet of clearance from anything that could produce a spark or flame.
What to Do if Gasoline Sprays on You
If pressurized fuel sprays onto your skin, remove any clothing that got soaked and rinse the affected area with plain water for two to three minutes, then wash gently with mild soap. Gasoline-soaked clothing holds fumes against your skin and is itself a fire hazard, so bag it separately rather than tossing it in a laundry basket.
If gasoline gets in your eyes, flush them with clean water or saline for 15 minutes. This is longer than most people think necessary, but gasoline is a chemical irritant that needs thorough rinsing. Remove contact lenses if you’re wearing them. If pain, blurred vision, or redness persists after flushing, get medical attention.
If you accidentally swallow any gasoline (from a spray hitting your mouth, for instance), do not try to vomit it up. Gasoline does more damage when it’s aspirated into the lungs during vomiting than it does sitting in the stomach, where it’s poorly absorbed.
Preventing the Problem Going Forward
The simplest fix is adding an aftermarket vent kit to your gas can. These small valves install in seconds and let pressure equalize automatically, the same way older gas cans worked before the 2007 regulation changed designs. They’re widely available at hardware stores for a few dollars.
Storage habits matter just as much. Keep gas cans in a shaded, ventilated area rather than in direct sunlight or a closed car trunk. A can stored at 70°F will build far less pressure than one that heats to 120°F on a sunny truck bed. If you know you won’t use stored gasoline for a while, keep the can less than 95% full to leave room for vapor expansion. And never store gas cans on surfaces that insulate them from the ground, like rubber mats or plastic shelving, since those prevent static from dissipating naturally.