Why have modern gas cans become so complex? | Fuel Facts

Have you bought a gas can lately? They’ve gotten a bit complicated with those newfangled nozzles and accoutrements, right? 

The reason for the changes: science, notes Zachary Santner, manager of Product Engineering and Business Optimization at Sunoco Performance Products.

Back in the olden times, gas cans were simple. You had a vent–that you likely never closed–and a simple spout. To dispense fuel, you just tipped the can and let gravity take over.

Why the mandate for today’s spring-loaded, automatic-sealing nozzles? Simple: to keep the vapors inside the can.

What’s the big deal? Well, those escaping vapors contain benzine and related compounds that can cause smog, cancer and other bad things.

What if you don’t care about that stuff? Well, those escaping vapors will also cause your fuel to go stale, leading to lagging throttle response and cold-starting issues. Again, science.

But can’t those trapped vapors cause a warm gas can to swell? Yes, that can happen. The cure: Santner advises that leaving about 10% headspace will prevent that hydraulic pressure, while moving the gas can to a cooler environment will lower the vapor pressures. 

Once the fuel cools, those vapors will condense back into a liquid form. This cycle doesn’t degrade the fuel, Santner continues.

What about just opening the cap to release those vapors? Reread the line about those escaping vapors causing health, environmental and drivability issues. 

The latest in gas can requirements: flame mitigation measures. Only gasoline vapors can ignite, but pouring gas is surrounded by these vapors, Santner reminds us. Should those vapors ignite, the localized heat further evaporates the fuel, and very quickly you have a runaway reaction. “It’s so dangerous and scary because you don’t see the vapors,” Santner notes. “You could be standing within a vapor cloud and not know it.”

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