What It Means If A Gas Can Is Swollen or Collapsed

A swollen or collapsed gas container can be an unsettling thing to discover in your garage, but it’s a great learning opportunity. The container changes shape because of the changing vapor pressure of gasoline, which is highly volatile and readily evaporates. Scientists have known since the 17th century that the pressure a vapor exerts on the sides of a container changes with temperature, and they formulated this insight into a mathematical relationship known as the Boyle-Mariotte Law (also known as the Ideal Gas Law). You may have heard about it in high school science classes.

According to this law, the product of pressure (P) and volume (V) of a gas is equal to the product of the amount of gas present (n), the ambient temperature (T) and a fixed number known as the universal gas constant (R). In mathematic terms, that’s written as PV=nRT. Since a gas container has a fixed volume, the equation can be rearranged to read P=kT, where k is a constant (nR/V). This tells us that when temperature goes up, vapor pressure goes up, and vice versa.

If science and math aren’t your specialty, you can take the word of HVAC pro Sergey Nikolin, who deals with vapor pressure as part of his job: “Gas cans swell and collapse due to temperature changes, as gasoline vapors expand when heated and contract when cooled.”

Unfortunately, a swollen or collapsed gas can be potentially dangerous, given the flammability of gasoline, but you can avoid accidents by using the right container and following some simple guidelines. We’ll tell you all about it.

Why Do Gas Cans Swell?

A gas container swells when the ambient temperature goes up, and if you’ve been paying attention, you already know why: It’s because the vapor pressure in the container has also increased. The pressure inside the container was the same as atmospheric pressure when you filled it and closed the cap, but when the pressure inside the container increases and exceeds atmospheric pressure, it pushes the sides out. “It’s completely normal for a sealed container, but honestly, it can be a little surprising if you’re not used to it,” says Chris Turner, a designer of luxury fire pits.

Is a swollen gas can dangerous?

It can be, warns Nikola especially if you’re using an old gas container. “Excessive swelling can weaken the can over time or even cause it to rupture if it’s old or damaged. Over time, the flexing can cause invisible micro-cracks, potentially leading to undetected vapor leaks.”

If your can conforms to Occupational Safety and Health Administration (OSHA) specifications, there’s less danger of an accident than if it isn’t. That’s because OSHA-approved containers:

• Hold a maximum of five gallons;
• have a flame-arresting screen under the cap;
• have a spring-closing lid and spout cover;
• have a valve that safely relieves pressure when the container is exposed to fire.

Not all containers on the market are OSHA compliant, so if safety is a priority, choose one that bears the OSHA label.

How to open a swollen gas can

Slowly and carefully. Some of the vapor will escape, so to prevent inhaling it and/or creating a fire hazard, you should always be in a well-ventilated areapreferably outside. You should never be near an open source of heat because if the vapor ignites, it can flash back to the can and ignite the liquid gasoline. Such accidents are rare, but they do happen. NBC News reported 11 deaths and 1,200 emergency room visits between 1998 and 2013 because of this phenomenon.

On hot days, the sun can potentially provide enough heat for flashbacks, so you should always be in the shade. One more thing: Don’t open the can while it’s resting on a metal surface because metal generates static electricity that can produce sparks.

Should I use the gas in a swollen gas can?

If the container is still intact and the swelling is moderate, the gas should be safe to use. However, an old container and/or extreme swelling can cause small ruptures and possible contamination. If this occurs, it’s a good idea to discard the fuel.

Why Do Gas Cans Collapse?

When the vapor pressure in a gas container decreases due to low ambient temperatures, it can’t resist the force of atmospheric pressure pushing on the sides, and the container collapses.

Is a collapsed gas can dangerous?

A swollen or collapsed gas can is never a good thing if it is old. Old cans “don’t always handle pressure changes well,” says Turner. Cracks or leaks can develop, and that’s where the fire hazard comes in.”

If an old can collapses and ruptures, it won’t release fumes while the temperature is low and the can is collapsed, but it very well might when the temperature rises, the vapor pressure increases and the can regains its normal shape and begins to swell. That’s a time bomb you want to avoid.

How to fix a collapsed gas can

It may seem strange, but a gas can is supposed to collapse, at least as far as the Environmental Protection Agency (EPA) is concerned. Unlike OSHA, the EPA prohibits pressure-relief vents because they allow gas fumes to escape into the atmosphere. With no way to equalize vapor pressure inside and outside of it, the container has no choice but to collapse.

Restoring an EPA-approved can without a pressure-relief vent it to its normal shape is easy. Simply remove the lid to equalize pressure, then replace the lid tightly and set the container in the sun. It should regain its normal shape in an hour or two.

How to prevent gas cans from collapsing

“Use modern gas cans with pressure-relief mechanisms and store them on raised platforms to avoid ground heat transfer,” advises Nikolin. “And periodically inspect for cracks or warping and replace every 57 years for safety.” Turner concurs and adds: “Don’t overfill them, this can make the whole situation worse. It’s one of those things that seems fine until it’s not.”

About the Experts

• Sergey Nikolin is the President of Product Air Heating & Cooling, LLC, which he established in 2019 with his brother.
• Chris Turner is the owner and designer at Studio Nisho, a brand renowned for luxury fire pits.

Sources

• Occupational Safety and Health Administration: Letter to Dennis Vance; (2004)
• NBC News: Warning: Scientists say gas cans carry risk of explosion; (2013)
• Sure Can: Collapsing Gas Cans, EPA Regulations; (2019)

The post What It Means If A Gas Can Is Swollen or Collapsed appeared first on Family Handyman.

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