This Generator Refueling Mistake Could Be Catastrophic

Each year, many homeowners attempt to refuel their generator while it’s running to avoid the inconvenience of having to shut off power during an outage. The Consumer Product Safety Commission estimates that as many as 1,000 fires each year are caused by generators, many of which are due to “hot-fueling.” Most major generator manufacturers, including Generac and Honda, explicitly warn against doing this, even threatening to void warranties if you do. I reached out to Eliot Vancil, CEO of FuelLogic, a company that specializes in fuel delivery to equipment, vehicles, and generators, to find out why refueling a generator while it’s running is such a bad idea. 

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Why Refueling a Generator While It’s Running is Dangerous

The dangers of refueling a running generator are no joke, says Vancil. “Refilling a generator while the engine is running is an invitation to instant death by thermal ignition,” he says. Here’s why:

• Hot parts plus fuel: Portable generators get very hot, especially if they’re running for hours. The exhaust manifold and muffler can reach up to 500℉, making spills extremely dangerous. “These surfaces spark liquid gasoline immediately and form a fire that spreads out through the unit,” Vancil says. 
  
• Increased likelihood of Spills: A gas powered portable generator is also difficult to fill without spilling, Vancil says. “A running engine is vibrating and makes pouring fuel into a narrow opening unstable,” he says, thus increasing the likelihood that you’ll spill it on the hot manifold or muffler.
  
• Flammable vapors: Even if you manage to not spill fuel, there's still the danger of starting a fire. Opening the fuel tank and fuel container releases flammable vapors, which can ignite from a spark caused by the running generator engine. “Vapor clouds form around the machine can flash back to the container if a spark occurs,” Vancil says.

How to Safely Refuel a Portable Generator

1. Start by shutting it off. Yes, this means cutting off power to whatever devices are attached to it, but safety trumps convenience.
   
2. Let it Cool. Those hot external parts create the fire hazard, so Vancil recommends letting the generator cool down for a good 15 minutes before adding fuel. “Safety relies on a cold engine to ensure that these volatile reactions do not transform a routine job into a catastrophe,” he says.
   
3. Refuel. Add fuel to the tank carefully, using a funnel to minimize spills. While you might be tempted to top off a generator fuel tank to extend its runtime between refills, doing so could cause  fire. Fuel expands as it heats up. If there’s no room in the tank for expansion, it can overflow onto the generator’s hot metal parts, causing a fire. “Filling the tank to 90 percent capacity allows for needed room for the liquid to expand when it heats up,” Vancil says.
4. Restart. Wipe up any spills from refilling before you start the generator back up.