Folks - there are two concerns about extension cords.
One is SHOCK (as in electrical shocks) and the other is FIRE.
1) One is exposure to moisture, and this is actually a concern for any indoor-rated appliance that you are using outdoors. Get an outdoor cord and appliance, and use an outdoor (wet rated) bulb. Outdoor outlets should be on Ground-Fault protected circuits. Not having outdoor-rated equipment or ground-fault protected circuits is a SHOCK hazard.
2) The second thing about extension cords is that if you use a little skinny extension cord to power a big-fat-power-hog-appliance, you will be overloading the extension cord wire capacity, which causes the wires to overheat, which causes FIRE.
The solution to this is to LOOK at how much power your appliance draws and use an appropriately rated (sized) extension cord. If your appliance draws 1500 watts, you need an extension cord that has wire thick enough around to handle the current of 1500 watts (watts = amps * volts, so if you are working with 110 volt current then that extension cord should be big enough to handle at least 13.6 amps.) You may know how many of the circuits in your house have 15 or 20 amp breakers. 15 amp circuits use minimum 14 gauge wire. So if I wanted to run a 1500 watt appliance, I'd look for a 14 gauge extension cord. It's probably ok to run a 1500 watt appliance temporarily on a smaller cord (many of those orange extension cords you buy are 16 gauge) - but I wouldn't leave it alone by itself or use it ongoing. For wire gauges, a smaller number = bigger wire.
You NEVER want to have a tiny skinny wire extension cord going to an appliance that has a big fat wire going into it.
Don't "hope" it will be safe - do the research and figure out what you need to be SURE it is safe. This is a matter of math and physics.