Is digging with a shovel near gas lines dangerous?
I speak as a former engineer for a utility that provides both gas and electricity.
Gas lines are typically metal or plastic. If plastic, they're very likely thick enough to withstand most hand digging with a shovel. Laws typically require hand digging within some distance (18&quot; in my state) of a marked line. If you do find a gas line with your shovel and notice any damage beyond, perhaps, very minor scraping, call the gas company back. They'll evaluate and will almost certainly be responsible for any costs of repairs since there were no markings.
It is also possible that there are underground lines that are not owned by a utility company and will not be marked.
Just dig reasonably. Age, manufacturing defects, and other factors can create all sorts of variations in the strengths of the lines, whether plastic or metal. Hand digging, though, is unlikely to create a spark that would ignite the gas, even in the very unlikely event your shovel does penetrate the line (still evacuate, call 911 AND the gas company, and get your neighbors away, too). Just don't smoke while you're digging!
Finally, while there may be warning tape or other devices, there are no guarantees! These things are installed by humans who don't always do everything perfectly, nor were they used in the oldest installations. Easements are a good indication; just be aware that an easement on a map may not reflect the actual location of a line, and a &quot;blanket&quot; easement gives NO indication of where the line might be.
Please also know that utility lines are almost always buried at proper depths; however, there is no guarantee that someone did not change the grading of the property after a line was installed. When people would ask me how deep our lines are buried, I'd answer &quot;all the way to the bottom of the trench&quot;.
Update:
In response to comments discounting risk of gas-related fires:


Not something to take less than seriously (the hose aimed upward keeps the fireball from curling around and burning the firefighters from above and behind). The fire continues until the gas is shut off, despite the water.
The tank in the photo is probably the most common size for residential propane customers. Buried lines are likely big enough to eliminate any claims of a &quot;small&quot; fire... and how much damage will be done, even if the shutoff is not engulfed, in the time it would take to shut it off? Sure, there are always rare exceptions. Do you care to place a financial wager with me that has a 99% probability of your losing? Stakes are even higher here.