Err , not with that level of information.

"Safe" is in the eye of the beholder. The gas pipeline owner will want the separation to be as big as possible.

A lot depends on who is there first and what rights they have in each countries laws and regulations or land rights.

Typically you see distances of between 0.5 to 1m separation, but it is very variable.

Some more information would help a lot.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

As LittlInch mentioned, it can vary widely by jurisdiction and utility owner. (A quick Google search yields as small as 0.5 ft. and as much as 10 ft. between gas and gravity sewer).

I suggest starting with researching local jurisdiction code and if that does not provide a specification, checking with the gas and sewer utility owners.

generally 12 inches is the minimum recommended. I cant guarantee that is safe though.
its usually not an issue since sewerlines are usually much deeper than gas lines

https://rga.lis.virginia.gov/Published/2000/SD24/P....

Gravity sewers yes, "forced mains", i.e. pressurised shit - usually laid at the 0.9 to 1.2m cover mark and level with the ground.

But the OP needs to define "safe". Safe for who? How "safe". It is a meaningless set of words at the moment.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

The standard 300 mm safety distance used to place natural gas pipe away from sewage pipeline facilities needs to be abstracted to consider accidental damage and provide a safety buffer to the natural gas pipe.