Sewing badges onto flame retardent overalls seems to defeat their purpose, unless the badges are also flame retardent.
As does wearing overalls that are so covered in dirt and oil that one spark would send the owner up in a ball of flames.
Overalls aren't cheap so it is worth looking after them carefully.
At a fire training session at Farnborough many years ago the instructor asked us to remove any metal badges from our overalls as they had a chance of getting extremely hot during the exercises.