A gas-free engineer (GFE) is a person who has successfully completed a similarly named training course offered by the United States Navy. The gas-free engineer is thereby qualified to certify a confined space as being safe to enter without the use of an air-purifying or supplied air (SAR/SCBA) respirator. The confined space would, however, need to be ventilated during entry to ensure an adequate supply of breathable air. Gas Free Engineering is equivalent to Firefighter team lead, Toxic Gas inspector, Confined space inspector, etc.
U.S. Navy GFE Resources Index
Actually the Navy Gas free course does not certify you to be a Gas Free Engineer. You are certified as a competent person for Gas Free spaces, To conduct hot work per OSHA standards, you have to use a certified Marine Chemist.