Section 58. In every town which accepted chapter two hundred and ninety-one of the General Acts of nineteen hundred and sixteen or chapter one hundred and forty of the General Acts of nineteen hundred and seventeen, or in which the provisions of chapter thirty-one were, on April third, nineteen hundred and seventeen, applicable to the chief of the fire department thereof, such chief shall hold his office continuously during good behavior unless incapacitated by physical or mental disability to perform the duties of his position; provided, that in every such city the official having the power of appointment, with the consent of the confirming board, if any, and in every such town, the selectmen, may, for just cause and for reasons specifically assigned by said official or selectmen, remove such chief, first giving him a copy of such reasons and allowing him a reasonable time to answer them in writing. A copy of the reasons, notice and answer, and of the order of removal, shall be filed with the town clerk.