Answer:  Good question! This opens up how standards work and are often misinterpreted.

 NFPA 70E says 130.6 (D) “Conductive articles of jewelry and clothing (such as watchbands, bracelets, rings, key chains, necklaces, metalized aprons, cloth with conductive thread, metal headgear, or metal frame glasses) shall not be worn where they present an electrical contact hazard with exposed energized electrical conductors or circuit parts.”

 ASTM F1506 which is cited by NFPA 70E for clothing requirements says the following:
“6.1.1 NOTE 4-If fasteners or closures, for example, zippers, snaps, or buttons, or a combination thereof, are used in a manner in which they are in contact with the skin, they can increase heat transfer and burn injury due to heat conduction or melting onto the skin. Fasteners or closures that are used in this manner should be covered with a layer of fabric between the fastener or closure and the skin. The fabric used for this purpose shall meet the requirements of this performance specification.” ASTM F1506-08
 
The issue in NFPA 70E is shock.  The issue in F1506 is arc flash. Metal can conduct electricity but small snaps have little chance of doing this (not NO chance). Companies may have whatever policies they wish and some manufacturers do not offer metal snaps.  Others cover the snaps but many offer either option.  This comes back to risk.  Very few companies regulate metal belt buckles but most regulate jewelry.

 Jewelry can fall off. Conductive aprons etc. cover large areas of the body with conductive materials.  This is a matter of interpretation and our internal consensus was that snaps would not be necessarily prohibited.  We have decided to take this to a survey and report the results next month.
 
OSHA, NFPA nor ASTM have any official mentions of metal snaps so the choice is still one for the market.

 We know of no incidents where metal snaps caused an arc or shock.  In Randy Feltholder’s accident, which was a medium voltage shock, the metal rivets in his jeans conducted the electricity better and caused deeper burns in that area. So even small amounts of metal aren’t NO risk. But metal snaps will probably not cause an arc or shock if all other PPE is worn correctly and proper safe work methods are used.

 Some manufacturers cover the snaps with a plasticized dielectric covering to allow the convenience of snaps and further lessen the risk of shock.