ASTM F1506 has NO prescription forbidding metal snaps or zippers.
It states in 6.1 that, “closures used in garment construction shall not contribute to the severity of injuries to the wearer in the event of a momentary electric arc and related thermal exposure.”
In 6.1.2, it requires covering “fasteners or closures, for example, zippers, snaps, or buttons, or a combination thereof, …[if] used in a manner in which they are in contact with the skin”
NFPA 70E (and CSA Z462) is also vague, but many read the requirement in 130.4 (D) prohibiting “any conductive object” from crossing the “restricted approach boundary” to forbid metal of any form in clothing. Logically, though, tools and many other items which are used in an electrical work situation and contain metal (including meter probes) cross this boundary. This section in NFPA 70E is not meant to address clothing but some opinions differ.
However, in 130.6(D) Conductive Articles Being Worn, clothing IS addressed with the following:
“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 within the restricted approach boundary or where they present an electrical contact hazard with exposed energized electrical conductors or circuit parts.” Battery work has a similar prohibition in 320.3 (A)(3) .
Noticeably, snaps and zippers are NOT mentioned. The items mentioned either can fall off of the worker, presumably CAUSING an arc flash, or are represented on a large area of the body with the same outcome. To get a little better understanding of the committee intent, we can look at other conductive materials in 130.6(E) Conductive Materials, Tools, and Equipment Being Handled. There it states that they “shall be handled in a manner that prevents accidental contact with energized electrical conductors or circuit part,” and that they do not cross the “restricted approach boundary”
Metal zippers and metal snaps are much more reliable on average, so for the minimal risk of entering a snap or a zipper into the restricted boundary, most companies do not have issues with metal zippers. Metal zippers with flame resistant, non-melting tapes are less likely to fail in an arc flash and WILL NOT fuse (fusing makes removal of the garment difficult). We have seen a few ignitions and fusing of zippers that are non-metal. Other hazards must also be taken into account. Brass zippers are non-sparking and do not cause static electricity in situations with flammable dusts or vapors, so they are most common in NFPA 2112 garments.
Many people have raised the point on the long version of the Randy Fellhoelter video, where he shows that he received worse burns under the rivets in his denim jeans. This can occur in a contact situation with higher voltages. Arc flash is very unlikely to cause worse burns under a metal rivet. The issue with metal is contact.
So a garment may contain snaps which are metal (and thus more reliable) but companies may prohibit them.
Image from alcalas.com