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8 Metal enclosure and metal components of the enclosure 8.1 Material composition The material of the enclosure or its components shall be specified in the documents required in Chapter 24. Note 1: This document does not require testing to verify the chemical composition of the materials. Note 2: The paint or coating applied to the metal enclosure is a non-metallic part of the enclosure, and the requirements of 7.4 apply. Note 3: Zinc and zinc alloys containing 80% or more zinc are prone to rapid deterioration (especially in terms of tensile strength), particularly in warm and humid air. Zinc is also considered to be more reactive than other metals; some explosion-proof specifications prohibit the use of zinc in enclosures. 8.2 Manufacturing of Class I equipment: For the casing materials of Class I EPL Ma or Mb equipment, the total content (by mass percentage) shall not exceed: 15% for aluminum, magnesium, titanium, and zirconium, with magnesium, titanium, and zirconium each accounting for no more than 7.5%. These requirements do not apply to Class I portable measuring equipment; such equipment shall be marked with the symbol “X” as specified in 29.3e), and special precautions for storage, transportation, and use shall be indicated under the conditions of special use. 8.3 For the manufacture of Class II equipment, the total content (by mass fraction) of the materials used for the enclosures of such equipment, intended for different levels of equipment protection, shall not exceed: —— For EPL Ga: 10% aluminum, magnesium, titanium, and zirconium, with magnesium, titanium, and zirconium each accounting for no more than 7.5%; —— For EPL Gb: 7.5% magnesium, titanium, and zirconium; —— For EPL Gc: No other requirements apply, except that fans, fan covers, and ventilation grille baffles must meet the requirements of EPL Gb. If the material composition limits for EPL Ga or Gb-class equipment as specified above are exceeded, the equipment shall be marked with an “X” in accordance with clause 29.3e). The special conditions of use must contain sufficient information to enable users to determine whether the equipment is suitable for use under specific conditions; for example, to prevent any risk of ignition caused by impact or friction. 8.4 Class III equipment manufacturing: The total content (mass fraction) of materials used for manufacturing Class III equipment enclosures intended for different levels of equipment protection shall not exceed: — For EPL Da: 7.5% magnesium, titanium, and zirconium; — For EPL Db: 7.5% magnesium, titanium, and zirconium; — For EPL Dc: Apart from fans, fan covers, and ventilation hole shields, which must meet the requirements of EPL Db, there are no other requirements. If the material composition limits for the EPL Da or Db class devices mentioned above are exceeded, the device shall be marked with an “X” in accordance with requirement 29.3e), and the special operating conditions shall contain sufficient information to enable the user to determine whether the device is suitable for use under specific conditions, such as to prevent the risk of ignition caused by impact or friction. 8.5 If copper alloys are to be used in environments containing acetylene, the enclosures of equipment and those of Ex components intended for external installation, when made of copper or copper alloys, shall meet the following requirements: — zinc plating, nickel plating, or other coatings ； Or – the maximum copper content in the alloy shall not exceed 65%. The cable entry devices, closures, threaded pipe fittings, and insulating sleeves specified in Appendix A shall not be considered as enclosure surfaces requiring coating or copper content limitations.