Arc-rated clothing is rated in what unit?

Arc-rated clothing is rated in calories per square centimeter (Cal/cm²). This unit measures the amount of heat energy that a material can withstand without igniting or allowing thermal injury to the skin beneath it. The rating indicates the thermal protection that the garment offers against an electrical arc flash, which can produce intense heat and potentially cause severe burns.

Using Cal/cm² provides a standardized measure that helps ensure that the clothing will provide adequate protection for workers in environments where they may be exposed to electrical hazards. Since arc flash incidents can vary significantly in terms of their energy levels, having a clear rating system allows for better decision-making in selecting personal protective equipment based on specific job hazards.

Other units such as joules, kilowatts, and watts pertain to different physical properties and do not directly relate to the thermal protection capability of clothing against arc flash events, which is the critical aspect being assessed in this context.