I think the major safety standard is set by the IEC (which is International); the exact safety standard is here behind a paywall: https://webstore.iec.ch/public

I think the major safety standard is set by the IEC (which is International); the exact safety standard is here behind a paywall: https://webstore.iec.ch/publication/494 https://webstore.iec.ch/publication/494 It's heavily referenced (with embedded snippets) in this report: https://www.researchgate.net/publication/295857251_Ouch_Hot_Laptop https://www.researchgate.net/publication/295857251_Ouch_Hot_... tl;dr: 40-50c for a device with metallic chassis. 60-70c for device with plastic chassis (I can't be sure what the precise recommendation is as I see 40c referenced but 50c also referenced in other parts, depending on contact period etc;)