Class I may refer to: Class I antiarrhythmic Class I electrical appliance, a device constructed according to electrical grounding specifications in the IEC 60536-2 standard Class I bacteriocin, a type of toxin produced by some bacteria Class I biosafety cabinet Class I laser, a type of eye-safe laser defined in the ANSI Z136 standard Class I rail carrier, a type of major freight railroad company in Canada Class I railroad, a type of major freight railroad company in the United States See also Class 1 (disambiguation) I class (disambiguation)