This intrinsically-safe model four-channel data logger has internal temperature and user-replaceable relative humidity sensors and two external channels that accept external temperature and DC voltage cables with passive sensors. Intrinsically Safe Rating (by US standards): IS, Class I, II, Division 1, Groups A-G, Temperature Code T4 (=135°C); NI, Class I, Division 2, Groups A-D, Temperature Code T4 (=135°C); S, Class II, Division 2, Groups F and G; as specified in the US National Electric Code and approved by Factory Mutual.