The Standard Horizon HX400IS is an Intrinsically Safe Radio. Intrinsically Safe Radios are certified by UL Laboratories for safe use in hazardous environments. Specifically, the Standard Horizon HX400IS meets the requirements of ANSI/UL 913 5th Edition for Class I, II, III Division 1, Groups C, D, E, F, G, T3 for hazardous locations. Select Standard Horizon have been certified to be used with the Standard Horizon HX400IS in hazardous environments. All accessories in this category are certified to use with your Standard Horizon HX400IS.