IEC 60079-11:2011 specifies the construction and testing of intrinsically safe apparatus intended for use in an explosive atmosphere and for associated apparatus, which is intended for connection to intrinsically safe circuits which enter such atmospheres. This type of protection is applicable to electrical equipment in which the electrical circuits themselves are incapable of causing an explosion in the surrounding explosive atmospheres. This standard is also applicable to electrical equipment or parts of electrical equipment located outside the explosive atmosphere or protected by another Type of Protection listed in IEC 60079-0, where the intrinsic safety of the electrical circuits in the explosive atmosphere may depend upon the design and construction of such electrical equipment or parts of such electrical equipment. The electrical circuits exposed to the explosive atmosphere are evaluated for use in such an atmosphere by applying this standard. The requirements for intrinsically safe systems are provided in IEC 60079-25. This standard supplements and modifies the general requirements of IEC 60079-0, except as indicated in Table 1. Where a requirement of this standard conflicts with a requirement of IEC 60079-0, the requirements of this standard shall take precedence. This sixth edition cancels and replaces the fifth edition of IEC 60079-11 published in 2006, the first edition of IEC 61241-11 published in 2005, and partially replaces the second edition of IEC 60079-27 published in 2008 and constitutes a full technical revision. The significant changes with respect to the previous edition are listed below: - Inclusion of non-edition specific references to IEC 60079-0. - The merging of the apparatus requirements for FISCO from IEC 60079-27. - The merging of the requirements for combustible dust atmospheres from IEC 61241-11. - Clarification of the requirements for accessories connected to intrinsically safe apparatus; such as chargers and data loggers. - Addition of new test requirements for opto-isolators. - Introduction of Annex H about ignition testing of semiconductor limiting power supply circuits. The contents of the corrigendum of January 2012 have been included in this copy.