This part of ISO/IEC 80079 covers the technical requirements necessary to avoid or minimize the significant hazards listed in Clause 4, which could occur during normal operation, maintenance or foreseeable malfunction of reciprocating internal combustion engines intended for use in explosive atmospheres including - Group I EPL Mb for use in underground workings susceptible to firedamp and/or combustible dust, - Group II EPL Gb and Gc for use in potentially explosive atmospheres of flammable gas and vapour and - Group III EPL Db and Dc for use in potentially explosive atmospheres of combustible dust. This part of ISO/IEC 80079 includes those tests of the engine and its ancillary devices that are required to verify compliance. This part of ISO/IEC 80079 applies to reciprocating internal combustion engines with compression ignition and spark ignition. This part of ISO/IEC 80079 does not define requirements relating to the driven machinery and equipment. This part of ISO/IEC 80079 does not apply - to flammable gas and vapour atmospheres containing carbon disulphide (CS2) and/or ethylene oxide (C2H4O) due to special properties of these gases; - to explosive mixtures of vapours and gases, which tend to self-decompose (e.g. acetylene) or which are chemically unstable.This International standard does not apply to engines used in areas for the processing manufacture or storage of explosives; - to gasoline engines and all other liquid injection spark ignited engines. This part of ISO/IEC 80079 solely deals with explosion protection requirements. Requirements on emissions are not covered by this standard. General safety requirements are not included in this International Standard. NOTE 1 General safety requirements i.e. those common to internal combustion engines, are covered for the EU in EN 1679-1:1998+A1:2011. This part of ISO/IEC 80079 does not specify requirements for safety, other than those directly related to the risk of ignition which may then lead to an explosion.The standard atmospheric conditions (relating to the explosion characteristics of the atmosphere) under which it may be assumed that engine can be operated are: - temperature -20 °C to +40 °C; - pressure 80 kPa (0,8 bar) to 110 kPa (1,1 bar); and - air with normal oxygen content, typically 21 % v/v. Such atmospheres can also exist inside the engine. In addition, the external atmosphere can be drawn inside the engine by natural breathing produced as a result of fluctuations in the engine's internal operating pressure, and/or temperature. NOTE 2 It is considered that −20 °C to +40 °C is appropriate for most engines. However for equipment designed for outside this range IEC/TS 60079-43 should be considered. NOTE 3 The requirements of this standard can also be helpful for the design, construction, testing and marking of engine intended for use in atmospheres outside the validity range stated above. In this case however, the ignition hazard assessment, ignition protection provided, additional testing (if necessary), manufacturer’s technical documentation and instructions to the user, should clearly demonstrate and indicate the engine's suitability for the conditions it may encounter. It should also be recognized that changes in temperature and pressure can have a significant influence on characteristics of the explosive atmosphere, such as ignitability (see Annex I). NOTE 4 Reciprocating internal combustion engines are not considered as pressure vessels.