IEC 60601-1:1988, Clause 1, applies, except as follows: Amendment (add at the end of 1.1): This International Standard includes requirements for the basic safety and essential performance of humidification systems, as defined in 3.6. This International Standard also includes requirements for individual devices specified for use in humidification systems such as heated breathing tubes (heated-wire breathing tubes) and devices intended to control these heated breathing tubes (heated breathing tube controllers). ISO 5367 specifies other safety and performance requirements for breathing tubes. NOTE Heated breathing tubes are medical electrical equipment and are subject to the requirements of IEC 60601-1. * This International Standard also includes requirements for active HME (heat and moisture exchanger) devices, which actively add heat and moisture to increase the humidity level of the gas delivered from the HME to the patient. This International Standard is not applicable to passive HMEs, which return a portion of the patient's expired moisture and heat to the respiratory tract during inspiration without adding heat and moisture. ISO 9360-1 and ISO 9360-2 specify safety and performance requirements for passive HMEs and describe methods for testing performance. Respiratory tract humidifiers can be gas-powered, electrically-powered, or both. However, this International Standard has been prepared as a Particular Standard based on IEC 60601-1, which gives general requirements for all aspects of safety, not only electrical safety, and many of the requirements are therefore applicable to humidifiers not powered by electricity. Where this International Standard specifies that a Clause of IEC 60601-1 applies, it means that the Clause applies only if the requirement is relevant to the humidification system under consideration.