IEC/TR 61292-4:2014(E) which is a technical report, applies to all commercially available optical amplifiers (OAs), including optical fibre amplifiers (OFAs) using active fibres, as well as Raman amplifiers. Semiconductor optical amplifiers (SOAs) using semiconductor gain media are also included. This technical report provides a simple informative guideline on the threshold of high optical power that causes high-temperature damage of fibre. Also discussed is optical safety for manufacturers and users of optical amplifiers by reiterating substantial parts of existing standards and agreements on eye and skin safety. It is important to point out that the reader should always refer to the latest international standards and agreements because the technologies concerned are rapidly evolving. The present technical report will be frequently reviewed and will be updated by incorporating the results of various studies related to OAs and OA-supported optical systems in a timely manner. This third edition cancels and replaces the second edition, published in 2010, and constitutes a technical revision with updates reflecting new research in the subject area. Keywords: guideline on the threshold of high optical power, maximum permissible optical power, optical amplifiers, Raman amplifiers, semiconductor optical amplifiers (SOAs)