IEC 61300-2-47:2016 details a procedure for determining the suitability of a fibre optic device to withstand the effects of thermal shock. In practice, this means a very short change over time between extreme temperatures. This fourth edition cancels and replaces the third edition published in 2010. This edition constitutes a technical revision. This edition includes the following significant technical change with respect to the previous edition: review of temperature limit in the test severity. Keywords: thermal shock, extreme temperatures