I am not an expert at this, but surely a steel refinery is much hotter, so it may depend on the industry. Do employers have to take reasonable step, as in install air con, proper ventilation so that the environment is better to work in, which probably makes people more productive anyway.
@zleap @br00t4c
There's no official maximum working temperature here in Britain either; but the employers are expected to manage the temperature. I suspect the real problem with the USA fast food places is the pace of work and lack of enforcement of what regulations exist (as unlike a steelworks they tend to hire younger, less skilled and non unionised staff)
https://www.hse.gov.uk/temperature/employer/managing.htm