There is no legal maximum temperature but a comfort range between 19ºC and 23ºC should be adequate.
Where the temperature in a workroom would otherwise be uncomfortably high (due to hot processes or the design of the building, for example) all reasonable steps should be taken to achieve a reasonably comfortable temperature. This might include insulating hot plant or pipes, providing air-cooling plant, shading windows, and sitting workstations away from places subject to radiant heat.
Where a reasonably comfortable temperature cannot be achieved throughout a workroom, local cooling should be provided. In extremely hot weather, fans and increased ventilation may be used instead of local cooling.
If, despite the provision of local cooling, workers are exposed to temperatures which don't give reasonable comfort, suitable protective clothing and rest facilities should be provided. Where practical, there should be systems of work (for example, task rotation) to ensure that the length of time for which individual workers are exposed to uncomfortable temperatures is limited.