Firms are being urged to relax workplace dress codes to help staff cope with the heatwave.
Temperatures have soared across Birmingham and throughout the West Midlands in recent days.
Very warm or hot conditions will affect much of the region on Monday with higher than normal temperatures expected through to the end of the working week.
Temperatures are unlikely to drop below the high 20s until Thursday at the earliest.
The heat could spark heavy thunderstorms later this week and it will begin to feel very humid.
Amid the soaring temperatures and stifling heat, the TUC has suggested that any outside work is done in the morning or afternoon to avoid the searing heat of the mid-day sun.
The union organisation again called for a change in the law to introduce a maximum indoor temperature, with employers obliged to adopt cooling measures when a workplace temperature reaches 24C. © Provided by Trinity Mirror Plc
Health warning as temperatures hover around 30C for second successive day
Companies should supply workers with cool drinks and allow them to take regular breaks, said the TUC.
General secretary Frances O'Grady said: "While many of us will welcome the sunshine and warm temperatures this week, working in sweltering conditions can be unbearable and dangerous.
"Employers can give their staff a break by relaxing dress code rules temporarily and ensuring staff doing outside work are protected.
"Obviously shorts and flip flops won't be the right attire for all workers, but no-one should be made to suffer unnecessarily in the heat for the sake of appearances."
How hot does it have to get before you can get a day off work?
The Workplace (Health, Safety and Welfare) Regulations 1992 lay down particular requirements for most aspects of the working environment. Regulation 7 deals specifically with the temperature in indoor workplaces and states that:
'During working hours, the temperature in all workplaces inside buildings shall be reasonable.'
The definition of reasonable is obviously quite ambigious.
The law does say that if enough employees are complaining about thermal discomfort then it's the employers responsibility to act on that.
Thermal comfort 'describes a person's state of mind in terms of whether they feel too hot or too cold'.
- Environmental factors (such as humidity and sources of heat in the workplace) combine with personal factors (ie your clothing) and work-related factors (how physically demanding your work is) to influence your 'thermal comfort'.
- Thermal comfort is very difficult to define as you need to take into account a range of environmental, work-related and personal factors when deciding what makes a comfortable workplace temperature.
- The best that you can realistically hope to achieve is a thermal environment that satisfies the majority of people in the workplace. Thermal comfort is not measured by room temperature, but by the number of employees complaining of thermal discomfort. To better understand why room temperature alone is not a valid indicator of thermal comfort.
A Health and Safety Executive spokesman said: "As an employer you should be aware of these risks and make sure the underlying reasons for these unsafe behaviours are understood and actively discouraged and/or prevented."
Guidance only states that you can change your behaviour if you're in danger of overheating.
This can include choice of clothing and the amount of physical work we undertake.