You may be getting requests from employees to work outside, and, of course, if you are in the business of roadside repairs then it may be necessary.
Exposure to sun can lead to sunburn, blistering, skin ageing and of course, the potential for skin cancer. Apparently there are 50,000 new cases of skin cancer every year.
Ideally employers should not permit work in the heat of the day unless the employee is wearing clothing to minimise exposure (sleeves, wide hats etc). Preferably work should be undertaken at the cooler times of day.
Working in heat also can lead to dehydration. Employers should provide sufficient cool water.