Section 39. The maximum hours of labor of laborers, workmen and mechanics, of ward attendants, ward nurses, industrial and occupational therapists and watchmen, and of employees in kitchen, dining-room and domestic services, in state and county institutions, and of officers and instructors of state penal institutions and county penal and reformatory institutions, shall not exceed forty in each week. The foregoing provision shall not be construed as authorizing the employment of any such officer or employee whose work day and week is fixed under section thirty A or any other provision of law at less than said forty hours maximum to be employed beyond the hours so fixed and within said maximum without the payment of overtime. This section shall not prevent the superintendent, warden or executive officer from requiring the services of any person in any emergency where the health or safety of patients or inmates would otherwise be endangered, or in any extraordinary emergency, or in apprehending an escaped inmate.