Under common law what are an employer's health and safety duties to its employees?

At common law, which creates a civil liability, an employer is under a duty to take reasonable care for the health and safety of its employees, with this duty covering both physical and mental injuries. The employer must take positive steps to ensure the safety of its employees in the light of the knowledge that it either has or ought to have. As the duty is owed to individual employees, circumstances that make any employee more vulnerable to injury must be taken into consideration in caring for that employee.