These happen for various reasons. Perhaps equipment / machinery was faulty or a floor was wet, slippery or greasy. Maybe insufficient or no training was given, such as correct lifting of materials.
Increasingly, in this country, we are seeing a steady rise in the number of Stress Related Illness claims and many of these arise as a result of Stress at Work. In some circumstances, a compensation claim can be made if it can be proved that your employer is the cause of the stress and that the employer has been made aware of stress related problems but has not acted on the information, resulting in a deterioration of an employee's health.