Occupational health is the identification and control of risks that comes from physical, chemical, and other hazards at the workplace. These commonly include cancers (eg mesothelioma), accidents, respiratory diseases (eg Emphysema), hearing loss, musculo-skeletal problems (eg - backache), stress related disorders and communicable diseases. It's important to establish and maintain a safe and healthy working environment and prevention of the workers from these hazards.
Occupational Health is also referred to as Occupational safety and health (OSH) or occupational health and safety (OHS) or workplace health and safety (WHS). Occupational health is important for legal, and financial reasons and most countries have laws that makes it the moral obligation of the employer to take reasonable care for the safety of their employees.