The system can deal with 29 hazards summarised as follows:

• Dampness, excess cold/heat
• Pollutants e.g. asbestos, carbon monoxide, lead
• Lack of space, security or lighting, or excessive noise
• Poor hygiene, sanitation, water supply
• Accidents - falls, electric shocks, fires, burns, scalds
• Collisions, explosions, structural collapse

More detailed information about these hazards can be found in the Operating Guidance issued by the Department of Communities and Local Government:

http://www.communities.gov.uk/publications/housing/hhsrsoperatingguidance

Each hazard is assessed separately, and if judged to be 'serious', with a 'high score', is deemed to be a Category One hazard. All other hazards are called Category Two hazards.