An appropriate understanding of structure design and construction materials is required to assess and monitor an unstable or collapsed structure. This will include identifying:

• Age, design and condition of the structure
• Structural materials and construction methods

Further information in relation to building construction can be found in Fires in buildings - Building Research Establishment supplementary information

All aspects of the structure, the actions taken, and the efforts made to distribute applied loads should be considered. An assessment of the unstable or collapsed structure should be made to determine the hazard area and, because of risks such as secondary collapse or falling debris, it should be monitored while personnel are working within the hazard area.

An unstable or collapsed structure should be assessed at the earliest opportunity, including its potential impact on surrounding structures and infrastructure. Although the initial assessment can be carried out by first responders, it may be necessary to seek specialist advice. It may be beneficial to appoint an external safety officer to monitor the stability of the structure.

Specialist advice and monitoring may be available from local authority building control teams, structural engineers or urban search and rescue (USAR) tactical advisers.

Signs of collapse may include:

• Cracks in walls
• Sagging floors or floors deflecting from wall
• Displaced columns
• Dropping arches
• Bulging walls
• Buckling columns or beams
• Unusual noises coming from the structure

The minimum number of personnel should be committed to the hazard area, especially if assessment or monitoring indicates the potential for further collapse. Emergency arrangements should also be in place, which can be initiated if required.

If safe routes are identified they should be marked, and exposed elements or other hazards should be marked or clear.