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Hazard

Buildings that are unoccupied, derelict or awaiting demolition

Hazard Knowledge

Buildings that are unoccupied, derelict or awaiting demolition may be well-secured to prevent trespassing or unauthorised habitation, but may also restrict access and egress. Security measures to doors or window openings include:

  • Timber boarding
  • Metal security screens could be installed, and
  • Bricks or blockwork
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Figure 10: Derelict building - photograph courtesy of G. Pottenger

Although buildings should be secure, security features may not have yet been installed or may have been compromised to gain unauthorised access resulting in the presence of:

  • Children
  • Rough sleepers
  • Discarded drug paraphernalia
  • Illegal activities including the cultivation and production of illegal drugs
  • Tampered utilities and meters
  • Malicious traps
  • Illegal storage of hazardous materials, including gas cylinders
  • Fly-tipped waste, which could increase fire loading
  • Various animals, animal waste and carcasses

There may be vandalism and theft, with damage to internal and external features. This may include:

  • Pipework being removed
  • Stairs, doors and floors damaged or removed
  • Damage to electrical cabling

The removal of fire doors and other passive fire protection features may directly impact on the rate of firespread through compartments. Poor maintenance may mean that fire protection features have been removed, deactivated or may not operate. They may not detect or help reduce or control fire development.

Although buildings may appear to be unoccupied, the property owner or management company may have 'property guardians' living in the building to provide security and general maintenance.

Although the building may appear to be empty, personnel should not assume that utilities have been isolated.

The previous use of the building should be considered to assist in identifying hazards - an abattoir may present a biological hazard or a vehicle servicing premises may have inspection pits, for example. Depending on the previous use of the building, dust may have collected on surfaces such as rafters, roofs, suspended ceilings, ducts and other equipment. If the dust is disturbed, a serious explosion could occur. The build-up of even a very small amount of dust can cause serious damage.

The structure of a building will deteriorate through being left open to the elements or without maintenance. This may result in additional hazards including:

  • Weakened or unsafe elements of structure
  • Exposed utilities
  • Unguarded edges
  • Objects falling from height

When buildings are in disrepair or scheduled for demolition, systems may be made redundant or often reclaimed for salvage. Compartmentation may be compromised if salvageable items have been removed, such as piping and wiring, and possibly doors or timber floors. A demolition project may involve:

  • Asbestos removal and disposal
  • Removal of non-structural elements such as:
  • Plasterboard
  • Pipes
  • Cables
  • Doors and windows
  • Structural demolition or dismantling
  • Decommissioning of hydrants

Larger demolition sites are generally well-managed and secured. During the demolition process, materials are generally sorted on site and arranged in piles.

On smaller demolition sites, combustible materials, such as timber, may be burned on-site to reduce costs. This may result in firespread and larger fires that are left to burn uncontrolled.

Contractors may unintentionally weaken the structure of the building prior to demolition - removing floors or joists that provided restraint, for example, could result in walls being less stable. Contractors may also deliberately weaken the structure to assist in a controlled collapse. This can involve:

  • Removing masonry panels or steelwork tie bars that provided bracing to a framed structure
  • Cutting fully or partly through steelwork columns or beams
  • Drilling holes into or through concrete walls
  • Exposing and/or cutting concrete reinforcement bars

Demolition sites may contain a variety of hazards including:

  • Weakened structures
  • Specialist plant
  • Explosives
  • Dust explosion
  • Debris, rubble, sharps
  • Unmarked basements or shafts

 

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Figure 11: Demolition site showing rubble - photograph courtesy of Brian Massie

The demolition contractor may not be demolishing the whole building. Sometimes sections of buildings are removed, leaving exterior facades standing, ready for reconstruction using modern building methods.

Façade retention is a specialist area that involves installing temporary supports - often a large frame - to hold up the façade before (not after) the rest of building is taken down. Any incident involving freestanding, unsupported, tall masonry walls presents a high risk of collapse without warning.

 

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Figure 12: Building collapse during demolition at a site in Aldwych, London - photograph courtesy of London Fire Brigade

Full demolition is more commonly performed using specialist high reach equipment, such as hydraulic 'nibbling' equipment, creating ramps out of demolition rubble to enable them to reach higher up the structure. On larger sites, flammable and hazardous materials should usually be removed before demolition.

Using explosives for demolition is strictly controlled, and they should be securely stored until the time of detonation. Buildings due for explosive demolition should have been stripped out and prepared. This usually involves considerable pre-weakening that can leave a structure vulnerable to high winds or other disturbances. If pre-weakening has been carried out ready for controlled demolition, collapse could occur without warning.

Explosives are used only in small quantities and will not be brought to site until shortly before the demolition. However, in some cases placing and connecting explosive charges may take several days, during which time the demolition contractor should ensure the site is not left unattended.