A collapse zone is an area around a structure

Structure

Structure is a fundamental, tangible or intangible notion referring to the recognition, observation, nature, and permanence of patterns and relationships of entities. This notion may itself be an object, such as a built structure, or an attribute, such as the structure of society...

, usually a burning structure

Structure fire

A structure fire is a fire involving the structural components of various residential buildings ranging from single-family detached homes and townhouses to apartments and tower blocks, or various commercial buildings ranging from offices to shopping malls...

, that may suffer structural collapse. A collapse zone affects firefighter

Firefighter

Firefighters are rescuers extensively trained primarily to put out hazardous fires that threaten civilian populations and property, to rescue people from car incidents, collapsed and burning buildings and other such situations...

s working on the exterior of a structure.

Signs of structural failure

The first indicator of possible structural failure is the type of wall

Wall

A wall is a usually solid structure that defines and sometimes protects an area. Most commonly, a wall delineates a building and supports its superstructure, separates space in buildings into rooms, or protects or delineates a space in the open air...

. The material of the wall may provide clues, as well as the structural significance. A free-standing wall has a higher collapse risk than a non-bearing wall.

Other indicatiors include:

• smoke
  Smoke
  Smoke is a collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-product of fires , but may also be used for pest...
  
   from mortar joint
  Mortar joint
  In masonry, mortar joints are the spaces between bricks, concrete blocks, or glass blocks, that are filled with mortar or grout. Mortar joints can be made in a series of different fashions, but the most common ones are raked, grapevine, extruded, concave, V, struck, flush, weathered and beaded.In...
  
  s
• bowing walls
• other areas of structural failure

After an interior collapse, the risk of an exterior collapse, and therefore the need for a collapse zone, rises significantly.

90º angle collapse

This is the most common type of structural collapse. It is similar to a falling tree. The wall falls straight out and the top hits the ground at a distance equal to the height of the wall.

Curtain-fall collapse

This type of collapse generally occurs with a masonry wall. It collapses like a curtain

Curtain

A curtain is a piece of cloth intended to block or obscure light, or drafts, or water in the case of a shower curtain. Curtains hung over a doorway are known as portières...

 dropping from the top, creating a pile of dibris at the base of the wall.

Inward/outward collapse

A wall leaning inward may not necessarily fall inward. The lower or upper portion may slide or "kick" outward.

Establishing a collapse zone

Collapse zones are traditionally established by a commanding officer. The collapse zone itself should be as wide as the structure and as tall, plus half the height. The reason for this increase in height is that the worst-case scenario (and the most common), a 90º Angle Collapse, must be assumed. A collapse zone should be established with barricade

Barricade

Barricade, from the French barrique , is any object or structure that creates a barrier or obstacle to control, block passage or force the flow of traffic in the desired direction...

 tape

Caution tape

Caution tape is resilient plastic tape of a signal color or highly contrasting color combination .-Usage:...

 and should be enforced if necessary.

Obstacles

A collapse zone can easily limit the access of hose line

Fire hose

A fire hose is a high-pressure hose used to carry water or other fire retardant to a fire to extinguish it. Outdoors, it is attached either to a fire engine or a fire hydrant. Indoors, it can be permanently attached to a building's standpipe or plumbing system...

s. Hose lines should operate outside the zone, on the sides. A secured (and unattended) deluge nozzle can also be put into operation, with caution. An aerial apparatus may be required. In this case, the collapse zone should be considered a three-dimensional arc, and aerial ladders may not operate in that arc.