Structural Collapse
Emergency providers have become an organized faction that responds to a
large number of diverse types of emergency and non-emergency incidents. These
incidents range from responses to automobile fires to collapses of multistory
buildings. Our emergency response personnel continue to provide life saving
action in all incidents whether they are formally trained or not. Due to that type of
culture it is important for responding companies to have the needed knowledge
to safely evaluate, and establish a method to start mitigation of each type of
incident without exposing our personnel. The safety of our personnel continues
to be the highest priority of each incident. Personnel that respond to these
incidents need to be aware of hazards associated with each type of incident.
In this section you will be able to identify general principles for a
structural collapse.
Earthquakes, wind storms, floods, heavy snow, inadequate construction
techniques, explosions, rain, fire, transportation accidents, and decay due to
age affect buildings no matter where they are located across the globe.
The following program will cover what you the responder should expect to
find at these incidents; including the initial response by the local
residents, selecting strategies during initial size-up, destructive forces
expected due to the type of disaster, and the initial information that is
needed to direct incoming rescue forces. Along with discussions of the
different building designs, their weaknesses, and how the different damaging
forces will cause adverse structural loading and the resultant collapse
patterns.
Emergency responders from each community have
a different method for addressing the same problems as found elsewhere in the
nation. Communities must evaluate the probability of each type of damaging
forces that affect their location. This will help us effectively plan for
these special emergencies, and their special hazards. Protecting our personnel
and the occupants that remain in those damaged structures will be the result
of these efforts.
It is the intent of this program to train fire
department personnel to be competent at surface rescues. Surface rescues
involve minimal removal of debris and building contents to extricate easily
accessible victims.
INITIAL INFORMATION GATHERING
Information gathering techniques will be
crucial to the efficient transition of the Technical Rescue Specialist into
the incident. It is important for these incoming forces to carefully verify
information obtained from the first responders and other individuals at the
disaster site. By the time the information exchange takes place, the first
responders will probably be subjected to the following:
A many hour period of physical and emotional
draining work. Feelings that it's not possible that other victims have
survived within a badly collapsed structure.
A need to experience closure; that the
incident is over.
Feelings by
relatives/friends of the missing that they have surely survived and are
entrapped.
The information gathering must therefore,
proceed as swiftly and unemotionally as possible, while testing all current
assumptions. Information from others on structural safety issues should be
recorded, but the Search Specialist should perform his own assessment,
independently, as in any good check.
This section will discuss the following issues
that relate to developing the structural approach to a specific disaster site:
Review initial Phases: Triage, Assessment &
Marking
Building Search & Rescue Basic Plans
Hazard Reduction & Victim Access
TRIAGE CRITERIA
The following information needs to be
considered in determining risk/benefit that will aid in prioritization.
Occupancy -the type of activity done in the
building, as well as, the potential maximum number of occupants.
Structural Type -what type of materials are
involved, in order to help identify difficulty of access, type of collapse,
potential hazard mitigation needs, etc.
Collapse Mechanism -how building failed in
order to provide an indication of type of voids that might be available for
victim survival.
Time of Day -refers to the time of the event which caused the collapse.
This is a critical factor when combined with the occupancy type. For example,
if an earthquake occurs at 2100 hours and collapses an office building and an
apartment building, the apartment building would normally represent the higher
potential for a success rescue than would the office building. If the event
occurred at 1000 hours, the opposite would be true.
Prior Intelligence -information from the general public, local authorities,
first responders, etc., relating to known trapped victims.
Search and Rescue Resources Available -does the particular building
require resources beyond what is readily available to the task force (i.e.,
heavy equipment required to gain access.)
Structural Condition of the Building -generally, can search and rescue
operations proceed with a minimum of stabilization effort.
OVERVIEW OF DESTRUCTIVE FORCES
Earthquakes -cause shaking that has its greatest effect on weak, heavy
structures that are dynamically coupled with their sites.
Wind -hurricanes and tornadoes cause damage due to wind velocity, airborne
missiles, tidal surge, and difference in atmospheric pressure. Wind affects
mostly light, un-engineered buildings and structures that are penetrated,
thereby causing high uplift/blowout forces.
Floods -are normally classified as riverine flooding and coastal flooding.
Riverine flooding may be flash type, which has a rapid water rise, high
velocity , and may produce a wall of water effect. Other river flooding may be
relatively slow unconfirmed flow over a low lying broad area. Coastal flooding
is caused by severe storms that may be combined with high tides. The step up
surges of hurricanes combined with their high winds produce combined forces
from wind and flooding. The damage from flooding is caused by hydrostatic
lateral pressure/lifting, hydrodynamic forces due to velocity and wave height,
and debris impact from waterborne objects.
Snow and Heavy Rain -cause roof collapse due to overload. Most often occurs
in long span construction with relatively flat roof, where roof beam or truss
fails, leading to partial collapse, Snow build up cause more complete collapse
due to failure of vertical supporting elements.
Construction Problems -most often caused by lack of temporary lateral
bracing or inadequate vertical shoring. Failures have occurred during concrete
pours, while placing large roof beams and trusses, and during lifting of large
concrete slabs. In addition, collapse has been caused by overloads due to
stockpiling materials and non-engineered alterations.
Explosions -have been caused by natural gas build-up as well as
deliberately set bombs. Light weight wood and steel structures often have the
weakest part blown out to reduce pressure (i.e., roof or wall skins, windows)
entire roof or the wall may be blown out. Reinforced concrete structures
contain blast better, often causing greater loss of life, and if columns or
walls are badly damaged, collapse of floors can result. Precast structures are
especially vulnerable since large concrete parts can become disconnected or
blown out leading to progressive collapse.
Structural Decay -has lead to collapse of older buildings and bridges.
Collapse can be most devastating when vertical support members fail leading to
multi-floor collapse. In older buildings, the exterior unreinforced masonry
walls can be left standing full height without any bracing by pancaked floors.
Walls could later fall in on floor debris pile, or out into the street, or
adjacent buildings -very significant hazard.
Fire -Wood or metal roof/floors often collapse
due to burn through and can pull exterior masonry or concrete walls in or
leave them standing in an unbraced condition. A steel structure left standing
after a fire can have significantly reduced strength due to loss of original
heat treatment. A remaining concrete structure can be damaged due to spalling
and shearwalls and can be cracked due to expansion of floors.
Transportation Accidents -have caused
structures to collapse due to impacts and spillage of large quantities of
materials.
PHASES OF COLLAPSE RESCUE INCIDENTS
It is important for all to understand the
typical chronology of a Technical Rescue incident. The emergency response
normally occurs in the following phases;
Initial spontaneous response -unskilled,
neighbors, community response teams, and passers-by will heroically help
remove lightly trapped and/or injured victims. These rescuers have often acted
far beyond their normal skill level and often save three-fourths or more of
the total. Survival rates are relatively high, since victims are not normally
entrapped. Professional firefighters, law enforcement officers, and emergency
medical personnel may participate and better organize the response. This phase
will often end during the first night.
Planned Community Response -by trained
community response teams. Call-out and visual searches would be used to locate
and rescue the non-structurally trapped. Some lifting of objects (furniture,
bookcases, etc.) would be done as well as mitigation of hazards ( extinguish
small fires, turn off gas, observe/refer hazardous materials).
Void Space Rescue - by emergency services
rescue forces. Search elements would help prioritize site to make better risk
vs. benefit judgments. Rescue would proceed using existing cavities,
duct/plumbing shafts, basements, and/or small cut openings in easily breachable floors and walls. Some shoring might be done to protect safe haven
areas and otherwise protect emergency responders and/or victims. This phase
may start the first day , but often, not until after some organizing efforts
have taken place, requiring at least one hour.
Technical, Urban Search & Rescue -by trained
Technical Rescue Specialists, aided by equipment. Site or sites would be
re-evaluated, re-searched, and prioritized for the ten-day long effort.
Extensive cutting, shoring, etc., may be done to penetrate the structure.
Cranes may be used to remove layers of structural debris or parts of the
structure that are hazardous.
INITIAL TASKS OF FIRST IN COMPANIES
During the infancy stage of an incident, first
in companies must realize that there are many tasks that are important to be
accomplished and/or verified.
First the scene should be identified: Size- of
structure, occupancy type, (structure type and collapse mechanism, if
possible). Also a consideration should be, weather, exposures, time of day and
possible locations of victims.
Next the scene should be isolated to control
the bystanders, family and personnel. Any type of isolation materials can work
(banner tape, cones, snow fence). A consideration in isolation would be a
possible collapse zone.
Mitigate any existing hazards (gas, electric
and water).
One of the final tasks is a complete survey of all four sides plus a view of
the top and bottom if possible. During the recon stage, personnel are noting
possible entry points and verify any contact with any viable victims. This
stage is the must hazardous to first in companies, mainly due to the
overwhelming urge to assist victims in need. The. most important factor that
one must remember is that Structures are unstable or unsupported and that
secondary collapse is a high concern.
