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Special Structures Demolition

Workers demolish 175-ft exhaust stack at the Hanford Site.

Inspection and Planning

OSHA’s Technical Manual (OTM) Section V: Chapter 1 designates the following as special structures:

  • chimneys
  • stacks
  • silos
  • cooling towers
Watch this video showing the demolition of three towers and a chimney at the Richborough Power Station.
(Click to play video)

When preparing to demolish any chimney, stack, silo, or cooling tower, the first step must be a careful, detailed inspection of the structure by an experienced person. If possible, architectural/engineering drawings should be consulted. Particular attention should be paid to the condition of the chimney or stack.

  • Workers should be on the lookout for any structural defects such as weak or acid-laden mortar joints, and any cracks or openings.
  • The interior brickwork in some sections of industrial chimney shafts can be extremely weak.
  • If a stack has been banded with steel straps, these bands must be removed only as the work progresses from the top down. Sectioning of the chimney by water should be considered.

Safe Work Practices

See what happens to a scaffold on a windy day in March 2015 in Portland Oregon, USA.
(Click to play video)
  • When hand demolition is required, it should be carried out from a working platform.
  • Experienced personnel must install a self-supporting tubular scaffold, suspended platform, or knee-braced scaffolding around the chimney. Particular attention should be paid to the design, support, and tie-in (braces) of the scaffold.
  • A competent person should be present at all times during the erection of the scaffold.
  • It is essential that there be adequate working clearance between the chimney and the work platform.
  • Access to the top of the scaffold should be provided by means of portable walkways.
  • The platforms should be decked solid and the area from the work platform to the wall should be bridged with a minimum of two-inch thick lumber.
  • A back rail 42 inches above the platform, with a midrail covered with canvas or mesh, should be installed around the perimeter of the platform to prevent injury to workers below. Debris netting may be installed below the platform.
  • When working on the work platform, all personnel should wear hard hats, long-sleeve shirts, eye and face protection (such as goggles and face shields), respirators, and safety belts, as required.
  • Care should be taken to assign the proper number of workers to the task. Too many people on a small work platform can lead to accidents.
  • An alternative to the use of a self-supporting tubular steel scaffold is to "climb" the structure with a creeping bracket scaffold. A competent person should inspect the masonry and decide about the safety of this alternative. The masonry of the chimney must be in good enough condition to support the bracket scaffold.
  • Rope off or barricade the area around the chimney. Post appropriate warning signs and do not permit unauthorized entry.
  • Keep a worker (i.e., a supervisor, operating engineer, another worker, or a "safety person") on the ground to communicate with workers above.
  • Pay attention to weather conditions when working on a chimney. Do not work during inclement weather such as during lightning or high wind situations.
  • Wet down the work site as needed to control dust.
  • Excess canvas or plywood attachments can form a wind-sail that could collapse the scaffold.

Demolition by Deliberate Collapse

Collapse of buildings and special structures don’t always go as planned.

Another method of demolishing a building, chimney or stack is by deliberate collapse. Deliberate collapse requires extensive planning and experienced personnel, and should be used only when conditions are favorable.

  • There must be a clear space for the fall of the structure of at least 45 degrees on each side of the intended fall line and 1½ times the total height of the chimney.
  • Considerable vibration may be set up when the chimney falls, so there should be no sewers or underground services on the line of the fall.
  • Post lookouts on the site and arrange for warning signals.
  • Keep the public and other workers at the job site well back from the fall area.
Check out this short GoPro video on building demolition.

Using Explosives

The use of explosives is one way of setting off deliberate collapse. This type of demolition should be undertaken only by qualified persons.

  • The entire work area must be cleared of non-essential personnel before any explosives are placed.
  • Though the use of explosives is a convenient method of bringing down a chimney or stack, there is a considerable amount of vibration produced, and caution should be taken if there is any likelihood of damage.


Before beginning this quiz, we highly recommend you review the module material. This quiz is designed to allow you to self-check your comprehension of the module content, but only focuses on key concepts and ideas.

Read each question carefully. Select the best answer, even if more than one answer seems possible. When done, click on the "Get Quiz Answers" button. If you do not answer all the questions, you will receive an error message.

Good luck!

1. When preparing to demolish any chimney, stack, silo, or cooling tower, the first step must be _____.

2. When demolishing chimneys, it is very important to be on the lookout for structural defects because _____.

3. When demolishing chimneys special structures how high should scaffold back rails be?

4. When performing deliberate collapse of special structures, be sure to clear space for the fall of the structure at least _____ on each side of the intended fall.

5. When performing deliberate collapse of chimneys or stacks, how long should the intended fall line be?

Have a great day!

Important! You will receive an "error" message unless all questions are answered.