Construction Safety - What is Demolition? What Are the Methods of Demolition? What are the Hazards and Control Measures in Demolition Work?

Demolition Safety: Essential Practices for High-Risk Work 

Demolition work isn't just construction in reverse—it's a specialized field with unique hazards that require careful planning and execution. Unlike construction, demolition teams face unknown factors: modifications made to the original structure, hidden materials, and uncertain structural integrity. These unknowns make demolition particularly dangerous. 
Common Accident Causes in Demolition

• Falls from heights and through openings

• Being struck by falling or flying objects

• Sudden structural collapse

• Electrical hazards

• Collisions with mobile equipment

• Fires

• Insecure materials

• Improper use of equipment on elevated surfaces

• Cutting equipment injuries

• Transport accidents from overloaded vehicles

Demolition work involves construction hazards plus additional dangers due to:

• Unknown modifications to the original structure
• Hidden materials (lead, asbestos, silica, chemicals)
• Unknown structural strengths/weaknesses
• Hazards from demolition methods themselves

Essential Safety Approach for Demolition - Plan, Provide, Train

PLAN ahead:

• Engineering survey by competent person
• Locate and secure utilities 
• Fire prevention and evacuation planning
• First aid and emergency medical services
• Health hazard assessment

PROVIDE proper protection:

• Personal Protective Equipment (PPE): eye, face, head, hand, foot protection
• Respiratory and hearing protection
• Personal Fall Arrest Systems
• Specialized protective clothing

TRAIN employees:

• Recognition and avoidance of hazards
• Safety training in understandable language

Common Demolition Methods

1. Hand Demolition:
   • Slow but controlled
   • Uses hand tools with possible crane assistance
   • Safety requirements: safe access, one story at a time, regular debris removal, fall protection
2. Ball and Crane:
   • Effective for multi-story structures with structural damage
   • Requires skilled operators and robust machines
   • Key safety points: boom angle under 60°, proper ball attachment, hourly inspections
3. Pusher Arm:
   • Uses hydraulic excavators with attachments
   • Good for masonry structures
   • Requires secure site, trained operators, and controlled debris buildup
4. Deliberate Collapse:
   • Requires engineering expertise
   • Suitable for isolated structures (bridges, silos, chimneys)
   • Demands careful planning, clear communication, and extensive safety zones
5. Wire Rope Pulling:
   • Form of controlled collapse using cables pulled by tractors/winches
   • Good for detached buildings with surrounding space
   • Requires proper rope sizing, secure anchoring, and operator protection
6. Explosion/Implosion:
   • Effective for reducing demolition time
   • Requires explosive experts, engineering consultation, and regulatory approvals
   • Extensive safety planning including public notifications and safe distances
7. Grapples and Shears:
   • Reduces fire risk and noise
   • Used for cutting concrete and metal
   • Requires avoiding equipment overloading
8. High-Reach Excavators:
   • For controlled deconstruction of tall structures
   • Requires specially trained operators, ROPS/FOPS protection, daily inspections
   • Must maintain stable platforms and proper working radius
9. Underwater Demolition:
• Requires certified construction divers
• Specific electrical safety protocols
• Proper gas management for confined spaces

Pre-Stressed Concrete Demolition: Key Safety Warnings

Demolishing pre-stressed concrete is inherently dangerous. Here's a breakdown of the critical points:

• Expert Engineering is a Must:
  • Always consult a qualified, registered engineer for any pre-stressed concrete demolition.
• Reverse Order Dismantling is Preferred:
  • The safest approach is typically to dismantle the structure in the reverse order of its construction.
• Complex Structures Demand Extra Caution:
  • Pay special attention to continuous, cantilevered, suspended, progressively stressed, pre-cast, and specialized structures like shells and tanks.
• Component Handling is Critical:
  • Pre-stressed components, like long beams, can become unstable if tipped. Support them only near their ends.
• Avoid Uncontrolled Methods:
  • Methods like balling or concrete breakers are generally unsuitable due to the risk of uncontrolled collapse and sudden release of stressed steel.
• Hidden Hazards Exist:
  • Ducts for post-tensioned tendons may be blocked, creating additional hazards. Verify the location of cables and ducts before starting.
• Potential for Explosive Release:
  • The pre stressing steel is under extreme tension, and if cut or released incorrectly the concrete can shatter explosively.

Following guidelines outlines several control measures to manage hazards in demolition work:

1. Proper Planning: ​

   • Conduct an engineering survey by a competent person to assess the structure's condition and potential for unplanned collapse. ​
   • Secure or relocate nearby utilities. ​
   • Develop fire prevention and evacuation plans. ​
   • Ensure first aid and emergency medical services are available. ​
   • Assess health hazards before starting demolition work. ​

2. Personal Protective Equipment (PPE): ​

   • Determine necessary PPE, including eye, face, head, hand, foot, respiratory, and hearing protection, as well as Personal Fall Arrest Systems (PFAS). ​
   • Train employees on the selection, use, fitting, inspection, maintenance, and storage of PPE. ​

3. Training: ​

   • Train all employees on hazard recognition and safe equipment use. ​
   • Ensure training complies with Occupational Safety and Health legal requirements and is provided in a language and vocabulary workers understand. ​

4. Safety Precautions: ​

   • Ensure safe access and egress, using scaffolds or machine-lifted platforms if necessary. ​
   • Demolish structures in a controlled sequence, typically from the top down. ​
   • Regularly remove debris to prevent overloading floors and potential collapses. ​
   • Implement fall protection measures, such as guardrails or safety harnesses, where necessary. ​
   • Secure the site to prevent unauthorized entry. ​

5. Specific Demolition Methods:

   • Follow guidelines and precautions for each demolition method, such as manual demolition, wrecking ball, pusher arm, deliberate collapse, wire rope pulling, explosion/implosion, grapples and shears, high-reach excavators, and underwater demolition. ​
   • Ensure methods are suitable for the structure and site conditions, and that operators are trained and competent. ​

6. Environmental and Public Safety:

   • Consider environmental effects, such as vibration, dust, and debris spread. ​
   • Keep the public at a safe distance and manage traffic and pedestrian control. ​

By implementing these control measures, hazards in demolition work can be effectively managed to ensure the safety of workers and the public. 

EHSHUB Channel Link: 

https://youtu.be/zMCtIdkeJ6U

Reference: 

Book by Sahyadri college of Fire Engineering and safety Management , Nashik  ​

NSO Notes