4.3 Structural Demolition Safety & Pre-Demolition Planning

4.2 Structural Demolition Safety & Pre-Demolition Planning

Structural demolition involves controlled dismantling, tearing down, or destruction of buildings, industrial facilities, bridges, and civil structures. Because demolition fundamentally alters structural load paths, DOLE OSHS Rule 1410 and DO 13-98 categorize demolition as an ultra-hazardous construction activity requiring mandatory pre-engineering planning, utility isolation, public protection, environmental controls, and rigorous sequence management.

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Pre-Demolition Engineering Survey & Hazard Assessment

Prior to commencing any demolition work or mobilizing heavy equipment, DOLE OSHS Rule 1410 mandates that a qualified professional structural engineer conduct a comprehensive structural engineering survey. The objective is to evaluate the condition of framing, floors, load-bearing walls, foundations, and adjacent structures to prevent premature or uncontrolled collapse.

Key Elements of the Engineering Survey

• Structural Assessment: Identifying load-bearing columns, post-tensioned concrete slabs, pre-stressed beams, cantilevered balconies, and modified structural components.
• Hazardous Materials Audit: Identifying asbestos-containing materials (ACM), lead-based paint, PCB transformers, mercury switches, silica, or toxic industrial chemicals. Hazardous substances must be abated by licensed specialists prior to general teardown.
• Adjacent Structure Stability: Evaluating whether shared party walls, footings, or soil embankments require underpinning or shoring during demolition.

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Utility Shutoff & Lockout/Tagout (LOTO) Verification

Uncontrolled energy sources pose fatal electrocution, explosion, and flooding risks during demolition. All electric, gas, water, steam, compressed air, and sewer utilities connected to the building must be shut off, disconnected, or sealed off at the property line.

Utility Isolation Requirements

• Written Confirmation: Demolition contractors must obtain formal written certificates of disconnection from public utility companies (e.g., electric power distributor, municipal water district, gas supplier) before breaking structural members.
• Temporary Power Safety: Temporary power lines required for demolition lighting or pumps must be independently routed, armored, and protected with Ground Fault Circuit Interrupters (GFCI).
• Lockout/Tagout (LOTO): Physical locks and warning tags must be locked onto main breakers and valves to prevent accidental re-energization.

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Demolition Execution Methodologies

Demolition must follow strict engineering rules regardless of whether manual, mechanical, or explosive techniques are used.

1. Manual Top-Down Demolition

In top-down manual demolition, workers dismantle the building level-by-level, starting from the roof and working down to the ground:

• Sequence Rule: Structural members (floors, beams, load-bearing walls) on an upper story must be completely removed before workers commence work on the floor below.
• Wall Removal Rule: Exterior walls and masonry partitions must be removed top-down. Demolishing or undermining load-bearing walls at lower levels while upper floors remain intact is strictly prohibited.
• Floor Load Limits: Demolition debris must not be accumulated on floors or scaffold platforms in quantities exceeding maximum allowable safe load limits ($kg/m^2$).

2. Mechanical Demolition

Mechanical demolition uses heavy machinery equipped with specialized attachments (high-reach hydraulic shears, concrete breakers, wrecking balls, or excavators):

• Operator Protection: Heavy equipment cabs must be equipped with Falling Object Protective Structures (FOPS) and Rollover Protective Structures (ROPS).
• Wrecking Ball Protocol: The wrecking ball weight must not exceed 50% of the crane's rated capacity or 25% of the wire rope breaking strength. Operating wrecking balls is restricted to trained crane specialists.

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Environmental Controls & Debris Management

Dust Suppression & Silica Control

Demolition generates dense respirable crystalline silica and dust. Sites must implement continuous water misting systems, wet suppression attachments on shears, and mandate N95 or P100 particulate respirators for workers.

Enclosed Debris Chutes

When dropping demolition debris and rubble from upper floors:

• Height Threshold: Any drop exceeding 6.0 meters (20 feet) in height must be conducted through a fully enclosed chute made of wood or heavy metal.
• Angle and Discharge: Chutes angled greater than 45 degrees must be entirely enclosed. The bottom discharge opening must be equipped with a mechanical gate and barricaded area to prevent debris from striking workers below.

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Public Walkway Protection & Exclusion Zones

Protection Canopies (Sidewalk Sheds)

When demolition occurs adjacent to public streets or walkways:

• Heavy-duty protective sidewalk canopies must be erected over walkways.
• Canopies must support a minimum live load of 7.3 kPa (150 lbs/ft²) and feature continuous toe-boards and catch platforms.

Demolition Exclusion Zone Radius

An exclusion zone must be established around the demolition perimeter:

• Distance Rule: Barricades and warning signs must be set at a minimum perimeter distance of 1.5 times the height ($1.5 imes H$) of the wall or structural section being demolished.
• Spotters equipped with air horns must continuously monitor the perimeter to prevent unauthorized entry.

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Pre-Demolition Checklist Table