7.4 Demolition and Dismantling: Surveys, Written Arrangements, Methods, Debris and Asbestos

Why demolition is different

New construction builds a structure whose loads and behaviour are known. Demolition works on structures that may be weakened, altered over the years, poorly documented, or under stress, such as prestressed members, cantilevers and post-tensioned slabs. Removing one element can trigger an unplanned collapse. Demolition also releases hazardous materials such as asbestos, lead paint and silica dust, and often happens next to occupied buildings and busy roads.

The law

• CDM 2024 regulation 3: "construction work" includes demolition or dismantling of a structure and the removal of the resulting products or waste.
• Regulation 22(1): the contractor must ensure that any demolition or dismantling is planned and carried out in a way that prevents danger, or where that is not practicable, reduces it to the lowest practicable level.
• Regulation 22(2): the arrangements for the demolition or dismantling must be recorded in writing before the work begins. Breaches carry up to RM500,000 or one year or both.
• Related CDM rules: regulation 21 (stability during the works, including temporary supports), regulation 23 (explosives), regulation 27 (services), and the Fourth Schedule items for explosives, chemical risks such as asbestos, and assembling or dismantling heavy prefabricated components, all of which need specific measures in the construction phase plan.
• Asbestos: controlled under USECHH 2000, where asbestos is a chemical hazardous to health listed in Schedule II for medical surveillance, and DOSH's Guidelines for Asbestos Removal 2017. Waste is controlled under the Environmental Quality (Scheduled Wastes) Regulations 2005.

DOSH's Guidelines for Public Safety and Health at Construction Sites (section 14) give practical guidance, much of it originally from BOWEC Part XI.

Before demolition: surveys and preparation

Structural survey and method

• Assess the structure. DOSH's guideline (14.1) says the method should consider the size, strength and location of the structure, and a risk assessment should identify possible causes of instability, with an action plan. The work must not affect the stability of the structure or neighbouring structures in a way that could cause an unplanned collapse.
• Engineer's method. Follow the demolition sequence and method set out by the demolition or structural engineer (14.4.1(b)). Identify cantilevers, transfer structures, prestressed or post-tensioned elements, and any need for temporary propping before work starts.
• Supervision. All demolition work should be done by trained personnel under the supervision of a designated person (14.1.5).

Hazardous materials

• Clear hazardous substances first. The structure should be free from toxic or hazardous substances, for example asbestos materials, before demolition starts (14.2.3).
• Remove loose items. Remove glass from doors and windows, loose objects, projecting parts, and explosive, flammable, toxic or harmful substances (14.2.5).
• Common hazardous materials: asbestos-cement roofing and ceiling boards, pipe lagging, lead paint, fuel tanks, chemical residues, refrigerants, and PCB-containing equipment.

Utilities

Before demolition, all utilities should be effectively disconnected or shut off at or outside the property line (14.2.1(c)). Obtain written confirmation from the utility owners. Where services must stay live, relocate or protect them. The former BOWEC regulation 100 also required gas, electric, water and steam lines to be shut off and capped, with the relevant authorities notified in advance.

Site preparation

• Fence and sign. Fence off the danger zone around the structure or post warning signs (14.2.2). Erect barricades along footpaths and roads, with lights at night.
• Scaffold netting. Where applicable, erect a metal scaffold with peripheral netting around the building (14.2.4).
• Catch platforms. For the exterior walls of structures originally more than 12.2 m high, provide catch platforms designed by a Professional Engineer, kept no more than 6 m below the storey being demolished and never used for storage or as walkways (14.3).
• Timing. Near public areas, demolish during non-peak hours (14.1.4). Stop in high wind or storms, which can collapse weakened structures (14.1.6).

Asbestos removal: DOSH Guidelines 2017

Never break, cut or crush suspected asbestos-cement sheets during general demolition. Stop and get the material assessed.

Demolition methods and sequence

General rules of sequence:

1. Soft strip first: fittings, finishes and hazardous materials out.
2. Work from the top down, generally floor by floor, so the remaining structure stays stable.
3. Prop cantilevers and balconies before removing the floors or walls that hold them back.
4. Do not let debris build up on floors. Overloaded suspended slabs collapse (CDM regulation 21(3)).
5. Inspect continuously. BOWEC regulation 103 required continuing inspection by a designated person to find weakened floors or walls and loose material, with no work allowed until such hazards were corrected. This remains good practice.

Historical mechanical demolition limits (BOWEC regulation 110)

The former regulation 110 allowed machine demolition only of structures no more than 24 m high. It also required:

• a demolition zone of at least 1.5 times the height for swinging weights or deliberate collapse
• a zone of 8 m from the line of travel for clamshell buckets
• substantial barricades, with only essential workers inside the zone

These remain useful benchmarks for exclusion zones, but today the engineer's method and the machine's reach decide.

Debris and dust

• Handle debris safely. Handle and dispose of debris in a way that does not endanger workers or the public, and do not let it accumulate into a hazard (DOSH public safety guideline 16.1 and 16.2).
• Damp down. Keep debris sufficiently moist to lay the dust (16.3 and 14.4.1(e)). Water suppression also controls silica dust (Section 10.3).
• Chutes. Where materials are dropped more than 6 m to a point outside the exterior walls, use an enclosed chute (16.4, from former BOWEC regulation 123).
• Dropping through floor holes (former BOWEC regulation 123(2)): barricade the landing area at least 1.2 m high and at least 1.8 m back from the projected edge of the opening above, post warning signs at each level, and do not allow removal below while debris is being dropped.
• Floor openings for debris: enclose floor to ceiling, or barricade so nobody can come within 6 m horizontally of an opening above (former BOWEC regulation 106).

Scenario: the shophouse balcony

A two-storey shophouse is being demolished by a small excavator. The SSS finds that:

• the rear balcony has been left cantilevered after the supporting wall was knocked out
• workers are pulling down asbestos-cement eaves boards by hand
• the gas meter is still connected

The SSS stops the work and:

1. Arranges propping of the balcony to the engineer's instruction before any further demolition.
2. Stops all work on the eaves until an asbestos assessment is done. Removal follows DOSH's 2017 guideline, including DOSH acknowledgement and enclosure or controlled wet methods as assessed, and disposal as scheduled waste.
3. Has the gas operator disconnect the supply at the property line and confirm it in writing.
4. Gets the written demolition arrangements (regulation 22(2)) revised to cover the sequence, propping, asbestos and services, and briefs the crew.