Question 6 of 6: Safety Practices and Regulations — demolition with hazardous-material removal

Question 6: Safety Practices and Regulations — demolition with hazardous-material removal (20 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Before any work starts. Demolition of an existing structure is one of the few construction operations in which the principal hazards are already present on the first day, so the controlling practices are the ones adopted before mobilisation. Two surveys are mandatory in practice and in law across Canadian jurisdictions. The first is a hazardous-materials survey — a designated-substance survey in Ontario under O. Reg. 213/91, and an equivalent survey under Part 20 of the WorkSafeBC Occupational Health and Safety Regulation — performed by a qualified person, involving destructive sampling and laboratory analysis, and identifying asbestos-containing materials, lead-bearing coatings, PCB-containing ballasts and transformers, mercury, silica, mould and any process residues. The survey report must be on site and must be provided to every contractor bidding or performing the work, because a contractor cannot control a hazard it has not been told about. The second is an engineering survey of the structure by a qualified professional engineer, establishing the condition of the frame, the load paths, the sequence in which elements may be removed, and the possibility of unplanned collapse; on all but the simplest buildings the demolition procedure itself is sealed by an engineer. To these are added the notice of project filed with the regulator, utility disconnection with written confirmation and physical isolation, a written demolition and abatement work plan, and confirmation that the abatement contractor holds the licence and that its workers hold the certification the jurisdiction now requires for asbestos work.

Removing the hazardous materials first. The governing principle is the hierarchy of controls, and its first level does the most work here: eliminate the hazard by removing the asbestos and lead before the structure is demolished, rather than attempting to control the dust generated by demolishing them in place. Where removal must proceed, engineering controls come next — full containment enclosures held under negative pressure with HEPA-filtered exhaust, decontamination facilities with a three-stage airlock, wetting agents applied to friable material, glove bags for pipe insulation, shadow vacuuming at the point of generation, and local exhaust ventilation on any powered tool. Administrative controls follow: classification of each task as low, moderate or high risk with the corresponding written procedure, exclusion zones and signage, restricted access with an entry log, trained and certified workers only, prohibition of eating, drinking and smoking inside the zone, and air monitoring both inside the enclosure and at its perimeter. Respiratory protection and disposable coveralls come last, not first — they protect the individual worker if everything upstream fails, and they require a written respiratory protection programme with fit testing, cartridge selection and maintenance to be worth anything. Lead deserves specific mention because the usual demolition method makes it worse: torch cutting or abrasive blasting lead-painted steel generates a respirable fume that a dust mask will not stop, so mechanical removal, wet methods and containment are preferred, supported by biological monitoring of blood lead and by HEPA vacuuming instead of dry sweeping.

The demolition itself. Once the building is clean, the structural work is sequenced from the top down, in the reverse order of erection, with no worker permitted on a structure that has been weakened to the point of instability — which is why remote methods, high-reach machines and deliberate deconstruction have displaced pulling and undermining. The practices that matter are the removal of debris from floors before they are overloaded, protection of workers below from falling material by exclusion zones and overhead protection rather than by warning alone, temporary shoring and bracing designed by an engineer as elements are removed, monitoring of adjacent structures for vibration and settlement, and hoarding, covered walkways and traffic management to protect the public. Fall protection is required above the regulated height at every open edge and floor opening; confined-space entry procedures apply to tanks, pits and vaults, with atmospheric testing, ventilation, attendants and a rescue plan in place before entry; hot work needs a permit and a fire watch; and dust suppression is needed continuously, both for respirable crystalline silica from concrete and masonry and for general nuisance dust affecting neighbours.

Moving the waste offsite. Removal to an offsite location is a regulated activity in its own right and is where a well-run abatement is most often undone. Asbestos waste is wetted, sealed in labelled six-mil bags, double-bagged, and placed in a covered, leak-proof and lockable container; lead-bearing debris and PCB-containing equipment are segregated, containerised and labelled to their own standards. The waste is classified under the applicable provincial hazardous-waste regulation, manifested, and carried by a licensed hauler in accordance with the federal Transportation of Dangerous Goods Act with correctly placarded vehicles and trained drivers, to a receiving facility authorised to accept that waste stream. Copies of every manifest are retained and reconciled against the volumes removed, so that the chain of custody is complete from the enclosure to the landfill. Before the containment comes down and the area is released, clearance air sampling and a visual inspection are performed by an independent qualified person and a clearance certificate issued.

The management system that holds it together. None of these practices survives contact with a busy site unless somebody owns them. The prime contractor carries the statutory duty to coordinate the health and safety of every employer on the site, which on a demolition project with a separate abatement contractor is a substantive and daily task: sequencing so that abatement and demolition crews are never exposed to one another’s hazards, running a joint health and safety committee, orientating every worker to the specific hazards of the building, holding daily toolbox talks tied to the day’s work, inspecting against a written schedule, investigating incidents and near misses, maintaining an emergency response and rescue plan with the local fire service informed, and making it plain that a worker’s right to refuse unsafe work will be respected without consequence. Records — surveys, procedures, training, monitoring results, inspections, manifests and clearance certificates — are the evidence of due diligence and are the first thing a regulator asks for.