Aerial Capture for a Decommissioning or Demolition Scope

Decommissioning and demolition work gets flown less often than it should, and almost always later than it should. The pattern is familiar: somebody thinks of aerial capture once the contractor is already on site and the first building is partly down, by which point the most valuable capture in the whole sequence is no longer available.

Whether it is a plant or facility being decommissioned, a grain elevator or set of farm buildings coming down, a commercial building being cleared for redevelopment or an industrial site being taken back to bare ground, the aerial work splits into three distinct captures with three different purposes, three different deliverables and three different deadlines.

The pre-demolition record, which has a closing window

This is the capture that matters most and the one most often skipped. Before anything is disconnected or pulled down, a capture establishes what was there, where it was, and what condition it was in on a stated date. After demolition, that record is whatever was captured and nothing else.

What it is actually used for, later:

• As-was documentation. Building footprints, structure locations and heights, yard layout, surfacing extents, tank and vessel locations, pipe racks and overhead runs, measured rather than described.
• The pre-existing condition baseline. Demolition generates claims about damage, to neighbouring property, to surfacing, to fencing, to adjacent structures and to the ground. A dated capture of the condition before mobilisation settles most of them without a conversation.
• The quantity starting point, because the volume and area of what is going to come down is the basis for the disposal estimate.
• Salvage identification. What is up high, how much of it there is, and whether it is worth recovering, visible at a resolution that does not require anybody to climb.
• The institutional record. For a site that is being closed, this is frequently the last complete record the organisation will ever hold of a facility that operated for decades.
• Inaccessible detail. Roofs, stack and flare tips, upper structure and areas already fenced off as unsafe, captured without putting anybody on them.

The deadline is mobilisation, not demolition start. Fencing, laydown areas, equipment staging and site preparation all change the yard before the first structure is touched.

Quantities for disposal and salvage, during

Demolition quantities are a volume problem with a complication that catches people out. The in-place volume of a structure and the volume of debris it becomes are different numbers, because material bulks up when it is broken. Concrete, masonry and mixed rubble all occupy substantially more space loose than they did in place.

What that means practically:

• Measure what actually exists. A capture of the debris stockpiles and the cleared areas gives a volume of loose material as it sits, which is the thing being hauled. That is a straightforward and defensible measurement.
• The conversion to tonnes or truck loads is somebody else's number. It needs a density and a swell factor appropriate to the material, and whoever owns that assumption should own it in writing. A survey that quietly applies a factor and reports tonnes is inviting an argument later.
• Segregate by material if the stream matters. Concrete, steel, wood, mixed waste and soil all have different disposal routes and costs. Separate piles get separate volumes, and that means separate boundary polygons agreed at the start.
• Capture on a cadence that matches haul-off. Debris leaves the site progressively, so a single capture at the end measures whatever is left rather than what was generated. If the total matters, the captures have to bracket the haul-off.
• Expect to measure piles that are being worked. This is exactly the active pile problem, with the usual consequences for equipment on the pile and for the toe. The conventions that make a working pile defensible apply directly.

Progress capture during demolition also does the same job it does on any construction site, which is establishing sequence and site condition on dated intervals. On a demolition that is often more valuable than on a build, because the work is inherently destructive and disputes about what was damaged when are common.

The post-demolition surface, which is usually missed

When demolition finishes, the contractor demobilises and the file closes. The next scope, whether that is reclamation, a redevelopment design, a sale or a regulatory closure submission, then needs to know what the ground looks like, and nobody has a surface of it.

That capture is cheap at the time and awkward later, because the site changes: fill gets placed, vegetation comes in, the surface weathers, and somebody drives on it. What the post-demolition capture provides:

• A bare-ground surface in a stated coordinate system and vertical datum, which is the starting surface for any earthworks design that follows.
• Remaining features located, meaning slabs left in place, exposed foundations, remaining surfacing, stockpiles and any structure retained.
• Grades and drainage as left, which decides whether water now ponds somewhere it did not before. On a flat Alberta site this is a recurring and expensive surprise.
• A completion record showing the site as handed over, which is what closes out the demolition contract and what a later reclamation or closure file refers back to.
• Volumes of imported or remaining material, relative to the pre-demolition surface, which is how backfill quantities get reconciled.

For a site heading towards a reclamation certificate, this capture is the surface the whole subsequent programme is measured against, and it pairs with the documentation discussed in reclamation certificate and site closure support.

What aerial capture does not cover on this work

The gaps are significant and worth stating plainly, because a demolition scope that relies on a flight for the wrong things will be an expensive one:

• Everything below grade. Foundations, basements, slabs, buried tanks, piping, cabling and historical fill are invisible to any aerial sensor. These are the usual source of cost overrun on demolition, and they need records, geophysics or test pits.
• Hazardous materials. Asbestos, lead paint, PCB-containing equipment, mercury and the rest are identified by a hands-on designated substance survey before work starts. No flight contributes to that, and the survey is a legal prerequisite rather than a nice-to-have.
• Structural condition and stability. A capture shows what a structure looks like. It does not tell a demolition engineer whether a wall is safe to work beside or how a frame will behave as it is cut.
• Interiors. Unless a collision-tolerant internal flight is specifically scoped, and even then the result is a visual and dimensional record rather than a survey.
• Anything under the debris. A pile hides the ground it sits on, so a surface under a stockpile has to be captured before the pile exists or after it is gone.

Scheduling it against the contractor's programme

The one practical point that decides whether any of this happens: the capture dates are set by the demolition sequence, not by a survey calendar. Three dates need to be in the programme before the contractor mobilises.

• Before mobilisation, for the as-was record and the pre-existing condition baseline. This is the hard deadline.
• At intervals matched to haul-off, for debris quantities and progress. Agreed with the contractor so the yard is in a flyable state.
• After final clearance and before anybody demobilises, for the completion surface. Booked in advance, because the window is short and nobody is thinking about survey at that point.

Weather applies to all three, which is the argument for booking each one with slack rather than on the last available day. On an Alberta site, winter adds the complication that snow cover sits on top of a surface and reads as ground, so a completion surface captured under snow is not the bare ground anybody wanted.