Running a Debris Chute Down a Building

The pallet arrives before the design does

A chute turns up as a pallet. Two dozen cones nested inside each other, a top hopper in halves, a coil of chain, a bag of shackles, and the installation manual in a polythene wallet cable-tied to the last cone. That wallet is the only document on the pallet worth anything, and it is the one most likely to be under a boot by Wednesday. Everything a supervisor is about to be asked — how far apart the brackets go, how many sections one bracket may carry, what the chain is rated at, what happens below freezing — is printed in it, and nowhere else.

It matters that the wallet is the only source, because the obvious place to look has nothing to give you. OSHA 29 CFR 1926.852 governs chutes in United States demolition work, and paragraph (g) states the requirement plainly: a chute must be designed and constructed of such strength as to eliminate failure due to impact of the materials loaded into it. That is a performance standard. It does not publish a spacing table, a bracket schedule or a load formula, and OSHA's own standard interpretation says as much. British practice puts the same obligation in a different place — BS 6187, Code of practice for full and partial demolition, with the procedural side under BS 5975 for temporary works — and it also stops short of telling you how far apart to bracket somebody else's product. The manufacturer is the authority because nobody else is.

So the first job on a chute is not rigging. It is reading, and then measuring. Eight floors is not the run length. The run is the path the chute actually travels: from the lip of the hopper on the top floor, down past every slab edge, around whatever offset the balcony or the string course forces, to the mouth over the container. On a building with a set-back at level four that path is longer than the height, and it is the path length the bracket count is taken from.

The run, top to bottom

Six things are being assembled here and they fail in different ways. The hopper is a receiving funnel with a guarded opening, sitting on the floor being stripped. The sections are the barrel — nested plastic cones on chain, or bolted steel, or, on older jobs, a site-built timber box that nobody has calculated. The bracket bands are the only thing between the barrel and the ground. The bottom section carries the gate that stops the flow. Under that sits the container. And under all of it is the structure everything is bolted to, which on a demolition site is by definition getting weaker every day.

Draw the load path once and the priorities sort themselves. Every section hangs off the section above until a bracket band takes it; the band throws that accumulated weight into a slab edge or a scaffold; the slab edge throws it into a frame that is being demolished from the top down. Each bracket is therefore a temporary works fixing on a structure whose condition is changing, which is why the engineering survey required before demolition begins under OSHA 29 CFR 1926.850 is worth re-reading before the first bracket is drilled rather than only when the programme is written.

Hanging it from the top down

The rig itself is short and unforgiving, and it is mostly done in the wrong order by crews who have only seen a chute already up. The sequence below assumes plastic cones on chain hung from a top frame, which is the common case; a bolted steel chute changes the joints and nothing else about the order.

Two constraints shape it before you start. A chute running at more than 45 degrees from horizontal — which is every chute hung down a facade — has to be entirely enclosed under 29 CFR 1926.852(b), the only breaks being openings with closures at or about floor level, and those openings are limited to 48 inches measured along the wall of the chute. Everything below the floor being worked stays shut. That single requirement decides how many openings you fit, where the closures live, and how a crew on level six is stopped from tipping into a run that level eight is already using.

1. Walk the line first, top to bottom, and clear the swept path — cills, cornices, string courses, scaffold ledgers, live services, satellite dishes and any window reveal inside the barrel's width.
2. Confirm the floor opening the chute passes through, and shore anything the demolition has already weakened. Under OSHA 29 CFR 1926.853 an opening cut in a floor for material disposal is limited to a quarter of the aggregate floor area unless the lateral supports of the removed flooring stay in place.
3. Set and fix the top frame or hopper support before a single cone leaves the pallet. Everything below hangs from this, and it is the fixing crews most often improvise.
4. Fit the hopper, then its guardrail and the closure over the gap between chute and floor opening. Where barrows or a skid-steer will tip into it, the toeboard or bumper required at the opening goes on now, not after the first load.
5. Lower the sections one at a time, coupling each to the one above at ground level or at the opening rather than leaning over an edge to do it.
6. Fit the bracket band at every marked slab as the barrel reaches it, and do not run more sections below an unbraced band than the manual allows.
7. Hang the bottom section high enough that the container can be exchanged without breaking the run, and fit the discharge gate.
8. Fit closures to every intermediate opening. Openings below the top floor are required to be kept closed when they are not in use, and an unclosed one on level three is how a load meant for the container ends up in a stairwell.
9. Hoard the discharge area, brief the gate operator, and run one bucket of clean rubble down the empty chute before any crew is allowed to load it.

Dust leaves at both ends

A chute is a chimney with rubble going down it, and the air goes the other way. Fines separate from the load on the way down and come back out of the top opening into the face of whoever is loading, then out of the bottom into the yard. Crews who would never dry-cut a slab will happily tip a barrow of screed dust into an unshrouded hopper and stand over it. Where the material contains concrete, mortar, brick or screed, that is respirable crystalline silica, and in United States construction work exposures sit under OSHA 29 CFR 1926.1153. Table 1 of that standard lists specified tasks with prescribed controls, and chute loading is not one of them, which means the exposure has to be assessed and controlled by the alternative route rather than assumed away.

The practical controls are dull and they work. Keep the barrel enclosed and every unused opening closed, which the standard requires anyway and which happens to be the best dust control on the job. Damp the material at the point it is generated rather than trying to wet it as it falls. Fit a shroud or a hood to the top hopper if the system offers one. Get a fine spray or a fog unit across the discharge, sited so it wets the falling stream rather than the operator. And accept that on a windy day with a dry stream the honest answer is sometimes to stop loading, because a chute discharging into a gale puts dust over the boundary and that becomes a complaint, then a visit.

What must never go down it

A chute is a general debris route and a surprising amount of what a strip-out generates does not belong in it. Long steel, scaffold tube, timber joists and anything else that can span the barrel will bridge, and a bridged chute is a loaded gun: material stacks above the blockage until it lets go all at once, which is the load nobody calculated and the moment the gate operator is standing under it. Sheet material behaves the same way. Anything with a dimension approaching the barrel's diameter goes down by hoist, in a bin, or not at all.

Asbestos is the categorical one. Under the asbestos NESHAP at 40 CFR Part 61 Subpart M, the demolition and renovation standard at section 61.145 requires regulated asbestos-containing material that has been stripped more than 50 feet above ground level, and not removed as intact units or sections, to be transported to the ground in leak-tight chutes or containers; units and sections have to be lowered carefully to ground level and not dropped, thrown or slid. A general debris chute is not a leak-tight chute, and treating it as one is a reportable failure rather than a judgement call. Sealed gas cylinders, drums with unknown contents, and any container that was holding something under pressure come off the floor by the same route: hoisted, not dropped.

Striking it, and what stays on the record

A chute comes down in the reverse of the order it went up, and the temptation at the end of a job is to shortcut it. Sections are removed from the bottom while the barrel is still hanging from the top, which is exactly the condition the bracket bands were sized to avoid. Take the load off in sequence, band by band, with the run above supported and no more free sections below an unbraced point than the manual permits during erection. Bracket fixings come out last, and the holes left in a slab edge that is still standing get made good or recorded.

Inspect the sections as they come off rather than as they go back on the pallet next year. Plastic cones craze, split at the chain lugs and go brittle in cold; steel sections wear thin at the impact points where every load has been changing direction. The manual states the service temperature range and the wear limits, and a section that has failed them is scrap, not stock. Chain, shackles and lifting accessories used to rig the run follow their own inspection regime and their own certificates, and those belong in the same file.

Close the job by writing down what was actually built. The chute model and its manual revision, the measured run, the maximum spacing taken from that manual, the bracket positions as fixed rather than as drawn, what the ties were fixed into, the gate operator's name against each shift, and the exclusion zone as it was set out. That is a short document, it takes twenty minutes, and it is the only thing that answers the question an inspector or an insurer will ask, which is not whether the chute was strong enough but how anyone knew.