Seven twenty, and the door is already busy
The strip-out is on the first floor. The entrance is directly under it, and it unlocks at seven. By twenty past, the lobby has taken a hundred and fifty people, two courier trolleys and a facilities manager who wants to know why there is a fan humming somewhere above the ceiling tiles. None of that is unusual on a commercial refit. None of it forgives a single gram of screed dust arriving downstairs at nine o'clock, because the moment it does, the job stops being a demolition programme and becomes an incident report.
What you are actually running is two containments that never touch. Above the slab, a sealed enclosure holding dust in against a pressure difference. Below it, a physical corridor holding people out, past a door that stays open all day. They fail differently. The enclosure fails quietly — a lifted tile, a cable tray penetration nobody sealed, a machine that lost half its airflow over a fortnight — and you find out from a wipe sample or a complaint. The route fails loudly and immediately, usually the first time somebody drags a scaffold tube across the footway at half past eight.
The order of the work follows that split. Survey and permits first, because they decide what the enclosure has to be. Then the route outside, because it is the thing the public sees on day one and the thing the local authority licenses. Then the enclosure, the plant that depressurises it, the exhaust route, and the noise. Fire and reoccupation close the day, every day, not just the job.
What sits between the works and the people below
- Enclosure ceiling seal — polyethylene taped to the soffit and to every service crossing it, defining the volume the negative-air plant is sized against Asbestos Enclosure Negative-Pressure Airflow Calculator
- Finishes coming off — screed, adhesive bed and floor covering — the layer generating the dust the enclosure exists to hold
- Separating floor slab — the only permanent element between the works and the occupied lobby; every core and riser through it is a leak path
- Protection deck below — boarded ceiling protection inside the live lobby, catching anything that comes through a penetration or a coring mishap
- Covered walkway over the footway — the licensed pedestrian route past the door, decked, edged and lit, standing on bays at a designed spacing Pedestrian Covered Walkway Support Bay Spacing Calculator
The building has an occupier, and the occupier has duties
On an empty site the principal contractor owns everything inside the hoarding. Here you own a slice of somebody else's operating asset, and half the controls you depend on belong to their facilities team: the air handling plant, the fire alarm panel, the access control, the cleaning contract, the lift you are not allowed to use. A method statement that assumes you can switch any of those off is a method statement that will be rewritten on the morning it matters. Get the interface written down early — who isolates what, who is called, and what the escalation route is at four in the afternoon when the occupier's staff are still at their desks.
The survey drives the rest. In a building of any age the refurbishment and demolition survey is the document that decides whether this is a strip-out or a licensed asbestos job, and it has to be intrusive enough to have opened the floor void, the riser and the ceiling above the entrance rather than describing them from a drawing. Where asbestos-containing material is present, the work class under OSHA 29 CFR 1926.1101 — or the licensed, notifiable non-licensed and non-licensed split set by the Control of Asbestos Regulations 2012 and its approved code of practice L143 — determines the enclosure, the decontamination arrangements and the clearance procedure before anyone prices a skip. Refit demolition also cuts, drills and chases concrete and masonry, which brings respirable crystalline silica and its own control regime under OSHA 29 CFR 1926.1153 with its Table 1 of specified exposure control methods.
The route past the door
The first thing the public meets is not your enclosure, it is the pavement. Overhead work near a live entrance means the footway either moves or gets a roof, and which of the two you get is decided by the height of the work and its distance from the boundary. In the United States that determination sits in the International Building Code, Chapter 33, Safeguards During Construction, whose pedestrian protection provisions key the required treatment — a construction railing, a barrier, or a barrier with a covered walkway — to those two dimensions. In the United Kingdom the footway closure or narrowing is licensed by the highway authority, and the temporary traffic management around it follows the national code of practice for street works. Neither route is quick, and both want drawings.
A covered walkway is a temporary structure with a real design behind it. It carries pedestrian loading on the deck, an impact or debris allowance on the roof, wind on its sheeted faces, and — where it stands in a carriageway or beside one — a vehicle containment requirement it will not meet on its own. Bay spacing is the output of that design, not a number chosen on site: it falls out of the standard's load case and the member sizes the system manufacturer publishes. Under BS 5975, temporary works procedures put a temporary works co-ordinator's name against the design check before erection, which is the mechanism that stops a gantry being extended by four metres on a Friday because the scaffolder had the tube spare.
Width and level are the parts that generate complaints. A route that squeezes below the clear width required by the accessibility standard in force — the ADA Standards for Accessible Design in the United States, BS 8300-2 in the UK — has excluded somebody, and a threshold or a cable ramp across it does the same. Keep the deck flush, run the lighting inside the walkway rather than relying on the street lamps you have just boxed in, and hoard the sides opaque only where you need to; a solid tunnel forty metres long with one light at each end is a route people will walk around, into the carriageway.
Then there is the door itself. The entrance stays live, which means the walkway has to deliver people to it without the doors' swing, the mat well or the revolving drum being obstructed, and without the walkway's own posts sitting in the escape route from the lobby. Set the bays out from the door outwards rather than from the scaffold end inwards, and the awkward bay lands where nobody walks instead of across the threshold.
Once the designer has given you a maximum bay spacing for the system and its load case, the run length decides how many bays and baseplates actually land on the footway — and whether one of them lands in the doorway.
The total length of the pedestrian covered walkway/canopy structure.
The maximum spacing allowed between structural support bays, from the system's structural design or manufacturer data.
Support frames needed
11 frames
Maximum bay spacing depends on the specific walkway/canopy system's structural design, load rating (pedestrian, debris/impact per local code), and member sizing — this must come from a qualified engineer's design or the manufacturer's system data, not an assumed value.
- Bays along the walkway
- 10
- Frame centres, as erected
- 9.8 ft
They open the calculator with your figures already in it
Pedestrian Covered Walkway Support Bay Spacing Calculator: 11 frames — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- Counts frames for one straight run at a single spacing. Every corner, doorway, hydrant, tree pit and vehicle crossing on the route pushes a frame off that grid, and each separate leg needs its own pair of end frames — a route that turns twice takes more frames than its total length divided by the spacing suggests.
- Says nothing about how each frame is held down. A walkway with a solid roof and sheeted sides is a sail, and wind uplift and overturning are what size the ballast blocks or ground anchors under every frame. The frame count can be exactly right and the run still shift in a gale because nothing was weighted.
- Bay spacing is a strength limit, not a clearance. The minimum clear width and headroom inside the walkway are set by the footway it replaces and by the local hoarding rules, and frames at the correct centres can still leave a route too narrow for the traffic diverted into it, or too low once lighting and barriers are hung underneath.
A hole you cannot see is the only hole that matters
An enclosure is only as good as its worst edge, and the worst edge is never the sheeting. It is the place where a service crosses the boundary: a cable tray, a chilled water pair, a fire damper, an old pneumatic tube, a floor box, the gap over a stud head that somebody sheeted to the ceiling tile grid instead of to the structural soffit. Air takes the easiest path out of a depressurised space and it will find every one of those before it comes through the polythene. Walk the boundary with a smoke pencil after the sheeting is up and before the machines run at full duty, and again after any trade has been inside.
Build the barrier as a barrier, not as a screen. Critical barriers seal openings, windows, diffusers and returns; the working walls want a frame stiff enough to survive being leaned on, because a poly wall that flexes in and out on every door movement is a wall that will unstick itself along the tape line by the third day. Where the enclosure fronts an occupied corridor, the sensible arrangement is a boarded partition with the sheeting on the work face — it takes the knocks, it takes a fire rating if the occupier's strategy needs one, and it takes the noise, which no amount of polythene does.
Getting people in and out is where most contamination happens. For asbestos work the decontamination arrangement is prescribed — the equipment room, shower and clean room sequence, with separate material and personnel routes — and even on clean strip-out an airlock with a tacky mat and a discipline about who crosses it is worth building. Deliveries and arisings are the leak nobody plans: a load of broken screed carried out through the lobby in an open barrow undoes the enclosure entirely, which is why the muck route, the bagging arrangement and the chute or hoist position belong in the same drawing as the barriers.
| Crossing | What it does when you ignore it | What has to be decided |
|---|---|---|
| Cable tray or busbar through the wall line | A permanent open duct between the works and the occupied floor | Sealed and firestopped, or the tray isolated and the section removed |
| Supply diffusers and return grilles | The base building system draws enclosure air into occupied space | Isolated and sealed by the occupier's team, with the shutdown recorded |
| Raised floor or ceiling void continuing past the barrier | The void becomes the bypass around every seal you built | Barrier taken down to the structural slab and up to the structural soffit |
| Floor cores, redundant risers, old lift shafts | A vertical leak straight down over the live entrance | Capped and protected from above, deck protection below |
| Doors on the occupied side of the barrier | Every opening swings the pressure differential | Sealed shut, or converted to an airlock with a signed access rule |
Air changes are a design target, not a measurement
Depressurising an enclosure does two jobs at once. It keeps the leakage direction inward, so the air that moves across an imperfect seal moves toward the dust rather than away from it, and it dilutes what is airborne inside by exchanging the enclosure volume through HEPA filtration several times an hour. The first job is the one that protects the people downstairs; the second is the one that lets your own operatives see what they are doing. The sizing arithmetic behind both is deliberately simple: enclosure volume times target air changes per hour, divided by sixty, gives the airflow the plant has to move. For negative-pressure asbestos containment, a floor of four air changes per hour is commonly required under EPA guidance in the Purple Book, EPA 560/5-85-024, and under state asbestos rules, and a differential of about 0.02 inches of water column relative to the area outside containment is the figure most programmes work to. Practice sizes the machines above that floor — six air changes an hour is the usual design target — because filter loading only ever moves the delivered flow downward.
Measure the volume rather than scaling it. Ceiling voids inside the enclosure count. So do the parts of a raised floor left in place, the stair enclosure you have taken in, and the airlock. What does not count is any assumption that a number you calculated makes the enclosure compliant: the required differential is a continuously monitored, field-verified quantity confirmed by a licensed supervisor, and the calculation is only the first pass that tells you how many machines to hire.
With the enclosure volume measured and a target air-change rate chosen, this gives the nominal airflow the negative-air plant has to move before any allowance for leakage, ducting or a loaded filter.
The total interior volume of the sealed containment enclosure.
How many times per hour the enclosure's full air volume should be exchanged.
Required negative-air machine airflow (CFM)
300 CFM
This ACH-based airflow calculation tells you the nominal CFM needed to theoretically cycle the enclosure's air — it says nothing about enclosure leakage, which is what actually determines whether a given negative-air machine can achieve and hold the required -0.02 in. water column (5 Pa) pressure differential in practice. Machine selection must also account for the manufacturer's rated CFM AT the actual static pressure/resistance imposed by ducting and HEPA filter loading, not free-air CFM. Regulatory compliance requires field-verified, continuously-monitored pressure differential confirmed by a qualified/licensed abatement supervisor — this calculator is a first-pass sizing estimate only, not a substitute for that verification.
They open the calculator with your figures already in it
Asbestos Enclosure Negative-Pressure Airflow Calculator: 300 CFM — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 300 CFM — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- Total airflow is not a machine schedule. This CFM has to be split across units at their rated output through the ducting actually installed, and a containment holding negative pressure on exactly enough machines has no margin: one unit tripping a breaker or loading its prefilter takes the enclosure positive within minutes, which is a release rather than an inconvenience. Put a spare in the count and treat the pressure recorder as the alarm.
- Air out requires air in. A negative-pressure enclosure needs a controlled makeup path — normally through the decontamination unit's chambers, so the inward sweep runs the right way across the airlocks — and this calculation neither sizes nor locates one. Seal an enclosure too tightly and the machines never move the design volume at all; they pull the poly off the walls and the ACH on paper simply does not happen.
- ACH sets an exchange rate, not a clearance. How long the enclosure keeps running after the last removal, before visual inspection and final air sampling, comes from the settling and clearance protocol in the applicable rule and the analytical method in use — never from a multiple of this figure. A correctly sized machine switched off early leaves fibers in suspension for the sampler to find.
What the machine gives you on day nine
A negative-air machine's headline rating is a free-air figure. Connect it to a duct run, a pre-filter and a HEPA and it delivers less; run it for a fortnight on gypsum and screed dust and it delivers less again, because a HEPA does not gradually leak, it gradually blocks. The resistance climbs from the manufacturer's clean pressure drop toward the final pressure drop at which the filter is meant to be changed, and the flow rides down that curve while the enclosure looks and sounds exactly as it did on day one.
This is why the manometer across the barrier is the instrument that matters and the fan noise is not. A magnehelic or a logging gauge reading the differential continuously, with an alarm, tells you the day the plant stopped holding the enclosure; a filter gauge on the machine tells you why. Both are cheap next to a re-clean of an occupied floor. Filter performance itself belongs to test standards rather than to trade opinion — HEPA classification under ISO 29463, in-place leak testing under IEST-RP-CC034, and general filter efficiency testing under ANSI/ASHRAE Standard 52.2 — and a filter that has been dropped, damp or force-fitted has a leak path the pressure drop will never reveal.
Build the redundancy in at hire. Sizing to the exact calculated flow with one machine means the enclosure fails the moment that machine is switched off for a filter change, and enclosures are always broken down at the worst possible moment. Two smaller units running below their maximum duty hold the differential more steadily, keep working through a change, and give you somewhere to go when the leakage turns out to be worse than the drawing suggested.
Between the filter's clean and final pressure drops sits the entire working life of the machine's airflow, so put both rated figures in with an honest estimate of how far the media has loaded and see what the blower is already fighting.
The filter's pressure drop when new and clean, per the manufacturer's data sheet.
The pressure drop at which the manufacturer recommends replacing the filter.
Your estimate of how far the filter has progressed from clean (0%) to final loading (100%).
Estimated current pressure drop
1.5 in. w.g.
Filter pressure drop is unique to each manufacturer's media and construction — always use the actual filter's data sheet for the rated clean and final pressure drop values, not an assumed default. This calculator only linearly interpolates between the two rated values you supply; real filter loading curves are not perfectly linear.
They open the calculator with your figures already in it
HEPA Filter Bank Pressure Drop Estimator: 1.5 in. w.g. — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 1.5 in. w.g. — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- Airflow appears nowhere in this, and the rated clean and final figures are quoted at the filter's rated face velocity. Media resistance rises with flow through the pack, near enough proportionally, so the same bank running 25 percent above rated flow reads about 25 percent higher than predicted here — and a room whose fans are chasing an air-change rate is rarely sitting exactly at rated.
- This is one filter, not the resistance the fan has to overcome. Housing, frame, the prefilter ahead of it and the approach ductwork all add drop, and the prefilter's condition is what governs how quickly the HEPA loads in the first place. A fan or a drive sized on this number alone runs out of head before the HEPA ever reaches its final rating.
- Pressure drop is not the only reason a HEPA comes out. In a classified space a filter is also replaced when it fails an integrity scan, and a pinhole in the media, a damaged gasket or a poor seal at the frame will pass particles while the differential pressure reads perfectly normal. Change-out decided on this figure alone can leave a leaking filter in a room that has to be clean.
The exhaust has to go somewhere, and somewhere is a lobby too
Filtered air still has to leave, and in an occupied building the discharge point is a decision with an occupier's name on it. Ducting out of a window on the elevation above the entrance puts a plume directly over the people you are protecting, and puts it near whatever outdoor air intakes serve the floors that are still trading; ANSI/ASHRAE Standard 62.1 sets minimum separation distances between intakes and contaminant sources for exactly this reason. Discharging into a plant room, a service void or a car park because it was the short run is how a filtered enclosure ends up contaminating a space nobody was monitoring. SMACNA's IAQ Guidelines for Occupied Buildings Under Construction is the document that deals with this class of problem, and it is worth reading before the duct is bought rather than after the complaint.
The run itself is what quietly eats the flow you paid for. Lay-flat ducting through a lobby ceiling, around two structural columns and up through a window panel adds equivalent length and fitting losses on top of the filter resistance, and the machine's blower answers all of it out of the same pressure budget. Keep the run short and straight, support it so it cannot kink behind a ceiling tile, and treat every additional elbow as flow you have decided to give up.
Makeup air is the other half of the arrangement and is usually left to chance. Air leaves the enclosure at the machine's rate and something has to replace it; if the enclosure is genuinely tight, it will replace it through the airlock, which is the one place you wanted flow to stay inward, and the differential will run higher than intended while the sheeting sucks flat against the studs. A deliberate, filtered makeup opening on the far side of the enclosure from the work face gives you a controlled sweep across the work rather than a random one.
This totals a duct system's external static against a blower's rating — it is written for ducted air handlers, but the arithmetic does not care that the fan is a negative-air machine, and the run out to the discharge point is the term that decides whether your sized airflow ever arrives.
Supply plus return, along the longest path.
Elbows, takeoffs, boots and transitions, expressed as the equivalent length of straight duct.
Design friction rate for the ductwork.
Everything that is not duct.
Total external static pressure
0.5 in w.g.
Exceeding the blower's rated external static pressure reduces airflow, which reduces capacity — a correctly-sized unit then behaves like an undersized one.
- Total effective length
- 250 ft
- Duct friction loss
- 0.25 in w.g.
- Components
- 0.25 in w.g.
- Pascals
- 124.54 Pa
- Against a 0.5 in w.g. blower rating
- 100 % of rating
They open the calculator with your figures already in it
Duct Static Pressure Calculator: 0.5 in w.g. — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 0.5 in w.g. — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- Fitting equivalent lengths must come from the Manual D tables for the specific fittings used; the default here is a plausible figure, not yours.
- Component pressure drops should come from the manufacturer's data at your design airflow, not from a typical value.
- Measured static pressure on a commissioned system frequently exceeds the calculated figure. Measure it rather than trusting the arithmetic.
Noise travels further than dust and complains sooner
Dust is what gets you a prohibition notice; noise is what gets you thrown off site. Breaking out a screed on a suspended slab puts structure-borne sound into every element connected to it, which in a frame building means floors two levels away and on the other side of the core. Nobody in the occupied space experiences that as construction progress. They experience it as a phone call they cannot hold.
Two documents do the heavy lifting here. BS 5228-1 and BS 5228-2 cover the control of noise and of vibration on construction and open sites, including the prediction methods and the mitigation hierarchy, and they are the reference a local authority will expect to see behind a section 61 style agreement on working hours. Occupational exposure inside the enclosure is a separate regime again — OSHA 29 CFR 1926.52 in the United States, the Control of Noise at Work Regulations 2005 in the UK — and hearing protection for your own crew does nothing for the tenant below.
Mitigation is mostly sequencing and mass. Percussive work moves to the hours the occupier will agree to, quieter methods take the work that cannot move, and the temporary partition gets built with enough of both to be worth its cost. A boarded stud screen with an insulated cavity and doubled linings is a different object acoustically from a single-skin hoarding, and the difference is worth estimating before the boards are ordered rather than discovering it after the first week of complaints.
Be honest about what any wall estimate is. Laboratory-measured sound transmission class comes from ASTM E90, with the single-number rating derived under ASTM E413, on a specimen with no flanking. On site the sound goes over the head of your screen through the ceiling void, under it through the raised floor, and along the slab regardless — so an additive screening figure tells you which build-up is better, not what the tenant will hear.
Before you specify the screen between the works and the tenant, this puts a screening number on what each extra layer, cavity batt or decoupled framing arrangement is actually buying.
The starting STC rating for a basic single-stud wall with one gypsum layer per side.
The estimated STC point gain from adding resilient channel or another stud-decoupling method.
The estimated STC point gain from adding sound-absorbing insulation in the stud cavity.
The estimated STC point gain for each gypsum layer added beyond one per side.
How many additional gypsum layers are being added beyond the base single layer per side.
Estimated wall STC rating
44 STC (estimated)
This is an engineering rule-of-thumb ADDITIVE estimate only, not a certified rating — actual STC performance depends on flanking transmission, workmanship, and specific product combinations. Always specify and verify acoustic performance using a manufacturer's actual ASTM E90 lab-tested assembly rating for any acoustic-critical project (e.g. multifamily party walls), never this estimate.
They open the calculator with your figures already in it
Multi-Stud Wall Sound Transmission Class (STC) Estimator: 44 STC (estimated) — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 44 STC (estimated) — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- STC says nothing about bass. The single-number rating is built from measurements between 125 Hz and 4,000 Hz and weighted around speech, so a subwoofer, a club system, a gym drop or a plant room next door sits largely below what the number describes. Worse, the decoupling that earns 8 points here has a mass-air-mass resonance down there, and around it a decoupled wall can perform WORSE than a rigid one. If low frequency is the actual complaint, the target is a third-octave curve from a test report, not a point score.
- Anything set into the wall governs the wall. A door, a glazed screen, a serving hatch or a transfer grille is a second and far weaker element in the same partition, and the composite result is dominated by it - a hollow-core door around STC 20 to 25 in an otherwise STC 50 wall drags the whole partition into the low thirties, however many layers of board are on it. This page rates a blank panel. A wall with an opening is figured as a composite of the two areas, and the door's seals and threshold are part of what the door is rated at.
The alarm you took out of service
Sealing an enclosure across a floor plate means sealing over smoke detectors, capping sprinkler heads and, on most jobs, taking part of the detection system out of service so that dust does not put the building into evacuation twice a day. That impairment is the single most dangerous thing on the project, and it is dangerous to the occupied floors rather than to you. NFPA 241, Standard for Safeguarding Construction, Alteration, and Demolition Operations, and the fire safety during construction provisions of the International Fire Code set out the programme around it: a named fire prevention programme manager, an impairment procedure, hot work control, and site-specific fire safety planning that stays current as the works change the building.
Run the impairment as a shift-level thing with a start time, an end time and a named person doing the fire watch, not as a permit filed once at the start of the job. Escape routes matter as much as detection — an enclosure across a floor can block a protected stair, a covered walkway can block a final exit discharge, and both are easier to spot on a plan with the escape routes drawn on than they are during a drill. In the UK, the Joint Code of Practice on the Protection from Fire of Construction Sites and Buildings Undergoing Renovation is the reference most insurers will hold you to on a live refurbishment, and it addresses exactly this overlap between the works and an occupied building.
Handing the floor back before the cleaners arrive
Every day ends with a handback, whether or not anyone calls it that. The occupier's cleaners come through the lobby, their contractors use the risers, and their staff arrive before your gang does. A floor that is left tidy but with the machines switched off overnight has been depressurised for eight hours out of twenty-four, and the enclosure has been quietly equalising through every leak path since the last man left.
At the end of the job the standard rises sharply. On asbestos work, reoccupation is not a judgement call: it follows a defined clearance procedure with a thorough visual inspection — ASTM E1368 covers the practice for visual inspection of abatement projects — and air clearance sampling analysed by the method the regime requires, with transmission electron microscopy clearance under the AHERA provisions at 40 CFR Part 763 Subpart E where those apply. The enclosure comes down after the clearance, not before it, and the negative-air machines run until it is signed off.
On clean strip-out the equivalent is less formal and more often skipped. A settled-dust wipe on the surfaces the occupier's staff touch, a look inside the ceiling void on the occupied side of the barrier, and a walk of the route with the facilities manager will find the things a broom pass will not. Photograph the state of the lobby, the walkway deck and the entrance doors on handover, because in a live building the argument about who scratched what starts the week after you leave.
- Leave the negative-air plant running and the differential logging overnight, with the alarm audible to whoever holds the out-of-hours key.
- Walk the barrier line with a smoke pencil at the end of any shift where a trade has crossed it, and re-tape before the machines are left unattended.
- Clear the covered walkway deck and its lighting, and check nothing has been stacked against a bay or across the entrance doors.
- Close the day's alarm impairment formally, with the reinstatement time recorded and the fire watch stood down by name.
- Bag and remove the day's arisings by the agreed muck route rather than leaving them inside the enclosure to be moved through the lobby in the morning.
Before the first barrier goes up
The six things that decide whether the entrance stays open, settled while the building is still whole and the occupier is still willing to talk about them.
- Enclosure volume, measured on site — Ceiling void, retained raised floor and airlock all included; a volume scaled off a plan is short by whatever the voids hold.
- Boundary crossing schedule — Every tray, duct, riser, core and diffuser on the barrier line, with a named decision against each: sealed, isolated, or removed.
- Plant sized at its ducted rating — Machine flow taken at the static pressure of the real duct run and a loaded filter, never the free-air figure on the datasheet.
- Discharge point agreed with the occupier — Checked against outdoor air intakes, openable windows and the entrance below before the duct route is bought.
- Protected route width, level and licence — Clear width against the accessibility standard in force, flush deck, walkway lighting, and the highway or lot-line permission in hand.
- Alarm impairment and fire watch procedure — Start and end times per shift, named fire prevention programme manager, and escape routes redrawn for the enclosure and the walkway.
Opens the calculators above on one screen with the dimensions from this article already filled in. Quantities only — this site publishes no price list, because local prices vary too much to publish honestly.