+---
+title: Dust and Fume Collection Systems
+category: Mechanical / Air Distribution
+toc_depth: 3
+description: >
+ When to use: Fixed industrial and laboratory-process dust collection and fume
+ exhaust systems that capture airborne particulates, mists, vapors, or process
+ fumes at the point of generation and convey them to air-cleaning equipment
+ before discharge — manufacturing plants, fabrication and welding shops,
+ metal-grinding areas, woodworking plants, and chemical and food-processing
+ spaces. Covers capture hoods, conveying ductwork and air-moving fans, primary
+ air-material separators (baghouses, cartridge collectors, cyclones, wet
+ scrubbers, electrostatic precipitators), explosion-isolation and fire
+ components in the exhaust stream, and system controls and monitoring, for
+ both new systems and modifications to existing ones, including combustible
+ and non-combustible streams.
+ Not intended for: Grease-laden kitchen exhaust (see sync/kitchen-exhaust-systems);
+ general building supply, return, and exhaust fans (see sync/hvac-fans) and
+ pressure-classed HVAC distribution ductwork (see sync/hvac-ductwork);
+ laboratory bench fume hoods and their VAV-controlled exhaust (see
+ sync/laboratory-exhaust-and-fume-hoods); fixed area gas detection and alarm
+ (see sync/gas-detection-systems); process instrument impulse tubing and sensor
+ installation (see sync/instrument-installation-and-tubing); and piping and
+ equipment identification (see sync/mechanical-identification).
+---
+
+# Scope {toc}
+
+## This standard covers the design, selection, specification, installation, and field testing of fixed industrial and laboratory-process dust collection and fume exhaust systems that capture particulates, mists, vapors, and fumes at the source and convey them to air-cleaning equipment before discharge. {note}
+
+## A dust and fume collection system is a local exhaust ventilation (LEV) system serving production equipment, not occupied building space. It comprises capture devices at the point of generation, conveying ductwork sized to keep particulate entrained, an air-moving fan, a primary air-material separator that removes the contaminant, and the controls and instrumentation that keep the system in balance. {note}
+
+## The system shall capture airborne contaminants at the point of generation in sufficient quantity to maintain employee exposures at or below the applicable OSHA Permissible Exposure Limit.
+
+## The system shall convey captured contaminant to the air-cleaning equipment without settling or accumulation in the ductwork.
+
+## The system shall discharge cleaned air at an emission concentration compliant with the governing air-quality permit and, where air is returned to occupied space, with the recirculation limits of this standard.
+
+## Combustible-dust streams and non-combustible-particulate streams are both within scope; a combustible stream invokes the additional hazard-analysis, explosion-protection, and isolation requirements of this standard. {note}
+
+## Welding fume extraction units, grinding fume collectors, downdraft tables, and central process vacuum systems are within scope as fixed source-capture configurations. {note}
+
+## The boundary between this standard and adjacent systems is the contaminant stream, not the room. {note}
+
+### Grease-laden kitchen exhaust is excluded; it requires listed hoods, grease filters, fire suppression, and NFPA 96 compliance and is covered by [[sync/kitchen-exhaust-systems]]. {note}
+
+### General building supply, return, and exhaust fans for occupant ventilation are excluded and are covered by [[sync/hvac-fans]]; pressure-classed HVAC distribution ductwork is covered by [[sync/hvac-ductwork]]. {note}
+
+### Laboratory bench fume hoods — listed, walk-up enclosures with a sash — and their VAV-controlled exhaust are excluded and are covered by [[sync/laboratory-exhaust-and-fume-hoods]]; a source-capture arm or backdraft hood over a grinder or welding table is within scope here. {note}
+
+### Fixed area gas detection and alarm for toxic or flammable gases is excluded and is covered by [[sync/gas-detection-systems]]. {note}
+
+### Process instrument impulse tubing and sensor installation at monitoring points are excluded and are covered by [[sync/instrument-installation-and-tubing]]; identification labeling of mechanical piping and equipment is covered by [[sync/mechanical-identification]]. {note}
+
+# Referenced Standards {toc}
+
+## Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
+
+## Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
+
+## NFPA 660 (2025) consolidated and superseded the six prior NFPA combustible-dust standards — NFPA 61, 484, 652, 654, 655, and 664 — effective December 2024; specifications drafted before that date and citing the individual standards shall be updated to NFPA 660. {note}
+
+| Standard | Title |
+|----------|-------|
+| NFPA 91 (2026) | Standard for Exhaust Systems for Air Conveying of Vapors, Gases, Mists, and Particulate Solids |
+| NFPA 660 (2025) | Standard for Combustible Dusts and Particulate Solids |
+| ANSI/ASSP Z9.2 (2018) | Fundamentals Governing the Design and Operation of Local Exhaust Ventilation Systems |
+| ANSI/AIHA Z9.5 (2022) | American National Standard for Laboratory Ventilation |
+| ANSI/ASSP Z9.9 (2016) | Portable Ventilation Systems |
+| ANSI/ASHRAE 199 (2016) | Method of Testing the Performance of Industrial Pulse-Cleaned Dust Collectors |
+| ASHRAE 52.2 (2017) | Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size |
+| OSHA 29 CFR 1910.94 | Ventilation — Abrasive Blasting, Grinding, Polishing, and Buffing Operations |
+| OSHA 29 CFR 1910.1000 | Air Contaminants (Permissible Exposure Limits) |
+| OSHA 29 CFR 1910.1053 | Respirable Crystalline Silica |
+| ACGIH | Industrial Ventilation: A Manual of Recommended Practice for Design (31st ed., 2023) |
+| UL 508A | Standard for Industrial Control Panels |
+| NFPA 70 (NEC 2023) | National Electrical Code, Article 502 — Class II (Combustible Dust) Locations |
+| IMC 2024 | International Mechanical Code, Section 510 — Hazardous Exhaust Systems |
+
+## The ACGIH Industrial Ventilation Manual is an engineering reference, not a code, but is the dominant design authority for hood geometry, capture and transport velocities, and system balancing, and is frequently invoked by the AHJ during permit review. {note}
+
+# Submittals {toc}
+
+## Action Submittals {toc}
+
+### The Contractor shall submit the following action submittals for review before fabrication or ordering:
+
+- Product data for each collector, fan, capture device, isolation valve, and explosion-protection device.
+- Shop drawings showing duct layout, branch and main sizing, transport velocities, hood geometry and capture velocities, and equipment locations.
+- System calculations: total system airflow, duct static pressure, fan operating point at the design dirty-state static pressure, air-to-cloth ratio, and capture-velocity verification at each hood.
+- The Dust Hazard Analysis (DHA) for any combustible-dust stream, with deflagration-vent area, isolation, and suppression sizing per NFPA 660.
+- Make-up air coordination data demonstrating that replacement air equals or exceeds total exhaust volume.
+- Manufacturer's explosion-protection device listings and deflagration-vent calculations.
+
+```datasheet
+label: Action submittals required
+type: checkbox
+options:
+ - Collector and fan product data
+ - Capture device and hood product data
+ - Isolation and explosion-protection device data
+ - Duct layout and sizing shop drawings
+ - Airflow, static pressure, and fan operating-point calculations
+ - Air-to-cloth ratio calculation
+ - Capture-velocity verification at each hood
+ - Dust Hazard Analysis (combustible streams)
+ - Make-up air coordination data
+default:
+ - Collector and fan product data
+ - Capture device and hood product data
+ - Duct layout and sizing shop drawings
+ - Airflow, static pressure, and fan operating-point calculations
+ - Air-to-cloth ratio calculation
+ - Capture-velocity verification at each hood
+ - Make-up air coordination data
+```
+
+## Informational Submittals {toc}
+
+### The Contractor shall submit the following informational submittals:
+
+- Factory performance test report per ANSI/ASHRAE 199 for pulse-cleaned collectors.
+- Filter media data sheets including efficiency rating, fabric, finish, and chemical-compatibility data.
+- NEC Article 502 electrical area classification drawing where a combustible-dust area is present.
+- Welder's qualifications and weld procedures for ductwork fabrication where welded duct is specified, per [[sync/welding-requirements]].
+
+```datasheet
+label: Informational submittals required
+type: checkbox
+options:
+ - ANSI/ASHRAE 199 factory performance test report
+ - Filter media data sheets
+ - NEC Article 502 area classification drawing
+ - Duct welding qualifications and procedures
+default:
+ - ANSI/ASHRAE 199 factory performance test report
+ - Filter media data sheets
+```
+
+## Closeout Submittals {toc}
+
+### The Contractor shall submit the following closeout submittals before final acceptance:
+
+- Field commissioning test report: pitot-traverse capture velocities, duct transport velocities, total system CFM, and total static pressure.
+- The 30-day re-test report confirming sustained performance after initial operation.
+- Operation and maintenance manuals, including filter-change procedure and combustible-dust hopper cleanout and lockout procedure.
+- Record drawings reflecting as-installed duct routing and equipment locations.
+
+```datasheet
+label: Closeout submittals required
+type: checkbox
+options:
+ - Field commissioning test report
+ - 30-day re-test report
+ - Operation and maintenance manuals
+ - Record drawings
+default:
+ - Field commissioning test report
+ - 30-day re-test report
+ - Operation and maintenance manuals
+ - Record drawings
+```
+
+# Quality Assurance {toc}
+
+## A Dust Hazard Analysis is the gateway deliverable for any combustible-dust system. NFPA 660 §7 requires the DHA to be completed before design proceeds, because the analysis outputs — the dust Kst value, deflagration class, and ignition-sensitivity data — drive the venting, isolation, and suppression that the collector must be built around. Specifying a collector without a DHA is the most common cause of AHJ rejection and the most consequential liability exposure on a combustible-dust project. {note}
+
+## A Dust Hazard Analysis conforming to NFPA 660 §7 shall be completed and accepted before the collector for any combustible-dust stream is sized or ordered.
+
+## The dust shall be classified as combustible or non-combustible by laboratory test data or by an authoritative reference acceptable to the AHJ.
+
+```datasheet
+label: Dust combustibility classification
+type: radio
+options:
+ - Non-combustible particulate
+ - Combustible dust — DHA required
+default: Non-combustible particulate
+```
+
+```datasheet
+label: Combustible dust deflagration class (from Kst)
+type: radio
+options:
+ - "St 0 — non-explosible (Kst = 0)"
+ - "St 1 — Kst less than 200 bar-m/s"
+ - "St 2 — Kst 200 to 300 bar-m/s"
+ - "St 3 — Kst greater than 300 bar-m/s"
+default: "St 1 — Kst less than 200 bar-m/s"
+```
+
+## The installing contractor shall be experienced in industrial exhaust and dust collection system fabrication and shall employ welders qualified to the procedures referenced in [[sync/welding-requirements]] where welded ductwork is specified.
+
+## Each collector and integral control panel shall bear the listing marks required by its application: UL 508A for the industrial control panel and the dust-ignitionproof or explosion-proof listings of NEC Article 502 where installed in a classified area.
+
+# Environmental and Service Conditions {toc}
+
+## Indoor versus outdoor collector placement is a primary design driver, not a field convenience. Outdoor placement removes the collector from the building electrical classification, simplifies deflagration venting to a safe outdoor location, and isolates a combustible-dust hazard from occupied space — but it imposes freeze protection on the filter media and on the pulse-cleaning compressed-air supply in cold climates. Indoor placement avoids weather exposure but pulls the building's electrical classification, venting path, and fire protection into the equipment room design. {note}
+
+## The collector location, hopper discharge, and pulse-cleaning air supply shall be protected against freezing where the design ambient falls below 35°F.
+
+## Make-up air is a system requirement, not an accessory. Exhausting large volumes from a shop without replacing them negatively pressurizes the space, which collapses hood capture velocities, pulls exterior doors open, and backdrafts combustion appliances. Without adequate replacement air, hood capture collapses and the system cannot achieve its design performance. {note}
+
+## Make-up air shall be provided in a volume equal to or greater than the total system exhaust volume.
+
+## The duct material shall be selected for the contaminant stream; standard galvanized steel fails rapidly in hygroscopic, acidic, or high-moisture service, where stainless steel or epoxy-lined duct is required.
+
+```datasheet
+label: Collector installation location
+type: radio
+options:
+ - Indoors, within building electrical classification
+ - Outdoors, weather-protected
+default: Outdoors, weather-protected
+```
+
+```datasheet
+label: Conveying duct material
+type: select
+options:
+ - Galvanized steel (dry, non-corrosive dust)
+ - Carbon steel, welded (abrasive dust)
+ - Stainless steel 304 (moist, mild-corrosive)
+ - Stainless steel 316 (acidic, chloride-bearing)
+ - Epoxy-lined carbon steel (hygroscopic dust)
+default: Galvanized steel (dry, non-corrosive dust)
+unit: ""
+```
+
+```datasheet
+label: Air recirculation strategy
+type: radio
+options:
+ - Exhaust to outdoors, no recirculation
+ - Recirculate to occupied space with secondary after-filter
+default: Exhaust to outdoors, no recirculation
+```
+
+# Capture Devices and Hoods {toc}
+
+## Capture occurs at the hood, and a system can be no better than its hoods. The hood must develop enough velocity at the point of generation to overcome the particle's escape velocity and the room cross-drafts, then taper into the duct without losing entrainment. Hood geometry and capture velocity follow the ACGIH Industrial Ventilation Manual and ANSI Z9.2; these are the figures the AHJ checks first. {note}
+
+## Each hood shall develop the design capture velocity at the most distant point of contaminant generation it serves.
+
+## Hood and duct transition geometry shall conform to the ACGIH Industrial Ventilation Manual to minimize entry loss and maintain transport velocity into the branch.
+
+## A source-capture arm or backdraft hood for welding and grinding shall be positioned to draw fume away from the operator's breathing zone.
+
+```datasheet
+label: Capture device type
+type: select
+options:
+ - Enclosing hood / booth
+ - Capturing hood (side-draft)
+ - Downdraft table
+ - Backdraft hood
+ - Articulated source-capture arm
+ - Receiving hood (canopy, buoyant streams only)
+default: Articulated source-capture arm
+unit: ""
+```
+
+```datasheet
+label: Design capture velocity at point of generation
+type: range
+unit: FPM
+min: 50
+max: 2000
+step: 50
+setpoints:
+ - 100
+ - 150
+ - 200
+ - 500
+default: 150
+```
+
+# Conveying Ductwork {toc}
+
+## Transport velocity is the single parameter that keeps a dust system alive. Below the minimum transport velocity for the dust, particulate drops out of the airstream, settles in horizontal runs, plugs the duct, and — for a combustible dust — builds a secondary deflagration fuel layer inside the system. Velocity is set by the heaviest, coarsest particle the branch carries, not by an average. {note}
+
+## Conveying ductwork shall maintain, at every point, the minimum transport velocity required for the dust it carries.
+
+## Round duct shall be used for conveying runs.
+
+## Rectangular duct shall not be used where it would create low-velocity corners that permit settling.
+
+## Horizontal duct runs shall be minimized and shall include cleanout access at changes of direction.
+
+## The system static pressure shall be calculated at the design dirty-state condition of the collector, not at clean-filter conditions, so the fan and motor are sized for the loaded system.
+
+```datasheet
+label: Minimum duct transport velocity by dust type
+type: range
+unit: FPM
+min: 3000
+max: 5500
+step: 100
+setpoints:
+ - 3500
+ - 4000
+ - 4500
+ - 5000
+default: 4000
+```
+
+```datasheet
+label: Duct construction joining method
+type: radio
+options:
+ - Welded seams (abrasive or combustible dust)
+ - Clamp-together with gaskets
+ - Flanged with full-face gaskets
+default: Clamp-together with gaskets
+```
+
+# Air-Moving Fan {toc}
+
+## The fan must be selected at the loaded operating point, in spark-resistant construction where the stream is flammable. A fan chosen off its clean-air curve will, once the collector loads up and back-pressure rises, slide left of peak efficiency and can overload the motor. For combustible or flammable streams the fan is also an ignition source unless built to a spark-resistant construction class, and it is placed downstream of the collector ("clean-air side") so it never handles the raw dust. {note}
+
+## The fan shall be selected to deliver the design airflow at the total system static pressure calculated at the design dirty-state condition.
+
+## The fan serving a combustible or flammable stream shall be of spark-resistant construction per the AMCA classification required by the DHA.
+
+## The fan serving a combustible or flammable stream shall be located on the clean-air side of the collector.
+
+## The fan motor shall not be overloaded at any point on the system operating curve between clean-filter and maximum-allowable-differential-pressure conditions.
+
+```datasheet
+label: Fan type
+type: select
+options:
+ - Centrifugal, backward-inclined (clean air)
+ - Centrifugal, radial-blade (material handling)
+ - Centrifugal, radial-tip (high static)
+ - Axial (low static, high volume)
+default: Centrifugal, backward-inclined (clean air)
+unit: ""
+```
+
+```datasheet
+label: Fan spark-resistant construction class (AMCA)
+type: radio
+options:
+ - None (non-combustible stream)
+ - Type A (all flow-path parts non-ferrous)
+ - Type B (non-ferrous wheel or rubbing-point ring)
+ - Type C (offset construction, no rubbing of ferrous parts)
+default: None (non-combustible stream)
+```
+
+```datasheet
+label: Fan static pressure
+type: range
+unit: in. w.g.
+min: 4
+max: 50
+step: 1
+setpoints:
+ - 8
+ - 10
+ - 12
+ - 20
+default: 10
+```
+
+```datasheet
+label: Fan motor speed control
+type: radio
+options:
+ - Fixed-speed across-the-line
+ - Variable frequency drive (VFD) with pressure feedback
+default: Variable frequency drive (VFD) with pressure feedback
+```
+
+```datasheet
+label: Fan motor horsepower
+type: range
+unit: HP
+min: 1
+max: 500
+step: 1
+setpoints:
+ - 5
+ - 25
+ - 75
+ - 200
+default: 25
+```
+
+# Air-Material Separator {toc}
+
+## The collector is the heart of the system, and its type is the central selection. The choice among pulse-jet cartridge, pulse-jet baghouse, cyclone, wet scrubber, and electrostatic precipitator is driven by particle size, dust load, moisture, stickiness, temperature, and the combustibility of the stream. The pulse-jet cartridge collector is the 80% case for general industrial and welding fume; baghouses dominate high-volume wood, grain, and chemical dust; cyclones serve as coarse pre-separators ahead of a fabric filter; wet scrubbers quench sticky, hygroscopic, or readily ignitable dusts. {note}
+
+## The collector type shall be selected for the particle-size distribution, dust load, moisture, temperature, and combustibility of the stream it serves.
+
+## A cyclone or spark-trap pre-separator shall be installed upstream of any fabric filter that serves grinding, cutting, or other spark-generating operations, so that a single hot particle cannot reach and ignite the filter media.
+
+```datasheet
+label: Primary collector type
+type: select
+options:
+ - Pulse-jet cartridge collector
+ - Pulse-jet baghouse
+ - Cyclone pre-separator + downstream fabric collector (two-stage)
+ - Single-stage cyclone (coarse dust only)
+ - Wet venturi scrubber
+ - Electrostatic precipitator
+default: Pulse-jet cartridge collector
+unit: ""
+```
+
+## Air-to-Cloth Ratio {toc}
+
+## The air-to-cloth (A/C) ratio is the airflow per unit of filter media, and it sizes the collector. Too aggressive a ratio drives particulate into the media, blinds the filter, and spikes the differential pressure at startup. A persistent error is using the gross media area for a cartridge collector instead of the net can-velocity area — the cartridges nest closely and the airflow squeezes through a much smaller effective face, so a gross-area calculation under-sizes the collector and it blinds in service. {note}
+
+## The air-to-cloth ratio for a cartridge collector shall be computed on the net (can-velocity) media area, not the gross media area.
+
+```datasheet
+label: Air-to-cloth ratio — pulse-jet baghouse (gross)
+type: range
+unit: "ft³/min per ft²"
+min: 3
+max: 10
+step: 0.5
+setpoints:
+ - 4
+ - 6
+ - 8
+default: 6
+```
+
+```datasheet
+label: Air-to-cloth ratio — cartridge collector (net)
+type: range
+unit: "ft³/min per ft²"
+min: 1
+max: 4
+step: 0.5
+setpoints:
+ - 1.5
+ - 2
+ - 3
+default: 2
+```
+
+## Filter Media {toc}
+
+## Filter media selection balances efficiency against the dust's physical and chemical character. Polyester felt is the general-purpose default; woven fiberglass tolerates high temperature; a PTFE membrane gives surface filtration and easy cake release for fine or sticky dust; spunbond polyester suits cartridge pleats. The MERV efficiency required is set by where the cleaned air goes and how toxic the contaminant is — nuisance dust recirculated to occupied space needs a higher floor than dust exhausted outdoors, and toxic or carcinogenic dust (silica, hexavalent chromium, lead) demands MERV 16-plus or true HEPA. {note}
+
+## The filter media shall be compatible with the temperature, moisture, and chemistry of the contaminant stream.
+
+## The collector filter media efficiency shall be no less than the MERV rating required for the contaminant's toxicity and the air's destination.
+
+```datasheet
+label: Filter media
+type: select
+options:
+ - Polyester felt (general purpose)
+ - Spunbond polyester (cartridge pleat)
+ - Woven fiberglass (high temperature)
+ - PTFE membrane (fine or sticky dust, surface filtration)
+ - Aramid felt (elevated temperature)
+default: Spunbond polyester (cartridge pleat)
+unit: ""
+```
+
+```datasheet
+label: Collector filter media efficiency (MERV)
+type: select
+options:
+ - MERV 11 (nuisance dust, exhaust outdoors)
+ - MERV 14 (fine metallic or wood dust)
+ - MERV 16 (recirculation to occupied space)
+ - HEPA, MERV 17 to 20 (toxic or carcinogenic dust)
+default: MERV 14 (fine metallic or wood dust)
+unit: ""
+```
+
+## Filter Cleaning and Differential Pressure {toc}
+
+## Pulse-jet cleaning fires a brief reverse blast of dry compressed air through each filter element to release the dust cake into the hopper, and it is governed by differential pressure across the media. The clean filter runs at a low pressure drop; as the cake builds the drop climbs, and a pressure switch triggers the pulse cycle at a setpoint. Wet or oily compressed air ruins media and freezes pulse valves, so the supply must be dry. A high-differential-pressure alarm is mandatory — without it the operator has no warning of filter breakthrough or a plugging duct. {note}
+
+## A continuous differential-pressure monitor across the collector media shall be provided, with a high-differential-pressure alarm.
+
+## The compressed-air supply for pulse cleaning shall be dry, with a pressure dew point below 35°F.
+
+## The compressed-air supply for pulse cleaning shall be regulated to the manufacturer's required pulse pressure.
+
+## The pulse-cleaning cycle shall be initiated on differential-pressure setpoint, not on a fixed timer alone, so cleaning frequency tracks the actual dust load.
+
+```datasheet
+label: Pulse-cleaning compressed-air supply pressure
+type: range
+unit: PSI
+min: 80
+max: 120
+step: 5
+setpoints:
+ - 90
+ - 100
+ - 110
+default: 100
+```
+
+```datasheet
+label: Clean-filter differential pressure (operating)
+type: range
+unit: in. w.g.
+min: 1
+max: 6
+step: 0.5
+setpoints:
+ - 2
+ - 3
+ - 4
+default: 3
+```
+
+```datasheet
+label: High-differential-pressure alarm setpoint
+type: range
+unit: in. w.g.
+min: 6
+max: 12
+step: 0.5
+setpoints:
+ - 8
+ - 10
+default: 10
+```
+
+## Dust Discharge and Hopper {toc}
+
+## Cleaned dust drops into a hopper and must be removed continuously or in controlled batches without breaking the system's air seal. A rotary airlock valve is the workhorse: it discharges the hopper while maintaining the pressure boundary and, for a combustible dust, doubling as a flame-isolation device. Hopper cleanout and bag-change maintenance is where a combustible-dust and confined-space exposure event most often occurs, so the design must include lockout provisions and a cleanout detail. {note}
+
+## A discharge device shall remove collected dust from the hopper while maintaining the system's air seal.
+
+## The collector shall include hopper cleanout access and lockout provisions so that bag-change and hopper-cleaning maintenance can be performed without an uncontrolled dust release.
+
+```datasheet
+label: Hopper discharge device
+type: select
+options:
+ - Rotary airlock valve
+ - Screw conveyor
+ - Slide gate to drum (batch)
+ - Tipping tray / dust drawer (small units)
+default: Rotary airlock valve
+unit: ""
+```
+
+# Explosion Protection and Fire Safety {toc}
+
+## A combustible-dust collector concentrates the exact conditions for a deflagration — fuel, oxygen, confinement — so the collector must be protected and isolated from the rest of the plant. NFPA 660 requires one or more protection methods sized from the DHA: deflagration venting (vent panels or a flameless vent device) that relieves the pressure to a safe place, chemical suppression that quenches the flame front, or pressure-containment that lets the vessel hold the explosion. Equally important is isolation: an abort gate, rotary airlock, or fast-acting valve in the duct keeps a deflagration from propagating back through the ductwork into occupied production areas. {note}
+
+## A combustible-dust collector shall be provided with an explosion-protection method — deflagration venting, chemical suppression, or pressure-containment — sized per the DHA in accordance with NFPA 660.
+
+## A deflagration vent shall discharge to a safe outdoor location, or a listed flameless vent device shall be used where outdoor discharge is not achievable.
+
+## An explosion-isolation device shall be installed in the duct between the collector and the process to prevent flame propagation back into occupied areas.
+
+## Spark detection and extinguishment shall be provided upstream of the collector where the served operation generates sparks or hot particles.
+
+## Electrical equipment within or adjacent to a classified combustible-dust area shall be dust-ignitionproof or explosion-proof per NEC Article 502; standard NEMA 1 motor and starter enclosures shall not be used in a Class II area.
+
+```datasheet
+label: Explosion protection method (combustible dust)
+type: radio
+options:
+ - Deflagration venting — vent panels to safe outdoor area
+ - Deflagration venting — listed flameless vent device
+ - Chemical (suppressant) explosion suppression
+ - Pressure-containment design
+ - Not applicable (non-combustible stream)
+default: Deflagration venting — vent panels to safe outdoor area
+```
+
+```datasheet
+label: Explosion isolation device (duct, collector-to-process)
+type: select
+options:
+ - Rotary airlock valve (passive)
+ - Fast-acting (high-speed) isolation valve
+ - Chemical isolation barrier
+ - Abort gate / diverter
+ - Not applicable (non-combustible stream)
+default: Rotary airlock valve (passive)
+unit: ""
+```
+
+```datasheet
+label: Spark detection and extinguishment
+type: radio
+options:
+ - Required — spark/ember detection with water extinguishment
+ - Not required (no spark-generating operation)
+default: Not required (no spark-generating operation)
+```
+
+```datasheet
+label: Electrical area classification at collector
+type: radio
+options:
+ - Unclassified (non-combustible stream)
+ - Class II, Division 2
+ - Class II, Division 1
+default: Unclassified (non-combustible stream)
+```
+
+# Controls and Monitoring {toc}
+
+## The control package keeps the system in balance and gives the operator visibility. A VFD on the fan holds duct velocity as branches open and close and trims energy when the full system is not running; differential-pressure monitoring reports filter health; and interlocks tie the cleaning cycle, fan, and process together. The control panel is a listed industrial control panel, which matters both for the AHJ and for any motor or controller placed in a classified area. {note}
+
+## The control panel shall be a listed industrial control panel conforming to UL 508A.
+
+## The system controls shall monitor and display collector differential pressure and shall annunciate the high-differential-pressure alarm.
+
+## Where a VFD is used, the controls shall maintain duct transport velocity across the operating range of branch dampers.
+
+## Recirculation of cleaned air to occupied space shall be interlocked so that a secondary after-filter breakthrough or loss of monitoring diverts the system to outdoor exhaust or shuts it down.
+
+```datasheet
+label: Control package
+type: select
+options:
+ - Across-the-line starter, DP gauge only
+ - Across-the-line starter, DP transmitter + alarm
+ - VFD with PLC, DP transmitter, pressure-feedback control
+ - VFD with PLC and integrated explosion-protection interlocks
+default: Across-the-line starter, DP transmitter + alarm
+unit: ""
+```
+
+# Recirculation and Emissions {toc}
+
+## Returning cleaned air to the building saves the heating and cooling energy that would be lost exhausting it outdoors, but it is the highest-risk decision in the system because a filter breakthrough now dumps contaminant directly into the breathing zone. ANSI Z9.2 and ACGIH require a secondary HEPA or MERV 16-plus after-filter on any recirculated stream, and OSHA 29 CFR 1910.94 prohibits recirculation of certain toxic dusts without AHJ approval. A specification that says "recirculate" without naming the after-filter is a guaranteed RFI. {note}
+
+## Recirculated air shall pass through a secondary after-filter of MERV 16 or HEPA before return to occupied space.
+
+## Recirculation shall not be used for a toxic dust prohibited from recirculation by OSHA 29 CFR 1910.94 without written AHJ approval.
+
+## The design capture efficiency shall maintain employee exposures at or below 50% of the applicable OSHA PEL as an engineering-control margin.
+
+## The exposure benchmarks that drive the design — total nuisance particulate 15 mg/m³ TWA and respirable 5 mg/m³, respirable crystalline silica 50 µg/m³ TWA, and general welding fume 5 mg/m³ TWA — are PEL ceilings, not targets; the system is sized to hold the breathing zone well below them. {note}
+
+```datasheet
+label: Secondary after-filter (recirculation only)
+type: radio
+options:
+ - MERV 16 final filter
+ - HEPA (MERV 17 to 20) final filter
+ - Not applicable (exhaust to outdoors)
+default: Not applicable (exhaust to outdoors)
+```
+
+```datasheet
+label: Governing exposure limit for capture design
+type: select
+options:
+ - Nuisance particulate (PNOC) 15 mg/m³ total
+ - Respirable particulate 5 mg/m³
+ - Respirable crystalline silica 50 µg/m³
+ - General welding fume 5 mg/m³
+ - Project-specific contaminant PEL
+default: General welding fume 5 mg/m³
+unit: ""
+```
+
+# Testing {toc}
+
+## Testing happens twice: at the factory for the collector and in the field for the assembled system. Factory acceptance for a pulse-cleaned collector follows ANSI/ASHRAE 199, the only standardized laboratory test for these collectors — requiring it ties the manufacturer to a measured initial and dust-loaded efficiency, average pressure drop, and compressed-air consumption rather than proprietary marketing data. Field commissioning verifies that the installed system actually develops capture velocity at every hood and transport velocity in every branch, by pitot-traverse per the ACGIH Manual and ANSI Z9.2. {note}
+
+## A pulse-cleaned collector shall be factory-tested in accordance with ANSI/ASHRAE 199, reporting initial efficiency, dust-loaded efficiency, average pressure drop, air-to-cloth ratio, and compressed-air consumption.
+
+## The installed system shall be field-commissioned by pitot-traverse per the ACGIH Industrial Ventilation Manual and ANSI Z9.2, verifying capture velocity at each hood, transport velocity in each branch, total system CFM, and total static pressure.
+
+## The field commissioning test shall be repeated after 30 days of operation to confirm sustained performance after the filter cake has stabilized.
+
+## Measured capture velocity at each hood shall meet or exceed the design capture velocity, and measured transport velocity in each branch shall meet or exceed the design transport velocity.
+
+```datasheet
+label: Required tests
+type: checkbox
+options:
+ - ANSI/ASHRAE 199 factory performance test
+ - Field pitot-traverse capture-velocity test (each hood)
+ - Field pitot-traverse transport-velocity test (each branch)
+ - Total system CFM and static pressure measurement
+ - 30-day re-test
+default:
+ - ANSI/ASHRAE 199 factory performance test
+ - Field pitot-traverse capture-velocity test (each hood)
+ - Field pitot-traverse transport-velocity test (each branch)
+ - Total system CFM and static pressure measurement
+ - 30-day re-test
+```
+
+# Installation {toc}
+
+## Installation discipline preserves the design on the floor. Duct that is reassembled with low-velocity rectangular fittings, hoods relocated away from the work, or make-up air omitted will fail commissioning regardless of how well the equipment was specified. Equipment locations, duct routing, and the discharge point are coordinated on the drawings because they cannot be reduced to a datasheet selection. {note}
+
+## Ductwork shall be installed to the routing shown on the drawings [[drawing: duct routing plan]] and shall be supported independently of the served equipment.
+
+## The collector shall be installed at the location shown on the drawings [[drawing: collector location]] with the manufacturer's required clearances for filter access and maintenance.
+
+## The deflagration-vent discharge shall be directed to the safe location shown on the drawings [[drawing: vent discharge zone]], clear of personnel access, building openings, and combustible exposures.
+
+## Ductwork shall be sealed so that joint leakage does not reduce transport velocity below the design minimum.
+
+## Equipment and ductwork shall be supported and braced for the project's structural and seismic loads.
+
+## Each collector, fan, and major duct branch shall be identified per [[sync/mechanical-identification]].
+
+```datasheet
+label: Duct support and seismic bracing
+type: radio
+options:
+ - Gravity and wind loads only
+ - Seismic bracing per project seismic design category
+default: Gravity and wind loads only
+```
+
+# Delivery, Storage, and Handling {toc}
+
+## Filter media and collector internals are the vulnerable items in transit and storage. Felt and membrane media absorb moisture and tear, and a wetted or damaged filter blinds or leaks from day one, so media is kept dry, sealed, and uninstalled until the system is ready to run. {note}
+
+## Filter media shall be delivered in the manufacturer's sealed packaging and stored dry and protected from physical damage until installation.
+
+## Collectors and fans shall be stored with openings covered to keep out construction debris and weather until connected.
+
+## Filter elements shall not be installed until the ductwork is clean and the system is ready for startup, to avoid loading the media with construction debris.
+
+# Warranty {toc}
+
+## The warranty splits between the equipment and the consumable media, which wears by design. The collector housing, fan, and controls carry the equipment warranty; filter elements are consumables and carry a separate, shorter media warranty that excludes normal loading and abrasion wear. {note}
+
+## The collector housing, fan, motor, and control package shall be warranted against defects in materials and workmanship for the project warranty period.
+
+## Filter media shall carry the manufacturer's media warranty against manufacturing defects, exclusive of normal service wear.
+
+```datasheet
+label: Equipment warranty period
+type: select
+options:
+ - 1 year
+ - 2 years
+ - 3 years
+ - 5 years
+default: 1 year
+unit: ""
+```
+
+# Spare Parts {toc}
+
+## A dust system depends on consumables that must be on hand, because a plugged filter or a failed pulse valve idles the production equipment the system serves. A complete spare set of filter elements, pulse-valve diaphragms, and door gaskets keeps a media change from becoming a production outage. {note}
+
+## The Contractor shall furnish one complete spare set of filter elements for each collector.
+
+## The Contractor shall furnish spare pulse-valve diaphragms and access-door gaskets in the manufacturer's recommended quantity.
+
+```datasheet
+label: Spare parts to be furnished
+type: checkbox
+options:
+ - One complete spare set of filter elements per collector
+ - Spare pulse-valve diaphragms
+ - Spare access-door and hopper gaskets
+ - Spare differential-pressure sensor
+default:
+ - One complete spare set of filter elements per collector
+ - Spare pulse-valve diaphragms
+ - Spare access-door and hopper gaskets
+```