NOTE 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. (1.1)

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. (1.2)

NOTE 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. (1.6)

NOTE Welding fume extraction units, grinding fume collectors, downdraft tables, and central process vacuum systems are within scope as fixed source-capture configurations. (1.7)

NOTE The boundary between this standard and adjacent systems is the contaminant stream, not the room. (1.8)

NOTE Grease-laden kitchen exhaust is excluded; it requires listed hoods, grease filters, fire suppression, and NFPA 96 compliance and is covered by Kitchen Exhaust Systems. (1.8.1)

NOTE General building supply, return, and exhaust fans for occupant ventilation are excluded and are covered by Hvac Fans; pressure-classed HVAC distribution ductwork is covered by Hvac Ductwork. (1.8.2)

NOTE Laboratory bench fume hoods — listed, walk-up enclosures with a sash — and their VAV-controlled exhaust are excluded and are covered by Laboratory Exhaust And Fume Hoods; a source-capture arm or backdraft hood over a grinder or welding table is within scope here. (1.8.3)

NOTE Fixed area gas detection and alarm for toxic or flammable gases is excluded and is covered by Gas Detection Systems. (1.8.4)

NOTE Process instrument impulse tubing and sensor installation at monitoring points are excluded and are covered by Instrument Installation And Tubing; identification labeling of mechanical piping and equipment is covered by Mechanical Identification. (1.8.5)

NOTE NFPA 660 (2025) consolidated and superseded the six prior NFPA combustible-dust standards — NFPA 61, 484, 652, 654, 655, and 664 — effective December 2024; specifications drafted before that date and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. (2.3)

NOTE 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. (2.4)

NOTE 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. (4.1)

NOTE 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. (5.1)

NOTE 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. (5.3)

NOTE 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. (6.1)

NOTE 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. (7.1)

NOTE 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. (8.1)

NOTE 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. (9.1)

NOTE 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. (9.5)

NOTE 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. (9.8)

NOTE 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. (9.12)

NOTE 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. (9.18)

NOTE 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. (10.1)

NOTE 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. (11.1)

NOTE 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. (12.1)

NOTE 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. (12.5)

NOTE 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. (13.1)

NOTE 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. (14.1)

NOTE 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. (15.1)

NOTE 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. (16.1)

NOTE 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. (17.1)