Duct Smoke Detector with Sampling Tube Array An advanced, air-handling safety sensor designed to sample air currents inside commercial ventilation ductwork for invisible smoke particles. Housed inside a sealed, heavy-duty external enclosure, this addressable device utilizes an aerodynamic differential-pressure sampling tube array to draw airflow through its internal photoelectric chamber, initiating automated fan shutdowns, closing motorized fire dampers, and sending localized alarms to the central Fire Alarm Control Panel (FACP) before toxic smoke can migrate through the facility.
Containing Toxic Smoke Transmissions Across Central HVAC Networks
In large-scale commercial structures and multi-story towers, central Heating, Ventilation, and Air Conditioning (HVAC) networks act as a massive highway system for air movement. If a fire breaks out inside a localized utility room, an active air handling unit (AHU) will naturally vacuum up the toxic smoke and pump it down the main distribution ducts, rapidly spreading suffocating gases to distant, unaffected floors and trapping occupants inside evacuation pathways. A Duct Smoke Detector is the primary automated defense against this threat, monitoring high-velocity air shafts to isolate the building's ventilation grid the moment a fire event begins.
Unlike standard ceiling detectors that are bypassed by high-velocity drafts, a duct smoke detector is mounted on the outside of the ventilation ducting. It relies on a mechanical Differential Pressure Sampling Array consisting of two hollow tubes extending across the inner duct stream:
The Intake Sampling Tube: Outfitted with a series of small, forward-facing collection ports facing into the oncoming air velocity. The kinetic force of the airflow pushes a continuous air sample into the tube.
The Exhaust Tube: Outfitted with a single rear-facing discharge port. Because air rushing over the exhaust tube creates a localized low-pressure zone (venturi effect), it naturally vacuums the air sample through the external detector housing and drops it back into the main duct line.
As the air samples move through the sealed external housing, they pass over an intelligent photoelectric sensing chamber. If smoke particles scatter the internal light beam, the on-board microprocessor triggers a multi-system emergency shutdown protocol.
Multi-System Interlock Integration
Per NFPA 90A guidelines, duct smoke detectors are critical system interlock nodes that execute synchronized safety overrides across the facility:
AHU Fan Shutdown: Instantly drops power to the main supply and return air fans, stopping the physical movement of air to halt smoke migration.
Motorized Damper Closure: Drops the 24V DC/120V AC holding current on localized electromagnetic fire dampers, allowing heavy internal spring arrays to seal off individual floor zones.
Fresh Air Exhaust Overrides: Signals the Building Management System (BMS) to open smoke evacuation louvers, diverting hazardous fumes directly outside the structural shell.
Key Performance Features
High-Velocity Aerodynamic Profiling: Precision-engineered to reliably sample air moving at extreme velocities from 3.0 to 20.3 meters per second ($100\text{ to }4000\text{ feet per minute}$) without experiencing light scatter distortion.
Tool-Free Modular Sampling Tubes: Available in heavy-gauge steel or aluminum tubing pre-cut to standard duct widths ($1\text{ft to }10\text{ft}$ lengths), featuring rapid twist-lock engagement pins for fast tool-free cleaning.
Transparent High-Impact Polycarbonate Cover: Outfitted with a clear front lens plate and a built-in magnet testing target, allowing technicians to visually inspect the internal sensor status, check for dust fouling, or execute code-mandated tests without opening the air seal.
Built-In Heavy-Duty Form C Relays: Features an internal 10A dry-contact relay board capable of switching high-voltage HVAC fan starters directly, bypassing software networks for fail-safe physical equipment shutdown.
True Addressable SLC Loop Control: Connects to the main FACP via a two-wire supervised data line, pinpointing the exact air handling branch or duct location under trouble or alarm states.
Ideal Infrastructure Applications
Main Air Handling Supply Units: Installed downstream of primary air filters to monitor whole-building circulating air loops.
Return Air Ducts & Floor Plenums: Positioned at primary return entry junction boxes on individual floors to catch localized fire breakouts early.
Supply Air Riser Splits: Deployed inside vertical distribution shafts traversing multi-story office or hotel infrastructure networks.
Technical Performance MatrixEngineering Metric ParameterAddressable Duct Detector ProfileConventional 4-Wire Duct ProfileSensing Technology CoreHigh-Sensitivity Photoelectric ChamberPhotoelectric Air Sampling ChamberAir Velocity Operating Range$100\text{ to }4000\text{ FPM } (0.5\text{ to }20.3\text{ m/s})$$500\text{ to }4000\text{ FPM } (2.5\text{ to }20.3\text{ m/s})$Duct Ingress ArchitectureExternal Mount / Internal Probe ArrayExternal Mount / Internal Probe ArrayInput Connection LoopTwo-Wire Supervised SLC Data Bus4-Wire Layout ($2\times\text{ Power}, 2\times\text{ Contacts}$)Internal Interlock RelaysForm C (SPDT), 10A @ 30V DC / 120V ACForm C (SPDT), 5A @ 30V DC / 120V ACEnclosure Material BaseNEMA 2 / IP54 High-Impact ABS PlasticHeavy Sheet Metal / Toughened PolymerCompliance CertificationsUL 268A Listed (Duct Application) / NFPA 90AUL 268A Listed / CSFM ApprovedStandard Procurement Package Components
Complete External Duct Smoke Detector Sealed Housing Assembly
Low-Profile Addressable Photoelectric Detector Core Unit
Heavy-Duty End-Plug, Air Seal Gaskets, and Self-Tapping Mounting Screws
Technical Airflow Velocity Calibration Sheet and Installation Manual
Required for On-Site Assembly: Specified Length Metal Intake/Exhaust Sampling Tubes (Sold Separately based on exact structural duct cross-sectional dimensions)