Difficulties in the Fit-out of Ventilation Systems for Organic Synthesis Laboratories
2026-07-08
I. Local Exhaust Ventilation: Fume Hoods (Core Hazard Points)
Air volume standards: The face velocity of standard synthesis fume hoods shall be maintained at 0.5–0.6 m/s; for processes involving large volumes of highly volatile solvents, the velocity shall be increased to 0.6–0.7 m/s. A single 1.5 m-wide hood has an exhaust air rate of 1,200–1,600 m³/h. Simultaneous operation of multiple hoods easily leads to insufficient air volume, so spare capacity must be reserved for the main duct cross-section.
Anti-corrosion and explosion-proof construction: The lining shall be made of 304 or 316 stainless steel or PP material. No standard power sockets shall be installed inside the hood; explosion-proof sealed lighting is mandatory. A liquid collection and drainage trough is fitted at the bottom to drain condensed solvents. PTFE flame-retardant flexible connectors are adopted at outlets, with metal hose clamps equipped with anti-static jumpers.
Layout restrictions: Fume hoods shall be placed away from doorways and direct air supply from air conditioners. Maintenance clearance shall be reserved at the rear to prevent airflow turbulence from dispersing VOC vapors.
II. Three Major Construction Challenges of Ductwork
Material Selection
304 and 316 stainless steel are mainstream options; 316 stainless steel is specified for working conditions with high halocarbon concentrations. FRP delivers excellent corrosion resistance yet is prone to deformation. PVC and PP exhibit poor anti-static performance and may only be used for small branch ducts of reagent cabinets, and are strictly prohibited for main ventilation ducts.
Anti-static treatment and sealing: All flanges, elbows and tees shall be bridged with copper braided straps and uniformly connected to the main equipotential bonding system. Solvent-resistant polyurethane adhesive shall be used for sealing; ordinary silicone sealant is forbidden.
Liquid accumulation and leakage prevention: Ducts shall be laid with a minimum gradient of 3‰. Liquid sumps and drain valves shall be installed at low points, and outdoor vertical risers shall be insulated to avoid condensation.
Floor height constraints: Main ducts have a diameter ranging from 600 mm to 1,000 mm. The ceiling cavity must have a minimum clear height of 900 mm when accounting for insulation and supports. Low beam heights reduce duct diameter and drastically raise air resistance.
III. Ventilation Fans and VAV Variable Air Volume Systems
Explosion-proof rating: Indoor fans shall be ExdⅡBT4 explosion-proof models. FRP anti-corrosion explosion-proof fans are installed on rooftops to eliminate electric sparks that may ignite organic vapors.
Mandatory VAV variable air volume configuration: Each fume hood is equipped with an independent air damper. Static pressure sensors on the main duct interlock with variable frequency fans to prevent excessive negative indoor pressure and door suction when multiple hoods are closed. A supporting UPS power supply is provided to sustain fan exhaust for more than 30 minutes in case of power failure.
Vibration isolation and noise reduction: Triple vibration reduction measures are implemented, including spring shock absorbers under fan bases, flexible duct connectors and shock-absorbing pads for supports. Sound-insulated fan enclosures are additionally installed for rooftop units.
IV. Makeup Air and Zoned Differential Pressure Control
Relying solely on air infiltration through door gaps causes unbalanced negative pressure and severe temperature/humidity fluctuations. High-risk synthetic laboratories must be equipped with a dedicated pre-treated outdoor makeup air system: outdoor air is filtered and conditioned for temperature and humidity before independent supply, and recirculation of corridor air is prohibited.
Differential pressure gradient (descending negative pressure): Reagent storage room (10–15 Pa) > laboratory working area (5–10 Pa) > buffer room. Interlocked supply and exhaust dampers maintain stable pressure control to block odor migration outward.
V. Independent Exhaust for Auxiliary Points (Frequently Overlooked)
Explosion-proof reagent cabinets, gas cylinder cabinets, waste liquid temporary storage zones and rotary evaporator workstations all require separate branch exhaust ducts. Exhaust for gas cylinder cabinets interlocks with combustible gas detectors to automatically boost extraction flow upon leakage. Manual shut-off valves are fitted on branches to facilitate maintenance.
VI. Terminal Waste Gas Treatment
Direct exhaust to atmosphere is forbidden. Treatment equipment shall be matched to operating conditions: activated carbon adsorption for low-concentration batch processes; condensation recovery combined with activated carbon for medium-to-high concentration distillation processes; catalytic combustion for high-concentration waste gas; absorption tower plus adsorption combination for halogenated waste gas containing dichloromethane, chloroform and similar substances. Fan static pressure selection must reserve allowance for resistance from waste gas treatment equipment.
VII. Safety Interlock Automatic Control System
- VOC / combustible gas alarm: Full exhaust activation and regional power cut-off upon concentration over-limit;
- Fume hood door magnetic sensor: Automatic air volume boost when the sash is raised excessively, plus audible and visual alarms for insufficient face velocity;
- Fire protection interlock: All ventilation dampers close when gas fire suppression systems activate; All signals are centralized in the main control room, with separate wiring routed through explosion-proof conduits.
VIII. Common Construction Defects and Acceptance Items
Typical Hidden Hazards
Omission of equipotential bridging, ducts laid without gradient, ordinary canvas flexible connectors, insufficient static pressure margin of fans, absence of independent makeup air, missing exhaust for auxiliary points, and improper use of non-explosion-proof fans.
Mandatory Acceptance Tests
Multi-point face velocity measurement for fume hoods, 24-hour zoned differential pressure monitoring, duct air tightness testing, grounding resistance measurement, simultaneous multi-hood air volume testing, full set safety interlock commissioning, and waste gas emission testing.
IX. Pain Points in Existing Laboratory Retrofits
Insufficient dimensions of original exhaust shafts, limited floor height restricting duct size, lack of UPS emergency power supply, fully corroded aged galvanized or plastic ducts requiring ceiling removal and complete replacement, and absence of installation platforms for rooftop makeup air equipment.
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