Knowledge Hub · Saxsons Lead-Lined Fume Hood
A dispensing fume hood looks like a stainless cabinet with a sash. What actually gates AERB inspection sign-off is the five-way intersection of face velocity, fan certification, shielding sizing, filtration and across-filter pressure monitoring. This page is the why behind each.
Why this matters
AERB face-velocity gate
The AERB Safety Code for Nuclear Medicine Facility expects ≥ 0.5 m/s face velocity at the sash opening on dispensing fume hoods. Below that, room air spills back into the cabinet under the operator's reach and carries volatile activity (I-131, F-18 vapours, Tc-99m aerosols) into the dispensing room. Above ~1.0 m/s, turbulence at the sash actually degrades containment and lifts particulates off the work zone. The 0.5–0.8 m/s sweet spot is where containment and aseptic-dispensing practice both work. Every Saxsons-built cabinet ships with a factory face-velocity certificate at the time of shipping; the optional hot-wire anemometer keeps the operator in spec day-to-day.
Based on: AERB Safety Code for Nuclear Medicine Facility — fume-hood face-velocity expectations; ASHRAE 110 fume-hood-containment test method.
Read source ↗AMCA-certified fan rating
An AMCA-certified centrifugal fan ships with a published performance curve that is laboratory-verified — pressure rise versus flow rate, measured against AMCA Standard 210 / ANSI / AMCA 210 test conditions. That curve is what lets a hot-lab designer match the fan to the duct-loss budget, the filter pressure drop and the sash opening such that the cabinet hits 0.5 m/s under loaded-filter conditions. Without the certification the published curve is a vendor claim; with the certification it's a third-party-verified design input.
Based on: AMCA Standard 210 / ANSI / AMCA 210 — Laboratory Methods of Testing Fans for Aerodynamic Performance Rating; AMCA Certified Ratings Program.
Read source ↗Lead-shielding selection
Lead shielding attenuates gamma through the half-value-layer relationship — 1 HVL of lead is about 0.12 mm at 80 keV (low-energy SPECT), 0.25 mm at 140 keV (Tc-99m), 1.5 mm at 364 keV (I-131), and 4–5 mm at 511 keV (F-18 / Ga-68 / Cu-64). Routine Tc-99m kit dispensing is comfortable at 3 mm. Mid-activity F-18 / Ga-68 / Lu-177 dispensing wants 5–6 mm. High-activity theranostic prep with weekly Lu-177 vials of 5–10 GBq wants 10–12 mm. Buying the highest tier for the whole department costs floor space and money; sizing per workflow keeps shielding where the activity actually is.
Based on: NCRP Report 49 / NCRP Report 147 — Structural Shielding for Medical Use Facilities; ICRP Publication 107 nuclear-decay data.
Read source ↗Active carbon for radioiodines
Active-carbon filtration on the cabinet exhaust captures volatile radioiodines (I-131 vapour, I-123 transients) before they reach the room ventilation and the site stack. The activated-carbon adsorption capacity for elemental and organic iodine species is well-characterised; a properly-sized charcoal stage in series with the HEPA pre-filter handles both particulate radioiodines (aerosols) and vapour-phase iodides. For I-131 therapy capsule decant and Lu-177 / I-131 hybrid programmes, the filter pack is what keeps the cabinet exhaust below the site stack release limit set in the AERB licence.
Based on: IAEA Safety Reports Series 38 — Applying Radiation Safety Standards in Nuclear Medicine; NRC Regulatory Guide 8.39 radioiodine air-sampling and filtration.
Read source ↗Negative-pressure monitoring
Face velocity at the sash and pressure differential across the filter pack are two readings of the same physical state — the filter loading. The face-velocity reading drifts when the filter is most of the way to choke; the ΔP reading drifts as soon as loading starts. A negative-pressure sensor with a PLC touch panel watches ΔP-across-filter continuously and flags the choke threshold weeks before face velocity gets close to the 0.5 m/s floor. The cabinet trips an alarm and the operator schedules a filter change — before AERB face-velocity log starts showing red.
Based on: ASHRAE 110 — Method of Testing Performance of Laboratory Fume Hoods; ISO 14644-3 cleanroom-test methods (ΔP differential).
Read source ↗In-cabinet dose calibrator
A traditional hot-lab fit-out separates the dispensing fume hood from the dose-calibrator bench by 1–1.5 m of operator traverse. Per dispense, the operator handles activity twice — once in the cabinet, once at the calibrator bench. The dose-calibrator-mount variant of this cabinet puts the ionisation chamber inside the shielded enclosure, with the display mounted externally. Activity stays in the shielded zone from draw to assay to release; the operator traverse drops to zero. For programmes dispensing 30+ patient doses per shift, the floor-space and dose-economy gains are substantial.
Based on: IAEA Operational Guidance on Hospital Radiopharmacy; AAPM TG-181 / TG-211 PET-NM workflow guidance.
Read source ↗AERB, IAEA, AMCA, NCRP and ASHRAE documents that anchor the lead-lined fume-hood design.
Indian regulatory framework for nuclear-medicine facility licensing including dispensing fume-hood face-velocity, ventilation and shielding expectations.
IAEA framework for hospital-radiopharmacy hot-lab design, ventilation, fume-hood expectations and operational radiation protection.
IAEA framework covering radioiodine air-sampling, filtration and operator-side dose protection in NM hot labs.
AMCA fan-performance certification framework — what an AMCA-certified centrifugal-fan rating guarantees on a cabinet exhaust train.
NCRP shielding-design framework covering lead-attenuation half-value layers used to size cabinet shielding to per-isotope workflow.
ASHRAE fume-hood-containment test method; the basis for the 0.5 m/s face-velocity expectation and across-filter ΔP monitoring.
Where next
Product page →
Lead-lined fume hood specs + variant matrix
Size × shielding × material × filter × accessory configuration matrix, Saxsons own-brand build.
For the radiopharmacist →
Sizing + shielding selection guide
Per-workflow size, shielding tier, filter pack and accessory selection with worked AERB-licensing scenarios.