Negative-Pressure Booth

Where a standard dispensing booth holds positive pressure (air flows out — protecting the product from the corridor), a negative-pressure booth holds negative pressure (air flows in — protecting the operator and the rest of the facility from what is in the booth). The booth captures and HEPA-filters air before exhausting it. Typically used for OEB 3–4 actives (OELs in the 1–100 μg/m³ range) where full operator isolation is not warranted but normal product-protection booths leave too much airborne residue.

• Negative ΔP of −15 to −30 Pa relative to the airlock/corridor.
• Single-pass airflow — no recirculation between batches or products.
• Final HEPA on exhaust, bag-in/bag-out filter change.
• Material airlock with interlock (both doors cannot be open simultaneously).
• PPE per the active's risk assessment — typically PAPR at OEB 4.

Containment performance is measured per ISPE SMEPAC: a standardised challenge with surrogate powder and breathing-zone air sampling produces an 8-hour TWA airborne concentration compared to the active's OEL. The booth is fit-for-purpose if its SMEPAC result is below the OEL with a safety margin. A standard booth achieves ~100 μg/m³ TWA; a well-designed negative-pressure booth achieves 10–50 μg/m³; an isolator achieves <1 μg/m³.

• Exhaust HEPA with bag-in/bag-out — filter changes occur without breaking containment.
• Differential pressure monitoring with continuous alarm; loss of ΔP halts dispensing immediately.
• Material airlock pass-through with interlocked doors and intermediate purge cycle.
• Smooth interior surfaces (stainless steel or coated, no flat horizontal ledges) for wet cleaning.
• Dedicated waste handling — sealed containers passed through dedicated waste airlock.
• Gowning and degowning rooms arranged so the contamination flow is one-way.

Working in a negative-pressure booth is more demanding than a standard booth: full PPE (often PAPR), restricted material flow through airlocks, mandatory dwell times for purges, post-shift decontamination shower. Sessions are time-limited per ergonomic and exposure assessment. Pre- and post-shift breathing-zone monitoring may be required by the EHS programme for OEB 4 actives.

• Sharing a negative-pressure booth between products without dedicated change-over and full clean — cross-contamination near-certain.
• Single-pass airflow defeated by recirculating HVAC inadvertently sharing a return duct with another room.
• Material airlock door interlock overridden during 'urgent' transfers — containment broken.
• Exhaust HEPA not change-controlled — filter age unknown; SMEPAC margin unverified.
• Operator PPE selected on assumption rather than active-specific risk assessment.
• Negative-pressure used where an isolator is actually required (OEB 5 actives below 1 μg/m³ OEL).

• Pharma — hormonal actives, β-lactams (where dedicated), moderate-potency cytotoxics in compounding pharmacies.
• Biopharma — viral vector handling at moderate risk levels (with biosafety overlay).
• Veterinary — high-potency anthelmintics and growth promotants.
• Cosmetics — restricted-use perfume bases and intense pigments.
• Chemicals — sensitiser handling; isocyanate sub-dispensing.
• Cannabis — isolated cannabinoid distillate weighing where dust control matters.