Weighing Booth (Dispensing Booth) Buyer's Guide: Airflow, H14 & Negative Pressure

A negative-pressure weighing booth is a containment enclosure for weighing and dispensing powder materials. A fan draws room air through the booth and its filtration train, holding the work zone under negative pressure so that airborne powder is directed downward and inward rather than escaping into the surrounding room. The operator works through an open front, using gloves or reach-in access as required by the process.

In pharmaceutical and chemical powder handling, the terms weighing booth, dispensing booth, and downflow booth are often used for this type of equipment. For enquiry purposes, treat them as synonyms, but describe the actual weighing or dispensing operation in your RFQ. SENPEI’s product page is negative-pressure weighing booths; it sits within the wider clean benches and containment range, alongside isolators, laminar-flow transfer carts, and other cleanroom equipment.

This guide explains how to turn the published booth family into a procurement specification without confusing reference airflow with rated exhaust airflow, or a general HEPA description with a confirmed H14 filter grade.

Why negative pressure matters for powder weighing

Weighing and dispensing can release powder when containers are opened, material is transferred, or residues are removed from scoops and balance surfaces. A negative-pressure work zone provides an inward airflow direction at the open front. Powder is therefore pulled into the booth rather than drifting toward the operator or adjacent room.

The fan, airflow path, and room air balance work together to maintain this condition. Negative pressure is a containment principle, not a universal pressure value: SENPEI confirms the negative-pressure setpoint separately rather than publishing a fixed Pa setpoint in the catalogue table.

Airflow also affects the weighing process. Room draughts and uncontrolled air movement can disturb a balance, while excessive or poorly directed airflow around the weighing equipment may affect stability. The booth’s negative-pressure arrangement and weighing-sensor arrangement are intended to help keep readings stable against room draughts and dust. Buyers should still identify the balance or weighing equipment, required weighing range, and accuracy when requesting a quotation.

US Validation’s guidance on dispensing and material-handling qualification makes a related point: airflow must be assessed against the intended combination of product protection, operator protection, and environmental containment. Do not assume that a downflow booth automatically protects both product and personnel without considering airflow, filtration, material hazards, work practices, and the room-pressure strategy.

Match working width and airflow to the operation

Start with the working opening and internal workspace, not the airflow figure alone. The booth must accommodate the balance, containers, scoops, and expected batch-handling movements while preserving a practical operator position. A wider enclosure can support more equipment or a larger transfer operation, but it also changes the published airflow family and fan power.

SENPEI publishes four working widths from 1100 to 1900 mm, with reference airflow values from 1400 to 2500 m³/h.

Housing size (mm)	Internal size (mm)	Airflow (m³/h)	Plenum	Power (W)	Filter stages	Noise at 1 m below HEPA (dB)
1200 × 1300 × 2350	1100 × 800 × 1900	1400	Stainless steel	300	Pre-filter, medium filter and HEPA	<67
1500 × 1300 × 2350	1400 × 800 × 1900	1800	Stainless steel	300	Pre-filter, medium filter and HEPA	<67
1800 × 1300 × 2350	1700 × 800 × 1900	2200	Stainless steel	600	Pre-filter, medium filter and HEPA	<67
2000 × 1300 × 2350	1900 × 800 × 1900	2500	Stainless steel	600	Pre-filter, medium filter and HEPA	<67

These are reference values; confirm the configuration with the quotation. In particular:

• The airflow in this table is not the rated exhaust airflow.
• Weighing range, accuracy, and the negative-pressure setpoint are confirmed separately.
• The noise values are measured 1 m below the HEPA face, not at an arbitrary operator or room position.
• The table does not publish face velocity, so buyers should not derive a catalogue face-velocity claim from the airflow and enclosure dimensions.

Use the table to shortlist a size and plan preliminary electrical and noise expectations. Then ask the supplier to confirm the proposed booth, exhaust arrangement, and control requirements against your process.

Understand the three-stage filtration train

The published filtration arrangement combines a primary filter, medium-efficiency filter, and HEPA filter in a stainless steel plenum. Each stage has a distinct role in the train: upstream stages capture larger and intermediate particulate loading, while the final HEPA stage provides high-efficiency particulate filtration before air leaves the filtration system.

For maintenance planning, identify replacement stages by their position in this train rather than treating every filter as the same item. SENPEI lists replacement filter stages per order, so the RFQ should state which stages and quantities are required.

Confirm H14 instead of assuming it

The live weighing-booth page specifies HEPA, but it does not publish H13 or H14 as a fixed stock grade. This distinction matters when a user requirement specification names a filter standard.

Under EN 1822, H14 has an overall efficiency of at least 99.995%, equivalent to penetration of no more than 0.005%, and a local efficiency of at least 99.975%. H13 has at least 99.95% overall efficiency and 99.75% local efficiency. EN 1822 maps H14 to ISO 45 H under ISO 29463, and the two standards remain in use alongside one another. The site’s EPA, HEPA and ULPA filter guide provides additional filter-class background.

If your URS requires H14, write “H14 to EN 1822” in the RFQ and request confirmation on the quotation. Also clarify the required documentation and any project-specific testing expectations. Do not treat the generic word HEPA as evidence of a particular EN 1822 grade.

Choose ducted exhaust or recirculation

The buyer must decide whether filtered exhaust is ducted away or recirculated to the room. This choice connects the booth to the facility’s containment and room-pressure strategy, so it should be resolved with the process owner and cleanroom or HVAC engineer rather than left as an installation detail.

A ducted arrangement requires a defined exhaust route and connection point. Recirculation returns air to the room and requires the buyer to assess whether that arrangement is suitable for the powder, process, and room cleanliness class. In either case, provide the intended arrangement and room class in the RFQ.

SENPEI’s quoted booth scope includes the fan set, three-stage filters, plenum, and control panel as configured. Positioning, site power connection, and ducting to the exhaust or recirculation point remain with the buyer or the buyer’s contractor. Agree these interfaces early so that the booth delivery, duct route, electrical supply, and commissioning responsibilities are aligned.

An open-front weighing booth is not a fully sealed barrier enclosure. Filter-installation sealing and the duct or recirculation interfaces should be confirmed by the buyer or the buyer’s contractor against the project procedure; the product page does not publish a separate sealing class or leakage rating for those interfaces.

The product page also mentions an automation and display system plus fault diagnosis and prompts. If your URS requires specific differential-pressure monitoring, airflow alarms, or alarm challenges, list those requirements as questions for confirmation rather than assuming a particular instrument or alarm configuration.

When a booth may not be enough

An open-front weighing booth is not automatically the right containment level for every powder or operation. Material hazard, batch quantity, transfer method, cleaning approach, operator procedure, and room-pressure design all influence the equipment decision.

Where the process requires a higher containment barrier, evaluate isolators instead of trying to stretch an open-front booth beyond its intended role. This is an engineering assessment, not a decision based on an assumed occupational exposure band or a universal equipment cutoff.

For formal containment-performance evaluation, ISPE’s SMEPAC Good Practice Guide provides an industry methodology for standardized particulate-containment assessment, with protocols that include downflow booths. Use it as a pointer when defining your own qualification strategy. It does not mean that a particular SENPEI booth has published SMEPAC results; any required evaluation and acceptance criteria must be established for the project.

Do not confuse containment with a laminar clean bench

A horizontal laminar-flow clean bench is primarily framed around product protection on an open bench. A negative-pressure weighing booth is framed around powder containment and protection of the operator and room. These are different airflow and protection objectives.

Select the equipment from the hazard and protection requirements. Do not substitute a product-protection bench for a powder-containment booth simply because both are used in cleanrooms.

Send a complete quotation checklist

Use the following checklist to turn the five buyer prompts on the product page into an RFQ. Add drawings, process descriptions, or URS clauses where available.

Application and material
- Process: weighing, dispensing, sampling, or another powder-handling step
- Material description and powder characteristics
- Particle size and quantity per batch
- Containment target and relevant material-hazard information
- Application sector: pharmaceutical, laboratory, food, research, or pilot facility

Booth size and weighing equipment
- Required working width
- Balance or weighing equipment to be placed inside
- Equipment dimensions and required operating space
- Required weighing range and accuracy

Airflow, filtration, and monitoring
- Selected catalogue size or preferred airflow family
- Confirmation that rated exhaust airflow will be stated separately
- Required HEPA class; state H14 to EN 1822 if required
- Replacement filter stages and quantities required
- Questions on negative-pressure monitoring and display
- Questions on airflow or differential-pressure alarms and fault prompts
- Required qualification or testing documentation

Exhaust and room interface
- Ducted exhaust away or recirculation to the room
- Room cleanliness class
- Proposed exhaust or recirculation connection point
- Buyer/contractor scope for positioning, power connection, and ducting
- Confirmation that open-front operation is acceptable; filter-seal and duct-interface responsibilities

Electrical, acoustic, and delivery information
- Site power-supply voltage and frequency
- Power and noise expectations based on the selected reference table row
- Quantity of booths
- Destination country or port

Request a configuration against your process

A useful booth specification connects the working width, weighing equipment, powder characteristics, filtration requirement, exhaust route, and site utilities. Keep catalogue values as reference figures, then obtain written confirmation of the airflow arrangement, negative-pressure setpoint, weighing details, and any required H14 grade.

Review the negative-pressure weighing booth product family and submit your process details through Request a Quote. This gives the supplier a clearer basis for configuring the fan set, filtration train, plenum, controls, and order-specific replacement filters.

Selected references

• Comparison of filter classes (EN 1822 / ISO 29463)
• US Validation — Dispensing and Material Handling Systems Qualification
• ISPE Pharmaceutical Engineering — Assessing Containment Equipment and Systems: New ISPE Guide

Questions buyers ask