A specification that asks for an “OEB 5 isolator” leaves the most consequential engineering decisions unresolved. The band may belong to an undefined system, the supplier may test a different task, and the clean-down procedure may expose technicians to residues that never appeared in the purchasing discussion. Start the user requirements specification with the compound, process and exposure scenarios. The equipment description follows that basis.
This article develops a practical URS for high potency containment. Its engineering checklists are GuideGxP recommendations, to be adapted by Engineering, Production, Occupational Hygiene, Toxicology, Maintenance and Quality. They are not universal exposure limits or a substitute for a site assessment. Use the companion containment strategy article to establish the risk basis before fixing the design.
1. Define the boundaries and the intended use
Describe where containment begins and ends: incoming package, dispensing, sampling, charging, processing, discharge, intermediate storage, waste removal and cleaning. Include utilities and interfaces supplied by others. A sealed processing vessel does not provide a complete system when its inlet requires an open bag pour or its filter must be removed without protection. Mark each intended opening on the process flow diagram.
For each operation, identify material form, relevant concentration, batch range, package geometry, task duration, frequency and foreseeable operator interaction. Distinguish dry API, diluted blend, wet cake, granules and final dosage forms. Their emissions and handling requirements can differ even when they contain the same active substance. Record uncertainty explicitly rather than substituting a reassuring equipment label.
Define the installed environment: available space, access routes, floor loading, utility capacity, adjacent activities and existing HVAC. Separate routine production from setup, product changeover, abnormal recovery and maintenance. The URS should tell bidders which modes must remain contained and which require an independently assessed safe opening procedure. Identify out-of-scope activities and the party responsible for them.
2. Establish a scientifically justified exposure basis
An occupational exposure limit addresses worker exposure for a specified route and reference period. An occupational exposure band groups substances within a named banding framework; its numerical boundaries are not universal. Ask Toxicology and Occupational Hygiene to approve the compound-specific assessment, including the data basis, confidence, relevant short-term effects, sensitisation and skin exposure considerations. Do not derive an OEL automatically from a PDE.
HBEL is the broader health-based exposure limit concept used in cross-contamination assessment. PDE and ADE describe daily exposure concepts used in different methodologies; document the derivation and application rather than assuming that their terminology establishes equivalence in every dossier. Product carryover limits require additional process and product information. They are not airborne occupational acceptance criteria.
Translate the approved exposure strategy into a containment performance objective for each task. This objective is an equipment or process design and verification target, selected with the total exposure picture in mind. It is not automatically the OEL itself. Document how repeated tasks, other sources, background and uncertainty are considered, and what actual workplace assessment remains necessary after surrogate testing.
3. Specify controls before protective clothing
Review whether the hazardous handling step can be eliminated, the material form changed or the process reorganised. Where feasible, reduce open handling through closed processing and engineered transfer. Then define the primary containment, secondary room controls, procedures and residual PPE requirements. This implements the hierarchy of controls described by NIOSH; it does not make one technology universally appropriate.
Avoid specifying an isolator simply because it sounds more protective. Requirements should identify the outcome and constraints that justify the choice: emission potential, interventions, cleaning access, throughput, ergonomics and demonstrated performance. Conversely, do not accept a booth on the basis of airflow alone when the task, operator position or powder release challenges its capture envelope.
List foreseeable deviations such as an incorrectly docked container, loss of extraction, a damaged glove, a blocked filter or failure during discharge. State the required process response, detection and recovery philosophy. A general “fail safe” requirement is incomplete unless the safe state, its dependencies and residual risks are defined for each failure.
4. Build a traceable requirement matrix
Give every critical requirement a unique identifier, accountable owner and verification route. Keep the requirement separate from the proposed solution and from the acceptance evidence. Quantitative criteria should be approved before testing; “to supplier standard” is inadequate when the standard is undisclosed or unrelated to the intended duty.
| Requirement | Hazard / risk basis | Containment objective | Acceptance criterion | Verification | Evidence |
|---|---|---|---|---|---|
| Dock and undock the receiving drum | Residues may be exposed at separation | Maintain the defined transfer boundary | Task-specific performance target and approved sequence | Representative transfer study | Protocol, observations and analytical report |
| Detect extraction failure | Outward release may follow pressure loss | Stop or secure the affected operation | Approved cause-and-effect behaviour and recovery conditions | Challenged failure test | Trend, alarm and interlock records |
| Replace an exhaust filter | Collected material remains hazardous | Protect the maintenance team and waste route | Approved safe-change and clearance criteria | Mock-up, procedure challenge and appropriate assessment | Maintenance demonstration and release record |
| Clean inaccessible product-contact locations | Retention can create carryover and exposure | Reach, remove and control residues | Separate cleaning and occupational criteria | Cleaning development and verification | Sampling rationale and results |
| Manage gloves and ports | Tears or poor installation can breach the barrier | Preserve integrity across intended use | Qualified component and site-defined test criteria | Compatibility review and integrity testing | Material dossier, test record and change procedure |
The examples deliberately contain no universal concentration, pressure or leak-rate numbers. The project must supply these where meaningful, with their derivation and decision authority. An unresolved criterion should remain a visible design action with an owner and deadline, not disappear into a generic qualification statement.
5. Define mechanical and transfer interfaces
Specify the enclosure, observation windows, glove ports, seals, penetrations and access doors as one boundary. Address material compatibility with the compound, cleaning chemicals and decontamination agents. Consider abrasion, repeated flexing, solvent exposure and service temperature. Surface finish and cleanability requirements must follow the actual residue and cleaning strategy; a polished surface does not prove containment.
For each transfer, document source and destination, docking alignment, supporting structure, closure sequence, residual powder and disconnection. Split butterfly valves, rapid transfer ports and continuous liners solve different interface problems. Specify which surfaces become exposed and how they are controlled. Include sample removal, rejected material and partially used containers rather than describing only full-batch transfer.
Ergonomics belongs in the acceptance plan. Representative users should be able to reach the task, see critical surfaces, manipulate tools and complete cleaning without improvisation. Evaluate drum lifting, glove reach, working height and maintenance clearances with realistic packages. Excessive reach can turn a nominally enclosed task into a routine request to open the barrier.
6. Connect pressure, extraction and automation
Describe the relationship between equipment pressure, room pressure and adjacent spaces. Define the intended direction of migration at each boundary and the consequences of a disturbance. Setpoints, tolerances, airflow and recovery criteria require a justified design basis. Negative room pressure alone cannot control exposure generated in the operator’s breathing zone.
Specify extraction capacity and control over the relevant operating envelope, including dirty filters, transfer cycles, door events and concurrent consumers. Address filtration, safe-change arrangements, exhaust discharge, recirculation assessment and isolation. HEPA filtration is a component function; it does not demonstrate that powder remains contained during charging, glove failure or filter replacement.
The automation specification should define permissives, interlocks, alarm priority, delays where justified, event recording and authorised recovery. Identify which indications are necessary for the operator to recognise a degraded state. Test the complete chain from sensor and power supply to controller, final element and displayed message. A simulated screen alarm alone does not prove the physical response.
7. Design cleaning, waste and maintenance early
The URS should state whether cleaning is dry, wet, manual, WIP, CIP or a combination, and what each method is expected to achieve. WIP is not automatically a validated cleaning process. Establish access, drainage, spray coverage where relevant, removal of retained material and management of contaminated tools. Keep occupational decontamination objectives distinct from product carryover acceptance.
List the interventions that break containment: filter change, glove replacement, seal replacement, instrument work, removal of a rotor or inspection of an exhaust path. For each, require a concept for isolation, decontamination, residual contamination assessment, temporary controls, waste packaging and return to service. Maintenance staff should review the concept before purchase.
Include contaminated liquids, liners, disposable components and extracted dust in the waste boundary. State container compatibility and closure needs, holding locations, transfer routes and the interfaces with environmental requirements applicable to the site. Do not allow the specification to end at a drain or exhaust flange without assigning the downstream responsibility.
8. Separate qualification from performance demonstration
DQ evaluates whether the design addresses approved requirements and risks. FAT and SAT can verify agreed functions and interfaces; installation and operational qualification establish the configured system and operating envelope. PQ considers intended use under representative conditions. Apply the lifecycle principles of EU GMP Annex 15 where relevant, with a risk-based allocation of tests.
Containment performance testing is a specific part of the evidence package, not a synonym for equipment qualification. A leak test, glove test, filter test or pressure trend cannot individually establish task exposure performance. Define the proposed surrogate study, sampling strategy, analytical capability, representative users, repeated tasks, data treatment and reporting responsibilities before commercial acceptance.
A supplier’s previous study may support technology selection, but assess its relevance to your powder characteristics, task, throughput and configuration. Specify which evidence can be leveraged, which must be repeated after installation and how differences are justified. Include actual workplace exposure assessment in the operational handover rather than presenting surrogate results as a permanent occupational clearance.
9. Apply the regulatory context accurately
For human medicinal product manufacturing within the EU GMP scope, Chapters 3 and 5 establish expectations for suitable facilities and prevention of cross-contamination; Annex 15 addresses qualification and validation. EMA HBEL guidance supports the scientific basis for shared-facility risk assessment. These product-quality expectations coexist with occupational and environmental obligations under the applicable jurisdiction.
ICH Q9(R1) provides quality risk management principles. ISPE SMEPAC, third edition published in December 2024, is industry guidance on defined containment assessments. ASTM E2500-25 is a technical guide for pharmaceutical manufacturing system specification, design and verification; its scope does not replace employee health and safety requirements. Label each reference accordingly in the URS.
Where sterile processing is involved, bring the aseptic specialist into the review and apply the relevant Annex 1 requirements within the contamination control strategy. Product protection and operator protection may impose competing pressure and transfer needs. Document how the combined design meets both objectives. Do not import every aseptic isolator requirement into a nonsterile powder enclosure without justification.
10. Work through a practical design decision
Consider a project that dispenses a potent powder into a process vessel and changes product between campaigns. The initial proposal includes a ventilated weighing enclosure and a closed mixer. The process walk-through reveals that the weighed material is carried between them in an opened liner, while the mixer filter is removed from above a walkway. The main risks lie at interfaces omitted from the equipment list.
The team revises the URS to require an assessed transfer connection, defined handling of partial quantities and a safe filter-change concept. It adds representative docking and changeover tasks to the performance plan and reserves space for maintenance access. The resulting specification may support several technical solutions, but bidders must now address the same duty and provide comparable evidence.
The procurement decision should follow closure of these interface questions. Accepting a low initial price while leaving transfer, analytical testing and contaminated maintenance out of scope transfers both cost and uncertainty to the site. Record commercial exclusions beside technical requirements so that an apparent compliance statement cannot conceal an essential missing service.
Engineering release checklist
- Are compound information, OEL basis and any banding framework identified, reviewed and version controlled?
- Are routine tasks, repeated tasks, cleaning, abnormal recovery and maintenance included in the operating envelope?
- Does every incoming and outgoing material stream have a defined containment boundary?
- Are critical requirements linked to justified criteria, a verification method and an evidence owner?
- Have operators and maintenance technicians reviewed access, reach and component replacement?
- Are pressure, extraction and control failure responses defined at system interfaces?
- Are surrogate testing and actual workplace assessment planned as distinct activities?
- Are cleaning acceptance, occupational clearance and environmental responsibilities separately assigned?
- Are supplier exclusions, consumables, spares, training and lifecycle review addressed?
The URS is ready for design review when the project can explain what it must control, why that control is necessary, how it will be verified and who owns the evidence. A list of impressive components cannot replace that chain.
Sources, scope and engineering recommendations
Source status checked on 25 September 2026. Apply each document within its jurisdiction and scope. GEP and GuideGxP recommendations are engineering advice, supported by risk assessment; examples are illustrative. For copyrighted standards and ISPE guides, the public scope and edition were verified; detailed licensed protocols are not reproduced.
- [REGULATORY REQUIREMENT] European Commission — EudraLex Volume 4, Chapters 3 and 5.
- [REGULATORY REQUIREMENT] European Commission — EU GMP Annex 15: Qualification and Validation.
- [GUIDANCE] EMA — Health-based exposure limits for shared manufacturing facilities.
- [QRM] ICH Q9(R1) — Quality Risk Management, EMA current version.
- [GUIDANCE] ISPE — SMEPAC, third edition: Airborne Particle Emissions from Containment Systems.
- [TECHNICAL STANDARD] ASTM E2500-25 — Specification, Design and Verification of Pharmaceutical Manufacturing Systems.
