Smoke Study Acceptance Criteria: How to Assess Airflow Risks in Aseptic Areas
A smoke study recording is useful only when you assess airflow observations against clear, predefined criteria. Without an agreed evaluation basis, reviewers may interpret the same airflow pattern differently.
EU GMP Annex 1 explains what airflow visualisation should demonstrate in cleanrooms and critical zones. However, it does not prescribe one universal set of numerical pass/fail limits for every smoke study. The study protocol should therefore establish criteria that reflect the facility design, process, equipment configuration, and contamination risks.
This article explains how smoke study acceptance criteria can be developed, how teams can assess airflow observations, and how findings should be documented and followed up.
For the execution sequence, see IncepBio’s smoke study procedure guide .
What EU GMP Annex 1 and FDA Guidance Say About Acceptance Criteria
Where unidirectional airflow is required, visualisation studies should be performed to determine compliance. Annex 1 also addresses airflow visualisation at certain small egress points, corrective action where airflow presents a contamination risk, studies at rest and in operation, video retention, and documentation of outcomes.
Paragraph 4.19 describes airflow protection expectations for isolators and RABS. For example, open isolators should provide first-air protection and unidirectional airflow over and away from exposed products. Closed isolators may not require fully unidirectional airflow for simple operations, provided turbulence does not increase contamination risk to exposed products.
Neither source provides one universal numerical acceptance limit for every visible smoke pattern. The manufacturer should establish and justify criteria through its approved procedures and risk-management system.
How Acceptance Criteria Are Built into an Approved Protocol
Acceptance criteria should be established before the study is performed. They should reflect the intended airflow pattern and the protection required for exposed products, components, and critical surfaces.
1. Start with the intended airflow pattern.
Review the cleanroom layout, HVAC design, airflow direction, equipment arrangement, and critical process locations. Identify where airflow should protect the product and where movement could introduce contamination.
For isolators and RABS, consider the relevant design expectations in Annex 1 paragraph 4.19. Do not assume that every enclosure has identical airflow requirements.
2. Consider product and critical-surface protection.
The criteria should address whether airflow protects exposed product and critical surfaces during routine operations and interventions.
Annex 1 paragraph 8.16 says that interventions should be designed to minimise contamination risks and that their potential impact on airflow, critical surfaces and products should be considered. This supports including representative interventions in the study design where relevant.
Paragraph 8.7 addresses the role of the Contamination Control Strategy (CCS) in defining critical control points and assessing the effectiveness of controls used to manage contamination risks.
3. Write observable and location-specific criteria.
Avoid vague statements such as “airflow should be acceptable” or “no significant turbulence". The protocol should describe what the study is expected to demonstrate, where it applies, and under which operating conditions.
For example:
Smoke released at [defined location] should move in the intended airflow direction and should not reverse towards [identified critical area] during [specified operation or intervention].
The example should be adapted to the actual process and facility. The protocol should also explain how observations will be recorded, how uncertain footage will be reviewed, and who is responsible for approving the results.
Assessing Airflow Observations Without Universal Limits
Smoke visualisation produces evidence of airflow behaviour. An observation should not automatically be classified as a failure without considering its location, duration, operating condition and potential effect on product protection.
The following table gives examples of observations that may require assessment.
| Observation | What the review should consider | Relevant reference |
|---|---|---|
| Turbulence or eddies | Whether the airflow disturbance affects a critical area, exposed product or first-air protection | Annex 1, paragraphs 4.15 and 4.19; protocol criteria |
| Stagnant or slow-moving areas | Whether the location requires protective airflow and whether the pattern creates a contamination concern | Protocol criteria and site risk assessment |
| Reversal or ingress | Whether air moves from a lower-grade or less clean area towards a higher-grade area or enters an open isolator or RABS during relevant operations | Annex 1, paragraphs 4.15 and 4.20 |
| Airflow disruption during an intervention | Whether operator movement or equipment handling affects airflow over critical surfaces or exposed product | Annex 1, paragraph 8.16 |
| Incomplete clearance after a disturbance | Whether the observed behaviour creates a process-specific risk; do not treat it automatically as a cleanroom recovery-test failure | Protocol criteria and applicable qualification evidence |
Define study-specific acceptance criteria and review airflow patterns to assess contamination-control measures. IncepBio can discuss your smoke study and documentation requirements.
Annex 1 paragraph 4.15 addresses airflow visualisation within cleanrooms and zones, including ingress from lower-grade to higher-grade areas. Paragraph 4.20 also specifically addresses airflow studies at open isolator interfaces and RABS interventions to demonstrate the absence of air ingress.
There is also an important distinction between visible smoke clearance and the cleanroom clean-up period. Annex 1, paragraph 4.29, addresses the clean-up period for restoring the qualified cleanliness state after operations. This is a particle-cleanliness requirement and should not be treated as a smoke-study acceptance limit. Visible smoke clearance alone does not demonstrate that the room has met its particle-cleanliness recovery requirements.
Smoke Visualisation vs Air Velocity and Room Pressure
Smoke visualisation, air-velocity measurement and room-pressure monitoring provide different types of evidence. They should be considered together where relevant, but they are not interchangeable.
| Assessment method | What it demonstrates | How it supports the review |
|---|---|---|
| Smoke visualisation | Visible airflow direction and patterns | Helps assess airflow behaviour around equipment, operators and critical areas |
| Air-velocity measurement | Measured air speed at defined locations | Provides quantitative evidence for airflow qualification |
| Room-pressure monitoring | Pressure differences between rooms or between an isolator and its background | Helps assess pressure relationships and the intended direction of air movement |
Annex 1, paragraph 4.30, gives a guidance range of 0.36–0.54 m/s for unidirectional airflow systems at the working position, unless otherwise scientifically justified in the CCS. It also states that airflow visualisation studies should correlate with air-speed measurements.
Paragraph 4.16 addresses pressure-difference indicators, monitoring and warning systems. A satisfactory pressure reading does not replace airflow visualisation, and a smoke pattern does not replace quantitative air-speed or pressure measurements.
Documenting Findings and Following Up
The study report should make it possible for reviewers to understand what was tested, what was observed and how the conclusion was reached.
Annex 1, paragraph 4.15, states that airflow video recordings should be retained and the outcomes documented. Paragraph 3.1 also addresses root-cause analysis of procedural, process, or equipment failures and the implementation of suitable corrective and preventive actions.
If an airflow pattern presents a contamination risk, the cause should be investigated. Depending on the findings, actions may involve reviewing equipment positioning, operator practices, airflow distribution, or facility design. Any changes should be managed through the site's quality system and change-control process.
Annex 1, paragraph 4.32, describes periodic requalification and its minimum test requirements. Paragraph 4.25 separately includes airflow direction testing and visualisation among cleanroom qualification tests, where relevant to the design and operation of the installation. A complete repeat smoke study should not be assumed necessary after every change; the need for additional airflow visualisation should be assessed through change control, risk assessment and applicable site procedures.
Where Smoke Study Services Fit
A smoke study service can support the planning, execution and documentation of airflow visualisation activities. The scope should be agreed against the facility's requirements and approved protocol.
IncepBio describes a process that includes review of cleanroom layouts and requirements, protocol development, selection of study locations and conditions, acceptance criteria, on-site execution, video documentation and reporting. Its service information also identifies applications involving UDAF systems, RABS, isolators, and critical work areas.
For project-specific requirements, visit IncepBio Smoke Study Services or request smoke study support.
Request SupportConclusion
Smoke study acceptance criteria should be defined before testing and linked to the intended airflow pattern, process conditions, and protection of critical areas. Reviewers should assess visible observations in context rather than applying the same pass/fail limits to every cleanroom.
By connecting protocol criteria with risk assessment, representative operating conditions, and documented findings, manufacturers can make airflow visualisation results more consistent and useful for contamination-control decisions.
Frequently Asked Questions
What are smoke study acceptance criteria?
They are predefined conditions used to assess whether observed airflow patterns provide the intended protection to exposed products, critical surfaces, and aseptic operations.
Does EU GMP Annex 1 specify fixed smoke study acceptance limits?
No. Annex 1 paragraph 4.15 describes what airflow visualisation should demonstrate, but it does not prescribe universal numerical pass/fail limits for every smoke pattern.
How should turbulence and airflow reversal be assessed?
Assess where the disturbance occurs, how long it persists, and whether it affects exposed products or critical areas. Compare the observation with the approved protocol criteria and contamination risk assessment.
What should a smoke study report include?
It should include the approved protocol, study conditions, locations, video recordings, observations, assessment against acceptance criteria, deviations, conclusions, and review approvals.
When should a smoke study be repeated?
A repeat study may be needed after changes that could affect airflow, such as HVAC modifications, equipment relocation, or process changes. The decision should be justified through change control and risk assessment.
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