SOP on Laminar Air Flow (LAF): Operation, Cleaning, Qualification

In short: This example SOP describes how a microbiology laboratory can operate, clean, maintain and periodically qualify a laminar air flow (LAF) workstation. It is a template: the intervals and limits marked “example in-house criterion” must be set under your own quality system and manufacturer’s manual.

A laminar air flow workstation passes air through a HEPA filter and moves it in a steady, unidirectional stream across the work surface. This protects open product, media or cultures from contamination by the surrounding room air. Its value depends on a clean, intact filter, correct airflow and disciplined use.

Purpose

To describe the operation, cleaning, maintenance and qualification of a laminar air flow (LAF) workstation.

Scope

This example SOP applies to LAF units in the microbiology laboratory or in other areas where a LAF is installed.

Definitions

• SOP: a written, authorised procedure giving instructions for performing operations.
• LAF (laminar air flow): HEPA-filtered, unidirectional airflow over the working surface that protects the work from contamination by viable and non-viable particles.

What the guidance says

EU GMP Annex 1 (revised, 2022) describes unidirectional airflow for grade A zones, such as workstations in sterile manufacturing. It says air speed should give appropriate unidirectional movement at the working position and should be homogeneous. As a guidance value, 0.36–0.54 m/s at the working position is given, unless a different value is scientifically justified in the contamination control strategy. Airflow visualisation studies (smoke studies) should correlate with the air speed measurement. For classification, Annex 1 Table 1 sets a maximum of 3,520 particles of 0.5 µm and above per m³ for grade A, at rest and in operation; no limit is specified for 5 µm particles unless the contamination control strategy calls for one. Annex 1 also notes that HEPA filters should be specified to a relevant international standard.

A microbiology laboratory bench is not necessarily a sterile manufacturing grade A zone. The tests and limits below are therefore example in-house criteria that mirror usual practice and should be checked against the manufacturer’s manual and your site standards. Where a LAF unit does serve as a grade A zone, Annex 1 (section 4.32) sets a maximum requalification interval of 6 months for grade A and B areas, covering at least particle classification, final filter integrity, airflow volume, pressure difference and air velocity. Annex 1 does not set test intervals for ordinary laboratory LAF units. Standards such as ISO 14644-1 describe cleanroom classification; they are not reproduced here.

Responsibilities

• Microbiologist / analyst: operates and cleans the LAF and fills in the records.
• Head of Microbiology: ensures the schedule is followed and approves records.
• Engineering: carries out filter work and arranges qualification.
• Quality Assurance: reviews the SOP and the qualification reports.

Procedure

1. Cleaning of the LAF

1. Switch off the airflow and UV light if they are on.
2. Wipe the working chamber with 70% IPA, working from the ceiling, then the side glass, then the platform.
3. Spray 70% IPA, switch off the visible light and switch on the UV light until the next use.
4. Do routine culture handling only after sample testing is finished.

2. Operation of the LAF

1. Switch on the mains.
2. Check that the manometer reads zero before starting.
3. Switch on the airflow. Check that the differential pressure across the filter is within the range given in the manufacturer’s manual and record it in the operation record (Annexure 2). Example in-house criterion: 8–15 mm of water gauge.
4. Switch on the UV lights.
5. Example in-house criterion: after 30 minutes, switch off the UV light and switch on the visible light. Record the UV burning hours.
6. Start work.

Note: replace the UV tube at the burning hours stated by the manufacturer (example in-house criterion: 999 hours). UV light is not a substitute for cleaning or disinfection, and staff must not look at it or work with exposed skin under it.

3. Cleaning the pre-filter

Example in-house criterion: clean the pre-filter every 3 months ± 7 days to protect the HEPA filter and keep airflow correct.

1. Switch off the mains. Loosen the bolts and remove the pre-filter gently.
2. Cover the open slot with clean paper so dust and room air do not enter the unit.
3. Take the filter to a wash area outside the microbiology room.
4. Remove dust with dry, oil-free compressed air, applied carefully so the filter is not damaged.
5. Wash 2–3 times with purified water and let all the water drain.
6. Dry in a clean, dust-free place. Do not dry in an open area.
7. Spray the stainless steel frame with 70% IPA (filtered through a 0.45 µm filter) and wipe before bringing it into the microbiology area.
8. Remove the cover paper, refit the filter and tighten the bolts.
9. Switch on the unit and check the differential pressure. If it is outside the range, label the unit “Under maintenance” and inform Engineering.
10. Clean the area and fumigate or fog it as per the laboratory’s fumigation procedure before use.
11. Record the work in the pre-filter cleaning record (Annexure 1).

4. Qualification of the LAF

Frequency (example in-house criterion): every six months ± 15 days.

Requalify also:

• after any failure seen in routine monitoring;
• after breakdown, maintenance or preventive maintenance that may affect airflow or the filters;
• after the unit is moved.

Tests and acceptance criteria (example in-house criteria):

Filter repair: a leak can be sealed with soft silicone sealant. Example in-house criterion: seal no more than 3% of the filter area, and no single patch larger than about 3 square inches (19 cm²). Retest after any repair.

If the site cannot perform these tests, have them done by a competent external agency. After qualification, attach the qualification status label (Annexure 3) and file the report.

5. Records

Operation records, pre-filter cleaning records and qualification reports are GMP records. Keep them at least 1 year after the expiry date of the respective product batch (EU GMP Part I, Chapter 4, section 4.11; 21 CFR 211.180(a)), longer if local law or the marketing authorisation requires.

Annexures

• Annexure 1: Cleaning record of pre-filter
• Annexure 2: Laminar air flow operation record
• Annexure 3: Qualification status label

Frequently asked questions

What is the difference between laminar air flow and a biosafety cabinet?

A LAF workstation protects the work from the room but may blow air towards the operator, so it should not be used for hazardous microorganisms. A biosafety cabinet is built to protect the operator, and often the product, too.

Why is a smoke study needed as well as an air velocity check?

Velocity numbers alone do not show how air actually moves around objects and hands. Annex 1 expects visualisation studies to agree with the air speed measurement.

Can UV light replace disinfection?

No. UV lamps lose output with age and do not reach shadowed surfaces, so they only supplement wiping with a disinfectant.

See also

• SOP for Good Microbiological Laboratory Practice
• SOP for Preparation of Disinfectant Solution
• SOP on Cleaning of Incubators

References

1. European Commission, EudraLex Volume 4, EU GMP Annex 1: Manufacture of Sterile Medicinal Products (revised, August 2022): section 4.15 (airflow visualisation), sections 4.27 and Table 1 (particle limits for classification), section 4.30 (unidirectional air speed guidance value), section 4.32 (requalification tests and intervals).
2. EU GMP Part I, Chapter 4 (Documentation), section 4.11: record retention.
3. US FDA, 21 CFR 211.180(a): record retention.
4. Manufacturer’s operation manual for the LAF unit.