Laminar Flow Hood

What is a Laminar Flow Hood?

A laminar flow hood is a specialized workbench used in sterile compounding that provides a continuous, unidirectional flow of filtered air to maintain an ISO 5 clean environment.

It protects compounded sterile preparations (CSPs) from contamination by filtering out particles ≥0.3 microns using HEPA (High-Efficiency Particulate Air) filters.

Parts of a Laminar Flow Hood / Key Components:

Pre-Filter

Located at the air intake; captures large dust and debris.
Protects the HEPA filter and extends its life.
Needs regular inspection and replacement.

HEPA Filter (High-Efficiency Particulate Air)

The heart of the system; removes ≥99.97% of particles ≥0.3 microns (dust, bacteria, mold spores).
Provides the sterile, particle-free air needed for aseptic compounding.

Fan/Blower

Pulls room air through the pre-filter and pushes it through the HEPA filter.
Ensures continuous, laminar (smooth, non-turbulent) airflow across the work area.

Work Surface

The clean, sterile area where compounding activities take place.
Must be kept free of unnecessary items to avoid disrupting airflow.

Airflow Grille

A protective grid that maintains the direction and balance of airflow.
Ensures clean air covers the entire work surface evenly.

Control Panel

Contains switches for turning the blower and lights on/off.
Some models include airflow monitors or alarms.

Optional Components (in some models)

UV Light (for surface disinfection when the hood is not in use, though not relied on as the primary cleaning method).
Sash or Front Shield (especially in vertical hoods, providing partial protection from splashes or aerosols).

Why is a Laminar Flow Hood Used in Compounding?

A Laminar Flow Hood is used in compounding to maintain a sterile, contaminant-free environment (ISO 5) by providing continuous, unidirectional airflow filtered through a HEPA filter that removes ≥99.97% of particles ≥0.3 microns.

✅ Protects sterile products from microbial and particulate contamination.
✅ Ensures compliance with USP <797> standards for sterile compounding.
✅ Reduces the risk of patient harm from contaminated injectables or ophthalmic preparations.
✅ Creates a controlled workspace where aseptic technique can be reliably applied.

It is essential for preparing IV medications, reconstituted antibiotics, and other sterile, non-hazardous compounds.

What types of Compounds are prepared in Laminar Flow Hood?

Sterile, non-hazardous compounds, including:

Intravenous (IV) solutions (e.g., antibiotics, electrolytes, chemotherapy diluents)
Total Parenteral Nutrition (TPN) solutions
Ophthalmic (eye) drops
Reconstituted sterile powders (e.g., powdered antibiotics for injection)
Syringes and infusion bags prepared under aseptic conditions

❌ Note: Hazardous drugs (like chemotherapy) are not prepared in a standard laminar flow hood; they require a biological safety cabinet or compounding aseptic containment isolator (CACI).

Types of Laminar Flow Hood?

1. Horizontal Laminar Flow Hood

Air flows horizontally from the HEPA filter at the back of the hood toward the operator.
Protects the product from contamination, but does not protect the user from exposure.
Commonly used for sterile, non-hazardous preparations (e.g., IVs, TPNs, ophthalmics).

2. Vertical Laminar Flow Hood

Air flows vertically from the HEPA filter at the top downward onto the work surface.
Provides slightly better protection from splashes or aerosols (but still not sufficient for hazardous drugs).
Used when vertical airflow is preferred, often for bulkier items or certain sterile preparations.

3. Biological Safety Cabinet (BSC, Class II)

Technically not a laminar flow hood, but often compared.
Provides both product and personnel protection when handling hazardous drugs (like chemotherapy).
Features vertical laminar airflow plus a front access sash and exhaust through HEPA filters.

4. Compounding Aseptic Containment Isolator (CACI)

Fully enclosed, glovebox-style isolator.
Used for sterile hazardous drug compounding under USP <800> standards.

How Laminar Flow Hood Works

A laminar flow hood (or clean bench) is a critical device used in pharmacies, laboratories, and medical facilities to maintain a sterile, particle-free workspace. It directs HEPA-filtered air in a smooth, unidirectional flow to prevent contamination of sensitive materials (e.g., sterile compounds, cell cultures, or electronics).

Step-by-Step Working Mechanism

1. Air Intake & Pre-Filtration

Ambient air is drawn into the hood through a pre-filter (usually a coarse filter).
Removes large particles (dust, hair, etc.) before air reaches the HEPA filter.

2. HEPA Filtration (High-Efficiency Particulate Air Filter)

The HEPA filter (99.99% efficiency at 0.3 µm) traps:
- Bacteria
- Fungi
- Dust particles
- Aerosols

Filter Class: Typically ISO Class 5 (USP <797> compliant) for pharmacy sterile compounding.

3. Laminar Airflow Creation

Filtered air is pushed through a perforated plate or honeycomb structure to ensure:
- Unidirectional flow (smooth, parallel streamlines).
- Minimal turbulence (prevents particle swirl-back).
Airflow Velocity: ~90–100 ft/min (0.45 m/s).

4. Sterile Workspace Maintenance

The vertical or horizontal laminar flow sweeps contaminants away from the work surface.
Vertical Flow Hoods (common in pharmacies):
- Air moves top-to-bottom, protecting both the product and the user.
Horizontal Flow Hoods:
- Air moves front-to-back, ideal for non-hazardous materials.

5. Contaminant Exhaust

In closed systems, air is recirculated after re-filtration.
In open systems, some air is exhausted to maintain pressure balance.

How to Clean a Laminar Flow Hood

Preparation

Wash hands and wear proper PPE (sterile gloves, gown, hair cover, mask).
Gather lint-free wipes and sterile 70% isopropyl alcohol (IPA).

Steps to clean work surface

Clear the work surface of all materials, equipment, and waste. Only keep what’s necessary for cleaning.
From cleanest to dirtiest areas.
From top to bottom.
From back to front.

Cleaning Horizontal Laminar Flow Hood:

Ceiling (top surface) → wipe side to side.
HEPA filter cover or diffuser (be careful, don’t press hard).
Sides (left, then right walls) → top to bottom, back to front.
Work surface → wipe front to back.

Cleaning Vertical Laminar Flow Hood:

Top (underside of HEPA filter cover).
Sides (left, right walls).
Back wall.
Work surface.

Use Correct Technique

Use lint-free wipes soaked in sterile 70% Iso Propyl Alcohol.
Use overlapping strokes to ensure complete coverage.
X Never spray Iso Propyl Alcohol directly onto HEPA filters.

Final Checks

Let surfaces air-dry (do not wipe dry).
Replace only necessary sterile supplies inside.
Ensure airflow is running at least 30 minutes before use if turned off.

Aseptic Techniques: Key Practices

No items should block airflow between the HEPA filter and the sterile product

In a laminar flow hood, the HEPA filter creates a continuous stream of sterile air.
This clean air must flow uninterrupted onto the critical compounding sites — like vial tops, ampule necks, or syringe tips.
If you place your hands, equipment, or packaging in front of or upstream of the sterile product, you block or disrupt the clean airflow, increasing the risk of contamination.
Always work so that the sterile air flows freely from the HEPA filter directly over the product.

Work Surface Distances and Hand Positions

Work Surface Zone

Keep all critical work (like vial puncturing, syringe filling) at least 6 inches inside the front edge of the hood — never work right at the edge, because room air can sweep in and contaminate.
Stay at least 3 inches away from the back and side edges to avoid airflow turbulence or “dead zones” near the walls.
Work in the center of the hood for optimal airflow coverage.

Hands and Supplies

Hands and materials should never block airflow between the HEPA filter and the critical sites (e.g., open ampules, vial septa, needle tips).
When using both hands, work side by side (not one hand behind the other) to avoid obstructing airflow.
Arrange supplies logically – clean and essential materials closest, less-used items further back, and waste or bulky items outside the hood if possible.

Part	Minimum Distance
From front edge	≥ 6 inches inside
From back and side edges	≥ 3 inches away
Blocking HEPA airflow	Avoid entirely

Laminar Flow Hood Certification

What Is Certification?

Certification is the official testing and inspection of the laminar flow hood (LAFW) to ensure it meets regulatory and performance standards, especially maintaining an ISO 5 clean environment for sterile compounding.

Who Performs Certification?

Performed by a qualified certifier trained to test cleanroom equipment.
Follows procedures set by USP <797> and manufacturer specifications.

How Often Is Certification Required?

Every 6 months (twice yearly) at minimum. Also required:

After the hood is moved or relocated.
After any repairs or maintenance that might affect airflow or filtration.
If the pharmacy fails environmental monitoring or suspects equipment issues.

What Is Checked During Certification?

Airflow velocity and uniformity (to ensure laminar, non-turbulent flow).
HEPA filter integrity (using smoke tests or particle counters to check for leaks).
ISO 5 particle counts (verifying air cleanliness meets required standards).
Air pressure differentials (if part of a cleanroom suite).
Proper function of alarms, controls, and gauges.

Why Is Certification Important?

Ensures sterile product safety by maintaining a contaminant-free workspace.
Keeps the pharmacy compliant with USP standards and state/federal regulations.
Protects patients from infections caused by contaminated compounded sterile preparations (CSPs).

Without valid certification, you cannot legally compound sterile preparations.
Certification is critical for patient safety, regulatory compliance, and pharmacy operation.

Biological Safety Cabinet vs Laminar Flow Hood

Feature	Laminar Flow Hood (LAFW)	Biological Safety Cabinet (BSC)
Main Purpose	Protects the product from contamination	Protects both the product and the worker/environment from hazardous materials
Airflow Direction	Horizontal (back-to-front) or vertical (top-to-bottom), positive pressure	Vertical airflow, negative pressure with HEPA-filtered exhaust
Types of Compounds	Sterile, non-hazardous preparations (e.g., IVs, TPNs, eye drops)	Hazardous drug preparations (e.g., chemotherapy, antineoplastics)
Hazardous Drug Use?	❌ Not allowed; air blows toward the operator in horizontal LAFWs	✅ Yes, designed specifically for safe hazardous drug compounding
USP Compliance	Meets USP <797> standards (sterile, non-hazardous compounding)	Meets USP <800> standards (hazardous drug handling and compounding)
Containment Features	No worker/environmental protection; only HEPA-filtered clean air over products	HEPA-filtered airflow plus negative pressure to contain hazardous vapors and particles
Examples	Horizontal LAFW, Vertical LAFW	Biological Safety Cabinet Class II, Biological Safety Cabinet Type A2 or Biological Safety Cabinet B2

Laminar Flow Hoods are used for non-hazardous sterile products only.
Biological Safety Cabinets are used when preparing hazardous drugs, especially chemotherapy, to protect both the product and the operator.
Biological Safety Cabinets are sometimes casually called “vertical laminar flow hoods,” but they have containment and exhaust systems that a regular vertical LAFW does not.

Laminar Flow Hood vs. ISO Environment and Pressure

Laminar Flow Hood (LAFW)

Provides ISO 5 clean air directly at the work surface (critical compounding area).
Achieves this using HEPA-filtered, unidirectional airflow that removes ≥99.97% of particles ≥0.3 microns.
Positive pressure inside the hood pushes air outward, preventing room air from contaminating the workspace.
However, the hood alone does not control the surrounding room — it only maintains the clean zone immediately within its airflow.

ISO-Classified Environments (Cleanrooms)

Classified by the maximum allowable number of particles per cubic meter (per ISO 14644-1).

Common pharmacy ISO classes:

ISO 5 → Critical work zone (inside the laminar flow hood).
ISO 7 → Buffer room housing the hood.
ISO 8 → Ante room (gowning, handwashing area).

The cleanroom suite is maintained by:

HEPA-filtered HVAC systems.
Proper air exchange rates (ACH, or air changes per hour).
Pressure differentials between rooms to ensure airflow moves from cleanest (ISO 5) → less clean (ISO 7, 8).

Beyond-Use Dating (BUD) for Sterile Compounding

What is BUD?

The Beyond-Use Date (BUD) is the date or time after which a compounded sterile preparation (CSP) must not be used and must be discarded. It is different from the manufacturer’s expiration date. Itects when sterility, stability, or potency can no longer be guaranteed after compounding.

USP <797> BUD Guidelines (Room Temp Storage)

Risk Level	Room Temperature	Refrigerated	Frozen
Low-Risk CSP	72 hours (3 days)	14 days	45 days
Medium-Risk CSP	30 hours	9 days	45 days
High-Risk CSP	24 hours (1 day)	3 days	45 days
Immediate-Use CSP	1 hour (no storage)	N/A	N/A

Definitions of Risk Levels

Low-risk: Simple transfers (e.g., reconstituting a vial into an IV bag), under ISO 5 conditions.
Medium-risk: More complex prep, like batching multiple doses or multi-day TPN solutions.
High-risk: Use of non-sterile ingredients or devices, or compounding in environments worse than ISO 5.

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