In-Depth Analysis of Cleanliness Levels in Pathology Departments

Precision Design from “Sterility” to “Contamination Control”

In hospital environmental control, “cleanliness levels” are typically associated with operating rooms or bone marrow transplant wards, where airborne particles and microorganisms must be tightly controlled. As the final authority in disease diagnosis, pathology departments also require strict environmental control—but with a fundamentally different logic.

Rather than pursuing traditional aseptic cleanliness, pathology departments adopt a risk-based, biosafety- and contamination-control–oriented approach. This article optimizes and clarifies the environmental control framework for pathology departments, explaining how it differs from conventional cleanroom grading while meeting clinical safety and diagnostic accuracy requirements.

1. Core Design Philosophy: Function-Driven and Risk-Based Zoning

The primary objectives of pathology department environmental design are:

• Protect personnel
• Protect specimens
• Prevent cross-contamination

Unlike clean operating suites that follow progressive cleanliness grading, pathology departments are organized according to biosafety risk levels.

Based on the Guidelines for the Construction and Management of Hospital Pathology Departments, General Requirements for Laboratory Biosafety, and WHO recommendations, pathology spaces are typically divided into four zones:

• Clean Areas: Diagnostic rooms, offices, conference rooms, archives
• Semi-Clean Areas: Changing rooms, shower rooms, specimen receiving buffers, internal corridors
• Contaminated Areas: Grossing and sampling rooms, specimen storage rooms, routine technical laboratories, cytology rooms
• Specialized Technical Areas: Immunohistochemistry laboratories, molecular pathology laboratories, electron microscopy rooms

This zoning ensures targeted environmental control proportional to actual biological and chemical risks.

2. Pathology Departments vs. Traditional Cleanroom Classifications

Key Differences

Control Targets
Traditional cleanrooms focus on airborne particle and microbial counts. In contrast, pathology contaminated areas prioritize control of toxic chemical vapors (e.g., formaldehyde, xylene) and bioaerosols released from specimens.

Applicable Standards
Conventional cleanliness relies on standards such as GB 50333 – Code for Design of Clean Operating Departments in Hospitals, which define particle limits. Pathology environments mainly follow GB 50736 – Design Code for Heating, Ventilation and Air Conditioning of Civil Buildings and occupational health standards, emphasizing air change rates, pressure differentials, and exposure limits.

Airflow Objectives
Operating rooms use HEPA-filtered supply air to protect the surgical field. Pathology areas—especially grossing rooms—use negative pressure and directional airflow to contain hazards and exhaust them at the source.

Key Similarities

• Strict pressure differentials to control airflow direction
• Mandatory mechanical ventilation systems with high reliability
• High-performance building materials with good airtightness, corrosion resistance, and ease of cleaning

3. Environmental Control Requirements by Functional Area

Although pathology departments do not use labels such as “Class 100” or “Class 10,000,” their performance requirements can be understood through equivalent environmental parameters.

3.1 Gross Examination and Sampling Rooms

Core Biosafety Negative-Pressure Zone

• Pressure: –10 Pa to –15 Pa relative to adjacent areas
• Ventilation: Independent exhaust only; ≥12 air changes per hour; top supply with low-level exhaust near the grossing station
• Local Control: Mandatory negative-pressure grossing stations with dedicated exhaust ducts; capture efficiency ≥95%
• Risk Profile: Comparable to a Biosafety Level 2 laboratory, with enhanced chemical hazard control

3.2 Molecular Pathology Laboratories

ISO Cleanliness Combined with Pressure Zoning

This is the only pathology area requiring explicit traditional cleanliness classification.

• Reagent Preparation Area: Positive pressure (~+10 Pa); ISO Class 7 or higher to protect reagents
• Specimen Preparation Area: Negative pressure (~–10 Pa); ISO Class 7; equipped with biological safety cabinets
• Amplification & Analysis Area: Negative pressure (~–5 Pa) to prevent nucleic acid leakage

Design must strictly comply with the Administrative Measures for Clinical Gene Amplification Laboratories.

3.3 Routine Technical Laboratories and Cytology Rooms

Chemical Contamination Control Zones

• Pressure: –5 Pa to –10 Pa
• Ventilation: ≥10 air changes per hour
• Local Exhaust: Required for staining machines, coverslippers, and other volatile reagent sources

3.4 Diagnostic Rooms and Offices

Comfort and Protection Zones

• Pressure: +5 Pa to +10 Pa
• Ventilation: Comfort HVAC with compliant fresh air supply
• Objective: Prevent backflow of contaminated air while ensuring staff comfort

3.5 Frozen Section Rooms

Rapid Diagnosis with Elevated Biosafety Risk

• Pressure: ≤ –5 Pa recommended
• Special Measures: Local exhaust for cryostats to remove refrigerants and potential bioaerosols

4. Key Environmental Parameters Summary

Functional Area	Pressure Strategy	Recommended Pressure (Pa)	Ventilation Focus	Mandatory Local Equipment
Grossing / Sampling Room	Forced negative	–10 to –15	Full exhaust, ≥12 ACH	Negative-pressure grossing station
Molecular Pathology Lab	Zonal gradient	+10 to –10	Clean HVAC, directional flow	BSCs, laminar flow hoods
Routine Technical Lab	Negative	–5 to –10	≥10 ACH, local exhaust	Fume hoods, exhausted cabinets
Frozen Section Room	Negative	≤ –5	Effective exhaust	Cryostat local exhaust
Diagnostic Rooms / Offices	Positive	+5 to +10	Comfort HVAC + fresh air	—
Buffers / Corridors	Transitional	0 to +5	General ventilation	—

5. Conclusion: Pathology “Cleanliness” as Systematic Contamination Control

Pathology departments do not conform to a single cleanliness class. Instead, they represent a comprehensive contamination control system integrating:

• Directional airflow via pressure differentials
• Source capture through local exhaust ventilation
• Rapid dilution and removal using high air change rates
• Precision control in specialized diagnostic areas

During planning, design, and acceptance, it is essential to avoid directly copying operating room cleanliness standards. Instead, pathology facilities must be designed based on biosafety risk assessment, with rigorous verification of pressure gradients, ventilation performance, local exhaust efficiency, and hazardous substance monitoring.

Only through this systems-engineering approach can a safe, accurate, and efficient modern pathology department be realized—protecting both healthcare professionals and patients.