Histopathology lab safety

Table of contents

Introduction

Histopathology involves processing biological tissues using various chemical, mechanical, and heat-based procedures. Lab personnel are exposed to:

Infectious agents
Toxic and carcinogenic chemicals
Sharp instruments and microtomy hazards
Electrical and fire risks
Physical hazards from equipment

Therefore, an effective safety program must integrate Biosafety, Chemical Safety, Fire Safety, Electrical Safety, and Ergonomic Safety.

Types of Hazards

A. Biological Hazards

Histopathology labs receive fresh or fixed tissues that may harbor:

Bloodborne pathogens (HBV, HCV, HIV)
Airborne infections (TB)
Fungal spores
Highly contagious organisms

Even fixed tissues may pose minimal risk, especially if fixation is incomplete.

B. Chemical Hazards

Commonly used hazardous chemicals include:

Formalin (10% buffered formalin): carcinogenic, respiratory irritant
Xylene: neurotoxic and flammable
Ethanol & isopropanol: flammable
Osmium tetroxide: strong oxidizer, eye/lung toxic
Paraffin wax heaters: burn risk
Stains & dyes: many are toxic or mutagenic

C. Physical & Mechanical Hazards

Microtome blades
Broken glass slides
Cryostat machines
Tissue processors
Centrifuges
Hot plates/water baths

D. Electrical Hazards

Equipment like tissue processors, automated stainers, cryostats, and ovens carry risk of:

Shock
Short-circuit
Fire

Personal Protective Equipment

Proper PPE is the first line of defense in a histopathology lab.

Essential PPE includes:

Lab coat or fluid-resistant apron
Nitrile or latex gloves (double glove during grossing)
Face mask or N95 when handling aerosols
Safety goggles or face shields
Closed-toe, anti-slip footwear
Cut-resistant gloves during grossing or handling blades

Safety Practices

This is the most critical step, as specimens may contain infectious agents.

Safe Practices:

Treat all tissue as potentially infectious (Universal Precautions)
Wear full PPE including face shield
Use biological safety cabinets for high-risk specimens
Avoid splashes during specimen transfer
Use forceps instead of bare hands
Ensure proper labeling and chain-of-custody
Dispose biological waste in appropriate containers
Decontaminate grossing area with disinfectants (1% hypochlorite)

Chemical Safety

A. Handling Formalin

Use fume hoods or ventilated grossing stations
Never store formalin in open containers
Wear eye protection and gloves
Label containers properly
Formalin spills should be handled with spill kits

B. Handling Xylene

Highly flammable—keep away from flames, heaters, and sparks
Always handle in a well-ventilated area
Use xylene substitutes where possible
Store in flame-resistant cabinets

C. Alcohols (Ethanol, IPA)

Avoid direct skin contact
Do not use near open flames
Dispose through approved chemical waste channels

D. Staining Reagents

Many dyes (hematoxylin, eosin, PAS reagents) are toxic
Wear gloves and use squeeze bottles to minimize spills
Follow Material Safety Data Sheets (MSDS) for each chemical

Microtomy and Cryostat Safety

Cutting thin sections of tissue requires strict attention to safety due to the use of extremely sharp blades.

A. Microtome Safety

Always engage the blade guard when not cutting
Never wipe the blade with fingers—use a brush or forceps
Replace blades using a blade-removal tool
Do not leave blade exposed on the workstation
Ensure stable seating and ergonomic posture to avoid repetitive strain

B. Cryostat Safety

Wear cut-resistant gloves
Handle frozen tissues carefully (risk of aerosolization)
Avoid “warm cutting” to prevent tissue sticking
Regularly defrost and disinfect cryostat using appropriate procedures
Follow TB protocols for high-risk samples

Equipment Safety

Tissue Processors

Ensure secure closing of reagent containers
Use compatible chemicals only
Follow electrical safety guidelines

Paraffin Embedding Stations

Set correct temperature to avoid overheating
Prevent wax spillage—slip hazard

Water Baths

Maintain at 40–45°C
Avoid electrical contact with water

Automated Stainers

Check for leaks
Use proper waste containers

Fire Safety in Histopathology Labs

Histopathology units are high-risk for fire due to flammable chemicals (xylene, alcohol).

Fire Safety Measures:

Store flammable chemicals in approved fire-safe cabinets
Keep fire extinguishers (CO₂, dry chemical) accessible
No smoking or open flames in the lab
Emergency showers and eyewash stations must be functional
Conduct regular fire drills

Biomedical Waste Disposal

Correct disposal is essential for environmental and worker safety.

A. Infectious Waste

Fresh tissues → yellow bag
Formalin-fixed tissues → yellow container
Blades → white (sharp) container

B. Chemical Waste

Xylene and alcohol → labeled chemical waste containers
Paraffin scraps → red or general waste depending on policy

C. Glass Waste

Slides and coverslips → puncture-proof containers

D. Cryostat Debris

Treat as potentially infectious
Dispose in biohazard bags

Decontamination and Disinfection

Daily cleaning protocols help control infection.

Recommended Cleaning Agents:

70% ethanol
1% sodium hypochlorite
Phenol-based disinfectants
Quaternary ammonium compounds

Areas Requiring Routine Cleaning:

Benchtops
Grossing tables
Cryostat & microtome handles
Embedding stations
Pipettes, timers, tools

Documentation, Training, and Quality Assurance

Safety is effective only when consistent.

Essential Quality Measures:

Maintain MSDS for all chemicals
Conduct staff training every 6–12 months
Display safety protocols & emergency numbers
Maintain logs for equipment maintenance
Encourage incident reporting without fear
Ensure internal audits (NABL/NABH compatible)

Emergency Preparedness

Labs must be prepared for accidents.

Emergency Kits Should Include:

Chemical spill kits
First aid kit
Eye wash bottles
Emergency shower
Fire extinguishers
Post-exposure prophylaxis (PEP) protocol

Common Emergency Situations:

Formalin or xylene spills
Blade injuries
Fire accidents
Cryostat aerosol exposure
Electric shock

MCQs

1. The most commonly used fixative in histopathology is:

A. Methanol
B. Xylene
C. 10% Neutral Buffered Formalin
D. Acetone

2. Which chemical in histopathology is classified as a carcinogen?

A. Ethanol
B. Formaldehyde
C. Distilled water
D. Paraffin wax

3. Xylene is primarily used in histopathology for:

A. Fixation
B. Staining
C. Clearing
D. Mounting

4. The best place to handle formalin is:

A. Open bench
B. Inside a fume hood
C. In the corridor
D. Near a heater

5. The most important PPE during grossing is:

A. Apron only
B. Gloves only
C. Face shield and gloves
D. No PPE needed

6. Sharps like microtome blades should be disposed of in:

A. Red bag
B. Black bag
C. White puncture-proof container
D. Yellow bag

7. Which hazard is associated with cryostats?

A. Heat burns
B. Aerosol generation
C. Radiation
D. Dehydration

8. The first step after a formalin spill is:

A. Evaporate it
B. Wipe with tissue paper
C. Use a chemical spill kit
D. Ignore if small

9. What is the ideal temperature of a paraffin embedding station?

A. 20°C
B. 37°C
C. 55–60°C
D. 90°C

10. The main fire hazard in histopathology labs comes from:

A. Water
B. Xylene and alcohol
C. Frozen tissues
D. Stains

11. Which disinfectant is commonly used for surface cleaning?

A. 1% sodium hypochlorite
B. Olive oil
C. Paraffin
D. Xylene

12. Tissue processors must be cleaned:

A. Once a year
B. Weekly
C. Monthly
D. Only when broken

13. TB-infected tissues should be handled in a:

A. Chemical hood
B. Biosafety cabinet
C. Open bench
D. Balcony

14. Proper labeling of specimens prevents:

A. Color change
B. Misdiagnosis
C. Dehydration
D. Overfixation

15. Overexposure to xylene causes:

A. Hypothermia
B. Skin irritation and CNS depression
C. Hair fall
D. Hypercalcemia

16. Safety goggles are essential during:

A. Section cutting
B. Tying bandages
C. Desk work
D. Microscopic examination

17. Microtome injuries are usually caused by:

A. Dull blades
B. Exposed sharp blades
C. Warm paraffin
D. Cold forceps

18. The best method for cryostat disinfection is:

A. Boiling water
B. UV exposure
C. Daily alcohol wipe + periodic deep cleaning
D. Hot air

19. Chemical waste like xylene should be disposed through:

A. Drainage system
B. Burning
C. Authorized chemical waste handlers
D. Regular trash

20. Which infection risk is common in histopathology labs?

A. Malaria
B. Bloodborne pathogens (HBV/HCV/HIV)
C. Rabies
D. Tetanus

21. Gloves should be changed:

A. Once a week
B. After contamination
C. Once in a shift
D. When torn only

22. Ergonomic safety applies to:

A. Proper sitting posture during microtomy
B. Chemical labeling
C. Staining
D. Fixation

23. Eyewash stations should be checked:

A. Never
B. Monthly
C. Annually
D. Daily

24. Which color-coded container is used for body fluids?

A. Red
B. Yellow
C. White
D. Black

25. Formalin-fixed tissues should be disposed in:

A. Yellow container
B. Red bag
C. White container
D. Green bag

26. Fire extinguishers in histopathology labs must be:

A. CO₂ or dry chemical type
B. Water type
C. Sand only
D. None

27. Which chemical is used as a dehydrating agent?

A. Xylene
B. Paraffin
C. Ethanol
D. Cresol

28. During grossing, splashes can be minimized by:

A. Working quickly
B. Using a splash guard
C. Using open containers
D. Cutting forcefully

29. Cryogenic burns occur due to:

A. Cold temperatures
B. Warm paraffin
C. Xylene
D. Ethanol

30. Biological waste should be collected in:

A. Blue bag
B. Yellow bag
C. Green bag
D. Black bag

31. Slides and coverslips are disposed in:

A. Red bag
B. White container
C. Cardboard box
D. Yellow bag

32. ZN staining hazards mainly involve:

A. Phenol exposure
B. Acetone fumes
C. Cold water
D. Wax splashes

33. The safest way to warm paraffin wax is using:

A. Bunsen burner
B. Hot plate
C. Embedding station with thermostat
D. Oven

34. Loud equipment like tissue processors causes:

A. Hearing damage
B. Skin burns
C. Hair loss
D. Eye irritation

35. Formalin is best neutralized with:

A. Vinegar
B. Sodium bisulfite
C. Tap water
D. Alcohol

Answers