1. What is a Fume Hood?
A fume hood is a ventilated enclosure designed to limit exposure to hazardous gases, vapors, dust, or aerosols in laboratories. It works by capturing and exhausting contaminants away from the user and the workspace, ensuring a safe environment for handling toxic, flammable, or odorous chemicals. Fume hoods are essential in chemistry, biology, pharmaceutical, and industrial labs.
2. How Does a Fume Hood Work?
Airflow Mechanism: A fan or central exhaust system creates negative pressure inside the hood, drawing room air through the sash (front window) opening. Contaminants are captured and expelled via ductwork to an external exhaust or filtered and recirculated (in ductless models).
Face Velocity: Optimal airflow velocity at the sash opening is 80–120 feet per minute (fpm). Too low (<60 fpm) risks exposure; too high (>150 fpm) causes turbulence, reducing containment.
Baffles and Airfoils: Internal baffles direct airflow evenly, while the airfoil (lower front ledge) minimizes eddies to enhance capture efficiency.
3. Types of Fume Hoods
Ducted (Conventional) Hoods: Contaminated air is vented outdoors. Ideal for high-risk chemicals.
Ductless (Filtered) Hoods: Air passes through HEPA or carbon filters and recirculates. Suitable for low-toxicity substances.
Auxiliary Air Hoods: Supply external air to reduce room air consumption.
Perchloric Acid Hoods: Equipped with wash-down systems to prevent explosive perchlorate buildup.
Radioisotope Hoods: Lined with stainless steel for easy decontamination.
4. Operating Procedures
Pre-Use Checklist
Verify airflow: Attach a ribbon or tissue to the sash; inward movement confirms proper flow.
Ensure the sash is at the recommended height (typically ≤18 inches / 45 cm).
Check inspection stickers for recent certification (annual testing is standard).
During Use
Sash Management: Keep the sash as low as possible while working. Close it completely when not in use.
Work Zone: Perform tasks at least 6 inches (15 cm) inside the hood to maximize containment.
Equipment Placement: Avoid blocking airflow by placing large equipment on blocks. Keep materials ≥1 inch (2.5 cm) from the sash.
Chemical Storage: Never store chemicals permanently inside the hood.
Post-Use Protocol
Clean spills immediately using approved methods.
Close the sash fully.
Label waste containers and dispose of them properly.
5. Safety Guidelines
Personal Protective Equipment (PPE): Always wear gloves, lab coats, and safety goggles. Use respirators if required.
Flammable Materials: Ground the hood and avoid ignition sources when handling flammables.
Emergency Stops: Know the location of emergency shut-off switches for power or airflow.
No Head Entry: Never place your head inside a operating hood.
Training: Only trained personnel may operate specialized hoods (e.g., perchloric acid, radioisotope).
6. Maintenance & Inspection
Routine Checks
Daily: Confirm airflow visually and check for obstructions.
Monthly: Clean surfaces with non-corrosive agents. Inspect filters (for ductless hoods).
Professional Maintenance
Annual Certification: Test face velocity, containment, and airflow patterns per ANSI/AIHA Z9.5-2020 standards.
Filter Replacement: Replace ductless filters when saturation alarms activate or per manufacturer guidelines.
Troubleshooting Common Issues
| Issue | Possible Cause | Solution |
|---|---|---|
| Poor airflow | Blocked ducts or filters | Inspect ducts; replace filters |
| Turbulence | High sash opening | Lower sash to ≤18 inches |
| Alarm activation | Low face velocity | Check fan; contact facilities |
7. Limitations
Not for Explosions: Fume hoods do not protect against explosions or high-pressure reactions. Use blast shields.
Ineffective for Nanoparticles: Standard hoods may not capture ultrafine particles; use HEPA-filtered enclosures.
Energy Consumption: Ducted hoods increase HVAC costs; balance safety and sustainability.
8. Best Practices
Minimize Traffic: Foot traffic near the hood disrupts airflow.
Use Secondary Containment: Place volatile chemicals in trays or bins.
Label Experiments: Note hazards and emergency contacts on the hood exterior.
9. Emergency Response
Chemical Spills:
Evacuate if toxic or volatile.
Use spill kits for small leaks; neutralize acids/bases as needed.
Power Failure:
Close the sash immediately.
Seal containers and evacuate if ventilation is lost.
10. Regulatory Standards
OSHA 29 CFR 1910.1450: Requires fume hoods for hazardous chemical handling.
NFPA 45: Fire safety standards for labs.
ANSI/AIHA Z9.5: Guidelines for ventilation and performance testing.