Common Fume Hood Mistakes: How to Ensure Safe and Efficient Use
Fume hoods are essential safety devices in laboratories, designed to protect users from hazardous fumes, vapors, and particles. However, misconceptions and misuse often compromise their effectiveness. Let’s explore the most common mistakes made when using fume hoods and provide best practices to help you maintain a safe and productive laboratory environment.
1. Misunderstanding the Purpose of a Fume Hood
Many assume that if a fume hood is present, it automatically provides the intended level of protection. However, a fume hood must be properly connected to a well-designed and maintained laboratory ventilation system for it to function properly.
A fume hood’s primary functions are to:
- Capture: Contain hazardous substances within the fume chamber.
- Contain: Prevent substances from escaping the chamber.
- Dilute: Mix contaminants with air to reduce their concentration.
- Exhaust: Safely expel contaminated air outside the building.
A fume hood’s effectiveness depends on the hood itself, the ventilation system, and proper user practices—like a three-legged stool that requires all three legs for stability.
2. Improper Use of the Sash
The sash is the interface between the user and the hazardous materials inside the hood. It acts as a protective barrier and should be positioned as low as possible during use. Common mistakes include:
- Working with the sash fully open: This reduces protection and increases energy consumption.
- Positioning the sash too close to the breathing zone: Contaminants near the sash’s edge can be inhaled.
- Failing to close the sash when not in use: This helps conserve energy and will minimize hazards.
Use fume hood sashes correctly, and remember that slow, deliberate movements reduce turbulence and improve containment.
3. Neglecting Airflow and Turbulence
Airflow is critical to a fume hood’s performance. Contaminated air should flow smoothly from the lab into the hood, through the baffles, and out through the ventilation system. Disruptions in airflow can cause loss of containment. Avoid these common mistakes:
- Blocking baffle openings: Keep equipment and materials away from the back wall and side panels.
- Placing objects directly on the work surface: Elevate items to allow air to flow underneath.
- Creating turbulence: Move slowly and avoid quick, jerky movements that can pull contaminants out of the hood.
- Allowing cross drafts: Minimize air movement near the hood by positioning it away from doors, supply air registers, and other fume hoods.
4. Relying Solely on Face Velocity Readings
Face velocity, measured in feet per minute, indicates how quickly air enters the hood. However, it doesn’t guarantee containment. Even hoods with proper face velocity can fail to contain hazardous substances. For optimal performance:
- Use hoods designed to operate between 60 and 100 feet per minute.
- Higher velocities above 125 feet per minute can create excessive turbulence and reduce containment.
- Conduct regular ASHRAE 110 tests to verify that the hood maintains containment under actual working conditions.
5. Ignoring Maintenance and Testing Requirements
Regular maintenance and performance testing are essential for ensuring that fume hoods function properly. Key practices include:
- Annual or biannual inspections by trained professionals.
- Internal audits by lab managers and safety personnel.
- Prompt reporting of any signs of malfunction, such as unusual airflow patterns or alarms.
- Ensuring the ventilation system is calibrated and maintained regularly.
6. Inadequate User Training
Many fume hood performance failures result from improper user practices. Comprehensive training should cover:
- The proper use of the sash and positioning within the hood.
- Identifying signs of poor airflow or loss of containment.
- Minimizing turbulence by moving slowly and keeping objects elevated.
- Understanding the limitations of face velocity readings.
- Knowing emergency procedures, including how to respond to fires and explosions.
Conclusion
Using a fume hood safely and efficiently requires an approach that considers the equipment, ventilation system, and user practices. By avoiding common mistakes and following best practices, you can maintain a safer laboratory environment while maximizing the effectiveness of your fume hood.