Laboratories are fast-paced environments where precision matters—and not just in your measurements. When it comes to chemical safety, lab fume hoods play a critical role in protecting users from harmful vapors, gases, and particles. These ventilated enclosures are essential for safely working with hazardous or volatile chemicals.
They help prevent inhalation of toxic substances, protect the environment by safely disposing of hazardous fumes, and shield experiments from contamination. However, despite their importance, fume hoods are often misused or taken for granted, leading to avoidable risks.
Below are ten common mistakes people make when using a lab fume hood, along with guidance on how to avoid them. Whether you’re new to lab work or simply need a refresher, maintaining proper technique is essential for your safety and the safety of those around you.
1. Working Too Close to the Sash Opening
Many users position themselves too close to the sash opening while working, often unconsciously. This compromises the airflow pattern and increases the likelihood of exposure. Think of the sash as a protective barrier. Keeping your hands and materials at least six inches inside the hood allows for optimal containment and minimizes turbulence that could carry contaminants outward.
2. Storing Chemicals Inside the Hood
A fume hood is not a storage cabinet. Placing chemicals inside the hood—especially permanently—disrupts airflow and introduces unnecessary hazards. Containers create obstructions and turbulence, which may affect how effectively vapors are captured and exhausted. All chemicals should be stored in appropriate chemical storage units unless they are actively in use during an experiment.
3. Blocking Airflow with Equipment
Large or improperly placed equipment can block airflow and reduce the hood’s effectiveness. Crowding the interior with glassware, instruments, or boxes impedes the smooth entry of air into the hood, compromising containment. To maintain proper airflow, use equipment stands to elevate devices and avoid placing items directly against the baffles or air slots.
4. Ignoring Face Velocity Readings and Alarm Alerts
Face velocity—the speed at which air is drawn into the hood opening—must be within a specific range, typically 80 to 120 feet per minute. According to the American Chemical Society’s guidelines on laboratory ventilation, maintaining proper face velocity is essential for effective containment. Many hoods display this value, and some are equipped with alarms to signal performance issues. These are not optional indicators. If the alarm activates or the velocity is out of range, stop work and consult your lab safety officer or facilities team.
5. Making Sudden Movements in Front of the Hood
Rapid movements near the hood, such as walking past quickly or waving your hands, can create turbulence and disrupt the airflow curtain. This can allow fumes or particles to escape into the lab environment. When working at a hood, movements should be deliberate and steady. Minimize traffic in front of the hood during active operations to maintain airflow stability.
6. Leaving the Sash Fully Open
The sash should be kept at its designated working height whenever possible. This height is typically marked with a label or indicator and is based on containment tests performed during installation. Leaving the sash fully open reduces the hood’s ability to contain hazardous vapors and increases your risk of exposure. Always lower the sash to its proper height during use, and fully close it when the hood is not in operation.
7. Neglecting Cleanliness and Organization
A cluttered or dirty hood is not just unprofessional—it is unsafe. Residual chemicals, broken glass, and disorganized materials can increase the risk of cross-contamination, spills, or reactions. At the end of each session, ensure that the workspace is wiped down and free of unnecessary items. Maintaining a clean hood supports proper function and helps protect everyone in the lab.
8. Not Allowing the Hood to Run Before and After Use
Turning the hood on only at the moment of use, and shutting it off immediately after, is insufficient. Fume hoods require time to stabilize airflow and clear residual vapors. It is good practice to let the hood run for at least five minutes before beginning work and to continue running for five to ten minutes after completing your procedure. This ensures that any lingering hazardous substances are fully exhausted.
9. Skipping PPE Because the Hood Is in Use
The presence of a fume hood does not replace the need for personal protective equipment. While the hood protects against inhalation hazards, it does not prevent skin contact or protect against splashes. Always wear proper PPE, including gloves, goggles, and a lab coat, when working in the hood. Relying solely on the hood for protection exposes you to unnecessary risk.
10. Relying on the Hood to Offset Poor Technique
A fume hood is a vital engineering control, but it is not a substitute for sound lab practices. Improper chemical handling, lack of planning, or negligence can render even the best hood ineffective. It is essential to approach all lab work with care, attention, and respect for safety protocols. Understand the limitations of your equipment, and never assume the hood will compensate for improper behavior.
Conclusion
Using a fume hood safely is not just about switching it on and placing your work inside. It involves an understanding of airflow dynamics, awareness of physical barriers, and a commitment to consistent, disciplined practices. By avoiding these common mistakes, you not only protect yourself but also contribute to a safer, more effective laboratory environment. The fume hood is an important tool—but it works best when combined with informed, responsible laboratory behavior.
