Chemical Fume Hood Safety
Chemical safety is achieved through continual awareness of chemical hazards and by minimizing chemical exposures through the use of engineering controls (i.e. ventilation), personal protective equipment, and good lab practices.
General room ventilation is not usually sufficient to prevent the accumulation of chemical vapors; therefore, when working with toxic chemicals, use a chemical fume hood. There are many different types and sizes of hoods as well as other forms of local exhaust ventilation such as snorkels and vented chemical storage cabinets on campus. Become familiar with the local exhaust ventilation units in your work area. NOTE: Biological Safety Cabinets are not designed for chemical ventilation!
1. Ventilation failure
Fume hoods and other ventilation controls should provide enough ventilation to adequately remove the chemical hazard from the work area. Be alert to detect any malfunction in the ventilation equipment. In the event that a ventilation system fails, shut down all operations within that system promptly and safely. Close or seal any open containers or equipment containing hazardous materials to prevent a release of vapors into the room. If the ventilation equipment is a hood or a snorkel, post a sign on the item stating the hood or snorkel is not working properly. Phone the FM Service Center (774-6547) and follow the procedures listed in section IV part H of the Chemical Hygiene Plan. Do not use chemicals in the hood or beneath the snorkel until further notice is given that the system has been repaired. If the ventilation shut down creates an emergency situation (i.e. hazardous chemical vapors are not controlled), then evacuate personnel from the area, dial 911, and give as much detail as possible to the CMU Police Dispatcher (i.e. location, name of chemical, etc.).
2. Ventilation testing
The chemical fume hoods will be tested biannually by Facilities Management. If any hood is not working properly, then it will be tagged out of service until the repairs are made. While the hood is out of service, it cannot be used for chemical applications.
3. Use of a chemical fume hood
Chemical fume hoods are protective equipment and must be used correctly to offer protection from chemical exposure. The following is a list of procedures that must be followed to ensure that the ventilation is properly working at all times.
1. Keep all laboratory doors to the hallway closed. This will aid in keeping the hallways at a positive pressure and the laboratories at a negative pressure so chemical odors will not migrate out of the lab. This is most pertinent to the occupants of the Dow Building, where the building is designed for the hallways to be positive to the labs.
2. Keep windows closed in the laboratory. Drafts and eddy currents can cause turbulence at the face of the hood that may allow chemical vapors to escape from the hood. Keeping the windows closed in the Dow Building will also aid in maintaining the proper air pressure gradient.
3. Keep hood sashes in a lowered position with a maximum opening of 18 inches at all times except when actively positioning equipment. The primary reason for this is safety. The hoods are designed to eliminate chemical inhalation exposure. When the sashes are wide open, the hood does not trap as much of the chemical vapor. In addition, the total air balance of the building ventilation system is compromised when the sashes are left wide open in the Dow Building. For your reference, the hoods have been marked with red tape at 18 inches. When the hood is not in use, close the sash completely. In this context, “not in use” means not being used to vent chemical vapors.
4. For hoods that contain manual flow controls, place the face velocity setting at 100 ft/min before using the hood. Allow 3-5 minutes for the hood to stabilize and reach the new face velocity setting prior to beginning work. A safe working range for a hood is 80-120 ft/min. When the hood is not being used, the setting should be turned to minimum for standby mode. To obtain a quick flush of the hood following a chemical spill in the hood, lower the sash to about an 8 inch open height, set the controller to 200 ft/min for a couple minutes, then return the controller to 100 ft/min for regular use. Hoods that do not contain manual flow controls will be adjusted to maintain a face velocity of around 100 ft/min when turned on with the sash raised to 18 inches.
5. Keep storage of chemicals and equipment in the hood to a minimum (i.e. only those materials in use). If the hoods become cluttered, then airflow is blocked. A spacious work area inside the hood will also allow the researcher more elbow room to work more efficiently.