The chemical fume hood is a primary safety device used to protect laboratory workers from chemical exposure, fires, or explosions. The Fume Hood protects the user from flammable, toxic or offensive chemicals by providing an enclosed work area or barrier between the user and the hazardous material.
Protection from chemical exposure is provided as air is drawn from the front (or face) of the fume hood to baffles located in the back of the fume hood. The air is then exhausted through duct work to a roof stack. Note: chemicals should be located at least 6 to 8 inches deep, from the face of the hood, so vapors or fumes can be captured and transferred to the back of the fume hood.
Protection from a fire or explosion is provided by the structure and type of material the fume hood is made of. The sash employs tempered safety glass, resistant to heat and explosive impact. The body of the fume hood is also made of material resistant to fire and explosions.
Chemical Fume Hood Performance Criteria
Research activities at The Ohio State University are so varied that it is difficult to establish chemical fume hood performance criteria for all research activities. In addition, the increased desire to lower energy consumption has influenced fume hood manufacturers to design and develop new low flow fume hood systems. These systems incorporate aerodynamic designs to maintain safe fume hood performance while lowering air flow velocities.
To accommodate the vast number of activities performed in chemical fume hoods and the changing designs of chemical fume hoods, a flexible air flow range has been established incorporating a recommended high and low. The established low is 100 linear feet per minute (lfm) and established high is 150 lfm, both measured with the sash open 18 inches. These numbers do not represent air flow limits, but provide a range that will keep a majority of the chemical fume hoods safe for researchers. New low flow chemical fume hoods will need to meet the manufacturers air flow design criteria.
To determine if fume hoods performing outside of the established range are safe to use, smoke tests can be performed to demonstrate visually that the contaminants are properly captured.
There are other factors that need to be considered when evaluating chemical fume hoods for safe performance. Large instruments or apparatus placed in a chemical fume hood can disrupt airflow, as can foot traffic in front of the fume hood. Fume hood structural integrity, broken or fractured sash glass, missing parts such as utility side panels, baffles or the air foil, blocked lower slots of the baffle, these all effect fume hood performance and safety.
Chemical Fume Hood Evaluation and Certification
Chemical fume hoods should be evaluated on an annual basis. If the flow indicator shows a change in face velocity or the user suspects a problem with performance, the FOD service desk should be contacted immediately (292-HELP). Note: laboratory workers should check the flow indicator daily.
Facility Operations and Development conduct these annual fume hood evaluations and certifies the fume hoods if they meet performance Criteria and the integrity of the fume hood is not compromised. There can be no cracks in the safety glass, the sash must slide properly and the hood must be structurally sound. For approved fume hoods, FOD personnel will leave a certification sticker on the sash and provide documentation for laboratory records. If the fume hood is not approved for use, an out of order sign will be placed on the sash.