Fume Hood Selection Considerations
Recent experience tells me that in the Bio-pharmaceutical world, there is a lot of confusion, misinformation, and ignorance when it comes to what can broadly be termed “separative devices”. These include fume hoods, bio-safety cabinets (BSCs), isolators, Restricted Access Barriers (RABs) etc. This article will concentrate on fume hoods, one of the most used devices in laboratories.
Separative devices are used in various industries and for various applications. Whether you are trying to protect personnel, the environment, the product or a combination of those a separative device is the engineering control you will most likely employ.
Fume Hoods are used to remove fumes from the process and protect the operator. These hoods are not design to protect the product from contamination, but instead to remove solvents, volatile chemicals and flammables to protect the environment in the laboratory and the operator from the adverse impacts of those substances. If you need to protect the product from contamination as well, a fume hood is not the right choice.
Fume hood certification is generally desirable/required and guidelines are produced by a number of agencies and organizations. Here are a few:
OSHA Part 1910.1450. The agency regulations regarding fume hood operation are listed in the Code of Federal Regulations Volume 29 Part 1910.1450. Regarding hoods this regulations is primarily concerned with airflow at the face of the hood, monitoring, maintenance and exhaust.
ANSI/ASHRAE 110-1995. Method of Testing Performance of Laboratory Fume Hoods. This standard is published by the American National Standards Institute and the American Society of Heating, Refrigerating and Air Conditioning Engineers, Inc. It concerns itself primarily with methods of testing fume hoods to check their operation.
NFPA 45. This standard is prepared by the National Fire Protection Association. It recommends hood construction, location, fire protection, specialty hoods, identification, inspection, testing, maintenance and exhaust.
SEFA 1.2-1996. SEFA is the Scientific Equipment & Furniture Association. Its publication “Laboratory Fume Hoods Recommended Practices” covers design requirements of hoods, face velocities and testing.
The most commonly used certification in the biopharm industry is ASHRAE 110, but it is important to know that the organizations listed above don't always agree on the requirements. It is also important to know that although you may hear (especially from old timers) that 100 feet per minute face velocity is an OSHA requirement. While that was once a rule of thumb, it is no longer the case.
Myth - OSHA requires 100 fpm face velocity for fume hoods.
Reality - since January 31, 1990 OSHA has been specific and clear stating that face velocity is not what determines hood performance, nor is 100 feet per minute a requirement or recommendation
OSHA: “General air flow should not be turbulent and should be relatively uniform throughout the laboratory, with no high velocity or static areas; air flow into and within the hood should not be excessively turbulent; hood face velocity should be adequate. (Typically 60-110 fpm.)”
ANSI/AIHA Z9.5: “Each hood shall maintain an average face velocity of 80-120 fpm with no face velocity measurement more than plus or minus 20% of average.”
SEFA: “Face velocities of laboratory fume hoods may be established on the basis of the toxicity or hazard of the materials used or the operations conducted within the fume hood. Note: Governmental codes rules and regulation may require specific face velocities. A fume hood face velocity of 100 fpm is considered acceptable in standard practice. In certain situations, face velocity of up to 125 fpm or as low as 75 fpm may be acceptable to meet required capture velocities of the fume hood.”
In addition to face velocity, there are other considerations when certifying a hood:
Certified by a qualified technician to ensure proper capture velocity, no excessive turbulence, etc.
Hoods must be equipped with monitors/alarms to allow convenient confirmation of adequate hood performance before use
OSHA: “Quality and quantity of ventilation should be evaluated on installation, regularly monitored (at least every 3 months), and re-evaluated whenever a change in local ventilation devices is made.”
ANSI/AIHA Z9.5: “Discharged in manner and location to avoid re-entry into the laboratory building or adjacent buildings at concentrations above 20% of the allowable concentrations inside the laboratory under any wind or atmospheric conditions.”
Fume hoods come in a variety of sizes and configurations. The standard widths are generally 4ft, 6ft, or 8ft, but custom sizes are also available. Hoods can also sit on standard casework or benches in the laboratory or they can be floor mounted and made to accommodate large equipment including the operator (walk-in hoods). Very small fume hoods (only big enough for your hands) are also available for specialty applications or small budgets.
Sash configuration is also an important consideration. Hoods have adjustable sashes that can be either vertical or horizontal depending on what the hood will be used for. Generally, I recommend vertical sashes unless there is a specific application where a horizontal sash is needed because it will be easier to control airflow.
Additional options for fume hoods include connections for water, specialty gasses, provisions for vacuum, cup sinks, and lattice frames (aka monkey bars) to attach equipment to.
There are many manufacturers of fume hoods and selecting one should be based on price, lead time, quality of construction and customer support. Most if not all of the major fume hood manufacturing companies offer all of the options mentioned above and can provide a hood that will do the job.
A fume hood is not the right choice for many activities, especially those where protecting the product from the environment is important or if you are working with biological materials. Those processes require different separative devices that may look similar to fume hoods, but operate differently and have different configurations and options. I will write more about those in a future post.