A Basic Design Guideline for Laboratory Exhaust and Ventilation Systems

Laboratory exhaust and ventilation systems are essential when it comes to the health and safety of laboratory workers, scientists, experimenters and other professionals who routinely use hazardous materials as part of their work. At the same time, these systems must also ensure that chemical fumes and residues are properly disposed of. Here are some basic guidelines for designing and installing effective laboratory exhaust and ventilation systems.

Regulatory Guidance

Detailed guidance on laboratory exhaust and ventilation systems, along with other components of laboratory health and safety, can be found in several national standards. These standards include 29 CFR 1910.1450, Occupational Exposure to Hazardous Chemicals in Laboratories, as well as related OSHA standards covering occupational health and safety. Useful guidance may be found in NFPA 45, Standard for Fire Protection for Laboratories, published by the National Fire Prevention Association. Check to see if there are any state or local codes that are also applicable to laboratory exhaust and ventilation systems.

Hazardous Exhaust Considerations

Certain types of exhaust systems that handle hazardous materials should not be installed in the same chase that houses standard HVAC ventilation and air circulation systems, such as environmental supply ducts, return ducts, and exhaust ducts. Hazardous exhaust systems include:

• Laboratory hoods and related fume exhaust
• Biological laboratory exhaust
• Radioactive hot lab exhaust
• Liquid nitrogen freezer room exhaust

These types of exhaust systems should be labeled with the word “hazardous” or another appropriate term, as specified by relevant standards and regulations.

Laboratory Fume Hoods and Fans

Fume hoods are a critical component of laboratory work. They provide a safe place for professionals to handle toxic and hazardous chemicals, while conducting experiments, combining materials and doing tests. Hoods provide constant ventilation and removal of fumes, vapors and gases that could be dangerous to their health and safety. Standards for fume hoods are part of a chemical hygiene plan under the OSHA laboratory standard in 29 CFR 1910.1450. Exhaust fans in laboratory hoods should be connected to an emergency power source in case of a power outage in the laboratory or building.

This allows for the continual ventilation of gases, while giving laboratory workers time to seal and secure sources of hazardous fumes. Hood systems should contain monitoring devices that provide constant condition updates. Alarm systems should also be installed to alert laboratory personnel of any problems or emergencies. Alarms should provide both audible and visual notifications.

Exhaust hoods should be able to provide air change rates (AC/hr) that promote the highest level of safety. For example, 6 A/C/hr is a good minimum air change rate for fume hoods, whether the room is occupied or unoccupied. Exhaust fans should be direct-drive models. Variable-speed models may be appropriate to maintain exhaust volumes during air filter changes.

Laboratory Exhaust System Ductwork

Laboratory exhaust ductwork should be routed through the roof at least 25 feet away from, and downwind of, outdoor air intake components. In some cases, it may be preferable to install ventilation air intake ductwork on the side of the building rather than the roof. This ensures even greater separation from sources of exhaust air that could contain hazardous fumes or substances. Wind tunnel testing should be conducted to determine final placement of laboratory exhaust ductwork. Materials for laboratory ductwork should follow these guidelines:

• Welded stainless steel, type 316L, for chemical fume hoods that could be exposed to corrosive materials.
• Polished welded stainless steel, type 316, for hoods exposed to radioactive isotopes.
• Welded stainless steel, type 316L, for environments where corrosive or toxic exhaust will be encountered.

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