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Chemical Fume Hoods


There are over 1,000 chemical fume hoods used by faculty, staff, and students at UVA. Every hood is surveyed annually by EHS.

These surveys are critical in determining whether or not the most important piece of safety equipment in a lab is performing satisfactorily.

The sticker on the face of the hood has instructions on how to operate the fume hood and provides contact information for repair or re-surveys. Modification of the local exhaust ventilation system without approval is prohibited, as changes made to the system may result in unsafe conditions.

When to use a chemical fume hood

Chemical fume hoods are the primary engineering control for capturing and removing hazardous airborne contaminants in laboratories. Use a chemical fume hood when handling chemicals that have high acute toxicity, are carcinogens, mutagens or are reproductive toxins; anytime your work involves potential exposure to chemicals with a NFPA Health rating of 3 and 4; chemicals are flammable, corrosive or irritating, reactive, potentially explosive; or where heating or agitation may cause chemicals to spatter or aerosolize. Chemicals with particularly low odor thresholds, (e.g., beta-mercaptoethanol, thiols, etc.) should also be handled in a chemical fume hood, regardless if hazardous or non-hazardous.

Use a chemical fume hood when the chemical's safety data sheet indicates under Section 8 Exposure Controls, "provide exhaust ventilation or other engineering controls to keep the airborne concentrations of vapors below their respective threshold limit value".

There may be instances where there is only a very low risk of exposure to the chemicals described above (e.g., use of minimal quantities in a closed system). A risk assessment can be performed to determine if a chemical can be safely handled outside of a chemical fume hood.

Consider upgrading to a glove box or other isolation device for particularly hazardous substances, toxic gases, and highly reactive or explosive/pyrophoric materials, as chemical fume hoods are, under the best of circumstances, only certified to a containment performance of less than 0.1 part per million (ppm) leakage rate.

Chemical Fume Hoods and Energy Conservation

Chemical fume hoods are highly energy-intensive as they continuously remove conditioned air from a space. Constant volume chemical fume hoods can use more than 3 times as much energy as a single family home on an annual basis. The energy required for filtering, moving, cooling or heating, and cleaning air is the largest cost in lab facilities. Innovations in chemical fume hood technology and design have succeeded in reducing airflow through chemical fume hoods while maintaining, or increasing, safety and performance.

Variable air volume (VAV) chemical fume hoods exemplify an innovation in chemical fume hood technology.

VAV systems adjust the amount of air that passes through a chemical fume hood while maintaining a minimum velocity for safety. The reduction in air passing through the chemical fume hood when the sash is lowered results in a reduction of outside air that must be reconditioned to replace the air exhausted. The less outside air that must be conditioned results in lower building costs.

Shut the Sash (energy saving) competition was initiated at UVA in October 2017 by the Green Labs Program.

Perchloric Acid Laboratory Hoods

The use of perchloric acid, particularly in concentrated form (>72%) and used above room temperature, can result in the accumulation of explosive perchlorates on chemical fume hood surfaces and inside ductwork. It is dangerous to use perchloric acid in a conventional fume hood and where other materials (organics, flammables) could mix with perchlorates, resulting in an explosion that could be touched off by friction from simply adjusting the panels and baffles in the hood. Work that involves heating any concentration of perchloric acid or evaporating concentrated perchloric acid must be performed in a perchloric acid fume hood that is designed specifically for use with materials that can deposit shock-sensitive crystalline materials. These hoods are constructed throughout of stainless steel and equipped with water wash-down capabilities.

The water spray should be used whenever perchloric acid is heated in the hood. If a conventional fume hood has been exposed to heated perchloric acid, tests must be conducted to determine if explosive perchlorates have formed on the hood walls and duct system. This must be completed before any inspection, cleaning, maintenance, or any other work is done on any part of the hood interior or exhaust system.

Based on these special needs, which are not provided for in most laboratories, perchloric acid may not be handled in concentrated form (>72%) or manipulated above room temperature (i.e. heated) in any laboratory that is not specially equipped to address the associated hazards.

Specialty perchloric acid hoods are in Jesser Hall and in Wilsdorf Hall. Contact EHS if you believe you need assistance in gaining access to one of these specialty hoods.

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