How to Get the Most Out of Your Lab's Fume Hoods

the Synergist

LABORATORIES

ASHLEY AUGSPURGER, PhD, CSP, is the biosafety officer and chemical hygiene officer for Corteva Agrisciences in Iowa.

ANGELA DARTT, PhD, CIH, is the Director of Chemical Safety at Washington University in St. Louis, Environmental Health and Safety Department.

MAHDI FAHIM, MS, is the assistant director-laboratory safety manager at North Carolina State University, Environmental Health and Safety Department.

RACHAEL PERRIELLO, MPH, is the Environment, Health, and Safety Specialist at the Energy and Environmental Research Center in North Dakota. Send feedback to The Synergist.

How to Get the Most Out of Your Lab’s Fume Hoods

BY ASHLEY AUGSPURGER, ANGELA DARTT, MAHDI FAHIM, AND RACHAEL PERRIELLO

Fume hoods are the most common engineering control used to protect laboratory workers from hazardous fumes, vapors, and dusts. However, lab safety and health professionals must properly select a fume hood product and ensure correct installation and use in the lab to maintain fume hood performance. What can laboratory managers and safety professionals do to ensure the reliability of fume hoods in their facilities?

As specified by the standard ANSI/AIHA/ASSP Z9.5, which applies to laboratory ventilation, developing a Local Exhaust Ventilation Management Program can lead to a safe, dependable, sustainable, and energy-efficient lab exhaust system. All laboratory stakeholders, including architects, facility owners and managers, end users, and health and safety professionals, should be involved with development. But for health and safety professionals to contribute adequately to program development, they must understand common challenges with fume hood design, installation, maintenance, and use.

DESIGN AND SELECTION SPECIFICATIONS Lab safety professionals should create an internal fume hood design and performance standard for their workplace that addresses the design, selection, installation, and test criteria for new projects and renovations. Under this internal standard, system and device selection will only occur following a careful risk and hazard evaluation. Factors to consider before selecting a fume hood and the associated exhaust system components and devices include laboratory building design; the hoods' short- and long-term applications; the project's budget; hood maintenance requirements such as training, personnel, and budget; and the potential for a product to reduce energy consumption.

The International Mechanical Code, a convention that protects public health and safety regarding building heating, ventilation, and air conditioning systems, has been adopted by most states and should have been considered during laboratory construction. Elements of this code that lab safety professionals will find relevant to laboratory exhaust design include its limitations on hazardous exhaust recirculation, energy recovery systems such as heat exchangers, and manifolding hazardous exhausts in occupied spaces.

When finally selecting a product, a safety professional's first consideration should be the type of materials that this laboratory will use in its hoods. Laboratories that use radioisotopes or nanomaterials will require safety professionals to research specific face velocity, exhaust ducting, and exhaust filtration requirements beyond this article's scope. Hoods used for acid digestion or perchloric acid also require certain design criteria to be met. These hoods need to run at a constant volume and should not be manifolded with other fume hoods—that is, for labs involved with these acid-related projects, separate fume hoods should not exhaust into one pipe.

The two main types of laboratory fume hood are constant air volume (CAV) hoods and variable air volume (VAV) hoods. CAV hoods exhaust a continuous volume of air. Face velocity—the speed at which air enters the hood's front opening—varies as sash position changes. VAV hoods, or demand-based systems, adjust the volume of air exhausted while maintaining face velocity at a predetermined level, regardless of sash position. Only VAV systems will reduce energy costs when the sash is lowered. The selected fume hood should have the right attributes for the lab that will use it.

Other design and performance components that lab safety professionals should consider when selecting a fume hood include base storage cabinets, either vented for corrosive substances or non-vented for flammable materials; digital flow monitors and alarms, along with their installation and calibration procedures; spill containment features, such as built-in recesses around cup sinks; automated sash closures, zone presence sensors, light sensors, emergency purge systems, and other technologies that can save energy or assist emergency response; ergonomic and accessibility features; and wall, counter, and ducting materials compatible with or resistant to specific substances relevant to the hoods' applications, such as hydrofluoric acid.

When finally selecting a product, a safety professional's first consideration should be the type of materials that this laboratory will use in its hoods.

Whether the new fume hoods will be installed in a newly built or renovated system, lab safety professionals should consider exhaust infrastructure during the planning stage. In some cases, exhaust from laboratories with similar hazards can be manifolded together to minimize the number of fan motors and roof penetrations needed. Also, exhaust system design must identify variables such as the velocity of gases and materials within the fume hood exhaust stacks, stack height, wind dispersion of exhaust from the building, and the distances between the stacks and building air intake to prevent hazardous exhaust re-entrainment. Fume hood exhaust fans should be connected to emergency power. Another critical factor is the fume hood locations relative to supply air vents, doorways, and high-traffic areas. Without acknowledging room mixing efficiency or supply air distribution, a high air exchange rate alone is not enough to promote a healthy indoor air environment and control fugitive emissions within a space. Selecting low-velocity diffusers and paying careful attention to the locations and distributions of supply and exhaust air diffusers (to avoid potential short-circuiting) are the basic design criteria for a room with high mixing efficiency. INSTALLATION It is crucial to maintain the same level of attention to detail during the installation phase so that the new fume hoods provide the most comprehensive protection possible. Substandard installation can impair the performance of a well-designed fume hood. After installation, inspect the hood to ensure that all components are in place, seams are aligned, baffle slots are correctly adjusted, and proper connections have been made. Before use, the hoods' performance must be tested and certified per the ASHRAE 110 "as installed" requirements and the internal standard for product use devised by the supervising safety professional. Safety professionals should review the ASHRAE 110 test results to ensure that all parameters tested lie within acceptable specifications and that the testing conditions reflect expected use conditions. If testing indicates a deficiency, the lab owner or operator should work with the installation contractors to troubleshoot the fume hood before running a second performance test. Airflow monitors are vital to notify laboratory workers when hood flow or velocity falls below predefined unsafe levels. Monitors installed for VAV fume hoods should be set up and calibrated at fume hood installation to ensure that all the VAV control system's electronic components are modulating properly. Safety professionals should also test and evaluate VAV response time, VAV time to steady state, and room pressurization with hood sashes in both open and closed positions, keeping track of any changes over time. Building remodeling can affect fume hood performance through changes in room pressures, VAV response time, minimum flow in VAV hoods, and system stability. When new construction projects take place in a laboratory building, the ventilation system must maintain its capabilities. Ideally, ASHRAE 110 testing should be performed on any impacted fume hood after construction is complete. Fume hoods should undergo annual testing—at a minimum—as decided by the lab's facility or institution. MAINTENANCE AND TESTING A robust preventative maintenance and testing program is imperative for an effective local exhaust ventilation management program. The lab should complete and maintain documentation of annual face velocity and room pressure testing and of evaluating airflow using small-volume smoke visualization, as per the lab's internal ventilation procedures. Frequent testing for VAV system failures should also be implemented and tracked over time. Major long-term problems in VAV systems include minimum flow drift from the original design; increased VAV response time and time to steady state; unstable or fluctuating flow or face velocity; and failure of supply or exhaust modulation. These issues may result in compromised room pressure or increased energy costs. If a fume hood fails routine testing, users should learn of the results immediately and should not use the fume hood again until it is fixed and retested. Lab managers and safety professionals should establish procedures to notify all affected individuals of test failure and subsequent developments such as the hiring of maintenance personnel, the retesting date and process, any retest results, and restored permission to work in the hood. A tagout procedure, in which a designated employee disconnects the affected equipment from power and installs a prominent "tagout" device to alert other employees of the equipment's disuse, is among the best practices for preventing lab staff from using out-of-commission hoods. USER TRAINING With the competent fume hood selection, monitoring, and maintenance procedures, safety professionals can ensure that their fume hoods maintain top performance to protect lab workers for years to come. However, this time and effort may be wasted if the fume hood users are not correctly trained to use the hood and work within it. All laboratory employees should receive training and information per ANSI Z9.5. Where specialty hoods designed for a particular kind of research are in place, safety professionals must reinforce key differences between these hoods and standard hoods and any necessary alternative safety measures. Improper use and lack of understanding of fume hood function by users can jeopardize their safety. In addition, saving on energy costs requires users' cooperation. Additional equipment that helps maintain intended fume hood performance and safety should be provided to laboratory personnel. For example, stands, risers, or attachable feet can help keep vital equipment ventilated inside the hood while preventing turbulent or blocked airflow. It is important to remember that lab personnel members are safety professionals' potential allies in maintaining safety equipment. If they are equipped for effective fume hood use, safety professionals will see that the hoods function better and last longer.

RESOURCE

The Synergist “Fume Hood Performance Tests: Methods to Verify Proper Functioning” (August 2008).