The reoccurring theme that plagues most lab renovation projects is the incidence of limited decision-making on capture devices. Typically, lab users tend to specify fume hoods without exploring or considering a myriad of other available options. This inclination stems from the fact that the modern fume hood has been around for almost a century with only modest changes since its 1923 debut at the University of Leeds.1 At the time, it was the only way to protect a scientist from airborne hazards, organic liquids, and odiferous compounds when synthesizing chemicals. Today, there are a variety of safe and energy efficient capture devices available for lab use.
Set the record straight
Lab exhaust represents approximately 30 percent of a laboratory building’s total energy consumption. Because a single hood can use up to three and a half times more energy than a house, choosing the right capture device can make a significant impact on a laboratory’s annual operating costs. In this sense, selecting the right capture device is like selecting the right tool. Just like a hammer is better than a wrench for driving a nail, a flammable cabinet is a better choice than a fume hood for storing chemicals. The savings in exhausted air alone is about 580 CFM and can go even higher if flammable cabinets are not exhausted.
Another challenge facing lab designers is the belief that if the velocity is higher, the researcher is better protected. In fact, when face velocities exceed 125 fpm, eddy currents can force contaminates out of the hood and potentially increase a worker’s exposure to hazardous materials. While many substitutions to a fume hood have lower face velocities, the containment of the device needs to protect people and ultimately contain the process. Part of the confusion over capture device selection is due to historical tendencies and misconceptions researchers have when designing their labs. It is the designer’s job to change these misconceptions by digging deeper into what is appropriate for the laboratory and presenting options that will save space and reduce operational funding.
In some lab applications where containment is required, the environment may also require an ISO cleanroom certification or compliance with EU GMP — Annex 1. The air changes vary from 10ACH to 650ACH based on the cleanliness required. The amount of exhaust that is required, based on the capture devices selected, will affect the sizing of the filter bank and make-up air handling unit, which in part increases both the operating cost and the cost of the HVAC system. In these types of labs, the fans, filter, and coils (if required) must be dedicated and only serve rooms with similar containment hazards to isolate the areas in the unfortunate event of decontamination and cleaning.
Fume hood limitations
It’s important to understand the primary function and limitations of a fume hood before examining options that provide a higher level of safety and may save on energy costs. A fume hood is designed to contain and remove the hazardous materials (gases and dust particles) generated as the result of lab procedures developed to protect lab personnel. But, fume hoods also have some limitations, including:
• Bio-samples. Fume hoods are not the best containment option to protect tissue and other bio sample from external contamination.
• Nanoparticles. 100 fpm face velocity creates highly turbulent air that can allow the nanoparticles to escape, causing a number of health risks.
• Location. Fume hoods are not the best option for high traffic areas. Humans walk at a velocity of 250 fpm, so someone passing by a fume hood during use may create vortices that will disturb the 100 fpm fume hood containment velocity and pull contaminates out of the hood.
• Diffusers. Supply devices that are within five feet of the hood and generate air velocities above 50 fpm at the fume hood opening will create vortices that can pull contaminates out of the hood.2
Examples from the field
The following case studies provide a few examples of alternative capture device options and the benefits they can deliver.
Case Study 1 — Rotovaps: It used to be common to see rotovaps out on the lab bench, but over the last 10 years these devices have moved into the fume hood due to the evaporation of solvents. Because rotovaps require space for the instrument as well as work space for other hood related operations, the hoods tend to be extra deep, eight feet long, and use 1,090CFM at 100 fpm. This configuration burns $6,867 in energy (based on 6.30 per CFM) each year.
In this example, the lab user requested four 8-foot hoods. During the initial stages of the design process, it was discovered that the real reason for the large hoods was the lab user planned to place a rotovap in each hood. Two options, including energy costs, were presented to the user groups (see Table 1).
Table 1
Working with all project stakeholders, a design solution of four ventilated enclosures with four smaller hoods was delivered. This saved the lab user 840cfm and $5,040 per year in energy costs, provided a safe work environment (including dedicated hood space) and lowered the operating costs of the lab space. An additional solution of a reduced face velocity on the ventilated enclosures in both occupied and unoccupied modes was presented; but due to the high toxicity of compounds, the health and safety group advised staying in a constant volume operating mode under all conditions.
Case Study 2 — Biochemistry Lab: This example demonstrates an approach for larger, more complicated labs, such as a 4,000 square foot biochemistry lab that works with toxic compounds and a fixed quantity of HEPA filtered exhaust. While supply air MERV 15 (>95 percent) was utilized to protect the lab and lab samples, the exhaust HEPA filters were provided to protect the environment around the building from toxic dust. The users’ initial request had 22 capture devices, including 16 six-foot fume hoods. The existing exhaust system was designed to support a one fume hood per lab module (11’6” wide by 26’ lab zone).
Using the same inclusive design process, all the key stakeholders were involved, including the user group, facilities, health and safety, and design teams. The health and safety team and an outside organization conducted an in-depth risk analysis to evaluate all the products used and processes performed in the lab. They provided a report which banded all the processes and identified where an enclosure would be required and the type of enclosure that should be used. An example of the evaluation table used to determine risk can be found in Table 2.
Table 2
This report was used to recommend exhaust options. The initial request of 16 fume hoods was reduced to four, combined with two glove boxes, three equipment connections, and 16 ventilated enclosures. The user group was provided with four more enclosures and the CFM usage was reduced by 5,145 cfm to deliver an energy savings of $6,760.97 per year (see Table 3).
Table 3
By working with all the stakeholders, a safe solution for the researchers was developed. At the end of the process the projected energy savings when compared to variable volume fume hood was minor but the maximum total exhaust was within existing fan and filter limitations. This solution included developing standard operating procedures (SOPs) for each process in the lab prior to the construction of the lab, thereby reducing operational costs.
Selection process
The best practices for lab design include the process of identifying the right capture device in the initial programming phase. Here is a three-step process you can utilize to help determine the right device for a lab:
1. Involve all the stakeholders and an industrial hygienist.
2. Describe the hazardous procedures using the primary characteristics to quantify these procedures including: frequency of use (How often is the hazardous material used?); duration of use (What interval of time is the hazardous material used?); toxicity (None, low to high, or an immediate hazard to life and health); volume of effluent or emissions (How much effluent or emissions are given off in the lab process?); characteristics of the effluent (Is the effluent a gas, fume, mist, a particulate or powder?); possible conditions to implement variable exhaust air strategies (not occupied in front of containment device, process not active or standby with containment device, sash or containment device door closed)
3. Select the best device and air management strategy for the task, based on the information you have gathered.
Once there is an understanding of what device is necessary, it’s time to review proper installation and testing of the selected device to validate that it is performing as described in the specifications. After ASHRAE/ANSI 110 testing is completed, it is important to train each person who uses the capture devices to ensure the devices will operate as designed.
While safety is the most important goal of the containment device, it’s critical for users to be trained to understand how a simple procedure, such as closing a sash or door opening, even when the device is not in use, will save energy and possibly provide additional operational funds for new research.
Rotovap enclosure. Image: Courtesy of BHDP
Each researcher who uses these devices should:
• Be able to identify the diverse types of devices utilized in the lab.
• Be able to understand the use for each device.
• Be trained by the lab safety manager on the SOP for each device.
• Be knowledgeable on how to adjust the devices.
• Be able to verify if the devices are operating correctly, including reading an air flow monitor if the device has one.
When laboratory personnel take the time to fully understand all the processes requiring an exhaust enclosure, they will have more opportunities to reduce the supply and exhaust required in their labs.
References
1. https://en.wikipedia.org/wiki/Fume_hood
2. RDWI Laboratory Airflow distribution
George L. Kemper, RA, is a senior laboratory planner for BHDP Architecture. Established in 1937, BHDP designs environments that affect the key behaviors necessary to achieve strategic results for clients by thinking creatively, staying curious, fostering collaboration, and delivering excellence. [email protected]
Raymond Doyle, PE, LEED AP, is the Principal and Director of Engineering for WB Engineers+Consultants in the Washington, D.C. office. As engineering experts and great communicators, WB designs MEP systems for clients’ business decisions — helping them solve problems they didn’t even know they had. [email protected]
