A laminar flow hood is a specialized device designed to create a sterile workspace by blowing a continuous stream of filtered air in one direction over a work surface. This controlled environment reduces the risk of introducing unwanted particles and microorganisms, which is particularly beneficial for sensitive tasks like microbiological research, pharmaceutical preparation, and tissue culture. Building a laminar flow hood for personal or hobby use offers a cost-effective alternative to purchasing commercial units, providing a clean zone for various applications. This article outlines the process of constructing your own laminar flow hood, guiding you through material selection, design principles, assembly, and maintenance.
Gathering Materials and Tools
A High-Efficiency Particulate Air (HEPA) filter is a primary component, responsible for capturing microscopic particles and airborne contaminants. For a DIY build, an H13 or H14-rated HEPA filter is typically recommended, capable of removing at least 99.97% of particles 0.3 microns in diameter. The choice between H13 and H14 depends on the desired filtration efficiency and airflow resistance, with H14 offering superior filtration but potentially higher resistance.
A fan or blower is necessary to draw air through the filters and create uniform airflow. When selecting a fan, consider its cubic feet per minute (CFM) rating and its ability to produce the required airflow against the static pressure created by the HEPA filter and any pre-filters. A pre-filter is recommended at the fan’s intake to capture larger particles, extending the HEPA filter’s lifespan.
For the housing, materials like plywood, medium-density fiberboard (MDF), or a sturdy plastic tote can be used to create an airtight enclosure. Essential tools include:
Saws for cutting housing materials.
Drills for fasteners.
A caulk gun for sealants like silicone to ensure airtight seams.
Basic measuring tools.
Electrical components such as a power cord and switch will also be needed to operate the fan.
Understanding Design Basics
The primary design consideration is the direction of airflow, which can be either horizontal or vertical. In a horizontal flow hood, air moves from the back of the unit across the work surface towards the user, offering advantages like less turbulence near the work surface and user hands being downstream of the sample. Vertical flow hoods direct air downwards from the top onto the work surface, exiting through the front or a perforated base. Vertical designs can save floor space and may be preferred when working with bulkier equipment, as the downward flow minimizes obstruction.
The housing must form a sealed box around the HEPA filter and fan, ensuring all air passes through the filter and no unfiltered air bypasses it. The plenum, an enclosed air distribution chamber located behind the HEPA filter, plays a significant role in achieving uniform airflow. Proper plenum design ensures air is evenly distributed across the entire surface of the HEPA filter before it enters the workspace. The fan’s static pressure capability must be matched with the resistance of the filters to ensure sufficient airflow velocity across the filter face, typically around 100 feet per minute for effective particle removal.
Assembling Your Flow Hood
The construction of your laminar flow hood begins with building the main housing or frame, which will enclose the fan and filtration system. Using materials like plywood or MDF, cut the panels precisely according to your design specifications, ensuring square edges for tight joins. The thickness of the material, such as 5/8-inch plywood, provides stability and helps minimize fan vibrations. After cutting, assemble the frame using screws and wood glue to create a robust structure.
Next, focus on creating the plenum, the chamber designed to distribute air evenly before it passes through the HEPA filter. This space, typically 10-12 inches deep, should be an enclosed area behind where the HEPA filter will be installed. The fan will push air into this plenum, and its design impacts how uniformly air emerges from the filter.
The HEPA filter must be installed carefully to prevent air bypass. The filter should fit snugly into its designated opening, and all edges where the filter meets the housing must be thoroughly sealed using silicone sealant. Weatherstripping can also be applied around the filter’s edges to enhance the seal and prevent air leakage.
Mounting the fan or blower is the next step, typically positioned to push air into the plenum. Create a precisely sized opening for the fan’s outlet in the housing, ensuring a tight fit. Secure the fan using bolts and washers, then apply silicone sealant around its housing where it connects to the hood to eliminate any gaps.
For electrical wiring, connect the fan to a power cord and switch, ensuring all connections are secure and insulated. It is important to prioritize electrical safety; if unsure, consult a qualified electrician. Finally, consider adding an access panel for future maintenance or pre-filter replacement, ensuring it also seals tightly when closed.
Verification and Upkeep
After constructing your laminar flow hood, verifying its proper function is an important step. A simple smoke test can visually confirm if air flows in smooth, parallel lines across the work surface. More advanced methods, such as particle counters, can provide quantitative data on air cleanliness, though these are typically beyond a hobbyist build.
Routine maintenance is essential to ensure the hood continues to provide a sterile environment. The work surface should be cleaned daily with appropriate disinfectants before and after each use to prevent contamination buildup. Deeper cleaning, including hard-to-reach areas, may be necessary weekly or monthly depending on usage. Pre-filters, which capture larger particles, should be inspected weekly and cleaned or replaced as needed, as clogged pre-filters can reduce airflow efficiency and strain the HEPA filter.
HEPA filters themselves do not require frequent replacement, with manufacturers often recommending replacement every 1-3 years when used with a pre-filter, or as indicated by a significant increase in pressure drop across the filter. HEPA filters cannot be cleaned and should be handled with care during replacement to avoid damaging the delicate media. Regularly inspecting seals and gaskets for wear or damage is also important, as compromised seals can allow unfiltered air to enter the workspace.