Still Air Boxes, Glove Boxes, and Flowhoods

When doing grain to grain inoculations, or agar work, sterility is key.  Since no room is sterile, cultivators have adopted modern lab techniques to significantly reduce the chances of contamination.  For the home cultivator, a still air box, or glove box is the most efficient means of creating a sterile environment to work in, and can be made for less than $20. For those with more funds and a higher level of commitment, a great flowhood can be built in the neighborhood of $300 to $400.

CONSTRUCTION

Still Air Box:  A still air box is easily made by taking a clear plastic bin that is large enough to hold your supplies in an organized manner, and drilling 2 hand holes into it.  Many cultivators drill 1 hand hole a little higher than the other to make inoculations and grain transfers more comfortable to perform.  A 4" hole saw is ideal for making hand holes, but you can also heat a 4" coffee can on the stove and melt the holes in if a hole saw is not available.

Glove Box:  A glove box is just a still air box with gloves.  A pair of PVC fittings and a set of dish gloves work very well in this application.  Note on seals:  Many guides suggest making a glove box air tight, and subsequently get comments from infuriated users about wide spread contaminates.  This is because when you make the box air tight, then start moving around in the gloves, positive and negative pressure gets created and sucks air into the box around your seal (think of the pressure reaction like an accordion, you put your hand in the glove, air gets pushed out, you pull away from the glove, air gets sucked in).  By not making the box air tight, you avoid positive and negative pressurization, and avoid sucking outside air into the box.

USE

When using a still air box or glove box, turn off any fans or air conditioning in the room, and allow the air to settle for 1 hour.  Remove the lid from the box, and place your jars, cultures, tools, ect inside and spray with Lysol and Oust immediately before replacing the lid.  Allow 15 to 30 minutes for the Lysol and Oust to dissipate.  The dissipation step is very important if flame sterilization will be necessary as Lysol and Oust are flammable.  I have read many accounts of cultivators burning their eyebrows off for not following this step.

CONSTRUCTION

A flowhood is the best tool for performing sterile work.  The laminar flow (100cfm) of sterile air it creates prevents contaminates from landing in your jars or cultures.  It also allows you to work without your movements being restricted by the walls of a box.  WARNING:  Some guides instruct you to use a HEPA air purifier as a flowhood, this WILL NOT WORK!  While air purifiers often advertise as using HEPA air filter, it is not a true HEPA filter, but an ionized filter which offers less purification.  A true HEPA air filter will cost a bare minimum of $100 all by itself, and come with a wealth of air flow stats that you will have to sort through during the flowhood design process.

HEPA filter rated 99.99% at .03 microns (a 6" thickness is preferred since it will have more resistance on the back side of the filter than a thicker filter)
Squrrel Cage Blower
a standard household air filter (small)(you will need 1 filter for each air intake on your blower, most have 2)
Wood
Carpenter's glue
1 1/4" wood screws
Silicone
Drill & bit set

Once you find a filter that is large enough to let air pass over the workspace you would like to use, measure the surface area in feet to determine how powerful your blower has to be.  The following example is for a 24"x24"x6" filter

2' x 2' = 4'squared
4'squared x 100 feet per minute = 400cfm

The math indicated that we need a blower rated at 400cfm to achieve laminar flow.  Since technology is inefficient, you should add about 20% to that rating, so you would want a blower capable of 450cfm to use with this filter.  If the only blowers you have access to are far more powerful than what you need, you can use a speed controller to bring the fan speed down, or you can block off part of the air intake with cardboard.

Construct a box so that your HEPA filter takes up 1 face of the box, and cut a hole at the top of the box for your blower to push air into.  Silicone all connections inside the box so that air cannot escape in any way except through the HEPA filter.

Install your blower so that it pushes air into the hole you made in the box.  Silicone the connection.  Secure the household air filter to the blower's air intake.  This will act as a pre filter that prevents dust particles from entering the blower, extending service life of both it and the HEPA filter.

When the blower is running, you should be able to light a lighter and hold it in front of the HEPA filter, the flame should be blown to a perfect 90 degree angle, and stay lit.

USE

Turn the flowhood on 1 hour before use.  Spray the work surface with Lysol.

When working in front of a flowhood, keep your jars and cultures as close to the HEPA filter as possible, and never get your hands between the flow of air and your culture.  When opening jars and cultures in front of a flowhood, lift the edge of the lid facing the flowhood first so that only sterile air will enter, reverse when sealing.