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DESIGNING AND BUILDING A SPAWN LABORATORY 465
culates the entire room once every 1.3 minutes.
This is far more than what is minimally necessary.
Here are a few key concepts in designing
laboratory, whether the clean room is in the
home or in its own building. If incorporated
into the design of your facility, contamination
vectors will be minimized. Following this list
are helpful suggestions of behavior which, in
combination, will give rise to an efficient,
steady state clean room.
1) Positive Pressurize Laboratory. The
laboratory should be continuously positivepressurized
with fresh air. The fresh, outside air
is serially filtered, first through a coarse pre-filter
(30% efficient at 1 u), then an electrostatic
filter (95—99% efficient at lu), and finally a
HEPA filter (99.99% efficient at .3u). Blowers
must be properly sized to overcome the cumulative
static pressures of all the filters. In most
cases, the combined static pressure approaches
1.25 inches. (1 inch of static pressure is the
measure of resistance represented by the movement
of water 1 inch, in a 1 inch diameter pipe.)
Air velocity off the face of the final filter should
be at least 200 feet per minute. For a 400 sq. ft.
clean room, 2 ft. x 2 ft. x 6 in. filters should be
employed. The construction of the intake air
system should allow easy access to the filters so
they can be periodically removed, cleaned, and
replaced if necessary. (See Figure 386.) Fresh
air exchange is essential to displace the carbon
dioxide and other gases being generated by the
mushroom mycelium during incubation.
Should carbon dioxide levels escalate, the
growth of contaminants becomes more likely.
Sensitive cultivators can determine the quality
of the laboratory immediately upon entering
using their sense of smell.
2) Stand-alone laminar flow bench. A
laminar flow bench constantly recirculates
the air within the laboratory. The air entering
the laboratory has been already filtered from
the positive pressurization system described
in the previous paragraphs. By having two
independent systems, the lifespan of the filter
in the laminar flow bench is greatly
extended. And, the clean room becomes easy
to maintain. Furthermore, I am a strong believer
in creating a laboratory that is
characterized by turbulent air streams, with
a high rate of impact through micron filters.
Turbulent, filtered air in the laboratory is far
more desirable than a still air environment.
The key idea: if airbo me particles are introduced,
they are kept airborne from
turbulence. If kept airborne, particles are
soon impacted into the micron filters. This
reduces the stratification of contaminant
populations in the laboratory, and of course,
temperature variations. It is important to
note that this concept is diametrically opposite
to the "old school" concept that still-air
in the laboratory is the ideal environment for
handling pure cultures.
3) Double to triple door entries. There
should be at least two doors, preferably three
doors, separating the clean room from the outside
environment. Double door entries are a
standard in the industry. Doors with windows
have obvious advantages in preventing accidents.
Furthermore, the doors should be
gasketed with dirt skirts. When the doors swing
outwards as you exit the innermost clean room,
the export of mature spawn or blocks is made
easier. (I prefer to kick the doors open upon exiting
as often times my hands are full.) As
workers travel towards the clean room, they enter
rooms hygienicly cleaner than the previous,
and into increasingly, higher pressure zones.
Floor decontamination pads, otherwise known
as "sticky mats" are usually placed before each
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