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By Steven M. Caulfield,
9-4-02,
October 02 issue of
IAQ and Schools
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It is
fall and schools are back in session. I have a telephone
conversation with the business manager for a nearby school district
about recurring mildew smells in a part of the elementary facility.
School administration folks had noticed a moldy odor in this part of
the school while touring the building. The business manager says
that the odors happen sporadically, but the smell is strong enough
to irritate the folks in the building. He tells me that there is a
crawl space under this part of the building and that they have
noticed a white, powdery deposit on the dirt floor. I agree to take
a look at the school to see what can be done. In fact, we agree to
evaluate the requirements for exhausting the crawl space, figuring
that the powdery substance is mold and it needs to be isolated from
the occupants. You know, if it looks like mold and smells like
mold, it probably is mold.
The area
in question turns out to be a wood frame building built in the early
fifties. It is attached to additions built in the 1970s and 1980s,
like many schools in the area. I go directly to the crawl space and
find a space that contains fire protection storage tanks and is
heated by unit heaters. The ceiling of the space is wooden beams
and wood flooring. I am told that the occupied space above has
carpet over asbestos floor tiles in the classrooms. The dirt floor
is dry at this time and the unit heaters are keeping the space and
the water storage tanks warm. I surmise that the surface of the
dirt floor reaches dew point in the spring and fall, during the time
when the boilers are off and the unit heaters can’t warm the space
up. That explains why it smells and looks moldy in the crawl space,
but what does that have to do with the space above? I notice that
the heating pipes for the radiators in the classrooms run through
the crawl space and up through the floor into each classroom. The
moldy odors are apparently traveling up into the classrooms through
the pipe openings in the floor. This is caused by the stack effect,
where air in the upper level is warmed and exits the building
through any cracks or openings and is replaced by air from the level
below, in this case from the crawl space.
In order
to evaluate the quantity of exhaust air required to maintain a
negative pressure in the crawl space relative to the occupied space
I use a blower door. This is basically a fan capable of moving a
large volume of air along with a fabric cover that is used to seal
off a doorway opening into the crawl space. The fan is operated at
varying airflows while the pressure difference between the two
spaces is recorded. A graph of airflow versus pressure is generated
to find the point where a negative pressure in the crawl space is
achieved. The result of this testing was (surprise) the crawl space
leaks a lot of air. In order to maintain a negative pressure in the
crawl space and keep the odors away from the kids, we would need to
install a relatively large fan that will suck up significant
electricity continuously. We opt for a solution that involves
covering the dirt floor surface with a fire-retardant polyethylene
sheet and exhausting from a perforated pipe in between the poly and
the dirt. This is done with a radon-type exhaust fan moving tens of
cubic feet per minute versus thousands for the space exhaust
solution. The “sub-membrane depressurization system” is installed
and in working order. The odors appear to be gone. Case closed…
The
Call-Back: No news for about a year, then I get the call that
all is not well. The membrane in the crawl space has improved
conditions, but occupants are still having air quality complaints.
I decide this time that I will not have him tell me what needs to be
done. Rather, I will direct the process to follow the more standard
building evaluation. I start with the occupant interviews to
evaluate the scope of the problem. The complaints were typical for
an air quality evaluation: odors, sinus problems, headaches, itchy
eyes, and sore throats. The complaints were reported to be worse
during the heating season, when windows and doors remain closed. Of
course, the most common report of odors was in the area of the
building with the dirt floor crawl space. The odors persisted even
after the exhausted membrane had been installed and operational.
This time
we looked at the entire school, rather than just the crawl space.
We measured carbon dioxide at various times during occupancy, looked
at how ventilation and exhaust systems were designed and operating,
took some samples of carpet dust to look for microbial
contamination, and generally looked over the various construction
types. We looked at drawings for the two additions, but none were
available for the original 1950s construction with the crawl space.
This is a typical situation in older buildings, especially in those
without a department responsible for the facilities (remember, I was
called by the business manager). We found that the old “gravity
vent” systems (exhaust grilles in the coat closets with exhaust
ducts through the roof) had been sealed to prevent drafts, the unit
ventilators had been turned off because they were too noisy, the
bathrooms did not have mechanical exhaust (operable windows were now
painted shut as well). We found that many of the problems that were
causing the occupant complaints were easily identified. Some of the
fixes for these problems were obviously longer-term solutions, such
as installing a modern ventilation system to replace the “gravity
vent” system and installing exhaust in the old bathrooms and
teacher’s room (where a significant amount of cooking and heat
generation occurred). Others were quicker solutions, like
calibrating thermostats and relocating an oil-burning heater exhaust
away from the entrance to a portable classroom building. However,
we still hadn’t solved the mystery of the odors in the area of the
building with the crawl space. Occupants continued to complain of
musty, moldy odors. The odors had seemed to go away after
installation of the membrane vent system, but had returned almost as
strong as previous times.
What
had we missed? We had followed our client’s observations and
had found that there was mold growth under the occupied area that
could transmit odors to the space through openings. We had
evaluated the interior of the space and looked at the old carpet on
the floor as a potential source of years of microbial deposition and
potential growth (the carpet dust samples had shown nearly normal
levels of fungus, when compared to hundreds of other samples from
complaint and non-complaint buildings). Although we had identified
causes and recommended solutions for many other air quality issues
throughout this part of the school and the two additions, we still
had not identified the cause of the odors that got us involved with
the school in the first place. The odors persisted.
What we
had seen looking up from the crawl space we thought was the wood
floor under the carpet and asbestos floor tile. However, that was
not the case. We had been looking at a wood sub-floor, not the
flooring under the carpet, on top of which were homosote boards with
the wood flooring, asbestos floor tiles, and carpet above that.
What we had missed was the homosote (basically ground up wood
boards) being exposed to virtually the same damp conditions that
were happening in the crawl space over the last 50 years. These
boards, apparently used to keep the wood floor from squeaking, had
been damp and growing stuff for a long time. We had correctly
identified the odor pathway through the pipe openings and had
identified the ultimate source of the moisture from the condensation
in the crawl space. What we had not seen was the material between
the crawl space and the occupied space being the moisture reservoir
and the odor source because we hadn’t known that this material
existed. And the way we finally found out? When the school decided
to replace the worn out carpets and remove the asbestos floor tile,
the abatement contractor ran into these damp boards under the tile.
The boards were soaked with moisture and were definitely odorous.
The good news was that the boards were removed along with the
asbestos in a contained work area and spores were not released
throughout the school.
This
experience taught us several important lessons about odors and
indoor air quality evaluation. First, always look at the entire
situation methodically without jumping to conclusions. Although
there may be an obvious source of the air quality complaint, there
usually are other contributing factors that will become apparent
soon after the obvious is addressed. And even if building owners
and managers think they can reduce the scope and cost of an air
quality evaluation by narrowing the focus to certain selected areas,
it pays in time and money to be more general. Second, find building
plans or recreate sections of key building components for your own
use. Verify the construction even if you do find building plans,
since many times construction details are changed during the
construction process and accurate as-builts are few and far
between. Third and most important, learn from your mistakes. This
case taught me again that the many hidden areas in a building are as
likely to cause problems as the accessible ones.
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