RE: Digest Number 215 - Sampling for Total VOCs

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FAO Bob (Message 4 in Digest No 215)

Dear Bob

The 'European Collabotarive Action on Indoor Air and its Impact on Man' has

produced a very useful and solid report on this issue.

The full reference for this report is: ECA-IAQ (1997) Total Volatile Organic

Compounds (TVOC) in Indoor Air Quality Investigations. Report No 19. EUR 17675

EN. Luxembourg: Office for Official Publications of the European Communities.

Regards and Season's Greetings

on

__________________________________________________________

Dr T C on, BSc, PhD, CBiol, FIBiol

Acting Director and Head of Environmental Toxicology Group

MRC Institute for Environment and Health

94 Regent Road

Leicester LE1 7DD, UK

e-mail: ptch1@...

fax: +44 (0)

telephone: +44 (0)

internet: www.le.ac.uk/ieh

Re: Getting Mold Started

Chronic high humidity can allow mold to develop but it does take much longer for

that development to occur than it would if a liquid moisture source were to be

present. The presence of moisture in liquid form makes all of the vulnerable

wall surfaces much more " sticky " to mold spores of all types. Suitably wetted

walls will therefore tend to collect and hold more of the available aerosolized

mold spores which may then form growing colonies if they should happen to have

an appetite for the particular substrate involved.

Also, a wetted wall will have a wide range of moisture levels as the drywall

absorbs and wicks up moisture in liquid form. In a rising water flood situation

for example, the moisture content at the bottom of the wall will be higher than

that above the flood line. This soaking up (via capillary action) creates a

gradient of moisture contents as you go up the wall surface. Since mold species

have differing water activity levels (Aw), there is likely to be a " sweet spot "

on the wetted wall somewhere for just about any particular mold species that

happens to have spores present at the time. This would logically increases the

odds that some kind of mold development is going to occur somewhere on that

wetted wall.

With just high humidity on the other hand, it can take a very long time for the

wall material to absorb enough moisture vapor out of the air to obtain a

particular surface moisture content that might be conducive to mold development.

Also, the circumstances have to be right to allow the wall material to actually

absorb the available moisture. A higher temperature on the wall surface than the

ambient air for example may actually be causing some drying to occur and the

vapor permeability of the paint may even come into play. There are also

circumstances that might prevent mold spores from readily sticking to the wall

surfaces even if the moisture level of the drywall actually does reach a

conducive level.

Having said all of that, I will say that I have seen mold develop on drywall as

a result of chronic high humidity. Let me describe two such cases.

Case one was mold that developed on a hallway ceiling and on the upper walls of

the hallway above the door openings. This was a small hallway between bedrooms

with a pulldown attic stairway installed. The problem was poor attic

ventilation. The attic was incredibly hot and humid and that air leaked down

into the living space through the poor sealing stairway. There was no impetus

for air movement in the upper ceiling area and that hot humid air just hung out

up high at the top area of the hallway. The mold began to appear one summer when

the house was about a year old.

Case two was in the home of a guy who was in the ceiling fan business. He was a

big believer in ceiling fans and literally has a ceiling fan in every room of

his house. One day he just decided to just turn off his A/C system and rely

solely on ceiling fans for comfort. This is Houston so you can imagin how hot

and sticky his house was (but he always had a good breeze going). Some time

during the second summer of this he began to notice mold growing in areas where

the air was generally stagnant (within closets and behind furniture placed close

to the walls).

As you can see, in both of the cases above it took at least a year (or more) of

chronic high humidity for visible mold to develop. It does seems then that under

very high humidity situations mold will eventually develop. There are however

many more variables involved than exist in a wetted-by-liquid scenario and the

time frame for onset (at least in my personal experience) would seem to be

measured in months rather than days. Just a few weeks is probalby not enough

time for a problem to develop under just a high humidity situation.

Phil S.

Getting Mold Started

Hello everyone.

Certain temperature and humidity ranges are written as very

condusive to mold, but from a recent experience it seems like mold

needs a physically saturated food source to get started.

My experience is from the effects of a hurricane. My home, a two

story town house, was flooded by storm surge however only 4 inches

made it inside and the ground floor has all concrete walls.

It was a couple days after the storm before we could get back into

our home and we had to bleach the baseboard trim to kill visible

mold, and rather than take chances we bleached all the trim.

I was without power for a month, and it typically averaged inside

close to 86F at 85% RH for three weeks, then when I managed to get a

small window AC unit running from my generator, it was a week of 83F

@ 68% RH.

I did not get an explosion of mold in the upper levels with all that

sheet rock.

My office is in an industrial 'butler' building and the high sea

water mark was 46 " . My ceiling is under a mezzanine and some roof

panels were lost in the storm and rain water was getting on the

mezzanine.

My walls quickly 'molded' up to the high water mark, and a couple

days later the ceiling was showing mold as well. Both the walls and

the ceilings were wet. I was forced to gut this office. I will never

buy particle board book cases again either as they all collapsed.

In both of these situations, with no power, there was no AC

operating and therefore there was nothing cooler than the ambient

dewpoint which howvers around 80F from June to the end of Novemeber.

I was reading ASHRAE's Humidity COntrol Design Guide, Chapter 7,

http://www.masongrant.com/pdf/design_guide/ASHRAE_HCDG_C7_Mold.pdf

and it comments how spore cases seem to have enzymes on them.

Moisture in the food source dissolves these enzymes, and through

osmosis the spores receive food that the enzymes have broken down to

liquid form.

It just seems to me that the high indoor RH levels are condusive to

mold, but they don't really seem to cause food source to be wet

enough to 'germinate' spores. I can see humid air getting trapped in

drawers, closets, behind furniture and then when the air

conditioning runs, it creates localized condensation in these out of

the way places and starts the mold.

I realize there are spores everywhere, but it does not seem like the

spores 'spontaneously germinate' from high relative humidities. From

what happend to me it looks like it needs a wet spot to get

established.

I am good at designing to maintain conditions that prevent the

humidity levels condusive to mold, I am just looking for some

comments on all the experts in here on what makes the mold grow.

Does mold need a wet saturated food source to start growing?

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