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Archived
Articles
Mold:
a major IAQ Concern for homeowners, building owners and tenant
By Ed Bas
SAN FRANCISCO
- Over the last 20 years, moisture damage in some North American commercial buildings
has become a serious problem. Fortunately, a design guide is now available to
keep indoor humidity at bay. The resulting book is 480 pages long, and took 100
years to write.
Well, not really. In fact, ASHRAE admits that during the first 100 years of its
history, "Humidity control in commercial buildings received much less attention
than temperature control."
It's easy to see why. Temperature is not only easier to control than humidity,
it is more visible. Building tenants and homeowners know when they see 708F on
their thermostat that it is an understandable definition of their comfort. Many
fewer know much about proper levels of relative humidity. Just as with indoor
air quality, few building tenants are willing to pay more for something they have
a hard time grasping the intricacies of.
Building practices since the 1970s are also contributing to increased mold growth.
"Tighter, warmer, with more furnishings" is how one researcher described
this trend. There is reduced air infiltration into our buildings because of added
insulation and tighter fitting doors and windows, which saves energy, but also
which can lead to a build-up of humidity and other pollutants.
There are other factors, which also contribute, but some of these are on a more
individualized per-building basis. For instance, oversized cooling systems continue
to be a sporadic problem.
News reports stated that Farmers Insurance Group is choosing not to renew homeowner
policies in Texas this year because of a dramatic increase in mold claims, which
increased from 12 in 1999 to more than 8,000 in 2001. Meanwhile, in Louisiana,
the state's insurance commissioner has been asked to rule on whether insurers
can exclude mold claims from their coverage. Schools and a state-owned office
building in New Orleans are the subject of recent mold claims and investigations.
"Design Guide for Humidity Control in Commercial Buildings" was funded
jointly by the U.S. Department of Energy and the Gas Technology, and comes from
ASHRAE research project 1047-RP. To better control indoor humidity, and to curb
any resultant mold growth, the authors encourage HVAC designers to:
Focus on adjusting the humidity of any incoming ventilation air Install dedicated
humidity control equipment that operates independently of the cooling and heating
equipment. Seal up all duct work and air handlers to avoid pulling untreated outdoor
air into building cavities.
Construction
claims from mold
Microbial
growth is a major cause of IAQ problems, according to ASHRAE. In one study of
695 buildings over 10 years, microbial growth accounted for 35% of the IAQ problems
encountered. And more than 50% of construction claims against architects, engineers
and construction firms were due to moisture and humidity problems, according to
a study of 5,000 claims.
The book
asks and answers two basic questions for readers:
"What humidity level leads to growth of mold and mildew;" and "How
high does the humidity have to be held to prevent electrostatic shocks?"
Proper use of humidity control through equipment, maintenance and design can avoid
these mistakes, according to ASHRAE. Fourteen chapters of the new volume focus
on applications designed to help the hvac designer ask the right questions for
a particular building before the design process begins.
Two chapters describe various types of humidification/dehumidification equipment
along with their strengths and weaknesses; the use of passive desiccant wheels
is also covered.
Importance of sealing ducts and the use of humidity sensors is reviewed in a section
on instruments and controls. "Some of the most notorious moisture damage
in commercial buildings is caused by suction from leaking ductwork and air handlers.
Duct suction pulls untreated, humid air from outdoors into cool building cavities,
where moisture condenses to feed mold and corrode the building structure."
Calculate the moisture load separately from the cooling and ventilation loads.
Whenever possible, control the dew point rather than relative humidity.
Calibration of humidity sensors is important, and should be done after installation
and prior to commissioning. Most hvac and controls contractors are not in the
habit of doing this, and factory-calibrated sensors may be fine in most cases,
with +/- 5% RH considered adequate. However, if a building owner has a more defined
need, "it is absolutely imperative that all humidity sensors be capable of
adjustment after installation, so that their signals are reliable indicators.
If sensors are not calibrated in the field before commissioning, it won't really
matter what dehumidifier and humidifier capacity is installed - the system will
not work as the designer intends."
Molds can produce toxic substances called mycotoxins. Some mycotoxins cling to
the surface of mold spores; others may be found within spores. More than 200 mycotoxins
have been identified from common molds, and many more remain to be identified,
according to the EPA. Some of the molds that are known to produce mycotoxins are
commonly found in moisture-damaged buildings.
Although some mycotoxins are well known to affect humans and have been shown to
be responsible for human health effects, for many mycotoxins little information
is available.
Colin Young, in a presentation at ASHRAE IAQ '01, said that while a 1989 NIOSH
(National Institute of Occupational Safety and Health) study revealed that only
5% of IAQ complaints were related to microbiological contamination, more recent
studies have shown that there is an association between bioaerosols and increases
in IAQ complaints.
In fact, Young concluded that "biological contamination is a commonly encountered
occupational and environmental, as well as public health, issue. Health care and
safety professionals should be cognizant of recognizing symptoms consistent with
biological exposures… Furthermore, periodic and preventive maintenance of
building components so as to avoid water intrusion may be as important as early
recognition and treatment of health effects secondary to biological contamination."
Time to clean the ducts
In a new guide, Mold Remediation in Schools and Commercial Buildings, the Environmental
Protection Agency advises: "Do not run the hvac system if you know or suspect
that it is contaminated with mold. If you suspect that it may be contaminated
(it is part of an identified moisture problem, for instance, or there is mold
growth near the intake to the system,) consult EPA's guide 'Should You Have the
Air Ducts in Your Home Cleaned?' before taking further action."
Also still under debate is the safety and effectiveness of using biocides in mold
remediation. According to the EPA, "It is necessary to clean up mold contamination,
not just to kill the mold. Dead mold is still allergenic, and some dead molds
are potentially toxic." Use of a biocide, such as chlorine bleach, is not
recommended. It doesn't completely rule out use of biocides by professionals,
if done with the proper care and guidelines.
The National Air Duct Cleaners Association (NADCA) tells consumers on its website
(www.nadca.com) that "Heating, ventilation, and air conditioning systems
have been shown to act as a collection source for a variety of contaminants that
have the potential to affect health, such as mold, fungi, bacteria, and very small
particles of dust. The removal of such contaminants from the hvac system and home
should be considered as one component in an overall plan to improve indoor air
quality."
Frequency of duct cleaning depends on several factors, according to NADCA, including
whatever there are:
· Smokers in the household.
· Pets that shed high amounts of hair and dander.
· Water contamination or damage to the home or hvac system.
· Residents with allergies or asthma who might benefit from a reduction
in the amount of indoor air pollutants in the home's hvac system.
· After home renovations or remodeling.
· Prior to occupancy of a new home.
Ductmate Industries, E. Monongahela, Pa., supplies High Temperature Sandwich Access
Doors to McDonald's Corporation, among others. McDonald's planned to build or
rebuild nearly 600 restaurants in a single year, with the Franke Corporation installing
over 60% of the kitchen systems.
Ductmate's access doors met standards set forth by NFPA96 and installed in just
minutes. They also make it easier for the duct cleaners later on, speeding up
the process by giving easy access to the ducts.
McDonald's traditional three hood design typically requires at least one access
door per hood. The access doors Franke was using were labor intensive, requiring
both welding and excess screwing to install - at least 15 minutes per door, after
the welding equipment is in place. A typical McDonald's restaurant is up and running
60 days after groundbreaking; a complete renovation takes only 20 days. It takes
Franke Corporation 100 man-hours to install an entire McDonald's kitchen, and
another 15 or 20 minutes can make a big difference when you are under such strict
scheduling.
The U.S. Environmental Protection Agency offers the following
checklist for mold remediation
Investigate and evaluate moisture and mold problems
· Assess size of moldy area (square feet)
· Consider the possibility of hidden mold
· Clean up small mold problems and fix moisture problems before they become
large problems
· Select remediation manager for medium or large size mold problem
· Investigate areas associated with occupant complaints
· Identify source(s) or cause of water or moisture problem(s)
· Note type of water-damaged materials (wallboard, carpet, etc.)
· Check inside air ducts and air handling unit
· Throughout process, consult qualified professional if necessary or desired
Communicate when you remediate
· Establish that the health and safety of building occupants are top priorities
· Demonstrate that the occupants' concerns are understood and taken seriously
· Present clearly the current status of the investigation or remediation
efforts
· Identify a person whom building occupants can contact directly to discuss
questions and comments about the remediation activities
Plan remediation
· Adapt or modify remediation guidelines to fit your situation; use professional
judgment
· Plan to dry wet, non-moldy materials within 48 hours to prevent mold
growth
· Select cleanup methods for moldy items
· Select Personal Protective Equipment - protect remediators
· Select containment equipment - protect building occupants
· Select remediation personnel who have the experience and training needed
to implement the remediation plan and use Personal Protective Equipment and containment
as appropriate
Remediate moisture and mold problems
· Fix moisture problem, implement repair plan and/or maintenance plan
· Dry wet, non-moldy materials within 48 hours to prevent mold growth
· Clean and dry moldy materials
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