Assessing Mould and Indoor Air Quality
INTRODUCTION TO MOULD AND MOISTURE
CAUSES OF MOULD GROWTH IN BUILDINGS
PRINCIPLES OF A MOULD ASSESSMENT
A PRO-ACTIVE COST EFFECTIVE APPROACH TO MOULD SCREENING
Introduction to Mould and Moisture
Indoor Air Quality (IAQ) is one of the most complex challenges facing the building industry today. Of all potential IAQ concerns, mould and moisture combined are by far the most serious of the IAQ challenges facing the building management and construction industry today. In fact Volume 2 of the Barrett Report (on leaky condos) determined that mould and moisture resulting from building envelope failures can impact both the structural durability of the building and the health of both the building occupants and the construction workers.
Our firm, Theodor Sterling Associates Ltd. (specializing in building related IAQ issues since 1973) has become directly involved in this issue investigating concerns resulting from exposure to toxigenic mould in moisture troubled buildings.
These investigations have enabled us to apply techniques developed for IAQ assessments to identify and solve moisture problems and in a sense explore this complex building envelope performance issue from a perspective different from that of engineering based building envelope experts.
Mould and moisture problems in buildings play an ever increasingly important role on human health. A recent study released by the U.S. Public Health Service found that the prevalence of respiratory illness, allergies and asthma have increased over 75% since 1983. Mould and moisture in buildings have been identified as a key risk factor for this increase.
This is not surprising when you consider that the optimum humidity level is above 60% RH for the growth of organisms that cause these illnesses and that this level is the same found commonly in the tightly sealed energy efficient homes being built since the mid 1980's.
There is a convergence of indoor air quality related mould and/or moisture problems with building envelope and HVAC system failures.
A recent International Conference, Healthy Building 2000, identified mould and moisture in buildings as a worldwide problem. Microbial contamination of building envelopes and mechanical systems was identified as the single most important IAQ issue of international attention.
Causes of Mould Growth in Buildings
Mould and moisture damage to the building is caused by a number of factors:
Water leakage of building envelopes due to climate conditions, construction techniques and changes to building codes and standards have become a billion dollar issue in the past decade in British Columbia.
Principles of a Mould Assessment
The primary method of assessing potential mould issues in buildings is through thorough visual inspections as defined in the Workers' Compensation Board of British Columbia Guideline 4.79 to the Occupational Health and Safety Regulation and the New York City Department of Health "Guidelines on Assessment and Remediation of Fungi in Indoor Environments".
Based on this protocol, Theodor Sterling Associates conducts inspections of HVAC systems and buildings for signs of moisture and/or visible mould growth. Sometimes baseboards and carpet are pulled back and other times a boroscope is used to inspect wall cavities or inside ductwork.
Based on the results of our visual inspections, there may be a need for sampling. There are three basic sampling methods used to assess mould contamination in buildings:
· Bulk sampling
· Surface sampling
· Air sampling
Bulk sampling involves aseptically cutting a sample of material such as wallboard, insulation, settled dust, or carpet; and determining contamination of viable organisms. This method produces qualitative rather then quantitative results by detecting the presence of a bioaerosol.
Surface sampling involves aseptically collecting a sample from the surface of a material such as shelves, walls or pillars. There are various methods used to collect the sample including: wetted swab, adhesive tape, contact plate, or a suction device such as a micro vacuum.
Again this method produces qualitative rather than quantitative results identifying the presence of a bioaerosol.
Air sampling is a method used to sample air in the occupied space of a room, in the building envelope or in the ventilation air provided by the HVAC system serving a building to determine biological contamination. There are two commonly used sampling methods:
1. Total (viable + nonviable) spores.
2. Viable (culturable) spores
These two air sampling methods may be used alone or together, depending on project variables such as scheduling and budgeting. Total spore sampling involves impacting sample air on a microscope slide with an adhesive coating. The organisms are then identified by a trained expert using microscopy. This provides a quick one day analysis whereas viable sampling collects sample air on nutrient agar. The samples are then incubated in a controlled sterile environment before identification of growing or viable organisms. This process requires three to five weeks to complete.
Each of these methods has advantages and disadvantages.
The advantages of air sampling for total spores are:
· Quick analysis of key indicator species
· Quick indicator of elevated concentration
· Will detect dead spores and mould fragments
· No cultures are required
The disadvantages of total spore analysis are:
· Identification is to genus only
· Cannot distinguish between Penicillium and Aspergillus.
The advantages of air sampling for viable spores are:
· Identification of the species
· This is the industry "gold standard" or benchmark used to compare other methods.
The disadvantages are that it requires three to five weeks for analysis and does not detect sterile or dead spores.
A Pro-active Cost Effective Approach to Mould Screening
Diagnosing and solving moisture-related problems, particularly those that occur in the building envelope, can be complex and costly. Often, some of the greatest cost incurred is caused by intrusive testing and inspection of the building envelope when moisture problems are suspected.
In many cases it may be possible to avoid this cost by implementing a less destructive and non-intrusive screening procedure. The process is based on sampling air in the occupied space and in the wall cavity for moisture and mould. Using this screening approach, the specific location of likely damage can be more accurately pinpointed. Once pinpointed, only those areas of likely damage require inspection using destructive and intrusive procedures. Once those areas of damage have been identified and the extent of damage has been determined, appropriate, cost-effective repairs can be implemented.
This building envelope performance screening procedure may also be effectively applied to proactively manage the risk of building envelope failures for new and existing buildings. For new buildings, a program of regularly scheduled sampling for mould and moisture, and inspection for water incursion should begin immediately after construction is complete.
For existing buildings, an initial inspection should first be undertaken to establish baseline performance parameters for mould and moisture levels and signs of water incursion. The baseline parameters will then form the basis for comparison with results of regularly scheduled testing. In addition to identifying envelope performance and durability issues, this pro-active program will also provide documentation that the optimal humidity conditions for occupant health and comfort are being achieved, and alert the building management to any occupant-caused humidity problems.
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