Background Information on Mold
Mold and Indoor Air Quality Assessment
Standards and Guidelines
Mold can be found almost anywhere; it can grow on any organic substance, as long as moisture and oxygen are present. When excessive moisture accumulates in buildings, mold growth will often occur, especially if the moisture problem is not addressed. Examples of materials on which mold can grow include, but are not limited to, wood, paper, carpet, insulation, stagnant water, organic binders in plaster, cellulose ceiling tiles, and paper backing on construction materials such as gypsum board. Interior furnishings, such as vinyl cove base and vinyl wall covering may hold moisture against gypsum board, plaster, or wood, enhancing conditions for fungal growth.
Mold reproduces by making spores that usually cannot be seen without magnification. These mold spores float through the indoor and outdoor environment continuously. When mold spores land on a damp spot indoors, they may grow and digest the material they land on and eventually destroy the material. It is impossible to eliminate all molds and mold spores in the indoor environment; however, mold growth can be controlled indoors by controlling moisture.
There are many types of mold, all of which have the potential to cause health effects. Mold can produce allergens in sensitive individuals, asthma attacks in people allergic to mold, irritants, and in some cases, potentially toxic substances, known as mycotoxins.
While it is generally accepted that molds can be allergenic, infectious and toxic, there are no generally accepted numerical guidelines for interpretation of microbial data. The absence of standards makes interpretation of microbial data challenging. The allergenic properties of molds make this interpretation even more challenging when considering the hypersensitive individual. Identification of the presence of a particular fungus in an indoor environment does not necessarily mean that the building occupants are or are not being exposed to antigenic or toxic agents.
A Mold Assessment is conducted to determine if microbial growth is present which includes a visual assessment for the presence of mold and the collection of air and swab samples to determine the type and amount of mold. Swab samples are collected from materials suspected of fungal contamination. Air samples are collected in the areas where swab samples are taken to determine the airborne concentrations of mold in these areas. In addition, air samples are collected in wall cavities, when it is determined to be necessary. Microbial growth in wall cavities can occur as a result of a number of circumstances ranging from construction and design defects to accidental water intrusion.
Indoor Air Quality Assessment
Indoor Air Quality Assessment includes measurements for carbon dioxide, carbon monoxide, temperature, and relative humidity. Moisture levels in various building materials are also determined.
Carbon dioxide (CO2) is often used as an indicator of indoor air quality. People exhale carbon dioxide and if there is inadequate outside air ventilation, carbon dioxide tends to accumulate in buildings. Although there are no indoor air quality standards for carbon dioxide, levels greater than 1000 ppm are typically indicative of inadequate outside air ventilation (American Society of Heating Refrigeration and Air Conditioning Engineers-ASHRAE 62-1989). Levels between 800 and 1000 ppm are considered to indicate marginal ventilation.
Carbon Monoxide (CO) is a colorless, odorless gas that is given off by incomplete combustion. Cigarette smoke, furnaces and gasoline engine exhaust are common sources of carbon monoxide. Carbon monoxide is often measured in indoor air quality assessments to ensure that it is not released from its' potential sources. The OSHA Permissible Exposure Limit for CO is 50 ppm; however, this is an industrial standard and not a standard for indoor air quality. The Environmental Protection Agency recommends a limit of 9 parts per million when averaged over an 8 hour day in order to prevent adverse health effects for those at risk of carbon monoxide exposure (such as those with heart disease). Levels greater than 3 ppm above ambient outdoor levels indicates a source of carbon monoxide and should be investigated further.
Temperature and relative humidity can have a significant impact on perceived air quality and comfort and can also help to determine the cause of mold proliferation. Relative humidity should be below 60%; ideally between 30 and 50%.
A Moisture Assessment is conducted to determine the potential for water intrusion. This is typically conducted behind porous materials (e.g. behind walls, under carpets, behind rafters in attics, etc.) suspected of microbial growth or in areas where water intrusion is observed.