By Robert A. Woellner, QUEST Environmental
We often think of residential mold as a homeowner issue, but sometimes the water damage that leads to mold growth impacts a shared location in a multi-unit residential building. Water damage may be caused by a roof leak, building envelope damage that has allowed water to intrude from the exterior, or migration of released water from one unit to another (particularly flowing downward into an underlying unit). In these instances, mold growth may become the community association’s concern. Should this be the case, it will be useful to know the basics of mold assessment in order to provide the best service to your homeowners and reduce the community association’s risk.
Ambient Microflora Assessments
An ambient microflora assessment is the best choice when it is not known whether indoor mold growth is present. Perhaps an occupant begins feeling sick in their home and suspects mold exposure, or perhaps there is a musty odor that can’t be traced to an obvious source. An ambient mold assessment could also simply be precautionary, such as following a water release that was promptly dried.
During an ambient mold assessment, an industrial hygienist or mold inspector will conduct a visual inspection to search for signs of water staining, damage, and visible mold growth. If any of these are observed, the inspector will attempt to identify the potential source(s) of moisture. The inspector should also utilize a moisture meter to check for moist building materials in the area of concern. (Building materials containing more than 12% moisture content are typically considered to be moist.) If available, an infrared thermometer/camera can be used to check for moisture-related temperature anomalies in locations that are difficult for the inspector to reach with the moisture meter.
The relative humidity should also be monitored throughout the area of concern to make sure that an environment conducive to mold growth is not being created by elevated indoor relative humidity. (We recommend that indoor relative humidity be kept at or lower than half of the indoor temperature, so we typically recommend around 35% relative humidity as an indoor maximum.) Finally, you may wish to have the inspector conduct a sampling survey for airborne fungi to assess whether the indoor air quality is being adversely affected by mold. There are two main categories of mold sampling:
- Non-viable/total fungi sampling visually identifies all mold spores in the sample, without discriminating between living and dead spores. This type of sampling can identify mold spores down to the genus level but cannot distinguish individual species.
- Viable fungi sampling identifies only living, culturable “colony forming units” of fungi. For this reason, laboratory results usually take 7-10 days to be issued, since the living fungi need this time to be cultured on agar plates. Viable analysis can identify fungi down to the species level, and is the method of choice if litigation or adverse health effects are anticipated.
Which sampling type you require is strongly dependent on the needs of the investigation—is the dead fungi content of old dust relevant, or are only living fungi relevant? Dead spores may be very old and not indicative of active growth, but they could still be contributory to adverse health effects for occupants. Do you need more precision in the fungal identification? Do you need faster—even same-day—results, or can you wait a week? Your industrial hygienist can help you navigate these options to optimize the bang for your sampling buck.
Pre-Mitigation Microflora Assessments
A pre-mitigation assessment assumes that mitigation is going to take place. It is likely that visible water damage and/or mold growth have already been observed. In this case, the inspector will carry out the assessment in much the same way as the ambient assessment, with all of the same elements of investigation described above, but with even further emphasis on identifying and quantifying the areas of concern to be mitigated and the potential contributory sources to be resolved. The industrial hygienist should also provide a detailed, site-specific scope of work for the mitigation contractor to follow in order to fully mitigate all of the areas of concern.
Post-Mitigation Microflora Assessments
After the mitigation work has been done, it is tempting to breathe a sigh of relief and assume the mitigation and cleaning work have been performed successfully. We recommend that the project not be considered a wrap, however, until a post-mitigation inspection and final clearance sampling survey have been conducted. Beyond providing peace of mind for the occupants, the post-mitigation assessment also reduces the risk assumed by the community association.
The same investigative elements as in the ambient and pre-mitigation inspections are employed, but with emphasis on assessing the completeness of the mitigation and cleaning activities, making sure there is no remaining visible mold growth, and confirming the absence of mitigation-related dust and debris in the work areas. An airborne fungi sampling survey should then be conducted to confirm that the indoor air quality is normal, with the total fungi concentrations in the indoor samples similar to or lower than that of an outdoor sample and expected background concentrations, and with the types of fungi identified indoors representative of normal outdoor air. Once these criteria have been met, we can be confident that the mitigation work was adequately performed.
In order to avoid a real or perceived conflict of interest, we recommend that the industrial hygienist or other inspector you hire to conduct any of the above assessments be a third party, entirely independent from the mitigation contractor. With these steps in mind, handling a mold concern need not be a confusing hassle. Instead, it can be an opportunity for a community association to shine.
